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Is particle physics dead, dying, or just hard?

quantamagazine.org

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Re: Is particle physics dead, dying, or just hard?

#61

Post by recursivecaveat »

klipt wrote: post #24
bananaflag wrote: post #7

It's basically the opposite situation from 150 years ago. Back then, we thought our theory was more or less complete while having experimental data which disproved it (Michelson-Morley experiment, Mercury perihelion, I am sure there are others). Right now, we know our theories are incomplete (since GR and QFT are incompatible) while having no experimental data which contradicts them.

Doesn't that imply our theories are "good enough" for all practical purposes? If they're impossible to empirically disprove?

Maybe? We seem to be able to characterize all the stuff we have access to. That doesn't mean we couldn't say produce new and interesting materials with new knowledge. Before we knew about nuclear fission we didn't realize that we couldn't predict that anything would happen from a big chunk of uranium or the useful applications of that. New physics might be quite subtle or specific but still useful.

Re: Is particle physics dead, dying, or just hard?

#62

Post by auntienomen »

Paracompact wrote: post #21
tasty_freeze wrote: post #15

Here is one fact that seems, to me, pretty convincing that there is another layer underneath what we know. The charge of electrons is -1 and protons +1. It has been experimentally measured out to 12 digits or so to be the same magnitude, just opposite charge. However, there are no theories why this is -- they are simply measured and that is it. It beggars belief that these just happen to be exactly (as far as we can…

Technically, the charge of a proton can be derived from its constituent 2 up quarks and 1 down quark, which have charges 2/3 and -1/3 respectively. I'm not aware of any deeper reason why these should be simple fractional ratios of the charge of the electron, however, I'm not sure there needs to be one. If you believe the stack of turtles ends somewhere, you have to accept there will eventually be (hopefully simple) c…

There does appear to be a deeper reason, but it's really not well understood.

Consistent quantum field theories involving chiral fermions (such as the Standard Model) are relatively rare: the charges have to satisfy a set of polynomial relationships with the inspiring name "gauge anomaly cancellation conditions". If these conditions aren't satisfied, the mathematical model will fail pretty spectacularly. It won't be unitary, can't couple consistently to gravity, won't allow high and low energy behavior to decouple,..

For the Standard Model, the anomaly cancellation conditions imply that the sum of electric charges within a generation must vanish, which they do:

3 colors of quark * ( up charge 2/3 - down charge 1/3) + electron charge -1 + neutrino charge 0 = 0.

So, there's something quite special about the charge assignments in the Standard Model. They're nowhere near as arbitrary as they could be a priori.

Historically, this has been taken as a hint that the standard model should come from a simpler "grand unified" model. Particle accelerators and cosmology hace turned up at best circumstantial evidence for these so far. To me, it's one of the great mysteries.

Re: Is particle physics dead, dying, or just hard?

#63

Post by Paracompact »

tasty_freeze wrote: post #48
Paracompact wrote: post #21

Earlier quoted context omitted.

Technically, the charge of a proton can be derived from its constituent 2 up quarks and 1 down quark, which have charges 2/3 and -1/3 respectively. I'm not aware of any deeper reason why these should be simple fractional ratios of the charge of the electron, however, I'm not sure there needs to be one. If you believe the stack of turtles ends somewhere, you have to accept there will eventually be (hopefully simple) c…

I'm aware of the charge coming from quarks, but my point remains. > you have to accept there will eventually be (hopefully simple) coincidences between certain fundamental values, no? When the probability of coincidence is epsilon, then, no. Right now they are the same to 12 digits, but that undersells it, because that is just the trailing digits. There is nothing which says the leading digits must be the same, eg, o…

If you imagine the universe is made of random real fundamental constants rather than random integer fundamental constants, then indeed there's no reason to expect such collisions. But if our universe starts from discrete foundations, then there may be no more satisfying explanation to this than there is to the question of, say, why the survival threshold and the reproduction threshold in Conway's Game of Life both involve the number 3. That's just how that universe is defined.

Re: Is particle physics dead, dying, or just hard?

#64

Post by tasty_freeze »

Paracompact wrote: post #63
tasty_freeze wrote: post #48

Earlier quoted context omitted.

I'm aware of the charge coming from quarks, but my point remains. > you have to accept there will eventually be (hopefully simple) coincidences between certain fundamental values, no? When the probability of coincidence is epsilon, then, no. Right now they are the same to 12 digits, but that undersells it, because that is just the trailing digits. There is nothing which says the leading digits must be the same, eg, o…

If you imagine the universe is made of random real fundamental constants rather than random integer fundamental constants, then indeed there's no reason to expect such collisions. But if our universe starts from discrete foundations, then there may be no more satisfying explanation to this than there is to the question of, say, why the survival threshold and the reproduction threshold in Conway's Game of Life both in…

Why do you assume the two have to be small integers? There is nothing currently in physics which would disallow the electron to be -1 and the proton to be +1234567891011213141516171819. The fact they are both of magnitude 1 is a huge coincidence.

Re: Is particle physics dead, dying, or just hard?

#65

Post by throwaway81523 »

hackingonempty wrote: post #53
klipt wrote: post #24

Earlier quoted context omitted.

