I'm reading "The Big Picture" (Sean Carroll) right now.
I'd love to have a real physicist explain this, but:
When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do.
But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess.
Physicist here. You are right that the mental picture we get when we use the term “particle” is a little ball or something like that. It is unfortunately a confusing name…
You need to begin with a field, like the electromagnetic field for instance. When you look at its properties like energy, polarization and so on, in order to write down a state of the field you need to specify all of them in a way or another. In quantum mechanics you can associate a vector space to each property, and then (here is the important bit) you need to pick a basis for your vector space in order to write down its vectors. Obviously there is an infinite number of possible choices, and we usually end up choosing what makes things simple, so in the case of energy we pick the basis of eigenvectors of the Hamiltonian, because to evolve them in time you just need to multiply them by a complex number and that’s it. Well, those basis vectors are the “particles“ because when taken individually they share some properties with macroscopic particles, but the analogy really only goes so far. And the thing is that usually the state of the field is not in a single one of these basis vectors unless the conditions are very special, so even saying that the field is “made of particles” is misleading because it’s like saying that the wind is made of air going vertically, horizontally and across, which sure it’s “correct” because you can combine those directions and get any other direction but it’s also not really that…
It's not quite right to call basis vectors particles, even in a free field theory. The particles correspond better to the creation / ladder operators that take you from one Hamiltonian eigenstate to another.
In a perturbative interacting case, people still think of particles as these same ladder operators, but they don't connect eigenstates so simply (the interactions generically mix all the states with the same quantum numbers).
In a strongly interacting case the story is even more subtle, because composite operators may be closer to the ladder operators between the asymptotic states, even though they're built of other... particles? Language isn't great in this instance.
Yeah it’s hard to use everyday language to exactly describe these things… And even more difficult to decide where to draw the line where some hand waving is acceptable.
As an amateur, I think I follow most of this, at least at some level, but I don't follow why you'd unify the basis elements and particles. Thinking of a quantum harmonic oscillator, the eigenstates have some kind of localization that feels particle-like, but the oscillating pattern of a coherent solution seems "more particle-like" and arises out of the interference between those eigenstates. In particle-speak, I might try on a sentence like "this classical particle is generated by the interaction between... other... particles" but I'm clearly at a loss there.
On basis of that, I'd be more likely to say "QM needs to describe everything as a wave, and sometimes certain kinds of localized 'wave-packets' move around coherently, and that's what we'd call 'particles'". That also seems to gel with less coherent states where it feels like there's not really a particle to be found.
So, I'm curious why you'd prefer to relate the eigenstates themselves as particles. Again in the oscillator case, the eigenstates themselves seem less coherent and seem to behave less classically than I'd hope.
My best guess is that the property those states have that is not as well replicated by the "particle as a coherent wave packet phenomenon" is that they have well-defined energy quanta. But that's just a bit of a stab in the dark here. It perhaps makes more sense from the perspective of "particles are the things that we're able to measure in detectors" POV, though.
You are exactly right at the end when you say that particles are what makes a detector go click. Let me try to clarify further. The "particleness" is not about localization, but about energy quantization. In fact, a single photon can be very non-localized, because spatial position is a different Hilbert space and it can be entirely independent of the energy. So the packets you are referring to are particles only if in their energy Hilbert space they correspond to a well-defined photon numbers, and that's why the analogy with classical particles only goes so far. To add to the confusion, one can speak of packets localized in phase space (e.g. coherent states, like the light produced by a laser) and packets localized in physical space like a short pulse, and these refer to different Hilbert spaces.
From what I understand of QFT, the Universe is made of fields of different types, and a “fundamental particle” is just an excitation (wave) in the corresponding field.
For example, a photon is a wave in the universal electromagnetic field,
A charm quark is a wave in the universal charm quark field, etc.
I’m not a trained physicist, so I might be wildly wrong.
I get it but I still think these sorts of concepts are also just another level of mathematical abstraction that isn’t necessarily “really what it is” any more than a rotating ball or a math equation or any of the other ideas are “really what it is”
If you don’t invest the statement “the universe is made of fields” with more meaning than necessary, then it makes more sense.
A quantum field is just a mathematical construct that models an aspect of what can happen at every point in spacetime. The fields follow rules for how they interact, and fluctuations in the fields and interactions between them, according to their respective rules, provide a good model for the universe we observe.
If you consider this purely mathematically, it’s hard to argue with. The models in question make very accurate predictions, can correctly model the vast majority of observations we know how to make, and don’t predict many things that we don’t observe. In other words, all the evidence is that it’s a very good model - a very good fit for the universe we observe.
From this perspective, one way to interpret the statement that “the universe is made of fields” is simply that the universe conforms to the quantum field model. Again, this claim is hard to argue with - it seems to me like a true statement, and there’s a lot of evidence for it.
If perspectives like these don’t satisfy you, and you want to try to develop an understanding beyond mathematical models, then you have a tough problem to solve: how to go beyond the models that we know how to construct, to something that somehow gives you some sort of more fundamental insight. But what would that even look like? How would you test it? What would make this approach more true than existing theories?
In short, an answer that satisfies the criteria that you want it to satisfy may simply not be possible.
Maybe it is "made of fields", maybe it isn't, but "I think that's nonsense", which is just a gussied up way of saying "my intuition rejects that", is not a valid judgment method. The universe does not check with our intuition before doing what it Damned Well Pleases.
Whether or is or it isn't, it does it without consulting you or me or our intuitions.
I assume you meant that as an obvious absurdity, but if you were going for that you probably should have avoided the concept of "language", which can be Turing Complete. Still, the main point is, whatever it is, it is, and it isn't asking us for permission to be what it is.
My point is that physical reality cannot be made of something that doesn't exist physically, such as mathematical objects, abstract concepts or more generally ideas of any kind. Do you not agree that this must be true?
You lack the capability to judge what those things are, not because of some personal deficiency but because humans lack the ability at this level. If you dug in far enough you'd find your definition of what an abstract concept is circular anyhow, from the looks of it.
Proving the universe isn't made out of "mathematical objects" in particular is equivalent to the difficulty of proving it's not a "simulation". This is one of the red lines that tells you you've gone too far; you can't prove that. You can't even non-circularly define such a thing in this context anyhow, let alone prove anything.
It is true, but also kind of trivial. More subtly, one can say that we tend to call what is real using the same words that we use for mathematical objects that model them.
I don't know that we do that. For instance, physicists are able to describe motion in physical terms and don't insist that it literally is a vector. It only happens with quantum fields.
One of the ultimately epistemological puzzles to me is the question of what math really is. Like, obviously, it is fundamentally descriptive. “Two and two makes four” is pretty straightforwardly talking about something “out there”. And when we’re talking about fields, we are clearly also describing something that is really happening, that is really “out there”; it’s not the math itself that is the real thing, but rather it is a language for accurately describing and analyzing real things. But at some level, the real things it’s describing become so abstract and immaterial that they might as well be magic, or spirit. And it seems to me like our minds also contain and experience such things, too. Very advanced math and physics necessarily start to border on philosophy or theology.
One way of viewing it is that math is games. Not in the winner sense, but in the activities with rules sense. Addition is a game.
Some games make you better at other activities. Like, playing chess could make you better at logistics because you’re practicing planning and managing losses.
Some games match some real world situations so tightly that we can go through them step by step and solve the real world situation in the game. You can play addition to figure out two apples and two more makes four apples.
Whether the game is “real” or not is immaterial. It just needs to be internally consistent and matched to the right thing.
There’s also the idea that math is another world that we can visit, similar to the dream world. But that’s a whole other thing.
The idea that it's an abstraction is 100% accurate. That physics is a discrete set of fields with field rules and interaction rules, and what we observe is a scaffold on top of that. It's like okay, let's say the math is right and we have a set of fields, what are they and where are they from, how do we manipulate them. Then the physicists, often driven by ego, is want for an explanation and points to vibrating strings and such, and finally they knock on the door of the empiric physicist and say "can you do an experiment to show that I'm right" "sure, build a machine the size of the universe and I could test that" and that's the state of physics the last gorillion years
So in the viewpoint I’m describing you can definitely call it an abstraction. And abstraction has a vibe of intentionality to it, at least for me. That brings up something I didn’t mention, which is you can make a math game on purpose, to match with something in the real world. You can also make them up for fun (people don’t usually call it “for fun”, but that’s actually a fair label for theoretical mathematics IMO) and then discover the application later.
This is neat! I think it happens less in the physical world, just making up a tool and then finding its application later. It does happen in chemistry.
The magnetic field is one which you've probably had a chance to experience for yourself. Wave a magnet around a magnetic field and you can feel it has a different effect at different points in space. Fields are just time and space varying values for physical properties. Is the universe being composed of magnetism and a few related fields really so nonsensical?
I disagree! I think fields are very intuitive and it's everything else that's nonsensical!
Magnetism isn't made of anything. It is a field, and it's one your can interact with directly.
Compare that with, say, table salt. "What's table salt made of?" Uh. It's made of atoms entirely unrelated to salt, like sodium and chlorine. "What are atoms made of?" Uh. They're made of tiny electric particles zipping around at relativistic speeds but bound together by forces like magnetism.
Richard Feynman does a better job than me of describing this exact problem in one of my favorite physics videos of all time:
A great lesson one learns as a physicist is that one must develop a new intuition mainly through years of practice. So when you say "It's very frustrating", I interpret it as "this doesn't seem reasonable to me". But it doesn't have to be reasonable - none of us have any intuition for what happens at scales far different from our everyday lives.
The real question you raise is a very good one - how seriously should physicists take mathematical theories. If we were building a statistical model of, say, house prices and construct a reasonable linear regression model, we certainly don't believe that the market plugs the parameters of a house into the model to decide the price. The model is an approximation of the real dynamics of the market and this approximation might not hold in the future.
On the physics front, I would argue no one would consider a quadratic in speed air resistance term in Newton's second law, a fundamental feature of the universe. One can build a reasonable model that results in that term and it might even be a good approximation for some fluids in some speed/density range.
But, when it comes to more fundamental (as of today) theories like quantum electrodynamics, electroweak theory, quantum chromodynamics (all quantum field theories), or even general relativity (modulo discussions of quantum gravity) - both the predictive power and accuracy of these theories is so stunning (matching all the data generated at colliders like the LHC), that one starts wondering if we are no longer dealing with models but a true description of nature. The mathematical descriptions are also so constrained unlike the house price example above, that one can't just make modifications to the theories without violating core principles (and experimental data) like unitarity, causality, locality, Lorentz invariance etc. This only reinforces this view that perhaps this is close to a true description of what we see.
Now it is entirely possible (but IMO not probable) that this whole view will be upended and replaced by a very different physical picture. In a sense, string theory (which is now discredited heavily in the public's eye but that's a story for another day) was an attempt at a different physical picture that resulted in very rich structures that had nothing to do with physical reality.
So, physicists say that because the more time you spent understanding and studying quantum field theory and as more experiments are done (all the collisions at the LHC verify the standard model's predictions including the Higgs once its mass was known), it only reinforces that there's something deep about the current theories even though we have several unsolved problems (dark matter, dark energy, quantum gravity, fine-tuning problems).
Addendum 1: I'll add a book that is not accessible to non-physicists but gives a glimpse into the actual struggle of research and building intuition for something very abstract:
Feynman, like many others, spent considerable time applying all his powers to understand general relativity from a QFT perspective but eventually it didn't pan out (for anyone).
Spin is easy as long as you avoid trying to draw a direct analogy with ordinary rotation.
It’s just the statement that the object spinning is attached to its surroundings in a smooth and continuous fashion. Less rigid object, more a patch of space-time fabric spinning.
It's worth keeping in mind that we don't yet have the sought-after Theory of Everything. We have a bunch of theories that mostly work in their domain of validity. These field theories are supposedly very accurate we don't actually know if they are the final word.
> we often think as though it were dirt, or a billiard ball, or something
The problem lies that it is hard to imagine something that does have zero dimensions. You can get the example of ant walking into 2D and it is unaware of third dimension to explain we are have something similar for space-time 4D (although not the same picture exactly as time is different from spatial dimensions). But we don't have an idea how to approximate a mental picture of what a zero dimension could be. So you have something that does not occupy a volume in space (Talking strictly about elementary particles here) in the classical sense.
This does not mean they are abstract concept. According to QFT -Quantum field theory- you would think (by training) of particles are excitations or quanta of their respective fields. Fields are there always (vacuum is just filled with fields) and particle appears when they are excited (more complex processes occurs). So you would think of each particle as a manifestation of a quantum field that permeates the universe. What is interesting (and probably confusing to most people) is that these fields are not zero-dimensional, instead, they exist everywhere in space and time. But the quanta (particles themselves) are considered point-like with no spatial extension.
In practice physicists will think about particles properties (i.e charge, mass, interactions, spin) ..etc instead of what this particle actually is from that point of view. This is often for practical reasons. You are a working physicist and you learned from your training that you shut up and calculate (or implement if you are doing experimental particle physics as you spend most of your time coding) by this stage.
I just think of a zero dimensial object as a ghost.
Topological defect. The unpictured thing the contour lines are swirling around. It's influence is only felt by seeing the effects on higher dimensional space, but you can never see the ghost itself.
> The problem lies that it is hard to imagine something that does have zero dimensions.
Do you really think so? It’s not hard to picture the real number line, with the point zero (or any other single point) distinguished. Sure — if you draw it in the standard schematic way you have to give it some area, but it still seems quite intuitive that it’s ‘zero-dimensional’. Especially if you play around with converging sequences and open sets and stuff; you quickly develop intuition for what it means to be a point rather than something higher dimensional.
So we have the three spatial dimensions, + time as 4. dimensions and at any of those 4-part coordinates there are additional properties like mass/spin/etc., some of much always come together or at least strongely correlate, and those values not being zero means there is a particle there and every value corresponds to a certain „field“ and it not being zero means the field is excited?
I've only got a physics minor, so hardly an expert, but I felt like quantum mechanics got a lot easier once I started thinking of a particle as merely a situation which has some probability of causing a state change in a detector of some kind.
In similar vein, the following question is very apt. Please read the question because it captures all of our intuition when we try to understand something.
One answer is that it is only meaningful to answer this question if the answer has physical consequences. Popularly speaking, string theory is supposed to be the innermost Russian doll of modern physics, and there are no more dolls inside that we can explain it in terms. However, we may be able to find equivalent formulations.
