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What if the LHC and further colliders can not find anything beyond the Standard Model?

Nightmare scenario:

  • LHC can not find anything beyond the SM-Higgs-like boson.
  • VLHC, the linear collider or the muon collider can not find anything beyond the SM-Higgs-like boson.
  • The 100TeV-1000TeV collider, likely in China, can not find anything beyond the SM-Higgs-like boson.

Then, what to do if no hints of dark matter particles, the axion or alike, new particles, superstrings, extra dimensions or anything beyond the SM-Higgs-like boson?

What if the nightmare scenario does happen? I mean the following: even if the SM holds to a very high energy, we should guess other ways to test its validity outside the collider realm or Dark Matter detectors. So, I believe it is NOT an opinion based question to ask what to do if the SM is unbreakable and nothing new arises in the next colliders.

Remark: I don't understand WHY you are closed this question. It is NOT an opinion based issue to point out WAYS to direct physics IF collider physics can not provide answers to fundamental physics questions like why the Higgs has a 125GeV mass? What is dark matter/dark energy? If the responses to some of these and others is not accessible with colliders, we should guess other ways, and that is NOT opinion based answers!

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We will do what is always done in science (when we come up short). We will look for new approaches. There are, perhaps, other ways to understand the fundamental particles/interactions of nature other than smashing particles together. (And, perhaps even methods that might be cheaper and less energy intensive than colliders.)

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    $\begingroup$ The question is, when exactly do you stop and reassess? After all, it "could still be over the next hill", so to speak. When does it just become not worth the expenditure to build a bigger collider given it's always possible "something" could be another 10x higher up the energy ladder? $\endgroup$
    – The_Sympathizer
    Aug 12, 2021 at 2:22
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    $\begingroup$ @The_Sympathizer what do you mean "Stop and reassess"? You are talking as if no one even trying to think how to test various theories without using the more powerful colliders $\endgroup$
    – OON
    Aug 12, 2021 at 3:33
  • $\begingroup$ @OON : I think I mean something like "when you stop building bigger colliders on the grounds it's just too expensive and too unlikely to yield new progress." $\endgroup$
    – The_Sympathizer
    Aug 12, 2021 at 3:58
  • $\begingroup$ @The_Sympathizer "Too expensive" changes with time - with technology and society. "Too unlikely" is simply impossible to predict. This is not a question of science. Science would always aim for further experiments and refinements of measurements even if we had no actual sign for the new phenomena. $\endgroup$
    – OON
    Aug 12, 2021 at 4:03
  • $\begingroup$ @The_Sympathizer As for society, it may happen tomorrow if all politicians would say together that they will not waste taxpayers money on the stuff only eggheads are really interested in. You can always consider any exploration "too expensive" if you have no actual interest in it (and if you know that you competitors don't do it, you don't really have a reason to fear that this neglect may be your downfall) $\endgroup$
    – OON
    Aug 12, 2021 at 4:06
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As we do now we will try to look for other experiments to test fundamental theories (like precision measurements of the dipole moments, search for proton decay, search for deviations from the newton law etc that we use now to constraint various ideas about beyond standard model physics), look for hints from the cosmic rays and astronomical observations and try to make even more powerful colliders possible.

And (as you mention testing superstrings) we know that at the Planck scale you MUST learn something new. So if we don't stop improving our experiments we will find the new physics sometime in the future (though if it appears only on ghe Planck scale it will likely be rather far future)

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If all particle physics data are consistent with the standard model (and inconsistent with various low-energy extensions of the standard model), then that will be an empirical fact about the world, that is to be taken into account when aiming for the deepest understanding that we can.

Theorists can still try to explain the parameters and structure of the standard model, for example. And in fact there would remain opportunity for prediction here, in that we only know those parameters to a finite degree of precision. If someone has a framework that predicts specific values for those parameters (e.g. a particular string theory vacuum), then improved measurements will make it possible to scientifically test their framework.

Cosmology and astrophysics also offer opportunities for new predictions to be made and tested, regarding energy ranges far beyond what a terrestrial collider can achieve.

Concretely, if nothing beyond-standard-model turns up, there are many things, both empirical and theoretical, that still need explaining: neutrino masses, dark matter (or the astrophysical and cosmological phenomena that are usually explained in terms of dark matter), the cosmological "lithium problem", cosmic baryon asymmetry, PeV cosmic neutrinos, the "hyperon problem" in neutron stars, why the Higgs mass doesn't receive large contributions from quantum-gravitational states.

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That would be the time to start studying theoretical physics because the legacy paradigms would have run their course and would have lost their explanatory power.

A paradigm shift would be imminent, and you could be part of it. The situation would resemble the second half of the 19th century when there seemed to be a consensus that the entirety of physics had been laid out and only details were left to fill in. Wasn't it Planck (thanks, lalala) who was told not to study physics because there was nothing of importance left to discover?

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    $\begingroup$ I am not downvoting, but it was actually Planck who got told not to study physics, and it was experimental data needing an explanation (black body radiation) which among other things led to the breakthrough. Not getting unexplainable data would be the opposite of that situation. $\endgroup$
    – lalala
    Aug 12, 2021 at 10:27
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    $\begingroup$ @lalala Thanks for the detail. My argument is of course that the experimental data leading to the paradigm change was unknown (or ignored in its implications) at the time he got that advice. (You could read my argument as "the situation that no unexplained experimental data is available and that the existing data does not lead to better explanations is not stable.") If you drill and drill in one place without result chances are you are drilling in the wrong place. $\endgroup$
    – Peter - Reinstate Monica
    Aug 12, 2021 at 10:56
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We learn things from "failed" experiments, too. For instance, there are a number of theories about what dark matter is made of, and they posit different energy levels that would be required to reveal them. As we increase the power of particle accelerators, the theories that say that something should appear at that level get ruled out, and we narrow down the possibilities.

If we succeed in eliminating all theories, it means we've been thinking about this all wrong to begin with, so we try to come up with new theories and hope that we can develop experiments to test them. This could be the "paradigm shift" mentioned in another answer.

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  • $\begingroup$ I can NOT believe you closed this question saying that "It is an opinion based topic". It is not opinion based to search for ways to go beyond the SM without colliders! $\endgroup$
    – riemannium
    Aug 12, 2021 at 15:04
  • $\begingroup$ I didn't have anything to do with closing it. $\endgroup$
    – Barmar
    Aug 12, 2021 at 15:34
  • $\begingroup$ I was referring to "others" with you... A pity they closed my question. $\endgroup$
    – riemannium
    Aug 12, 2021 at 23:29
  • $\begingroup$ But you posted it as a comment to my answer. Why single me out? $\endgroup$
    – Barmar
    Aug 12, 2021 at 23:30
  • $\begingroup$ Oh, i see! I'm sorry! I did not realize that point! I was upset due to the fact they closed my question so I didn't care where I was complaining! I apologize! $\endgroup$
    – riemannium
    Aug 12, 2021 at 23:33

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