Recently there has been a lot of debate going on regarding CERN's announcement of a Future Cicular Collider (FCC) that will be able to reach energies of 100 TeV [1]. The circumference of this new collider is planned to be around 60 miles (more than 3 times that of the LHC) and it will cost around $22 billion (more than twice the money to build the LHC) [2]. The question a lot of physicists are asking is whether this investment is worth while if Higgs boson is the only particle the LHC has discovered.
As Sabine Hossenfelder points out, one of the main reasons for building the LHC was arguments from naturalness. One way to explain this problem is as follows: The Higgs boson receives large corrections to its mass and one reason that its mass is small (~ 125 GeV) is that there is new physics at the TeV scale. So, if no new physics is discovered at the LHC then we might as well start thinking about new directions in particle physics. I asked Prof. Matt Strassler a question regarding this on his website a while ago and he replied as follows:
"Me: If no SUSY and extra dimensions, then what in your opinion is the next best way to solve the hierarchy problem?"
"Prof. Strassler: I have not been a big fan of either supersymmetry OR extra dimensions in the past few years, but I have no other good ideas that would replace them. The best other ideas out there involve various forms of compositeness for the Higgs particle. And then there’s the possibility that the hierarchy problem is purely a selection effect. All I can say is that I’m hoping nature will give us a clue soon, because without additional clues I do not know what to think, and have not known what to think for over a decade." [3]
So it appears that Nature has given us a clue and that is to rethink our approach in particle physics. Also when Prof. Matt Strassler says that he does not know of "other good ideas that would replace them" he is actually representing the current mind set of most particle physicists. Currently, the community is not sure which direction to move in.
So, what should we invest in if not the LHC, this is indeed a difficult question. Remember that one of the most important discoveries made by the LHC is the Higgs boson. The Higgs mechanism was inspired from spontaneous symmetry breaking in superconductors. I believe that this discovery itself is giving us a hint on where to go next. Yes, I think that particle physicist should invest this money in finding alternative ways to test the theories they have been working on for the last few decades. Condensed matter physics can be the next play ground for particle physicists. Instead of spending $22 billion on the next collider we should, may be, build an institute or fund programs that look at interdisciplinary approaches between the two fields.
There have already been some effort placed in this approach. If the Higgs mechanism can be manifested in a condensed matter system, why not test other ideas? For example, there is an indication that supersymmetry might be manifested in a condensed matter system [4]. Similarly there are a lot of common problems in high energy physics and condensed matter physics that the community might think of [5]. But, is the community willing to change their approach? It is always difficult to convince the older generation of doing something new because they find it difficult to change their ways. We should therefore let the younger generation of particle physicists have more say in these issues.
So I think that particle physicists need to return to their black boards and find new and economical ways to test their ideas until they have a definite direction to go to yet higher energies.
[1] https://home.cern/news/press-release/accelerators/international-collaboration-publishes-concept-design-post-lhc
[2] https://goo.gl/zjfoDx
[3] https://profmattstrassler.com/2012/04/24/is-supersymmetry-ruled-out-yet/
[4] https://www.sciencedaily.com/releases/2014/04/140409155748.htm
[5] https://science.energy.gov/~/media/hep/pdf/Reports/HEP-BES_Roundtable_Report.pdf
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