You can't explain it in terms of anything else, which was sorta my original point. Maybe he could have been more touchy-feely in his answer, but that wasn't his nature.
Feynman grapples with the question the same way we would grapple with a question from a child: "why is the sky blue?" If you drill down into the explanation, you ultimately reach a statement that everyone just accepts as true, or you simply end with, "no one knows".
The way Feynman answered it looked extremely condescending and anti curiousity. Being pedantic for no reason. When answering you should try to guesstimate what the asker who is not an expert in your field is looking for and then start explanation relative from there.
At certain point, yes, you do have to say that either you don't know or humans haven't figured it out yet.
I took it very differently. I took it as him encouraging curiosity, because his point was, if you are curious, and nobody's explanation is satisfying you, then you should go research it yourself and be the first one to be able to explain it to the level you were looking for.
It's Richard Feynmann. He wasn't gonna be like "Magnets attract and repel because the spins of the electrons in atoms in the magnet are preferentially aligned which causes a macroscopic dipole in the magnetic field", and just leave it at that, like he just shared de-facto science gospel, because he doesn't want to assume that you won't ask something like "why do aligned electron spins create a macroscopic magnetic field?" or "Why do electrons spin?" or "is a magnetic monopole possible?"
He is teaching the core of curiosity itself. You can ask as many questions you can think of, but if you're not happy with the answers, then there's no other option than to go out there and do your own science. He is one of the smartest physicists of the last century and he is telling you that you don't have to take his word for it, he will not be able to answer everything for you and nobody will. And hopefully you are still curious after that.
Having read some of his lectures, and his autobiography, he was anything but anti-curiosity in him or in others. Watch that through the lens of someone who valued nothing more than asking questions and it might come across differently.
The additional important point, of course, is that there are many more 'Why' questions to be asked (often more interesting, and more important than corner cases like human-scale magnetism) that do not get asked just because of familiarity. Familiarity however is not understanding, and it is the same as simplicity.
He does repeatedly. And continues to explain why there is no satisfying answer, because we normally stop asking "why" once we reach a level of familiarity. That level of familiarity to the layperson is different between electromagnetism and slippery ice.
His attitude really bugs me, and it’s on full display in this clip - everything about this to me says “I am so smart and you have asked me a question so dumb that I don’t know how to dumb down my answer for you, now I will show how smart I am in the course of explaining how dumb your question is in excruciating detail, so next time you’ll know not to waste my smart time with dumb questions.”
Instead of playing games and being evasive and ‘owning’ the interviewer, he could have just worked with the guy to clarify the question and to talk through the guy’s understanding - he didn’t try to do that, though, and you can tell how delighted he is for this chance to show the guy up. His autobiography is written the same way, it’s a series of anecdotes about times where he was smart and other people were dumb. Really rubs me the wrong way.
You must have missed the part where he says that it's an excellent question.
> he was smart and other people were dumb
But he was smart. A lot smarter than you and me and the vast majority of people. He was also pretty humble about it, once famously saying that if he couldn't explain something to a freshman it's because he himself didn't understand it.
This might sound tautological but a particle is, well, a thing that behaves like a particle.
Those behaviors are something like:
- it has momentum
- it's state is uniquely defined by a position in space and a velocity
What's not a particle? A wave (well, until 1900 or so ...).
Sort of like asking "what is a number?"
A number is a thing that obeys certain rules. (You can add them; there's an `identity `, for every number there's a number which if you add together gives zero, etc).
That allows things like `(3 + 5i)` to be a number, for example.
The same is true about the terms "waves" and "fields" when it comes to quantum mechanics.
They're analogies. The concepts need names, but I think they do more harm than good because people then start with a mental model of a membrane or a surface - something they have experience seeing waves in. And then after 1 or 2 steps where the analogy helps, it breaks down, and people start being confused.
Of course the alternative isn't any better. If they had named it a "Wazoo function" and a "Quantum Flarg" everyone would've just kept asking "OK but what IS a Wazoo? What IS a Flarg" and not been satisfied with a "Yeah, it's a fundamental own thing".
I mean I can not speak for you, but I do not think that the problem necessarily is that people think of them as made from some stuff, I think what causes the most trouble is the desire to visualize particles.
The trouble is that an electron is an electron and it is nothing like anything you have ever seen in your macroscopic classical world. It shares some aspects with billiard balls and some with water waves but it is not like either. And it does not switch between being a billiard ball and a water wave, it always is the same thing, it always is an electron.
It just happens that in certain situations the billiard ball properties are more apparent and in others the water wave properties and in yet other situations neither of the two analogies will help. I think that is what trips people really up, they want to visualize their electron as one thing they know, as something they have an intuition for, but no such thing exists.
And electrons being electrons also means that they are not excitations in quantum fields. Those fields are mathematical models that describe the behaviour of electrons, they are not the electrons. Certainly not in the very direct sense of nature is just mathematics because I can differentiate, integrate, and square fields at will but I can not do this to electrons. And even the less direct interpretation, there are real entities in the universe that behave exactly like our mathematical fields, does not seem likely, what would the gauge symmetries mean?
I have no idea whether or not most physicist think that there are actually quantum fields in the universe. The Navier–Stokes equations provide a good description of milk mixing into my coffee, but should I therefore conclude that my coffee mug is filled with density and velocity fields and that what coffee really is, is a region in spacetime with a nonzero value of the coffee density field?
Quantum fields have gauge symmetries which means that they are a redundant description, i.e. any given physical situation is represented by an entire equivalence class of field configurations which makes me highly suspicious of there being real quantum fields. Quantum fields are a nice mathematical tool but I do not think we have any good reasons to think they are real, but I am not a physicist and I am certainly in dangerous half-knowledge territory here.
I have been wondering for years whether this might actually be a non-issue, could the universe secretly have fixed a gauge and just ran with it? Or would this somehow be inconsistent?
> I am not a physicist and I am certainly in dangerous half-knowledge territory here.
Gauging is just dealing with the fact that there is no absolute universal fixed value against which can compare a value at some point in a field; but we still want to consider values at one or more points in the field.
Let's do a really simple static model of the atmosphere, with a single scalar value: air pressure at each point. Let's use a simple device: an air pressure gauge which reports some fraction of a pressure measured when we push a "calibrate now" button. We'll call this a calibrated barometer. We can then recover the full air pressure field by measuring at every point in space (not space-time, the staticity means there is no time-dependence to the measurements; we can do them in any order and not have to worry about time of day or season).
Where do we push the "calibrate now" button? At some point on the surface? At mean sea level? At the top of the atmosphere? The choice of any of these will provide different readings on our gauge (i.e., it reports some fraction of the calibrated pressure, will differ when the calibration point is 101 kPa vs some fraction of the value actually measured at a specific point on the surface). But with a bit of care in choices of units, whatever we use as the calibration point, the difference between two different points in space will be the same.
A good choice of gauge lets use our calibrated barometer as an altimeter. In aviation, aircraft pressure altimeters have a calibration knob, which is used to recalibrate during different stages of a flight. Common calibration points are: QFE, field elevation, which lets one know how far above an airfield one is if separated only vertically from it, at the cost of being unable to simply compare the vertical separation between two aircraft above two different airfields; SPS (the pressure of the standard atmospheric pressure, 1013.25 hPa) is a global setting useful for quickly determining the vertical separation between two reasonably nearby aircraft, at the cost of not being able to quickly determine height above terrain, or even the height above mean sea level; QNH is another local setting which lets one compare how high above mean sea level the aircraft is, at the cost of needing to know the height above mean sea level of local terrain, and not being able to easily compare vertical distances with aircraft using one of the other two calibrations.
All three settings are "redundant descriptions" of the aviator's atmosphere. They describe the same column of air, but each makes it easier to pinpoint different hazards scattered through that column (the ground, other aircraft in level flight, the aircraft's operating ceiling).
We could complicate the atmosphere by introducing time dependency (at night in cold dry winter a QNH altitude will be fewer RADAR-measured metres above the same patch of ground), and atmospheric interactions (atmospheric waves, Bernouilli effects from winds). Each complication can be made to vanish via a careful choice of gauge, although it gets harder and harder to write down such a gauge as complications increase. (As a result, in aviation they allow for a certain amount of measurement error and safety margin, and comparisons with different means of measuring altitude like radio altimeters and satellite multilateration.)
In a quantum field theory (QFT), one might choose a gauge in which some particles vanish. A sibling comment pointed out that very commonly one wants to choose a gauge in which gauge bosons like photons don't need to be counted, rather than a gauge in which there is a sea of an enormous number of low-energy gauge bosons. Choosing the gauge does not eliminate the low-energy gauge bosons; in general QFT field values are time-dependent (and usually gauged to admit only "relevant" fluctuations). Low-energy fluctuations can be boosted into "real particles" by relativistic observers, and strongly accelerated observers can count more particles than a weakly accelerated one. Therefore the choice of a gauge for one observer might make calculations for another observer more difficult.
In QED there are several well-known and frequently-used gauges roughly analogous to SPS/QFE/QNH, and one often chooses one of them for convenience. Each of tehse gauges breaks the gauge freedom.
Gauge freedom means simply an uncalibrated system waiting to be calibrated. A common illustration of this is to choose a non-rotating sphere and setting down latitude/longitude. A less-gauge-symmetrical rotating sphere naturally picks out latitudes (the poles and the equator, notably), but there's still gauge freedom in longitude that we can fix by choosing a prime meridian, and gauge freedom in picking out one of the primary compass directions. These choices do not change the sphere or its rotation (or non-rotation), and of course one can choose any other set of coordinates one wants.
Once one has fixed the gauge on the sphere, though, one can more easily compare positions on the surface: is point A in the northern hemisphere, is point B in the eastern hemisphere? Just asking if point B is North-East of point A requires us to at least choose a north pole -- that can be one of two places on a rotating sphere, and it can be anywhere at all on a non-rotating one. The "right hand rule" is the conventional "gauge" for rotating astronomical bodies: anticlockwise rotation around the north pole (right hand: thumb up, fingers curled). But we don't have to use that convention as our "gauge". (We also have a problem for a truly non-rotating spherical object: where's the north pole? We might solve that by using an imagnariy axis parallel to the axis of a relevant body like the local star or the parent galaxy).
Finally, in many gauge theories there are gauge invariant quantities. On our spheres the geodesic intervals between two points are gauge invariant. The gauge tells us something about direction. In practice, fixing a gauge also usually involves choosing (and scaling) units: on our geodesic which might run south-east to north-west (gauge problem), the length might be measured in metres or light seconds (units problem) or kilometres and light-years (scaling problem). We might want to label different points along the geodesic in latitude/longitude (coordinate problem) rather than adapted Cartesian sphere-centred/sphere-fixed ("ECEF" on Earth) or tangential ("Local East-North[-Up]", "LENU") ones.
Because according to QFT they only exist because of the gauge symmetries. Photons are the solution to the redundant symmetries. Remove those redundant symmetries and you also need to remove the photons.
Universe "fixing a gauge" means no photons and no electromagnetic field, because the electromagnetic field IS the gauge symmetry.
Yep. Also, ignoring all the ways in which an electron isn't an electron. Electrons can be created and destroyed, and they are both indistinguishable and exchangeable. We can't assign identity to them, thanks to their Fermi statistics. They're just methods of explaining clicks in a detector.
I worked in particle physics for years and never once saw an electron. :-)
I’m not a physicist, but as an arrogant philosopher of science: isn’t it just field excitation? Like, every particle looks like a circle bouncing around a 2D piece of paper, but if you look reeaaaaally closely it’s just a localized 3D spike of energy in a usually 2D field of energy? So it’s made of the field/paper itself.
I must be under-thinking this, but that’s what’s worked pretty convincingly for me.
That's a bit too simple, not all functions work well as fields (differentiability is quite desirable) and you have no way to interact with the fields that way.
I think principal bundles come closest to what physicists call fields. Though I'm holding open the option that really the things in most equations are more like elements of the corresponding Lie-algebra.
It’s everything! Idk, I don’t think the universe owes us an answer there. What is a human? Well, it’s a human. You can think of all sorts of mental tools for understanding humans (eg “species”), but ultimately they just are.
Ok fair: they're things that right now are best understood using the term Field. I don't understand what kind of answer you're hoping for that would be better than this -- what kind of answer to "what is a particle" wouldn't be describable by mathematics?
By saying "the universe is fields", I'm saying "it's distributions of energy across spacetime". That's seemingly a consensus. Why demand that that energy must also form into strings or even tinier spheres or spheres in an alternate dimension or something? We have described fields in detail, I say Mission Accomplished
Let's say we describe a particle as being an excitation of a field. Can't we describe any physical phenomenon in the same way? For example, describe a football as an excitation of the football field. I think we all agree that this description does a terrible job of actually describing a football. In fact, I don't think it can be called a description at all. Likewise, I find describing a particle as an excitation of a field to be equally unsatisfactory.
A metaphor with another physical object will always fall short. Why not just state the number of bits a particle represents? It's much easier to describe going through each dimension (colloqiual, I hate string theory for the same reason of unnecessarily using a physical analogy) and describing how it interacts with other particles. Sure you'll lose a lot of your audience but those that remain will have a much clearer picture than via a comparison to a billiard ball. This also makes the more advanced topics like singularities, entanglement, teleportation, the lack of true vacuum, etc much easier to manage.
(I'm aware we don't have an understanding of how quantum physics interacts with singularities, but the whole billiard ball metaphor certainly is incoherent with it)
Particle is a cloudy, fuzzy thing that can fly and wobble through space. It can be more sharp or more fuzzy and when it overlaps with another fuzzy particle object they might exchange a neat portion of momentum, angular momentum and energy and violently reshape becoming sharper or fuzzier (that's the wave function collapse and expansion) then they go again on their separate merry ways.
Sometimes when particles meet or even spontaneously they can split or merge altering other parts of their nature (unrelated momentum, energy and angular momentum). This happens for example when neutron decays into proton and electron.
Sometimes they get stuck together because of electromagnetic force and they resonate in interesting harmonies and travel together. That's atoms. Interestingly when they are resonating in those harmonies they become quite fussy about amounts of energy they prefer to exchange and they do it only in a very specific quanta.
And there's a class of particles called quarks that travel together all the time as they are always tightly bound with each other and can never get free despite possessing incredible amounts of energy they continuously exchange. That's nucelus.
