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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?

#71

Post by mattlangston »

Experimental particle physicist here. It's just hard.

I measured the electron's vector coupling to the Z boson at SLAC in the late 1990s, and the answer from that measurement is: we don't know yet - and that's the point.

Thirty years later, the discrepancy between my experiment and LEP's hasn't been resolved.

It might be nothing. It might be the first whisper of dark matter or a new force. And the only way to find out is to build the next machine. That's not 'dead', that's science being hard.

My measurement is a thread that's been dangling for decades, waiting to be pulled.

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

#72

Post by beezle »

bsder wrote: post #10

Theoretical physics progresses via the anomalies it can't explain. The problem is that we've mostly explained everything we have easy access to. We simply don't have that many anomalies left. Theoretical physicists were both happy and disappointed that the LHC simply verified everything--theories were correct, but there weren't really any pointers to where to go next. Quantum gravity seems to be the big one, but that…

Please do not conflate the broad "theoretical physics" with the very specific "beyond the standard model" physics questions. There are many other areas of physics with countless unsolved problems/mysteries.

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

#73

Post by sliken »

ggm wrote: post #46

I am sure others will say it better, but the cat-in-the-box experiment is a shockingly bad metaphor for the idea behind quantum states and observer effect. I will commit the first sin, by declaring without fear of contradiction the cat actually IS either alive or dead. it is not in a superposition of states. What is unknown is our knowledge of the state, and what collapses is that uncertainty. If you shift this to th…

Along similar lines, the double-slit experiment, seems simple. Two slits let light though and you get bands where they constructively or destructively interfere, just like waves.

However I still find it crazy that when you slow down the laser and one photon at a time goes through either slit you still get the bands. Which begs the question, what exactly is it constructively or destructively interfering with?

Still seems like there's much to be learned about the quantum world, gravity, and things like dark energy vs MOND.

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

#74

Post by jiggawatts »

tasty_freeze wrote: post #69
jiggawatts wrote: post #34

Earlier quoted context omitted.

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 sens…

> this is just observation

Sure, but that's fundamental to observing the universe from the inside. We can't ever be sure of anything other than our observations because we can't step outside our universe to look at its source code.

> It doesn't explain why these rules must behave as they do.

Not yet! Once we have a a theory of everything (TOE), or just a better model of fundamental particles, we may have a satisfactory explanation.

For example, if the theory ends up being something vaguely like Wolfram's "Ruliad", then we may be able to point at some aspect of very trivial mathematical rules and say: that "the electron and proton charges pop out of that naturally, it's the only way it can be, nothing else makes sense".

We can of course never be totally certain, but that type of answer may be both good enough and the best we can do.

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

#75

Post by Paracompact »

tasty_freeze wrote: post #64
Paracompact wrote: post #63

Earlier quoted context omitted.

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.

I'm not assuming they have to be small integers—I'm saying that if the universe is built on discrete rather than continuous foundations, then small integers and coincidences at the bottom-turtle theory-of-everything become much less surprising. You're treating the space of possible charge values as if it's the reals, or at least some enormous range, but I consider that unlikely.

Consider: in every known case where we have found a deeper layer of explanation for a "coincidence" in physics, the explanation involved some symmetry or conservation law that constrained the values to a small discrete set. The quark model took seemingly arbitrary coincidences and revealed them as consequences of a restrictive structure. auntienomen's point about anomaly cancellation is also exactly this kind of thing. The smallness of the set in question isn't forced, but it is plausible.

But I actually think we're agreeing more than you realize. You're saying "this can't be a coincidence, there must be a deeper reason." I'm saying the deeper reason might bottom out at "the consistent discrete structures are sparse and this is one of them," which is a real explanation, but it might not have the form of yet another dynamical layer underneath.

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

#76

Post by ggm »

sliken wrote: post #73
ggm wrote: post #46

I am sure others will say it better, but the cat-in-the-box experiment is a shockingly bad metaphor for the idea behind quantum states and observer effect. I will commit the first sin, by declaring without fear of contradiction the cat actually IS either alive or dead. it is not in a superposition of states. What is unknown is our knowledge of the state, and what collapses is that uncertainty. If you shift this to th…

Along similar lines, the double-slit experiment, seems simple. Two slits let light though and you get bands where they constructively or destructively interfere, just like waves. However I still find it crazy that when you slow down the laser and one photon at a time goes through either slit you still get the bands. Which begs the question, what exactly is it constructively or destructively interfering with? Still se…

I had a conversation about this in HN some months back. It's a surprisingly modern experiment. It demanded an ability to reliably emit single photons. Young's theory may be 1800 but single photon emission is 1970-80.

(This is what I was told, exploring my belief it's always been fringes in streams of photons not emerging over repeated applications of single photons and I was wrong)

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

#77

Post by jhanschoo »

Legend2440 wrote: post #45
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?

Typically whenever you look closely at an object with complex behavior, there is a system inside made of smaller, simpler objects interacting to produce the complexity. You'd expect that at the bottom, the smallest objects would be extremely simple and would follow some single physical law. But the smallest objects we know of still have pretty complex behavior! So there's probably another layer underneath that we don…

I agree, and I think that your claim is compatible with the comment that you are responding to. Indeed, perhaps it's turtles all the way down and there is systematic complexity upon systematic complexity governing our universe that humanity has been just too limited to experience.

For a historical analogy, classical physics was and is sufficient for most practical purposes, and we didn't need relativity or quantum mechanics until we had instruments that could manipulate them, or that at least experienced them. While I guess that there were still macroscopic quantum phenomena, perhaps they could have just been treated as empirical material properties without a systematic universal theory accounting for them, when instruments would not have been precise enough to explore and exploit predictions of a systematic theory.

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

#78

Post by [deleted] »

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…

[deleted]

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

#79

Post by f30e3dfed1c9 »

smnplk wrote: post #44
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…

There are layers science can not access.

Well OK then! Let's tell all the physicists they can close up shop now. They might not have realized it, but they're done. All their little "theories" and "experiments" and what not have taken them as far as they can go.

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

#80

Post by elashri »

jdshaffer wrote: post #16
GMoromisato wrote: post #11

The use of "AI" in particle physics is not new. In 1999 they were using neural nets to compute various results. Here's one from Measurement of the top quark pair production cross section in p¯p collisions using multijet final states [ https://repository.ias.ac.in/36977/1/36977.pdf ] "The analysis has been optimized using neural networks to achieve the smallest expected fractional uncertainty on the t¯t production cro…

I remember back in 1995 or so being in a professor's office at Indiana University and he was talking about trying to figure out how to use Neural Networks to automatically track particle trails in bubble chamber results. He was part of a project at CERN at the time. So, yeah, they've been using NNs for quite awhile. :-)

Particle identification using NN classifiers was actually on the early success stories of NN. These are pretty standard algorithms in tracking and trigger software in HEP experiments now. There are even standard tools in the field to help you train your own.

What is more interesting currently is things like anomaly detection using ML/NN and foundational models..etc.

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