The uncertain future of particle physics


The field known as particle physics has as an important goal the search for the fundamental constituents of matter and it has proved very fruitful, leading us to our present understanding of matter being made up of quarks, gluons, and leptons. Pretty much everyone has heard of the Large Hadron Collider, the massive accelerator of radius 27 km near Geneva that was built mainly to search for the Higgs boson, and found it. But as is always the case with physics, immediately after any discovery comes the question: What next? And in this case, the answer is not clear. The Higgs was the last remaining particle in the Standard Model of particle physics so in one sense one can say that that chapter has come to end. But is the end merely that of the chapter or is it the end of that particular physics book, that we have reached the end of particle physics and all that remains are just mopping up operations?

Such questions do not have easy answers and so the physics community is in a quandary as to where to go from here. At the moment the LHC has shut down for upgrades to raise the luminosity of the machine where ‘luminosity’ refers to the number of particles colliding. But the particle physics community is already drawing up plans for a next generation accelerator called the Future Circular Collider, an even larger one on the same site that would have a circumference of 100 km.

The FCC would initially be an electron-positron collider which is much ‘cleaner’ that the proton-proton collider that is the LHC. The latter collisions are sometimes described as smashing two watches together and then searching through the debris to find tiny parts. Electron-positron collisions are much more precise and easier to control and analyze. In the second phase, the FCC would revert to being a messy proton-proton collider but with energies close to 100 TeV, much higher that the current LHC energies of 13 TeV

As you can imagine such a large project is going to be very expensive, of the order of $10-20 billion, though the cost is very likely to rise as time goes by. Proponents of the FCC are touting that it could lead to all manner of astounding discoveries but critics says that such claims are highly speculative and lack the solid theoretical basis that the Higgs had. But that has not stopped a level of theorizing that has alarmed some physicists.

Theoretical physicist Sabine Hossenfelder is optimistic about the future of her field, seeing many potential avenues of exploration. Questions about the nature of dark matter, dark energy, zero-point energy, quantum gravity, the measurement problem in quantum mechanics, all present fascinating puzzles for physicists to untangle.

But she also warns that we may have reached the “nightmare scenario” in a particular branch of the discipline: particle physics.

The problem? The best theories imply that there may be no more new elementary particles left to discover.

She argued that physics has entered something of a crisis as the nightmare scenario draws closer, and many unscientific, speculative and ad hoc theories have been published. Researchers have incentives to concoct new hypotheses and models that posit the existence of particles that could, in theory, be detected at attainable collider speeds. But there’s no credible basis for most of these theories, she said — they’re essentially fantasies dressed up in math. Anyone can create farfetched and falsifiable claims, but unless they’re somehow grounded in reality, there’s little value in disproving them..

[Particle physicist Adam Falkowski] also said he cringed when he heard advocates invoke claims about potential new particles, dark matter, or the relationship between matter and anti-matter to justify the collider.

The chances that the collider would shed light on these topics “are pretty slim,” he said.

That brings us to one of Hossenfelder’s biggest complaints about the collider. While its advocates are making dubious arguments in its favor — she argued that a promotional video for the project was “full of lies” — they’re asking for a massive amount of money for it: $10 billion, at the low end of the estimate, ranging to over $20 billion.

Outstanding questions about dark matter, anti-matter, and the masses of neutrinos continue to bewilder particle physicists and suggest fascinating new discoveries are still waiting.

What’s “nightmarish,” Falkowski said, is that physicists don’t have a plan to solve these mysteries. For decades, there had always been a clear path forward. Starting in the 1950s, they started building particle colliders and making discoveries. And there was always a good reason to build the next, bigger collider.

Now, while the justifications for building another collider are getting thinner, the costs are getting higher. And the costs don’t only come in dollars but in time. The next collider, if built, might not come online until 2040, and it won’t be fully operational until the 2050s — pushing the bounds of many working physicists’ lifetimes.

As I discuss in my forthcoming book THE GREAT PARADOX OF SCIENCE: Why its theories work so well without being true that will appear some time this summer (it’s been a while since I plugged it!), when areas of physics reach this kind of dead end, more and more speculative theories are proposed that are exciting but less grounded in data. What we are seeing in particle physics now is a replay of sequences that have happened many times before but in a more extreme form.