We really don't like this image because fuzziness is actually two dimensional in every point of our already 4 dimensional space-time and described by complex numbers so we prefer to focus on those brief moments when particles interact since if we have a lot of particles that are bound together to form measurement apparatus they are so sharp that the interaction they participate in squash other particles nearly to a point and we can declare that the measure particle collapsed to have some momentum, or location, or spin described by a single vector instead of a cloud. It neatly turns out that the square of complex number fuzziness describes the probability that a fuzzy particle will interact with a sharp one (one of those bound together in measurement apparatus) with a specific outcome.
I truly appreciate the discussion your comment has brought about. Some really great sibling comments.
There's also a lot of overlap with the article itself however. From the sibling comments too. At risk of breaking the rules, it's very much worth the read if you haven't read it!
It's a useful fiction, but the map is not the territory. This sounds blithe but ... it is as close as you will get to the truth.
I only got the bachelors' version of physics, though I did take some grad classes, so here is what I will tell you:
The human mind learns from experience and it thinks of things in terms of the past experiences it has had. We are big assemblages which exist in a narrow range of temperatures (think in terms of Kelvin). Our experience is classical, in the Newtonian sense: we move at not a particularly notable fraction of c, we are too warm to note the strangenesses which happen below, say, twenty or four or a thousandth of a Kelvin (superfluids and BECs are out), we are too cold to have a great internal experience of plasma, leaving us to be creatures of solid and liquid, with a sort of inferred understanding of gas. We are too large to feel the quantum realm, in the sense that the uncertainty principle is not obvious to us from what we have felt.
So, we must make do with abstractions, with fictions, with approximations. Conscious that we are the epitome of the six blind men trying to understand the elephant through touch alone, we try to break our understanding, to search for flaws in our inferences. Yet this does not grant us true experience when we run across, say, the electron. We try to think of it like a billiard ball, but we can say that a billiard ball is this wide, yet we are fairly sure at this time that the electron has no radius, no diameter, that it might as well be a geometric point. Every time we try to measure, we can only establish a smaller and smaller upper bound for the confounded thing's radius. That's not like our lives at all!
The reality of this electron is that if we get it going fast enough, it stops getting much faster no matter how hard we smack it. That's not like our reality. If we try to pin down where it is, the more we do it, the harder it is to figure out how fast and in what direction it moves. And as we work to ascertain the velocity (and therefore momentum), we lose sense of this bit of weirdness' position.
You eventually have to develop an understanding based not on experience at all.
Perhaps this was unique to me, but the first time I understood integration in calculus, I had a brief moment of dizziness as I apprehended this new thing. You know how you are working a math problem and you have a good idea of what the answer is already, a sense of what the magnitude and direction might be? I had ground my way through vector and tensor calculus, and had been working a problem in gravitation and relativity class when I sensed what the resulting tensor would look like, the shape of it, in the sense that I would know if my figures were way off. I nearly fell off the chair, my head spun so.
Thank you for this post. Given the limitations of human understanding and experience, one could safely use one metaphor or another for casual description. But at a deeper level of understanding, we do understand that our common experience does not apply, and that human language is too imprecise.
If anyone that attempts to explain the nature of consciousness in a non-falsifiable is a pseudo-scientist, then yes. I thought it was fun to hear perspectives like this.
Also, the soul discussion was pointing more at the history of language and concepts versus a crude equation of the two :)
This is essentially the Bohr take on the matter. There is no physicality in the sense that we interact with the world in. There are also no real dimensions as they are just our understanding of what we consider the physical world.
If that gets around your head, you’ll throw the physicality and real world away and you’ll come to see everything as information interaction.
I think I'm getting a glimmer of understanding on this now
From what I gather, a set of possible transformations is a group in group theory
Physical space is a type of group, i.e. a Poincare group, and is described by the set of all transformations on objects, or something (i.e. motion or lack thereof)
An irreducible poincare group is a tinest example of physical space, i.e. a 'particle'
So although it has no physical space, yet the irreducible Poincare group is intrinsically (but not practically) capable of those same types of transformations within itself as in the larger Poincare group within itself
E.g. a larger object (many particles) can undergo shears and strains, i.e. internal motion. In theory an infinitesimal particle can, it just doesn't have the space to undergo those
I'm inferring from this that a subset of physical space is also a Poincare group?
The Poincare group is the set of symmetries of spacetime (in special relativity), not spacetime itself. It characterizes the basic geometry of spacetime, so the dynamics of any physical system must be invariant under the action of this group, e.g. a physical system has the same dynamics as a rotated version of itself (as long as you rotate the whole physical system), and a physical system has the same dynamics as a version of itself with the velocities of all its components boosted uniformly in some direction (this is the principle of relativity). So the important things, like the dynamics, are invariant under the Poincare group, and the things that change are just dependent on the perspective of an observer.
Where the irreducible representations come in is in quantum mechanics, where physical systems are described by Hilbert spaces. These are spaces in the abstract mathematical sense of a vector space. They're used in quantum mechanics as a way to mathematically describe the fact that there are multiple possible outcomes of an experiment or interaction. The way this is done is by describing a quantum state as a unit vector in Hilbert space, each possible outcome corresponds to a dimension (a basis vector) in this space, and the probability of each outcome corresponds to the projection of the unit vector onto one of these dimensions. You can picture this as an arrow of unit length with its tail at the origin, and evolution of the state makes the arrow rotate about the origin, consequently changing its projection onto the basis vectors.
A representation of a group on a vector space is a way of describing the action of that group on the vectors in the space. Any vector space can be decomposed into subspaces which are invariant under the group action, meaning that if a vector starts off in that subspace, then the action of the group will not move it out of that subspace - these subspaces are the irreducible representations of the group.
So the irreducible representations of the Poincare group correspond to the components or properties of a physical system that are invariant under the basic symmetries of spacetime, i.e. that are independent of one's perspective, and in that sense they're considered basic or fundamental.
Yes, mathematical constructions are merely a model of reality
It is interesting to note that (correct me if I'm wrong) perhaps our mathematical constructs are based on a classical intuition and perception of the universe?
And here we are trying to fit that classical intuition into the quantum realm
Perhaps that can be related to why shit gets complicated with particle physics?
I am not sure if the modern mix of group theory and differential geometry which forms the foundation of theoretical physics today can qualify as such, even though the word "geometry" does bring the expectation that we should be able to "see" the things we are talking about.
That's certainly part of it. But part of it is we're not really terribly good at talking about the universe even with classical intuition.
That said, model-theoretic semantics go back to, at least, William of Ockham, who developed a formalized subset of Latin (which kind of reminds me of the Google C++ style guide in a way). We're clearly not utterly incompetent in this space, but it helps to stand on the shoulders of the giants to see clearly.
This makes me remember the time I looked at a random book at my university library, and it happened to be a physics book from 1905.
Which was both fascinating and unintentionally hilarious due to it proudly asserting that we knew most of physics now because we knew about atoms, and assuring the plum pudding model as how atoms worked.
n.b. Plum Pudding was the old-school idea that atoms were a positively-charged blob with negative electrons embedded. It was refuted when you measure the radiation scattering patterns off gold foil and discover that, actually, there's an extremely dense nucleus.
As a physics (and SF) enthusiast, I've come to realize that we've discovered most of the physics that exists, and all of what we can use. This is disappointing for those who yearn for FTL or teleportation, but it's good news when you consider that it creates an impregnable defense against interstellar invasion. Within the limits of modern physics, there remains a great deal to understand and apply, especially in QM because to quote Feynman "there's plenty of room at the bottom". Biology and nanotechnology can still revolutionize human existence.
The key problem humans must grapple with an solve, if we are to make it long-term, is how to harness greater and greater power without destroying ourselves. Nuclear destruction has been a very real option for 80 years. Biological weapons could do the job, too. And of course, climate change looms. For many years I agreed with the thinkers that wish for a "backup plan" for humanity; however, I don't think Mars will do it simply because its environment is even harsher than a post-nuclear holocaust Earth. The important reality that THIS is our home, and we must protect her even if it's hard. Yearning for advanced physics to solve all our problems has the unfortunate side-effect of undermining motivation to solve the problems we have now with the tech we have now. It underlies an unfortunate "disposable planet" attitude that we'd be better off without.
You don't think there's an einstein jr that will come one day and change some fundamental model in the weirdest way that will flip physics on its head again ?
I feel a curious mix of excitement and disconcerted to discover humans don’t really understand what matter is.
Reading the article, I understood so little of it. And I guess it’s because so much of the language is just words chosen through some sort of consensus to represent an abstract idea itself composed of such words-idea-representations which I’ve never encountered before.
We understand matter perfectly well. Look at the size and scope of the engineering marvels that have been constructed on the surface of this planet and in our low orbit. It's astonishing.
What we don't understand is the fundamental structure of that matter or of our Universe. I personally feel that the people ostensibly "in charge" of this effort are a little chagrined at their decades of inability to produce not only a cohesive result but even a reasonable intermediate explanation that they intentionally couch these problems in the most arcane and impenetrable language available to them.
In any case, you shouldn't feel discontent for humanity, as we've simply discovered all the easy problems, cleverly worked out all the average problems, and now all we're left with is the intractably hard ones. It's very likely that a different type of effort we haven't engaged in yet will be necessary to make progress.
I think there's a useful distinction to be made between "we understand it" and "we can make use of it." Certainly the latter is true, as you describe in your examples. I don't know that it implies the former, though.
I mean heck, even something as mundane as concrete is still the subject of active research as to the chemical reactions and complexities involved.
I guess it's more a spectrum of understanding than a yes/no situation.
For myself, I find it exciting to keep discovering how little we understand, despite our abilities. We seem to be barely a step removed from alchemy, from some points of view.
I think the distinction is more "we understand it" and "we can explain it." Understanding doesn't generally imply totality of comprehension.
Going the other way, you most likely cannot explain why your body or your brain works, yet, here we are, using and understanding them just fine.
Which leads to what I was trying to get at. Perhaps our tentative understandings and our means of receiving them are what gets in the way of deeper comprehension.
I personally don't think perfection is actually achievable, so I'm completely unwilling to accept your definition of our present state as "failing miserably." That's a rather miserable point of view and I prefer to have and encourage hope.
There are about 16 particles in the standard model. We've only mastered the electron, proton, photon, and have dabbled in using neutrons and neutrinos. Imagine the possibilities if we some day are able to use all the remaining particles?
If I recall correctly, the we can't really solve the equations for anything more complex than a helium atom (or is it hydrogen?). That's not to say there isn't useful work we can do, numerical approximations, etc. But things do get astoundingly complex very quickly, even with the "mastered" bits.
That's why calling Higgs Boson the God particle is not quite right. It's the Higgs field that gives mass to the other particles, not the Boson. A Higgs Boson is just an excitation of the Higgs field; it doesn't give mass to other particles. In fact it's the Higgs field modifying the other fields causing their excitations (particles) to slow down when passing each other, thus gaining masses.
Actually it doesn't seem to be that simple. Higgs Boson seems to contribute mainly to masses of leptons (mostly electrons) and bosons W and Z. And that influence goes to zero at high energies of the measures system making W and Z weightless and merging electrostatic and weak interactions into a singular electroweak interaction.
Quarks get most of their mass from QCD with very minor contribution from Higgs Boson. And nobody has any idea where the mass of neutrinos comes from.
It also has no influence on photons and gluons.
Higgs seems to be very peculiar and not very universal mechanism. I wonder if one of the potential future approaches won't do away with Highs Boson (together with virtual particles) as artifacts of specific math approach and interpretation without any physical manifestation.
Higgs was detected, sure, but it was detected through an interpretation of the data through the best available mathematical model which some postulate might contain some purely mathematical constructions along the way to the ultimate real world result.
it was in fact called the "Goddamn Particle" originally, referring to how difficult it was to detect it. The name was changed later to "God Particle" for publishing reasons.
Consider Young's double slit experiment: So, have plane with two slits and some distance away a parallel plane with detectors. (A) Several times, shoot a photon at the slit. Observe that the detection locations form parallel lines, i.e., fringes. (B) Cover one slit, repeat, and observe that the detection locations from a smooth hill without fringes.
So, from (A) we conclude that the something about the photon went through both slits and interacted with itself to form the fringes, the ones we didn't see from (B).
Q. Between the two planes, where was the energy?
(2) Mass and Charge
Set aside (1) with its photons and two planes.
Now one at a time shoot electrons, i.e., with not just energy but also mass and charge. And shoot the electrons at a beam splitter, i.e., a plane, partially transparent to the electrons, and at 45 degrees to the path of the electrons.
Some electrons pass through the plane with no change in direction and some get deflected 90 degrees.
On the paths after the plane, have some very sensitive detectors for mass and charge. These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors.
Q. What do the detectors read? For each of the two paths, whole mass and charge, half, or something else?
My idea for resolving this is that electron is never a point-like particle. It's always a cloud, just larger or smaller. When it's detected it gets reshaped to be narrower. Mass, energy, momentum and such are a quantities ascribed to the whole cloud and exchanged only on the moment of interaction.
Think about diffraction. Photon or electron that passes through a small hole had it's moment messed up proportionally. It becomes large again.
Interesting question is where's the gravity in all of this. There are various ideas how to match quantum uncertainty to shape of space-time.
What about interaction-free measurements, such as in the Elitzur–Vaidman bomb-tester thought experiment [1], which was later shown experimentally to be correct?
"These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors."
We detect gravitational waves without "affecting".
The electron mass and charge send out signals. Have the detectors sufficiently far away that they can't affect the particle yet. Get the detection and then know where the particle was and its mass and charge then. Have the particle reflected by some mirrors and then know the current path of the particle and its mass and charge, all without affecting the particle.
So LIGO detects a gravitational wave. Optical telescope data indicates that the wave was generated 10 billion light years away from two neutron stars. So, then, LIGO today affected the two neutron stars 10 billion years ago? Affected them today?
This article contains a very neat description of what is energy, momentum and spin and why they there. Energy is just a quantity that's preserved when shifting through time, momentum is a quantity preserved by shifting through space. And spin is a quantity preserved by rotation in space-time.
General relativity treats energy and momentum jointly so I guess basically energy-momentum is a quantity preserved in space-time translations and spin is a quantity preserved in space-time rotations. (in flat space-time, I think?)
I guess that's why those Poincare symmetries are rarely mentioned when talking about particles. They seem to come more from sheer geometry of space-time than anything else. Particle physicists are mainly interested in all other symmetries (because they were harder to figure out). It also must be bad feeling that while you are trying pull gravity into your framework, more than half of the symmetries that the objects you spent your career observing obey, come from general relativity not from your framework.