Doesn't that imply our theories are "good enough" for all practical purposes? If they're impossible to empirically disprove?

Yes, for all practical purposes. This is the position of physicist Sean Carroll and probably others. We may not know what is happening in the middle of a black hole, or very close to the big bang, but here on Earth we do. "in the specific regime covering the particles and forces that make up human beings and their environments, we have good reason to think that all of the ingredients and their dynamics are understood…

ER=EPR says something completely shocking about the nature of the universe. If there is anything to it, we have almost no clue about how it works or what its consequences are.

Sean Carroll's own favorite topics (emergent gravity, and the many worlds interpretation) are also things that we don't have any clue about.

Yes there is stuff we can calculate to very high precision. Being able to calculate it, and understanding it, are not necessarily the same thing.

Re: Is particle physics dead, dying, or just hard?

#66

Post by tasty_freeze »

PaulHoule wrote: post #18
tasty_freeze wrote: post #15

Here is one fact that seems, to me, pretty convincing that there is another layer underneath what we know. The charge of electrons is -1 and protons +1. It has been experimentally measured out to 12 digits or so to be the same magnitude, just opposite charge. However, there are no theories why this is -- they are simply measured and that is it. It beggars belief that these just happen to be exactly (as far as we can…

If it wasn't the case then matter wouldn't be stable.

Agreed (well, assuming the delta is more than a small fraction of a percent or whatever). But this is begging the question. If they are really independent then the vast, overwhelming fraction of all possible universes simply wouldn't have matter. Ours does have matter, so it makes our universe exceedingly unlikely. I find it far more parsimonious to assume they are connected by an undiscovered (and perhaps never to be discovered) mechanism.

Some lean on the multiverse and the anthropic principle to explain it, but that is far less parsimonious.

Re: Is particle physics dead, dying, or just hard?

#67

Post by sixo »

klipt wrote: post #24
bananaflag wrote: post #7

It's basically the opposite situation from 150 years ago. Back then, we thought our theory was more or less complete while having experimental data which disproved it (Michelson-Morley experiment, Mercury perihelion, I am sure there are others). Right now, we know our theories are incomplete (since GR and QFT are incompatible) while having no experimental data which contradicts them.

Doesn't that imply our theories are "good enough" for all practical purposes? If they're impossible to empirically disprove?

The point is not to make better predictions of the things we already know how to predict. The point is to determine what abstractions link the things we don't presently understand--because these abstraction tend to open many new doors in other directions. This has been the story of physics over and over: relativity, quantum theory, etc, not only answered the questions they were designed to answer but opened thousands of new doors in other directions.

Re: Is particle physics dead, dying, or just hard?

#68

Post by gowld »

emmelaich wrote: post #3
tehjoker wrote: post #2

It's kind of legitimate, but it's kind of sad to see some of the smartest people in society just being like "maybe AI will just give me the answer," a phrase that has a lot of potential to be thought terminating.

That's mentioned in the article too: > Cari Cesarotti, a postdoctoral fellow in the theory group at CERN, is skeptical about that future. She notices chatbots’ mistakes, and how they’ve become too much of a crutch for physics students. “AI is making people worse at physics,” she said.

AI chatbots are also making people better at physics, by answering questions the textbook doesn't or the professor can't explain clearly, patiently. Critical thinking skills are critical. Students cheating with chatbots might not have put in the effort to learn without chatbots.

Re: Is particle physics dead, dying, or just hard?

#69

Post by tasty_freeze »

jiggawatts wrote: post #34
tasty_freeze wrote: post #15

Here is one fact that seems, to me, pretty convincing that there is another layer underneath what we know. The charge of electrons is -1 and protons +1. It has been experimentally measured out to 12 digits or so to be the same magnitude, just opposite charge. However, there are no theories why this is -- they are simply measured and that is it. It beggars belief that these just happen to be exactly (as far as we can…

This is "expected" from theory, because all particles seem to be just various aspects of the "same things" that obey a fairly simple algebra. For example, pair production is: photon + photon = electron + (-)electron You can take that diagram, rotate it in spacetime, and you have the direct equivalent, which is electrons changing paths by exchanging a photon: electron + photon = electron - photon There are similar for…

> This is "expected" from theory, because all particles seem to be just various aspects of the "same things" that obey a fairly simple algebra.

But again, this is just observation, and it is consistent with the charges we measure (again, just observation). It doesn't explain why these rules must behave as they do.

> This very, very strongly hints that the fundamental particles aren't actually fundamental in some sense.

This is exactly what I am suggesting in my original comment: this "coincidence" is not a coincidence but falls out from some deeper, shared mechanism.

Re: Is particle physics dead, dying, or just hard?

#70

Post by beezle »

I never liked that the physics community shifted from 'high energy' particle physics (the topic of the article) to referring to this branch as just 'particle physics' which I think leaves the impression that anything to do with 'particles' is now a dead end.

Nuclear physics (ie, low/medium energy physics) covers diverse topics, many with real world application - yet travels with a lot of the same particles (ie, quarks, gluons). Because it is so diverse, it is not dead/dying in the way HEP is today.

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