Comments

  1. says

    But hasn’t physics been here before, at the end of the 19thC? I’m sure your “all that remains are just mopping up operations?” question seems familiar…..

  2. Rob Grigjanis says

    richardelguru @1: There are a couple of major differences between then and now.

    First, it wasn’t until the end of the 19th century that classical statistical mechanics reached its maturity, and exposed a major flaw in classical physics: the ultraviolet catastrophe. That, and the photoelectric effect, would eventually lead to quantum mechanics. There are certainly outstanding problems with quantum field theory, but nothing (that I know of) of that magnitude.

    Second, there are no physicists who think the Standard Model is a valid theory at arbitrarily high energies (i.e. that it really is the last word). The problem is that new physics (i.e. new particles) may not be evident at any energy we could access.

  3. John Morales says

    I thought ‘luminosity’ referred to energy per unit time, not to the number of particles colliding.

    Anyway, best as I can tell, looking at higher energies and finding nothing new/contradictory to the current model is still a worthwhile endeavour, because not finding something in a new domain is no less informative than finding something.

    So I make it that the objection is whether physics is getting “value for money” with its big-budget colliders, not that it’s a worthless enterprise because it isn’t still rewriting the books.

  4. John Morales says

    “It has the dimensions of events per time per area”

    Thanks, Rob. The more events, the easier to detect; I get that.

    (So, they’re not upping the energy?)

  5. Rob Grigjanis says

    John @5: As far as I can tell, they’re not upping the energy with this upgrade. Just increasing the amount of data per run.

  6. EnlightenmentLiberal says

    Let me add one of my favorite articles by Sean Carroll.

    http://www.preposterousuniverse.com/blog/2011/05/23/physics-and-the-immortality-of-the-soul/

    In short, we’re really in a unique place in that we have 1- a theory that correctly describes (almost?) every test on Earth every put to it, and 2- a theory whose math predicts that if there was new physics relevant to everyday life, then it would have been discovered in the LHC. That second part is new, and we didn’t have that before.

  7. Rob Grigjanis says

    EL @7: Oh no, not that nonsense again. Some things really never do die.

    a theory whose math predicts that if there was new physics relevant to everyday life, then it would have been discovered in the LHC.

    I’m not going to rehash an argument that already went too long a couple of years ago. I’ll just point out that, as crappy as Carroll’s argument is, it does not say what you think it says. After (ridiculously) invoking the Dirac equation, Carroll writes

    As far as every experiment ever done is concerned, this [Dirac] equation is the correct description of how electrons behave at everyday energies. It’s not a complete description; we haven’t included the weak nuclear force, or couplings to hypothetical particles like the Higgs boson. But that’s okay, since those are only important at high energies and/or short distances, very far from the regime of relevance to the human brain.

    See that last sentence? He’s ignoring terms that would be relevant in the domain explored by the LHC.

  8. says

    “As you can imagine such a large project is going to be very expensive, of the order of $10-20 billion”

    Or, in other words, about the same amount as a sizable portion of the US population would like to piss away on an inane and ineffective border wall with Mexico.

    Priorities, people!

  9. EnlightenmentLiberal says

    See that last sentence? He’s ignoring terms that would be relevant in the domain explored by the LHC.

    I said: “a theory whose math predicts that if there was new physics relevant to everyday life, then it would have been discovered in the LHC.”
    What happens inside the LHC is not “everyday life”. I thought “everyday life” would be clear enough.

  10. Rob Grigjanis says

    EL @10: So

    “if there was new physics relevant to everyday life, then it would have been discovered in the LHC.”

    and

    “What happens inside the LHC is not “everyday life””.

    This is what it looks like through the looking glass.

  11. EnlightenmentLiberal says

    I’m sorry. I think you’re trying to highlight a problem – maybe a contradiction – where none exist.

  12. Rob Grigjanis says

    EL @12: Then tell me how new physics relevant to everyday life would be discovered in the LHC. Was high-temperature superconductivity discovered in the LHC? Spoiler: No, it wasn’t.