I'm honestly surprised that more people don't go mad in certain fields. If I ponder for 10 minutes the inexplicability of the universe's existence, or the vastness of space, my mind starts to breaks down.
1.1 INTRODUCTION: THERMODYNAMICS AND STATISTICAL MECHANICS OF THE PERFECT GAS
Ludwig Boltzmann, who spent much of his life studying statistical mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study statistical mechanics.
That's from Goodstein's "States of Matter" [1]. The next paragraph starts "Perhaps it will be wise to approach the subject cautiously".
That appears to be sufficient to allow non-fatal studying of statistical mechanics. Goodstein wrote that book 49 years ago and didn't die until a few months ago at the age of 85.
Constantly trying to resolve an incomplete abstraction. They are trying to reverse engineer the Universe. I can usually read half way through these articles before I'm completely lost in the abstractions.
When I consider your heavens,
the work of your fingers,
the moon and the stars,
which you have set in place,
what is mankind that you are mindful of them,
human beings that you care for them?
You have made them a little lower than the angels
and crowned them with glory and honor.
You made them rulers over the works of your hands;
you put everything under their feet:
all flocks and herds,
and the animals of the wild,
the birds in the sky,
and the fish in the sea,
all that swim the paths of the seas.
The answer of "the universe was created by a creator" is no more satisfying. It claims to answer everything, by answering nothing (since "a creator always existed" is axiomatic).
So basically a tree doesn't fall in the forest if there's no one around to see it? There's no forest and there are not trees. It's all spawned as needed when we go for a hike? Kinda arrogant don't you think?
A tree interacts with many things, not just human observers. We are not special in any way. This discreteness is only relevant and/or observable when we look at individual particles that rarely interact with anything else.
I have another definition, or at least this is how I think of it. I’m not sure many people would buy into it. In the standard model, the fermions are particles, like the electrons, quarks, neutrinos. Electroweak, strong force, gravity are fields. This means the photon is not a particle, but just a field excitation. I know people can think of fermions as fields, I just think of them as particles.
I did study quantum field theory and I have a hard time viewing a fermion as a continuous field, whereas a gauge field I do view as a continuous field. I view a fermion as a true point particle, kind of like it is in a lattice. The fermion still has a wave function of course. It is very different from the wave function of a gauge field. The wave function of an electric field is a wave function over field configurations. The fermion wave function is a wave function of fermion spins. I don't think this is an unreasonable view, but I am not trying to force it on anyone else.
I'm still new to learning about these things, but is the viewpoint that a particle is a field excitation sort of the thing about starting with a lattice in the ground state with a field defined on the points of the lattice, then some excitations happen which cause the field to enter a particular "mode". This mode is the particle?
No it would be very hard to actually have a consensus on proton decay. If it decays then according to the measurements (or the limits on the lack of the measurement) lifetime of such decay will be more than the universe age (Even without all the puzzle about Hubble constant tension and age of universe measurement disagreements). It was predicted first time by SU(5) theory and many other theories since then but the experiments rules out some of them (including original SU(5)) [1]
I would be personally interested in proton decay as it could be indirect indication for magnetic monopoles [2].
thank you! -- I meant more that is it consensus that those that know or would need to know think it should/does even if it's not been observed or proven to needfully do so (or disproven, if possible) but I get your point.
Why are magnetic monopoles interesting to you? I've seen some articles on them but I can't still wrap my head around how they'd work.
One of the biggest problems of a scientific education is the lack of hubris taught. Science has a very clear box it works remarkably well in, but it far too often strays outside of this box.
We should have been told that science is about the prediction and description of things. This is very different to what things actually are. If only scientists didn't believe from the very beginning that they were studying what reality of things are, they wouldn't spend so much time unlearning this later in life.
As usual comments here are more informative than the article. But no one mentioned that this is not a physics subject. The question “What is a particle?” belongs to philosophy not to physics. The problem for physicists is that they assume the Newtonian worldview that the world is made of indivisible units of matter called particles. [1] This assumption cannot be questioned. It is a dogma of the profession. But their experiments tell physicists again and again that the world is not made of indivisible units of matter. Physicists can either respect their experiments and accept that the world is not made of indivisible units of matter called particles or choose sophistry and try to fit their dogma into nature by wordplay. Physicists chose the latter and instead of dropping their dogma they keep changing the definition of the word “particle”. It does not matter what you call those indivisible units of matter. Physicists used to call them “particle” then “field”, then “excitation” and many other names that can be used case by case to save their sacred Newtonian dogma. Physicists’ dilemma is that they do business under the professional name of “particle” physicists. If there is no particle their profession would be redundant. Obviously they cannot call themselves “excitations of the field physicists”. So they keep the word particle but keep changing the meaning of it and they blame the public for not understanding physics jargon. My advice to physicists: respect the authority of your own experiments and drop the Newtonian dogma of a material world made of indivisible units of matter.
[1] "God in the beginning formed matter in solid, massy, hard, impenetrable movable particles." Isaac Newton, Optics, 1704, Book III, page: 375
A particle is a thing you can "look" at, and say "that's a particle". It is whatever one says it is. They're not exactly discovered, they're invented. Fundamental in this context is not so much a word as it is an analogy.
And, don't get me wrong, that doesn't mean particles don't exist. They do. But, a particle is whatever we say it is.
We're not asking questions about human constructs like what is moral or what is the ideal form of government. We're trying to understand what the most fundamental building block of reality is, which is something objective. Something independent of whether of not people ever existed.
So no, countless people around the world aren't wasting their lives researching particles when the answer is simply, it's whatever we say it is.
What can we see? Vapor trails, patterns burned into a plate, etc. The evidence of some "thing" slowing down, perhaps, but really the environment that slowed it down necessarily changing irreversibly. Irreversible effects cannot be arbitrarily small (apparently). We never see a particle, only effects such as these -- if we did see anything else, well, we couldn't possibly remember. Particles are an attempt to explain/theorize evidence that is fundamentally observational.
Did you take the time to read the original piece? Even the smart people can't agree.
What gives you the faith that a "particle" is not a human construct? What on earth does "fundamental" even mean except being the bottom turtle we can see on the particular mountain of turtles at which we're looking.
"Countless"(?) people around the world are not researching particles. They're doing particle physics as they understand "particles". That's how it should be and particles are whatever they say they are. In that field, no measure means no reality. *Unless*, of course, you have faith in some platonic reality.
When you say particles are whatever we say they are, I assume you believe particles are subjective. I'm saying particles are objective, like a "wavelength" as opposed to subjective, like "morals".
If you are saying even objective things are whatever we say they are, then this is a useless discussion. Obviously every word is defined with other words and all words are human creations. So yea in that sense, literally everything we know of is whatever we say it is. That's a pointless statement to make in response to this article or really ever.
I was saying that I don't know what a particle is, and neither does anyone else, but subjective isn't quite the correct word.
What I am sayings is that there are many useful interpretations of what a particle "is" that allows science to progress. The theoreticians and the experimentalists use, sometimes even form, those interpretations to help them along in their work. I'm saying that they yet remain interpretations, even analogies; and it really doesn't matter whether those folks believe in an objective reality or not, good work still gets done. Maybe it's subjective in that sense, but a particle is whatever they say it is; and nothing more can be said with certainty unless you dive into philosophy.
You can measure a perturbation in a field, or a track in a bubble chamber, and call it a particle. Then you can work backwards to an "objective" representation, and a particle still becomes whatever you say it is. It's still scientific, consistent, mathematically rigorous, and in line with theory and observation, but it remains a human construct. You can't escape that. Ultimately, one is free to believe that there is some fundamental thing; and, maybe there is and maybe there isn't.
> literally everything we know of is whatever we say it is
Of course "literally everything we know of is whatever we say it is". That, precisely, is my point. It most certainly does not mean that we can just state anything as true unless it is sensible, consistent, observable and verifiable; and expect not to be challenged.
Is the first law of thermodynamics whatever we say it is? If that's how you want to phrase it, then again, this is a useless discussion. All you're really saying is that the literal English words and sentences we use to define something are human constructs. That's so obviously true.
Yeah, I don't get that, because it seems to me that the friends you make along the way are mathematically indistinguishable from particles being real and having properties. It's a distinction without a difference.
Or at least, I'm interpreting "the friends you make along the way" as the sum total of the effects of a particle on the surrounding world. Saying "the particle doesn't exist, but it has effects X, Y, and Z" is the same as "the particle exists and has effects X, Y, and Z". If a distinction is not observable, then it's meaningless to quibble over whether it's "real" or not.
(Which all just proves that my interpretation isn't the one you were using....)
discovery vs invention is a question in mathematics as well. trying to say they're invented isn't clever, it's just a trick of language, like how gravity is merely a theory. particles are theorized to exist via theoretical physics and math, and then tested for experimentally. or as the saying goes, all models are wrong, some are useful.
I can't find the reference at the moment. But, I think it was about the "creation" of the quark. (I'll find it eventually). Either way, a search for reality, no matter how far we've progressed thus far, is either a search for a platonic reality, or an experimental reality. The former is "discovery" and the latter is "invention". It really doesn't matter. I don't think, right now, we're quite smart enough to pry into the mind of the universe, so we'll keep "inventing" things until we actually approach "discovery" asymptotically. Maybe we'll get there, but we've never been closer :-)
It's both discovery and experiment (but not invention). Forms are real, but not in the way Plato thought. He thought they existed in some empyrean realm. In reality, they exist in objects themselves. We discover what a thing's form is by experimenting with (or on) it. Aristotle was largely right.
The big philosophical problem with much of this is that people assume that the smallest things are the most fundamental. So people think that stuff, whatever that stuff is, is fundamentally made up of much smaller stuff, and that stuff is fundamentally made of yet smaller stuff, and so the smaller you get, the more fundamental you get. And so (they think) if you want to work out what is really going on at any layer of reality, you need to figure out what the smallest possible things are.
Yet this is ultimately a philosophical posit -- it's not empirically-informed. There's no good reason for thinking it.
To be clear, none of this is about physicists doing physics. It's about the philosophy that many people bring into, and therefore take away from, these kinds of discussions.
It's representative of a view that there's a thing (a particle) that explains another thing (a force) that was consistent with both theory and experiment. Thus, a quark could be a particle, and it was whatever the experimentalists and theorists said it was, however it was measured or contemplated.
For a deeper meaning it becomes an exercise in hermeneutics i.e what does it mean when we say "particle"? That was the point of the original piece - there is no uncontested view of a particle's form, should one even exist. Each field, in order to advance, finds it useful to interpret it, or think about it, in different ways.
I'm reading "The Big Picture" (Sean Carroll) right now.
I'd love to have a real physicist explain this, but:
When we think of what a particle IS, we often think as though it were dirt, or a billiard ball, or something. As though there were some other substance of which it's made. At least I do.
But the definition is as low as you can go. It's hard to wrap your head around that. Unless you're trained to do so, I guess.
Physicist here. You are right that the mental picture we get when we use the term “particle” is a little ball or something like that. It is unfortunately a confusing name… You need to begin with a field, like the electromagnetic field for instance. When you look at its properties like energy, polarization and so on, in order to write down a state of the field you need to specify all of them in a way or another. In quantum mechanics you can associate a vector space to each property, and then (here is the important bit) you need to pick a basis for your vector space in order to write down its vectors. Obviously there is an infinite number of possible choices, and we usually end up choosing what makes things simple, so in the case of energy we pick the basis of eigenvectors of the Hamiltonian, because to evolve them in time you just need to multiply them by a complex number and that’s it. Well, those basis vectors are the “particles“ because when taken individually they share some properties with macroscopic particles, but the analogy really only goes so far. And the thing is that usually the state of the field is not in a single one of these basis vectors unless the conditions are very special, so even saying that the field is “made of particles” is misleading because it’s like saying that the wind is made of air going vertically, horizontally and across, which sure it’s “correct” because you can combine those directions and get any other direction but it’s also not really that…
Also a physicist.
It's not quite right to call basis vectors particles, even in a free field theory. The particles correspond better to the creation / ladder operators that take you from one Hamiltonian eigenstate to another.
In a perturbative interacting case, people still think of particles as these same ladder operators, but they don't connect eigenstates so simply (the interactions generically mix all the states with the same quantum numbers).
In a strongly interacting case the story is even more subtle, because composite operators may be closer to the ladder operators between the asymptotic states, even though they're built of other... particles? Language isn't great in this instance.
Yeah it’s hard to use everyday language to exactly describe these things… And even more difficult to decide where to draw the line where some hand waving is acceptable.
As an amateur, I think I follow most of this, at least at some level, but I don't follow why you'd unify the basis elements and particles. Thinking of a quantum harmonic oscillator, the eigenstates have some kind of localization that feels particle-like, but the oscillating pattern of a coherent solution seems "more particle-like" and arises out of the interference between those eigenstates. In particle-speak, I might try on a sentence like "this classical particle is generated by the interaction between... other... particles" but I'm clearly at a loss there.
On basis of that, I'd be more likely to say "QM needs to describe everything as a wave, and sometimes certain kinds of localized 'wave-packets' move around coherently, and that's what we'd call 'particles'". That also seems to gel with less coherent states where it feels like there's not really a particle to be found.
So, I'm curious why you'd prefer to relate the eigenstates themselves as particles. Again in the oscillator case, the eigenstates themselves seem less coherent and seem to behave less classically than I'd hope.
My best guess is that the property those states have that is not as well replicated by the "particle as a coherent wave packet phenomenon" is that they have well-defined energy quanta. But that's just a bit of a stab in the dark here. It perhaps makes more sense from the perspective of "particles are the things that we're able to measure in detectors" POV, though.
You are exactly right at the end when you say that particles are what makes a detector go click. Let me try to clarify further. The "particleness" is not about localization, but about energy quantization. In fact, a single photon can be very non-localized, because spatial position is a different Hilbert space and it can be entirely independent of the energy. So the packets you are referring to are particles only if in their energy Hilbert space they correspond to a well-defined photon numbers, and that's why the analogy with classical particles only goes so far. To add to the confusion, one can speak of packets localized in phase space (e.g. coherent states, like the light produced by a laser) and packets localized in physical space like a short pulse, and these refer to different Hilbert spaces.
Particle spin explained:
Imagine a ball that’s rotating,
Except it’s not a ball, and
It’s not rotating.
(popular particle physics meme)
From what I understand of QFT, the Universe is made of fields of different types, and a “fundamental particle” is just an excitation (wave) in the corresponding field.
For example, a photon is a wave in the universal electromagnetic field, A charm quark is a wave in the universal charm quark field, etc.
I’m not a trained physicist, so I might be wildly wrong.
I get it but I still think these sorts of concepts are also just another level of mathematical abstraction that isn’t necessarily “really what it is” any more than a rotating ball or a math equation or any of the other ideas are “really what it is”
It's very frustrating. The idea that the universe is made of fields is nonsensical. I don't understand why so many physicists keep saying that.
If you don’t invest the statement “the universe is made of fields” with more meaning than necessary, then it makes more sense.
A quantum field is just a mathematical construct that models an aspect of what can happen at every point in spacetime. The fields follow rules for how they interact, and fluctuations in the fields and interactions between them, according to their respective rules, provide a good model for the universe we observe.
If you consider this purely mathematically, it’s hard to argue with. The models in question make very accurate predictions, can correctly model the vast majority of observations we know how to make, and don’t predict many things that we don’t observe. In other words, all the evidence is that it’s a very good model - a very good fit for the universe we observe.
From this perspective, one way to interpret the statement that “the universe is made of fields” is simply that the universe conforms to the quantum field model. Again, this claim is hard to argue with - it seems to me like a true statement, and there’s a lot of evidence for it.
Hawking & Mlodinow explored this in their description of what they called “model-dependent realism” - see: https://en.wikipedia.org/wiki/Model-dependent_realism
If perspectives like these don’t satisfy you, and you want to try to develop an understanding beyond mathematical models, then you have a tough problem to solve: how to go beyond the models that we know how to construct, to something that somehow gives you some sort of more fundamental insight. But what would that even look like? How would you test it? What would make this approach more true than existing theories?
In short, an answer that satisfies the criteria that you want it to satisfy may simply not be possible.
The Universe May Do As It Damned Well Pleases.
Maybe it is "made of fields", maybe it isn't, but "I think that's nonsense", which is just a gussied up way of saying "my intuition rejects that", is not a valid judgment method. The universe does not check with our intuition before doing what it Damned Well Pleases.
So you think the universe might be made of, say, subordinate clauses?
Whether or is or it isn't, it does it without consulting you or me or our intuitions.
I assume you meant that as an obvious absurdity, but if you were going for that you probably should have avoided the concept of "language", which can be Turing Complete. Still, the main point is, whatever it is, it is, and it isn't asking us for permission to be what it is.
My point is that physical reality cannot be made of something that doesn't exist physically, such as mathematical objects, abstract concepts or more generally ideas of any kind. Do you not agree that this must be true?
You lack the capability to judge what those things are, not because of some personal deficiency but because humans lack the ability at this level. If you dug in far enough you'd find your definition of what an abstract concept is circular anyhow, from the looks of it.
Proving the universe isn't made out of "mathematical objects" in particular is equivalent to the difficulty of proving it's not a "simulation". This is one of the red lines that tells you you've gone too far; you can't prove that. You can't even non-circularly define such a thing in this context anyhow, let alone prove anything.
Is there some experiment you can do that shows some 'physical realityness' that the mathematical object can't describe?
If not, then whose to say whether the mathematical object is 'real' or just a perfect description? Is the difference meaningful?
Yes, the difference is absolutely critical. Being unable to differentiate imaginary from real is a serious mental disorder.
It is true, but also kind of trivial. More subtly, one can say that we tend to call what is real using the same words that we use for mathematical objects that model them.
I don't know that we do that. For instance, physicists are able to describe motion in physical terms and don't insist that it literally is a vector. It only happens with quantum fields.
One of the ultimately epistemological puzzles to me is the question of what math really is. Like, obviously, it is fundamentally descriptive. “Two and two makes four” is pretty straightforwardly talking about something “out there”. And when we’re talking about fields, we are clearly also describing something that is really happening, that is really “out there”; it’s not the math itself that is the real thing, but rather it is a language for accurately describing and analyzing real things. But at some level, the real things it’s describing become so abstract and immaterial that they might as well be magic, or spirit. And it seems to me like our minds also contain and experience such things, too. Very advanced math and physics necessarily start to border on philosophy or theology.
One way of viewing it is that math is games. Not in the winner sense, but in the activities with rules sense. Addition is a game.
Some games make you better at other activities. Like, playing chess could make you better at logistics because you’re practicing planning and managing losses.
Some games match some real world situations so tightly that we can go through them step by step and solve the real world situation in the game. You can play addition to figure out two apples and two more makes four apples.
Whether the game is “real” or not is immaterial. It just needs to be internally consistent and matched to the right thing.
There’s also the idea that math is another world that we can visit, similar to the dream world. But that’s a whole other thing.
The idea that it's an abstraction is 100% accurate. That physics is a discrete set of fields with field rules and interaction rules, and what we observe is a scaffold on top of that. It's like okay, let's say the math is right and we have a set of fields, what are they and where are they from, how do we manipulate them. Then the physicists, often driven by ego, is want for an explanation and points to vibrating strings and such, and finally they knock on the door of the empiric physicist and say "can you do an experiment to show that I'm right" "sure, build a machine the size of the universe and I could test that" and that's the state of physics the last gorillion years
https://www.youtube.com/watch?v=FYJ1dbyDcrI
So in the viewpoint I’m describing you can definitely call it an abstraction. And abstraction has a vibe of intentionality to it, at least for me. That brings up something I didn’t mention, which is you can make a math game on purpose, to match with something in the real world. You can also make them up for fun (people don’t usually call it “for fun”, but that’s actually a fair label for theoretical mathematics IMO) and then discover the application later.
This is neat! I think it happens less in the physical world, just making up a tool and then finding its application later. It does happen in chemistry.
The magnetic field is one which you've probably had a chance to experience for yourself. Wave a magnet around a magnetic field and you can feel it has a different effect at different points in space. Fields are just time and space varying values for physical properties. Is the universe being composed of magnetism and a few related fields really so nonsensical?
Not really, until you go “well, what’s magnetism made of?” and the answer is “a field!” That’s pretty nonsensical.
I disagree! I think fields are very intuitive and it's everything else that's nonsensical!
Magnetism isn't made of anything. It is a field, and it's one your can interact with directly.
Compare that with, say, table salt. "What's table salt made of?" Uh. It's made of atoms entirely unrelated to salt, like sodium and chlorine. "What are atoms made of?" Uh. They're made of tiny electric particles zipping around at relativistic speeds but bound together by forces like magnetism.
Richard Feynman does a better job than me of describing this exact problem in one of my favorite physics videos of all time:
https://www.youtube.com/watch?v=Q1lL-hXO27Q
A great lesson one learns as a physicist is that one must develop a new intuition mainly through years of practice. So when you say "It's very frustrating", I interpret it as "this doesn't seem reasonable to me". But it doesn't have to be reasonable - none of us have any intuition for what happens at scales far different from our everyday lives.
The real question you raise is a very good one - how seriously should physicists take mathematical theories. If we were building a statistical model of, say, house prices and construct a reasonable linear regression model, we certainly don't believe that the market plugs the parameters of a house into the model to decide the price. The model is an approximation of the real dynamics of the market and this approximation might not hold in the future.
On the physics front, I would argue no one would consider a quadratic in speed air resistance term in Newton's second law, a fundamental feature of the universe. One can build a reasonable model that results in that term and it might even be a good approximation for some fluids in some speed/density range.
But, when it comes to more fundamental (as of today) theories like quantum electrodynamics, electroweak theory, quantum chromodynamics (all quantum field theories), or even general relativity (modulo discussions of quantum gravity) - both the predictive power and accuracy of these theories is so stunning (matching all the data generated at colliders like the LHC), that one starts wondering if we are no longer dealing with models but a true description of nature. The mathematical descriptions are also so constrained unlike the house price example above, that one can't just make modifications to the theories without violating core principles (and experimental data) like unitarity, causality, locality, Lorentz invariance etc. This only reinforces this view that perhaps this is close to a true description of what we see.
Now it is entirely possible (but IMO not probable) that this whole view will be upended and replaced by a very different physical picture. In a sense, string theory (which is now discredited heavily in the public's eye but that's a story for another day) was an attempt at a different physical picture that resulted in very rich structures that had nothing to do with physical reality.
So, physicists say that because the more time you spent understanding and studying quantum field theory and as more experiments are done (all the collisions at the LHC verify the standard model's predictions including the Higgs once its mass was known), it only reinforces that there's something deep about the current theories even though we have several unsolved problems (dark matter, dark energy, quantum gravity, fine-tuning problems).
Addendum 1: I'll add a book that is not accessible to non-physicists but gives a glimpse into the actual struggle of research and building intuition for something very abstract:
https://www.amazon.com/Feynman-Lectures-Gravitation-Richard-...
Feynman, like many others, spent considerable time applying all his powers to understand general relativity from a QFT perspective but eventually it didn't pan out (for anyone).
"It's very frustrating. The idea that Earth revolves around the Sun is nonsensical. I don't understand why so many astronomers keep saying that."
Spin is easy as long as you avoid trying to draw a direct analogy with ordinary rotation.
It’s just the statement that the object spinning is attached to its surroundings in a smooth and continuous fashion. Less rigid object, more a patch of space-time fabric spinning.
There’s a video here: https://youtu.be/LLw3BaliDUQ?feature=shared
It's worth keeping in mind that we don't yet have the sought-after Theory of Everything. We have a bunch of theories that mostly work in their domain of validity. These field theories are supposedly very accurate we don't actually know if they are the final word.
> we often think as though it were dirt, or a billiard ball, or something
The problem lies that it is hard to imagine something that does have zero dimensions. You can get the example of ant walking into 2D and it is unaware of third dimension to explain we are have something similar for space-time 4D (although not the same picture exactly as time is different from spatial dimensions). But we don't have an idea how to approximate a mental picture of what a zero dimension could be. So you have something that does not occupy a volume in space (Talking strictly about elementary particles here) in the classical sense.
This does not mean they are abstract concept. According to QFT -Quantum field theory- you would think (by training) of particles are excitations or quanta of their respective fields. Fields are there always (vacuum is just filled with fields) and particle appears when they are excited (more complex processes occurs). So you would think of each particle as a manifestation of a quantum field that permeates the universe. What is interesting (and probably confusing to most people) is that these fields are not zero-dimensional, instead, they exist everywhere in space and time. But the quanta (particles themselves) are considered point-like with no spatial extension.
In practice physicists will think about particles properties (i.e charge, mass, interactions, spin) ..etc instead of what this particle actually is from that point of view. This is often for practical reasons. You are a working physicist and you learned from your training that you shut up and calculate (or implement if you are doing experimental particle physics as you spend most of your time coding) by this stage.
I just think of a zero dimensial object as a ghost.
Topological defect. The unpictured thing the contour lines are swirling around. It's influence is only felt by seeing the effects on higher dimensional space, but you can never see the ghost itself.
So more like a poltergeist really
Or a magnet
> The problem lies that it is hard to imagine something that does have zero dimensions.
Do you really think so? It’s not hard to picture the real number line, with the point zero (or any other single point) distinguished. Sure — if you draw it in the standard schematic way you have to give it some area, but it still seems quite intuitive that it’s ‘zero-dimensional’. Especially if you play around with converging sequences and open sets and stuff; you quickly develop intuition for what it means to be a point rather than something higher dimensional.
I do - specifically, it’s hard to imagine a group of things which collectively constitute mass, but individually constitute no mass.
How can something come from nothing?
[dead]
So we have the three spatial dimensions, + time as 4. dimensions and at any of those 4-part coordinates there are additional properties like mass/spin/etc., some of much always come together or at least strongely correlate, and those values not being zero means there is a particle there and every value corresponds to a certain „field“ and it not being zero means the field is excited?
I've only got a physics minor, so hardly an expert, but I felt like quantum mechanics got a lot easier once I started thinking of a particle as merely a situation which has some probability of causing a state change in a detector of some kind.
Richard Feynman gave what I consider to be the best possible answer to questions like this:
https://www.youtube.com/watch?v=Q1lL-hXO27Q
In similar vein, the following question is very apt. Please read the question because it captures all of our intuition when we try to understand something.
https://physics.stackexchange.com/questions/46573/what-are-t...
What are strings made of?
One answer is that it is only meaningful to answer this question if the answer has physical consequences. Popularly speaking, string theory is supposed to be the innermost Russian doll of modern physics, and there are no more dolls inside that we can explain it in terms. However, we may be able to find equivalent formulations.
At first I was impressed with that video. Then I felt he does not have an answer and unnecessarily gets edgy with it, because question is valid.
I just watched it. I don't think he's edgy.
You can't explain it in terms of anything else, which was sorta my original point. Maybe he could have been more touchy-feely in his answer, but that wasn't his nature.
Hmm I think he's merely explaining what physics is and is not. Physics isn't really answering "why" questions, at least not ones with infinite scope.
Feynman grapples with the question the same way we would grapple with a question from a child: "why is the sky blue?" If you drill down into the explanation, you ultimately reach a statement that everyone just accepts as true, or you simply end with, "no one knows".
The way Feynman answered it looked extremely condescending and anti curiousity. Being pedantic for no reason. When answering you should try to guesstimate what the asker who is not an expert in your field is looking for and then start explanation relative from there.
At certain point, yes, you do have to say that either you don't know or humans haven't figured it out yet.
I took it very differently. I took it as him encouraging curiosity, because his point was, if you are curious, and nobody's explanation is satisfying you, then you should go research it yourself and be the first one to be able to explain it to the level you were looking for.
It's Richard Feynmann. He wasn't gonna be like "Magnets attract and repel because the spins of the electrons in atoms in the magnet are preferentially aligned which causes a macroscopic dipole in the magnetic field", and just leave it at that, like he just shared de-facto science gospel, because he doesn't want to assume that you won't ask something like "why do aligned electron spins create a macroscopic magnetic field?" or "Why do electrons spin?" or "is a magnetic monopole possible?"
He is teaching the core of curiosity itself. You can ask as many questions you can think of, but if you're not happy with the answers, then there's no other option than to go out there and do your own science. He is one of the smartest physicists of the last century and he is telling you that you don't have to take his word for it, he will not be able to answer everything for you and nobody will. And hopefully you are still curious after that.