  13. EnlightenmentLiberal says

    Sorry. I misspoke. I should have said “new fundamental fields / particles”. Sean Carroll and I would be the first to tell you that knowledge of the fundamental components does not mean physics and learning is done. By way of analogy, knowing the rules of chess does not make you a good chess player, and knowing the basic rules of how all of the parts of reality work does not mean that you know how to predict the weather, or build high temperature superconductors, etc etc. However, if you’re a reductionist, and I am, and Sean Carroll seem to be too, and if you take seriously what the math of quantum field theory is telling you and what the experiments are telling you, then it’s an unavoidable conclusion that your mind is a result of the physical brain, and that there’s basically no room for any mechanism for life after braindeath ala Christian heaven, and relevant to this discussion, it appears that there’s no room left for discoveries of new particles that we’ll be able to use in our daily lives.

    In another place, it was explained to me that we discovered radio waves, and then we could use them, but radio waves were already all around us. Whereas, any new particle / field that we discover will very probably certainly not be relevant for any mundane Earth technological application.

  14. John Morales says

    EL, ffs. (My emphasis)

    Whereas, any new particle / field that we discover will very probably certainly not be relevant for any mundane Earth technological application.

    (cf. Wittgenstein, Proposition 7 — aka: humility)

    … and if you take seriously what the math of quantum field theory is telling you and what the experiments are telling you …

    Well, I once knew how to do math with quaternions and with tensors, and how to derive Taylor series and suchlike, but I sure as fuck can’t claim to know the math of quantum field theory, nevermind what it is supposedly telling me. I only know what people familiar with the math are telling me, but then I also know about epistemology at a basic level.

    FWIW, I had the same reaction to your claim as Rob, quite independently. But that’s logic, not math.

    In another place, it was explained to me that we discovered radio waves, and then we could use them, but radio waves were already all around us. Whereas, any new particle / field that we discover will very probably certainly not be relevant for any mundane Earth technological application.

    And de Broglie worked out matter waves a hundred years ago.

    (What’s their most common use, in your estimation? 😉 )

  15. Rob Grigjanis says

    EL @14: I really shouldn’t be doing this again, but I can’t help myself.

    I should have said “new fundamental fields / particles”

    See, that’s where Carroll’s argument falls on it arse. He immediately starts talking about the existence of a soul requiring as yet unobserved particles/fields/interactions at the fundamental level (i.e. the level of electrons, photons, etc). Why? Wouldn’t it be far more likely (whatever it is) to be an emergent phenomenon based on known physics, as consciousness is* (whatever tf we mean by that)? Carroll seems to dismiss this with some first-class handwaving that amounts to “if there were something, we would have seen it”, which is an egregious thing to say.

    Have we done every possible low-energy experiment? Have we taken and properly interpreted every possible measurement from these experiments? No! Will we discover “everyday” effects based on known physics which will surprise us? Almost certainly. You (and others) have said we’ve done enough to know, without ever saying what “enough” means.

    I don’t give a toss about “soul”. It’s a silly concept based on wishful/magical thinking. What I do care about is making outrageous claims for science just to score some points in an argument with theists (or perhaps to “fortify” your atheism?).

    I love quantum field theory, and I loved working with it. And, incidentally, the Dirac equation is my favourite equation. It really is a thing of beauty and power. So when I see these things misused it makes my blood boil.

    *BTW, you could just as convincingly argue that “the math of quantum field theory” rules out consciousness. Has it been measured anywhere?

  16. EnlightenmentLiberal says

    Wouldn’t it be far more likely (whatever it is) to be an emergent phenomenon based on known physics, as consciousness is* (whatever tf we mean by that)?

    It’s a silly concept based on wishful/magical thinking.

    He’s not constructing a strawman to knock down. He’s just attacking a particular claim that has been presented to him. Most religious people are quite clear that whatever a soul / spirit is, the thing that is integral to consciousness after braindeath, it’s not an emergent property of the standard model of particle physics, e.g. it’s not mere materialism. They say that it must be supernaturalism. Of course that’s wrong, and Sean Carroll’s argument is a fine argument to show that.

    Also, I think we know more than enough to conclude that conventional particle physics is not getting you consciousness after braindeath in a place like “heaven” either. Which leads into this bit:

    Carroll seems to dismiss this with some first-class handwaving that amounts to “if there were something, we would have seen it”, which is an egregious thing to say.

    Wait – do you really believe that conscious experience after braindeath ala the typical story of Christian heaven is plausible in the slightest!? I don’t know what to say to that. Of course it’s not plausible at all. It might be true, but it might also be true that tooth fairies exist. Both conjectures are extremely unlikely to be true, so much so that I readily dismiss the possibility outright in normal imprecise everyday conversations.