Having read some of his lectures, and his autobiography, he was anything but anti-curiosity in him or in others. Watch that through the lens of someone who valued nothing more than asking questions and it might come across differently.
> he does not have an answer
Well, yeah. That's the whole point.
The additional important point, of course, is that there are many more 'Why' questions to be asked (often more interesting, and more important than corner cases like human-scale magnetism) that do not get asked just because of familiarity. Familiarity however is not understanding, and it is the same as simplicity.
He could simply say so.
He does repeatedly. And continues to explain why there is no satisfying answer, because we normally stop asking "why" once we reach a level of familiarity. That level of familiarity to the layperson is different between electromagnetism and slippery ice.
I see what you did there.
I knew it would be that video.
His attitude really bugs me, and it’s on full display in this clip - everything about this to me says “I am so smart and you have asked me a question so dumb that I don’t know how to dumb down my answer for you, now I will show how smart I am in the course of explaining how dumb your question is in excruciating detail, so next time you’ll know not to waste my smart time with dumb questions.”
Instead of playing games and being evasive and ‘owning’ the interviewer, he could have just worked with the guy to clarify the question and to talk through the guy’s understanding - he didn’t try to do that, though, and you can tell how delighted he is for this chance to show the guy up. His autobiography is written the same way, it’s a series of anecdotes about times where he was smart and other people were dumb. Really rubs me the wrong way.
> you have asked me a question so dumb
You must have missed the part where he says that it's an excellent question.
> he was smart and other people were dumb
But he was smart. A lot smarter than you and me and the vast majority of people. He was also pretty humble about it, once famously saying that if he couldn't explain something to a freshman it's because he himself didn't understand it.
This might sound tautological but a particle is, well, a thing that behaves like a particle.
Those behaviors are something like:
- it has momentum - it's state is uniquely defined by a position in space and a velocity
What's not a particle? A wave (well, until 1900 or so ...).
Sort of like asking "what is a number?"
A number is a thing that obeys certain rules. (You can add them; there's an `identity `, for every number there's a number which if you add together gives zero, etc).
That allows things like `(3 + 5i)` to be a number, for example.
> a particle is, well, a thing that behaves like a particle
Except when they don’t
https://en.wikipedia.org/wiki/Electron_diffraction
The same is true about the terms "waves" and "fields" when it comes to quantum mechanics.
They're analogies. The concepts need names, but I think they do more harm than good because people then start with a mental model of a membrane or a surface - something they have experience seeing waves in. And then after 1 or 2 steps where the analogy helps, it breaks down, and people start being confused.
Of course the alternative isn't any better. If they had named it a "Wazoo function" and a "Quantum Flarg" everyone would've just kept asking "OK but what IS a Wazoo? What IS a Flarg" and not been satisfied with a "Yeah, it's a fundamental own thing".
Feynman, of course, has a pretty definitive response on the difficulty of this problem: https://www.youtube.com/watch?v=Dp4dpeJVDxs
I mean I can not speak for you, but I do not think that the problem necessarily is that people think of them as made from some stuff, I think what causes the most trouble is the desire to visualize particles.
The trouble is that an electron is an electron and it is nothing like anything you have ever seen in your macroscopic classical world. It shares some aspects with billiard balls and some with water waves but it is not like either. And it does not switch between being a billiard ball and a water wave, it always is the same thing, it always is an electron.
It just happens that in certain situations the billiard ball properties are more apparent and in others the water wave properties and in yet other situations neither of the two analogies will help. I think that is what trips people really up, they want to visualize their electron as one thing they know, as something they have an intuition for, but no such thing exists.
And electrons being electrons also means that they are not excitations in quantum fields. Those fields are mathematical models that describe the behaviour of electrons, they are not the electrons. Certainly not in the very direct sense of nature is just mathematics because I can differentiate, integrate, and square fields at will but I can not do this to electrons. And even the less direct interpretation, there are real entities in the universe that behave exactly like our mathematical fields, does not seem likely, what would the gauge symmetries mean?
> And electrons being electrons also means that they are not excitations in quantum fields
You’re going against the dominant interpretation of QFT here, aren’t you?
I have no idea whether or not most physicist think that there are actually quantum fields in the universe. The Navier–Stokes equations provide a good description of milk mixing into my coffee, but should I therefore conclude that my coffee mug is filled with density and velocity fields and that what coffee really is, is a region in spacetime with a nonzero value of the coffee density field?
Quantum fields have gauge symmetries which means that they are a redundant description, i.e. any given physical situation is represented by an entire equivalence class of field configurations which makes me highly suspicious of there being real quantum fields. Quantum fields are a nice mathematical tool but I do not think we have any good reasons to think they are real, but I am not a physicist and I am certainly in dangerous half-knowledge territory here.
I have been wondering for years whether this might actually be a non-issue, could the universe secretly have fixed a gauge and just ran with it? Or would this somehow be inconsistent?
> I am not a physicist and I am certainly in dangerous half-knowledge territory here.
Gauging is just dealing with the fact that there is no absolute universal fixed value against which can compare a value at some point in a field; but we still want to consider values at one or more points in the field.
Let's do a really simple static model of the atmosphere, with a single scalar value: air pressure at each point. Let's use a simple device: an air pressure gauge which reports some fraction of a pressure measured when we push a "calibrate now" button. We'll call this a calibrated barometer. We can then recover the full air pressure field by measuring at every point in space (not space-time, the staticity means there is no time-dependence to the measurements; we can do them in any order and not have to worry about time of day or season).
Where do we push the "calibrate now" button? At some point on the surface? At mean sea level? At the top of the atmosphere? The choice of any of these will provide different readings on our gauge (i.e., it reports some fraction of the calibrated pressure, will differ when the calibration point is 101 kPa vs some fraction of the value actually measured at a specific point on the surface). But with a bit of care in choices of units, whatever we use as the calibration point, the difference between two different points in space will be the same.
A good choice of gauge lets use our calibrated barometer as an altimeter. In aviation, aircraft pressure altimeters have a calibration knob, which is used to recalibrate during different stages of a flight. Common calibration points are: QFE, field elevation, which lets one know how far above an airfield one is if separated only vertically from it, at the cost of being unable to simply compare the vertical separation between two aircraft above two different airfields; SPS (the pressure of the standard atmospheric pressure, 1013.25 hPa) is a global setting useful for quickly determining the vertical separation between two reasonably nearby aircraft, at the cost of not being able to quickly determine height above terrain, or even the height above mean sea level; QNH is another local setting which lets one compare how high above mean sea level the aircraft is, at the cost of needing to know the height above mean sea level of local terrain, and not being able to easily compare vertical distances with aircraft using one of the other two calibrations.
All three settings are "redundant descriptions" of the aviator's atmosphere. They describe the same column of air, but each makes it easier to pinpoint different hazards scattered through that column (the ground, other aircraft in level flight, the aircraft's operating ceiling).
We could complicate the atmosphere by introducing time dependency (at night in cold dry winter a QNH altitude will be fewer RADAR-measured metres above the same patch of ground), and atmospheric interactions (atmospheric waves, Bernouilli effects from winds). Each complication can be made to vanish via a careful choice of gauge, although it gets harder and harder to write down such a gauge as complications increase. (As a result, in aviation they allow for a certain amount of measurement error and safety margin, and comparisons with different means of measuring altitude like radio altimeters and satellite multilateration.)
In a quantum field theory (QFT), one might choose a gauge in which some particles vanish. A sibling comment pointed out that very commonly one wants to choose a gauge in which gauge bosons like photons don't need to be counted, rather than a gauge in which there is a sea of an enormous number of low-energy gauge bosons. Choosing the gauge does not eliminate the low-energy gauge bosons; in general QFT field values are time-dependent (and usually gauged to admit only "relevant" fluctuations). Low-energy fluctuations can be boosted into "real particles" by relativistic observers, and strongly accelerated observers can count more particles than a weakly accelerated one. Therefore the choice of a gauge for one observer might make calculations for another observer more difficult.
In QED there are several well-known and frequently-used gauges roughly analogous to SPS/QFE/QNH, and one often chooses one of them for convenience. Each of tehse gauges breaks the gauge freedom.
Gauge freedom means simply an uncalibrated system waiting to be calibrated. A common illustration of this is to choose a non-rotating sphere and setting down latitude/longitude. A less-gauge-symmetrical rotating sphere naturally picks out latitudes (the poles and the equator, notably), but there's still gauge freedom in longitude that we can fix by choosing a prime meridian, and gauge freedom in picking out one of the primary compass directions. These choices do not change the sphere or its rotation (or non-rotation), and of course one can choose any other set of coordinates one wants.
Once one has fixed the gauge on the sphere, though, one can more easily compare positions on the surface: is point A in the northern hemisphere, is point B in the eastern hemisphere? Just asking if point B is North-East of point A requires us to at least choose a north pole -- that can be one of two places on a rotating sphere, and it can be anywhere at all on a non-rotating one. The "right hand rule" is the conventional "gauge" for rotating astronomical bodies: anticlockwise rotation around the north pole (right hand: thumb up, fingers curled). But we don't have to use that convention as our "gauge". (We also have a problem for a truly non-rotating spherical object: where's the north pole? We might solve that by using an imagnariy axis parallel to the axis of a relevant body like the local star or the parent galaxy).
Finally, in many gauge theories there are gauge invariant quantities. On our spheres the geodesic intervals between two points are gauge invariant. The gauge tells us something about direction. In practice, fixing a gauge also usually involves choosing (and scaling) units: on our geodesic which might run south-east to north-west (gauge problem), the length might be measured in metres or light seconds (units problem) or kilometres and light-years (scaling problem). We might want to label different points along the geodesic in latitude/longitude (coordinate problem) rather than adapted Cartesian sphere-centred/sphere-fixed ("ECEF" on Earth) or tangential ("Local East-North[-Up]", "LENU") ones.
Do you think photons are real?
Because according to QFT they only exist because of the gauge symmetries. Photons are the solution to the redundant symmetries. Remove those redundant symmetries and you also need to remove the photons.
Universe "fixing a gauge" means no photons and no electromagnetic field, because the electromagnetic field IS the gauge symmetry.
I think this is why “shut up and calculate” is popular
Or as Newton more eloquently put it hypothesis non fingo.
Yep. Also, ignoring all the ways in which an electron isn't an electron. Electrons can be created and destroyed, and they are both indistinguishable and exchangeable. We can't assign identity to them, thanks to their Fermi statistics. They're just methods of explaining clicks in a detector.
I worked in particle physics for years and never once saw an electron. :-)
Joke: “birds aren’t real”
Woke: “electrons aren’t real”
I’m not a physicist, but as an arrogant philosopher of science: isn’t it just field excitation? Like, every particle looks like a circle bouncing around a 2D piece of paper, but if you look reeaaaaally closely it’s just a localized 3D spike of energy in a usually 2D field of energy? So it’s made of the field/paper itself.
I must be under-thinking this, but that’s what’s worked pretty convincingly for me.
So what is a field?
a thing that can have particle-like excitations
Historically, electrical and magnetic fields were discovered first. Then em-waves. Then photons.
This should tell us that fields are useful in their own right, without referencing particles.
A function that takes a point in space as input. The output can be various things, e.g. a scalar field gives a (possibly complex) number as output.
That's a bit too simple, not all functions work well as fields (differentiability is quite desirable) and you have no way to interact with the fields that way.
I think principal bundles come closest to what physicists call fields. Though I'm holding open the option that really the things in most equations are more like elements of the corresponding Lie-algebra.
It’s everything! Idk, I don’t think the universe owes us an answer there. What is a human? Well, it’s a human. You can think of all sorts of mental tools for understanding humans (eg “species”), but ultimately they just are.
No... a field is mathematical representation. The universe is most definitely NOT made of fields.
Are you saying that the universe cannot be represented by mathematics?
I imagine you could use that argument to shoot down pretty much any explanation.
I'm saying that a mathematical representation of a physical phenomenon isn't the physical phenomenon.
Ok fair: they're things that right now are best understood using the term Field. I don't understand what kind of answer you're hoping for that would be better than this -- what kind of answer to "what is a particle" wouldn't be describable by mathematics?
By saying "the universe is fields", I'm saying "it's distributions of energy across spacetime". That's seemingly a consensus. Why demand that that energy must also form into strings or even tinier spheres or spheres in an alternate dimension or something? We have described fields in detail, I say Mission Accomplished
Let's say we describe a particle as being an excitation of a field. Can't we describe any physical phenomenon in the same way? For example, describe a football as an excitation of the football field. I think we all agree that this description does a terrible job of actually describing a football. In fact, I don't think it can be called a description at all. Likewise, I find describing a particle as an excitation of a field to be equally unsatisfactory.
A probability.
A metaphor with another physical object will always fall short. Why not just state the number of bits a particle represents? It's much easier to describe going through each dimension (colloqiual, I hate string theory for the same reason of unnecessarily using a physical analogy) and describing how it interacts with other particles. Sure you'll lose a lot of your audience but those that remain will have a much clearer picture than via a comparison to a billiard ball. This also makes the more advanced topics like singularities, entanglement, teleportation, the lack of true vacuum, etc much easier to manage.
(I'm aware we don't have an understanding of how quantum physics interacts with singularities, but the whole billiard ball metaphor certainly is incoherent with it)
Particle is a cloudy, fuzzy thing that can fly and wobble through space. It can be more sharp or more fuzzy and when it overlaps with another fuzzy particle object they might exchange a neat portion of momentum, angular momentum and energy and violently reshape becoming sharper or fuzzier (that's the wave function collapse and expansion) then they go again on their separate merry ways.
Sometimes when particles meet or even spontaneously they can split or merge altering other parts of their nature (unrelated momentum, energy and angular momentum). This happens for example when neutron decays into proton and electron.
Sometimes they get stuck together because of electromagnetic force and they resonate in interesting harmonies and travel together. That's atoms. Interestingly when they are resonating in those harmonies they become quite fussy about amounts of energy they prefer to exchange and they do it only in a very specific quanta.
And there's a class of particles called quarks that travel together all the time as they are always tightly bound with each other and can never get free despite possessing incredible amounts of energy they continuously exchange. That's nucelus.
We really don't like this image because fuzziness is actually two dimensional in every point of our already 4 dimensional space-time and described by complex numbers so we prefer to focus on those brief moments when particles interact since if we have a lot of particles that are bound together to form measurement apparatus they are so sharp that the interaction they participate in squash other particles nearly to a point and we can declare that the measure particle collapsed to have some momentum, or location, or spin described by a single vector instead of a cloud. It neatly turns out that the square of complex number fuzziness describes the probability that a fuzzy particle will interact with a sharp one (one of those bound together in measurement apparatus) with a specific outcome.