    If you agree with me that it’s basically impossible, then I have to ask: Why do you think that it’s basically impossible? If you investigate your own beliefs, surely it’s because of arguments similar to Sean Carroll’s: We know enough about how the world works that it’s implausible that there’s enough space left in our ignorance to fit this additional massive edifice of unconventional physics. Otherwise, you would have to be agnostic on the matter, which is IMHO extremely silly. It’s silly in the same way that it would be silly to be agnostic about the existence of tooth fairies.

    So when I see these things misused it makes my blood boil.

    Also, I don’t understand your objection. I know that we’ve had this discussion before, and I have never really been satisfied by its conclusion. Perhaps the error is on my fault for not remembering your position, but I also have a bad recollection that I never understood your objection to Sean Carroll’s argument here. If you would explain again, I’ll try to pay extra attention this time. Sorry for being a pain.

    I know that you are a much better expert than I am, and I know very little on this topic on a working technical level unlike you. However, Sean Carroll is also such an expert, and his argument makes sense to me, and so I’m not going to be swayed by an appeal to your expertise.

    *BTW, you could just as convincingly argue that “the math of quantum field theory” rules out consciousness. Has it been measured anywhere?

    I fail to see how Sean Carroll’s argument can be readily extended to make this new claim. Could you please explain?

    It can be readily extended to rule out many kinds of dualism. It rules out the notion that there is some “consciousness mind” that acts independently of the brain and which drives the body like a person drives a car.

    However, there are other models of consciousness out there, i.e. compatibilism. In this model, the mind is a result of the mind, a reflection of the brain, a projection of the brain. Consciousness still exists, qualia still exists, but the immaterial mind has no independent causal power – I am my brain. The decisions that I make are because of ongoing physical decision-making processes in my brain. Here, I strongly suggest the work of Dan Dennett.

  17. EnlightenmentLiberal says

    Also.

    *BTW, you could just as convincingly argue that “the math of quantum field theory” rules out consciousness. Has it been measured anywhere?

    That last sentence, “has it been measured anywhere?” makes me suspect that you’re attacking a strawman of Sean Carroll’s argument. Sean Carroll’s argument is not “we haven’t detected the soul yet, and therefore it doesn’t exist”. Rather, it’s “if the soul exists, and it’s made of new fields / particles, then that implies violations of experiments that we’ve already done, or it implies even weirder things like special physics for the particles / fields in the human brain when no scientist is looking, and therefore the supernatural soul does not exist”. It’s not merely that we haven’t measured it. It’s that if such new particles / fields existed, assuming quantum field theory is otherwise correct, we should have observed some consequences of such thing already in large particle accelerators, and we have not, and therefore something has to go. The claim of immaterial souls made of new particles / fields has testable consequences, and one of those testable consequences is that we should have seen it already in large particle accelerators. That’s a failed consequence of the theory of supernatural souls. Either quantum field theory has to be thrown out – not just modified but “thrown out” e.g. huge changes to it to permit the existence of new particles / fields that do not interact with the other fields in the usual way, such that they can operate at the energy and distance scale of the brain while also escaping detection at the LHC – or the existence of souls made of undiscovered kinds of particles / fields needs to be thrown out.

    Also, regarding emergentism, sure, I can be on board, depending on what you mean. For example, one of Dan Dennett’s favorite descriptions of his position is one time an Italian reporter described Dan Dennett’s position as something like: “Sì, abbiamo un’anima. Ma è fatta di tanti piccoli robot” / “Yes, we have a soul, but it’s made of lots of tiny robots!”. Dan Dennett later responds: “And I thought, exactly”.

  18. Rob Grigjanis says

    EL: I’m done with your constant (deliberate?) misreading of what I write. It’s just too fucking tiring to keep track of it all. Just this one thing before I’m done:

    I’m not going to be swayed by an appeal to your expertise.

    It wasn’t an appeal to my “expertise” in the sense of “believe what I say because I’m an expert”. It was an explanation of my annoyance at this sort of rubbish.

  19. Rob Grigjanis says

    EL: No need to apologize. On reflection, I don’t really think you’re deliberately misreading me. But I do think you’re not hearing me. That’s OK. Maybe I’m not explaining well, but I don’t have the energy to continue on this topic.

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