I truly appreciate the discussion your comment has brought about. Some really great sibling comments.
There's also a lot of overlap with the article itself however. From the sibling comments too. At risk of breaking the rules, it's very much worth the read if you haven't read it!
It's a useful fiction, but the map is not the territory. This sounds blithe but ... it is as close as you will get to the truth.
I only got the bachelors' version of physics, though I did take some grad classes, so here is what I will tell you:
The human mind learns from experience and it thinks of things in terms of the past experiences it has had. We are big assemblages which exist in a narrow range of temperatures (think in terms of Kelvin). Our experience is classical, in the Newtonian sense: we move at not a particularly notable fraction of c, we are too warm to note the strangenesses which happen below, say, twenty or four or a thousandth of a Kelvin (superfluids and BECs are out), we are too cold to have a great internal experience of plasma, leaving us to be creatures of solid and liquid, with a sort of inferred understanding of gas. We are too large to feel the quantum realm, in the sense that the uncertainty principle is not obvious to us from what we have felt.
So, we must make do with abstractions, with fictions, with approximations. Conscious that we are the epitome of the six blind men trying to understand the elephant through touch alone, we try to break our understanding, to search for flaws in our inferences. Yet this does not grant us true experience when we run across, say, the electron. We try to think of it like a billiard ball, but we can say that a billiard ball is this wide, yet we are fairly sure at this time that the electron has no radius, no diameter, that it might as well be a geometric point. Every time we try to measure, we can only establish a smaller and smaller upper bound for the confounded thing's radius. That's not like our lives at all!
The reality of this electron is that if we get it going fast enough, it stops getting much faster no matter how hard we smack it. That's not like our reality. If we try to pin down where it is, the more we do it, the harder it is to figure out how fast and in what direction it moves. And as we work to ascertain the velocity (and therefore momentum), we lose sense of this bit of weirdness' position.
You eventually have to develop an understanding based not on experience at all.
Perhaps this was unique to me, but the first time I understood integration in calculus, I had a brief moment of dizziness as I apprehended this new thing. You know how you are working a math problem and you have a good idea of what the answer is already, a sense of what the magnitude and direction might be? I had ground my way through vector and tensor calculus, and had been working a problem in gravitation and relativity class when I sensed what the resulting tensor would look like, the shape of it, in the sense that I would know if my figures were way off. I nearly fell off the chair, my head spun so.
If you care to, you can do this for a particle.
Thank you for this post. Given the limitations of human understanding and experience, one could safely use one metaphor or another for casual description. But at a deeper level of understanding, we do understand that our common experience does not apply, and that human language is too imprecise.
this
https://youtu.be/j2oSyAfPzWg?si=bwM2NAsORzkqLQLk
Fun fields discussion on what particles are…
What a trip, the guest speaker was clearly a pseudoscientist, talking about "evolution fields" and "mind fields" and equating fields to souls.
If anyone that attempts to explain the nature of consciousness in a non-falsifiable is a pseudo-scientist, then yes. I thought it was fun to hear perspectives like this.
Also, the soul discussion was pointing more at the history of language and concepts versus a crude equation of the two :)
This is essentially the Bohr take on the matter. There is no physicality in the sense that we interact with the world in. There are also no real dimensions as they are just our understanding of what we consider the physical world.
If that gets around your head, you’ll throw the physicality and real world away and you’ll come to see everything as information interaction.
> “What is a particle?” > > “An irreducible representation of the Poincaré group,” a precocious classmate answered.
Me: Looks up Poincare group
Also me: Oooookay, that makes absolute perfect zero sense to me
But - again - that is a mathematical construction, which a physical particle is not.
I think I'm getting a glimmer of understanding on this now
From what I gather, a set of possible transformations is a group in group theory
Physical space is a type of group, i.e. a Poincare group, and is described by the set of all transformations on objects, or something (i.e. motion or lack thereof)
An irreducible poincare group is a tinest example of physical space, i.e. a 'particle'
So although it has no physical space, yet the irreducible Poincare group is intrinsically (but not practically) capable of those same types of transformations within itself as in the larger Poincare group within itself
E.g. a larger object (many particles) can undergo shears and strains, i.e. internal motion. In theory an infinitesimal particle can, it just doesn't have the space to undergo those
I'm inferring from this that a subset of physical space is also a Poincare group?
The Poincare group is the set of symmetries of spacetime (in special relativity), not spacetime itself. It characterizes the basic geometry of spacetime, so the dynamics of any physical system must be invariant under the action of this group, e.g. a physical system has the same dynamics as a rotated version of itself (as long as you rotate the whole physical system), and a physical system has the same dynamics as a version of itself with the velocities of all its components boosted uniformly in some direction (this is the principle of relativity). So the important things, like the dynamics, are invariant under the Poincare group, and the things that change are just dependent on the perspective of an observer.
Where the irreducible representations come in is in quantum mechanics, where physical systems are described by Hilbert spaces. These are spaces in the abstract mathematical sense of a vector space. They're used in quantum mechanics as a way to mathematically describe the fact that there are multiple possible outcomes of an experiment or interaction. The way this is done is by describing a quantum state as a unit vector in Hilbert space, each possible outcome corresponds to a dimension (a basis vector) in this space, and the probability of each outcome corresponds to the projection of the unit vector onto one of these dimensions. You can picture this as an arrow of unit length with its tail at the origin, and evolution of the state makes the arrow rotate about the origin, consequently changing its projection onto the basis vectors.
A representation of a group on a vector space is a way of describing the action of that group on the vectors in the space. Any vector space can be decomposed into subspaces which are invariant under the group action, meaning that if a vector starts off in that subspace, then the action of the group will not move it out of that subspace - these subspaces are the irreducible representations of the group.
So the irreducible representations of the Poincare group correspond to the components or properties of a physical system that are invariant under the basic symmetries of spacetime, i.e. that are independent of one's perspective, and in that sense they're considered basic or fundamental.
Yes, mathematical constructions are merely a model of reality
It is interesting to note that (correct me if I'm wrong) perhaps our mathematical constructs are based on a classical intuition and perception of the universe?
And here we are trying to fit that classical intuition into the quantum realm
Perhaps that can be related to why shit gets complicated with particle physics?
> classical intuition
I am not sure if the modern mix of group theory and differential geometry which forms the foundation of theoretical physics today can qualify as such, even though the word "geometry" does bring the expectation that we should be able to "see" the things we are talking about.
That's certainly part of it. But part of it is we're not really terribly good at talking about the universe even with classical intuition.
That said, model-theoretic semantics go back to, at least, William of Ockham, who developed a formalized subset of Latin (which kind of reminds me of the Google C++ style guide in a way). We're clearly not utterly incompetent in this space, but it helps to stand on the shoulders of the giants to see clearly.
> "It has been thought of as many things"
This makes me remember the time I looked at a random book at my university library, and it happened to be a physics book from 1905.
Which was both fascinating and unintentionally hilarious due to it proudly asserting that we knew most of physics now because we knew about atoms, and assuring the plum pudding model as how atoms worked.
n.b. Plum Pudding was the old-school idea that atoms were a positively-charged blob with negative electrons embedded. It was refuted when you measure the radiation scattering patterns off gold foil and discover that, actually, there's an extremely dense nucleus.
while I often wonder what part of today's knowledge will appear brutally obsolete for those born in the 2100s
As a physics (and SF) enthusiast, I've come to realize that we've discovered most of the physics that exists, and all of what we can use. This is disappointing for those who yearn for FTL or teleportation, but it's good news when you consider that it creates an impregnable defense against interstellar invasion. Within the limits of modern physics, there remains a great deal to understand and apply, especially in QM because to quote Feynman "there's plenty of room at the bottom". Biology and nanotechnology can still revolutionize human existence.
The key problem humans must grapple with an solve, if we are to make it long-term, is how to harness greater and greater power without destroying ourselves. Nuclear destruction has been a very real option for 80 years. Biological weapons could do the job, too. And of course, climate change looms. For many years I agreed with the thinkers that wish for a "backup plan" for humanity; however, I don't think Mars will do it simply because its environment is even harsher than a post-nuclear holocaust Earth. The important reality that THIS is our home, and we must protect her even if it's hard. Yearning for advanced physics to solve all our problems has the unfortunate side-effect of undermining motivation to solve the problems we have now with the tech we have now. It underlies an unfortunate "disposable planet" attitude that we'd be better off without.
You don't think there's an einstein jr that will come one day and change some fundamental model in the weirdest way that will flip physics on its head again ?
I feel a curious mix of excitement and disconcerted to discover humans don’t really understand what matter is.
Reading the article, I understood so little of it. And I guess it’s because so much of the language is just words chosen through some sort of consensus to represent an abstract idea itself composed of such words-idea-representations which I’ve never encountered before.
We understand matter perfectly well. Look at the size and scope of the engineering marvels that have been constructed on the surface of this planet and in our low orbit. It's astonishing.
What we don't understand is the fundamental structure of that matter or of our Universe. I personally feel that the people ostensibly "in charge" of this effort are a little chagrined at their decades of inability to produce not only a cohesive result but even a reasonable intermediate explanation that they intentionally couch these problems in the most arcane and impenetrable language available to them.
In any case, you shouldn't feel discontent for humanity, as we've simply discovered all the easy problems, cleverly worked out all the average problems, and now all we're left with is the intractably hard ones. It's very likely that a different type of effort we haven't engaged in yet will be necessary to make progress.
I think there's a useful distinction to be made between "we understand it" and "we can make use of it." Certainly the latter is true, as you describe in your examples. I don't know that it implies the former, though.
I mean heck, even something as mundane as concrete is still the subject of active research as to the chemical reactions and complexities involved.
I guess it's more a spectrum of understanding than a yes/no situation.
For myself, I find it exciting to keep discovering how little we understand, despite our abilities. We seem to be barely a step removed from alchemy, from some points of view.
I think the distinction is more "we understand it" and "we can explain it." Understanding doesn't generally imply totality of comprehension.
Going the other way, you most likely cannot explain why your body or your brain works, yet, here we are, using and understanding them just fine.
Which leads to what I was trying to get at. Perhaps our tentative understandings and our means of receiving them are what gets in the way of deeper comprehension.
> yet, here we are, using and understanding them just fine.
I think we’re failing miserably precisely because we don’t.
I personally don't think perfection is actually achievable, so I'm completely unwilling to accept your definition of our present state as "failing miserably." That's a rather miserable point of view and I prefer to have and encourage hope.
We understand _low_ resolution matter.
There are about 16 particles in the standard model. We've only mastered the electron, proton, photon, and have dabbled in using neutrons and neutrinos. Imagine the possibilities if we some day are able to use all the remaining particles?
For some definition of "mastered" (:
If I recall correctly, the we can't really solve the equations for anything more complex than a helium atom (or is it hydrogen?). That's not to say there isn't useful work we can do, numerical approximations, etc. But things do get astoundingly complex very quickly, even with the "mastered" bits.
Muons and positrons are used regularly in industry. Neutrinos have been used to image the inside of the Sun.
(2020)
Some discussion then: https://news.ycombinator.com/item?id=25091742
That's why calling Higgs Boson the God particle is not quite right. It's the Higgs field that gives mass to the other particles, not the Boson. A Higgs Boson is just an excitation of the Higgs field; it doesn't give mass to other particles. In fact it's the Higgs field modifying the other fields causing their excitations (particles) to slow down when passing each other, thus gaining masses.
Actually it doesn't seem to be that simple. Higgs Boson seems to contribute mainly to masses of leptons (mostly electrons) and bosons W and Z. And that influence goes to zero at high energies of the measures system making W and Z weightless and merging electrostatic and weak interactions into a singular electroweak interaction.
Quarks get most of their mass from QCD with very minor contribution from Higgs Boson. And nobody has any idea where the mass of neutrinos comes from.
It also has no influence on photons and gluons.
Higgs seems to be very peculiar and not very universal mechanism. I wonder if one of the potential future approaches won't do away with Highs Boson (together with virtual particles) as artifacts of specific math approach and interpretation without any physical manifestation.
Higgs was detected, sure, but it was detected through an interpretation of the data through the best available mathematical model which some postulate might contain some purely mathematical constructions along the way to the ultimate real world result.
it was in fact called the "Goddamn Particle" originally, referring to how difficult it was to detect it. The name was changed later to "God Particle" for publishing reasons.
https://en.m.wiktionary.org/wiki/God_particle
The line between whimsy and intellectual negligence seems blurry, in this case… how many people have been tricked by bad-faith gurus using this?
Thanks for sharing, TIL and it’s fascinating.
So, its all gravity, if you turn the sock inside out? Just taking different colors and shapes?
It’s more like Higgs field gives mass to other particles whose masses warp spacetime that gives gravity.
What do you mean? How do you reach that conclusion? I wasn’t aware there was a connection with gravity
best way to reveal a TOE
Discussed at the time:
What Is a Particle? - https://news.ycombinator.com/item?id=25085286 - Nov 2020 (37 comments)
Issues:
(1) With Itself:
Consider Young's double slit experiment: So, have plane with two slits and some distance away a parallel plane with detectors. (A) Several times, shoot a photon at the slit. Observe that the detection locations form parallel lines, i.e., fringes. (B) Cover one slit, repeat, and observe that the detection locations from a smooth hill without fringes.
So, from (A) we conclude that the something about the photon went through both slits and interacted with itself to form the fringes, the ones we didn't see from (B).
Q. Between the two planes, where was the energy?
(2) Mass and Charge
Set aside (1) with its photons and two planes.
Now one at a time shoot electrons, i.e., with not just energy but also mass and charge. And shoot the electrons at a beam splitter, i.e., a plane, partially transparent to the electrons, and at 45 degrees to the path of the electrons.
Some electrons pass through the plane with no change in direction and some get deflected 90 degrees.
On the paths after the plane, have some very sensitive detectors for mass and charge. These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors.
Q. What do the detectors read? For each of the two paths, whole mass and charge, half, or something else?
You're very close to understanding to quantum eraser experiment / the even more upsetting delayed-choice quantum eraser.
Even though it sounds as though your arguments are gotchas that prove quantum mechanics to be nonsense, it turns out the world really is that way.
https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
Gee, I'm not the first to make this mistake about quantum mechanics!
You can't detect without affecting.
My idea for resolving this is that electron is never a point-like particle. It's always a cloud, just larger or smaller. When it's detected it gets reshaped to be narrower. Mass, energy, momentum and such are a quantities ascribed to the whole cloud and exchanged only on the moment of interaction.
Think about diffraction. Photon or electron that passes through a small hole had it's moment messed up proportionally. It becomes large again.
Interesting question is where's the gravity in all of this. There are various ideas how to match quantum uncertainty to shape of space-time.
> You can't detect without affecting
What about interaction-free measurements, such as in the Elitzur–Vaidman bomb-tester thought experiment [1], which was later shown experimentally to be correct?
[1] https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_t...
> You can't detect without affecting.
"These detectors are distant enough that what they do cannot affect the electron, i.e., the electron does not know about the detectors."
We detect gravitational waves without "affecting".
The electron mass and charge send out signals. Have the detectors sufficiently far away that they can't affect the particle yet. Get the detection and then know where the particle was and its mass and charge then. Have the particle reflected by some mirrors and then know the current path of the particle and its mass and charge, all without affecting the particle.
> The electron mass and charge send out signals.
This affects them.
So LIGO detects a gravitational wave. Optical telescope data indicates that the wave was generated 10 billion light years away from two neutron stars. So, then, LIGO today affected the two neutron stars 10 billion years ago? Affected them today?
Absolutely. But this not a causal effect, but it collapses the probabilities of what has occurred.
This article contains a very neat description of what is energy, momentum and spin and why they there. Energy is just a quantity that's preserved when shifting through time, momentum is a quantity preserved by shifting through space. And spin is a quantity preserved by rotation in space-time.
General relativity treats energy and momentum jointly so I guess basically energy-momentum is a quantity preserved in space-time translations and spin is a quantity preserved in space-time rotations. (in flat space-time, I think?)
I guess that's why those Poincare symmetries are rarely mentioned when talking about particles. They seem to come more from sheer geometry of space-time than anything else. Particle physicists are mainly interested in all other symmetries (because they were harder to figure out). It also must be bad feeling that while you are trying pull gravity into your framework, more than half of the symmetries that the objects you spent your career observing obey, come from general relativity not from your framework.
I'm honestly surprised that more people don't go mad in certain fields. If I ponder for 10 minutes the inexplicability of the universe's existence, or the vastness of space, my mind starts to breaks down.
That's from Goodstein's "States of Matter" [1]. The next paragraph starts "Perhaps it will be wise to approach the subject cautiously".
That appears to be sufficient to allow non-fatal studying of statistical mechanics. Goodstein wrote that book 49 years ago and didn't die until a few months ago at the age of 85.
[1] https://www.amazon.com/States-Matter-Dover-Books-Physics/dp/...
And away we go!
The impression this article and many other things like it leaves me with is that we are struggling to get language and an abstractions out of our way.
We have to use them to talk about things and work with them, but they all “leak.”
Constantly trying to resolve an incomplete abstraction. They are trying to reverse engineer the Universe. I can usually read half way through these articles before I'm completely lost in the abstractions.
The answer of "the universe was created by a creator" is no more satisfying. It claims to answer everything, by answering nothing (since "a creator always existed" is axiomatic).
> It claims to answer everything, by answering nothing.
You missed the wisdom in your own statement.
It's just a puzzle and should be taken as such.
The universe is a puzzle?
If you try to understand things about it, yes.
As someone once said, "There is no requirement on the Universe to make sense".
Starting with the axiom that what I am experiencing is actually representative of reality to begin with.
But never has physicists’ conception of a particle changed more than it is changing now.
A concerning statement for a four year old article. Has anything in it been superseded?
A particle is a node in the universal interaction graph.
“Space”, however, is a derivative attribute emerging as the “distance” between particles in the graph; there is no “space”, only metrics.
Reality does not exist between measurements/interactions; the outcome is calculated on demand.
So basically a tree doesn't fall in the forest if there's no one around to see it? There's no forest and there are not trees. It's all spawned as needed when we go for a hike? Kinda arrogant don't you think?
A tree interacts with many things, not just human observers. We are not special in any way. This discreteness is only relevant and/or observable when we look at individual particles that rarely interact with anything else.
So we have no idea what's observable in this generic way and what's not.
[dead]
I have another definition, or at least this is how I think of it. I’m not sure many people would buy into it. In the standard model, the fermions are particles, like the electrons, quarks, neutrinos. Electroweak, strong force, gravity are fields. This means the photon is not a particle, but just a field excitation. I know people can think of fermions as fields, I just think of them as particles.
Aren't you describing quantum field theory (QFT)?
Anyway, what exactly is a field besides a mathematical object? What is it made of?
I did study quantum field theory and I have a hard time viewing a fermion as a continuous field, whereas a gauge field I do view as a continuous field. I view a fermion as a true point particle, kind of like it is in a lattice. The fermion still has a wave function of course. It is very different from the wave function of a gauge field. The wave function of an electric field is a wave function over field configurations. The fermion wave function is a wave function of fermion spins. I don't think this is an unreasonable view, but I am not trying to force it on anyone else.
I'm still new to learning about these things, but is the viewpoint that a particle is a field excitation sort of the thing about starting with a lattice in the ground state with a field defined on the points of the lattice, then some excitations happen which cause the field to enter a particular "mode". This mode is the particle?
Checkout energywavetheory.com. It's essential the Aether, but really makes you think.
I flipped through some of the content. It's very well presented, but unfortunately it is pseudo-science gibberish.
tangentially: is it consensus at this point that the proton decays -- it just does so on a really large timescale?
No it would be very hard to actually have a consensus on proton decay. If it decays then according to the measurements (or the limits on the lack of the measurement) lifetime of such decay will be more than the universe age (Even without all the puzzle about Hubble constant tension and age of universe measurement disagreements). It was predicted first time by SU(5) theory and many other theories since then but the experiments rules out some of them (including original SU(5)) [1]
I would be personally interested in proton decay as it could be indirect indication for magnetic monopoles [2].
[1] https://en.wikipedia.org/wiki/Proton_decay?useskin=vector#Pr...
[2] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.52...
thank you! -- I meant more that is it consensus that those that know or would need to know think it should/does even if it's not been observed or proven to needfully do so (or disproven, if possible) but I get your point.
Why are magnetic monopoles interesting to you? I've seen some articles on them but I can't still wrap my head around how they'd work.
This article is fantastic because it makes the subject so accessible
See also
Hobson (2012): There are no particles, there are only fields
https://arxiv.org/abs/1204.4616
For some reason this page makes my monitor flicker. Anyone else have this problem? Anyone know why it happens?
Do you have an external monitor connected to your Mac Pro Laptop?
If so, disable True Tone and disable auto brightness on all screens. That might help.
[dead]
One of the biggest problems of a scientific education is the lack of hubris taught. Science has a very clear box it works remarkably well in, but it far too often strays outside of this box.
We should have been told that science is about the prediction and description of things. This is very different to what things actually are. If only scientists didn't believe from the very beginning that they were studying what reality of things are, they wouldn't spend so much time unlearning this later in life.
As usual comments here are more informative than the article. But no one mentioned that this is not a physics subject. The question “What is a particle?” belongs to philosophy not to physics. The problem for physicists is that they assume the Newtonian worldview that the world is made of indivisible units of matter called particles. [1] This assumption cannot be questioned. It is a dogma of the profession. But their experiments tell physicists again and again that the world is not made of indivisible units of matter. Physicists can either respect their experiments and accept that the world is not made of indivisible units of matter called particles or choose sophistry and try to fit their dogma into nature by wordplay. Physicists chose the latter and instead of dropping their dogma they keep changing the definition of the word “particle”. It does not matter what you call those indivisible units of matter. Physicists used to call them “particle” then “field”, then “excitation” and many other names that can be used case by case to save their sacred Newtonian dogma. Physicists’ dilemma is that they do business under the professional name of “particle” physicists. If there is no particle their profession would be redundant. Obviously they cannot call themselves “excitations of the field physicists”. So they keep the word particle but keep changing the meaning of it and they blame the public for not understanding physics jargon. My advice to physicists: respect the authority of your own experiments and drop the Newtonian dogma of a material world made of indivisible units of matter.
[1] "God in the beginning formed matter in solid, massy, hard, impenetrable movable particles." Isaac Newton, Optics, 1704, Book III, page: 375
A particle is a thing you can "look" at, and say "that's a particle". It is whatever one says it is. They're not exactly discovered, they're invented. Fundamental in this context is not so much a word as it is an analogy.
And, don't get me wrong, that doesn't mean particles don't exist. They do. But, a particle is whatever we say it is.
"Things are named before they are understood." -- Matt Strassler
Further: Things are named, then the linguistic burden actually comes to limit understanding.
We're not asking questions about human constructs like what is moral or what is the ideal form of government. We're trying to understand what the most fundamental building block of reality is, which is something objective. Something independent of whether of not people ever existed.
So no, countless people around the world aren't wasting their lives researching particles when the answer is simply, it's whatever we say it is.
What can we see? Vapor trails, patterns burned into a plate, etc. The evidence of some "thing" slowing down, perhaps, but really the environment that slowed it down necessarily changing irreversibly. Irreversible effects cannot be arbitrarily small (apparently). We never see a particle, only effects such as these -- if we did see anything else, well, we couldn't possibly remember. Particles are an attempt to explain/theorize evidence that is fundamentally observational.
Did you take the time to read the original piece? Even the smart people can't agree.
What gives you the faith that a "particle" is not a human construct? What on earth does "fundamental" even mean except being the bottom turtle we can see on the particular mountain of turtles at which we're looking.
"Countless"(?) people around the world are not researching particles. They're doing particle physics as they understand "particles". That's how it should be and particles are whatever they say they are. In that field, no measure means no reality. *Unless*, of course, you have faith in some platonic reality.
Positive materialists will disagree.
When you say particles are whatever we say they are, I assume you believe particles are subjective. I'm saying particles are objective, like a "wavelength" as opposed to subjective, like "morals".
If you are saying even objective things are whatever we say they are, then this is a useless discussion. Obviously every word is defined with other words and all words are human creations. So yea in that sense, literally everything we know of is whatever we say it is. That's a pointless statement to make in response to this article or really ever.
I was saying that I don't know what a particle is, and neither does anyone else, but subjective isn't quite the correct word.
What I am sayings is that there are many useful interpretations of what a particle "is" that allows science to progress. The theoreticians and the experimentalists use, sometimes even form, those interpretations to help them along in their work. I'm saying that they yet remain interpretations, even analogies; and it really doesn't matter whether those folks believe in an objective reality or not, good work still gets done. Maybe it's subjective in that sense, but a particle is whatever they say it is; and nothing more can be said with certainty unless you dive into philosophy.
You can measure a perturbation in a field, or a track in a bubble chamber, and call it a particle. Then you can work backwards to an "objective" representation, and a particle still becomes whatever you say it is. It's still scientific, consistent, mathematically rigorous, and in line with theory and observation, but it remains a human construct. You can't escape that. Ultimately, one is free to believe that there is some fundamental thing; and, maybe there is and maybe there isn't.
> literally everything we know of is whatever we say it is
Of course "literally everything we know of is whatever we say it is". That, precisely, is my point. It most certainly does not mean that we can just state anything as true unless it is sensible, consistent, observable and verifiable; and expect not to be challenged.
Is the first law of thermodynamics whatever we say it is? If that's how you want to phrase it, then again, this is a useless discussion. All you're really saying is that the literal English words and sentences we use to define something are human constructs. That's so obviously true.
I'll go even further and point out that in 2003, it was proven that particles are not, in fact, the friends we made along the way.
Do expand. What happened in 2023?
Yeah, I don't get that, because it seems to me that the friends you make along the way are mathematically indistinguishable from particles being real and having properties. It's a distinction without a difference.
Or at least, I'm interpreting "the friends you make along the way" as the sum total of the effects of a particle on the surrounding world. Saying "the particle doesn't exist, but it has effects X, Y, and Z" is the same as "the particle exists and has effects X, Y, and Z". If a distinction is not observable, then it's meaningless to quibble over whether it's "real" or not.
(Which all just proves that my interpretation isn't the one you were using....)
discovery vs invention is a question in mathematics as well. trying to say they're invented isn't clever, it's just a trick of language, like how gravity is merely a theory. particles are theorized to exist via theoretical physics and math, and then tested for experimentally. or as the saying goes, all models are wrong, some are useful.
I can't find the reference at the moment. But, I think it was about the "creation" of the quark. (I'll find it eventually). Either way, a search for reality, no matter how far we've progressed thus far, is either a search for a platonic reality, or an experimental reality. The former is "discovery" and the latter is "invention". It really doesn't matter. I don't think, right now, we're quite smart enough to pry into the mind of the universe, so we'll keep "inventing" things until we actually approach "discovery" asymptotically. Maybe we'll get there, but we've never been closer :-)
It's both discovery and experiment (but not invention). Forms are real, but not in the way Plato thought. He thought they existed in some empyrean realm. In reality, they exist in objects themselves. We discover what a thing's form is by experimenting with (or on) it. Aristotle was largely right.
The big philosophical problem with much of this is that people assume that the smallest things are the most fundamental. So people think that stuff, whatever that stuff is, is fundamentally made up of much smaller stuff, and that stuff is fundamentally made of yet smaller stuff, and so the smaller you get, the more fundamental you get. And so (they think) if you want to work out what is really going on at any layer of reality, you need to figure out what the smallest possible things are.
Yet this is ultimately a philosophical posit -- it's not empirically-informed. There's no good reason for thinking it.
To be clear, none of this is about physicists doing physics. It's about the philosophy that many people bring into, and therefore take away from, these kinds of discussions.
I found the reference. It was an interview with Freeman Dyson where he said "quarks were invented", and I don't think it's a slip of the tongue.
It's at 3:17 in this video of an interview with him https://www.youtube.com/watch?v=hV41QEKiMlM
It's representative of a view that there's a thing (a particle) that explains another thing (a force) that was consistent with both theory and experiment. Thus, a quark could be a particle, and it was whatever the experimentalists and theorists said it was, however it was measured or contemplated.
For a deeper meaning it becomes an exercise in hermeneutics i.e what does it mean when we say "particle"? That was the point of the original piece - there is no uncontested view of a particle's form, should one even exist. Each field, in order to advance, finds it useful to interpret it, or think about it, in different ways.