We live in the wrong kind of world to be described by string theory. No physicist has ever won a big prize for string theory. I can tell you with absolute certainty that it is not the real world that we live in. So we need to start over.
- Lenny Suskind (a famous theoretical physicist) via Peter Woit's blog.
what TOE do you prefer
ReplyDeleteI'm not convinced that we need a TOE, or that a TOE in the usual narrower sense of the term is even possible. In particular, the implicit hypothesis of GUT theories that the SM can be reduced to a single Lie Group like SU(5) or SU(10) or E(8) x E(8), or that the three SM forces unify into a single force at high energy scales is one that I am skeptical is true or possible. Likewise, string theory clearly isn't the answer for our world, even though it has some mathematical beauty.
ReplyDeleteSM + GR (with some fix to make the two mathematically consistent) could, in principle, be called a TOE if there aren't any "new physics" out there to discovery that are inconsistent with them (which seems more likely than not), although that isn't really what people mean by TOEs and GUTs which imagine more reductionism and more unification.
It would be nice to have a theory that explained the value of more of the SM physical constants and I think that eventually we'll have one. I've mentioned possibilities to do that at this blog with an extension of Koide's rule that dynamically balances Higgs Yukawas via W boson interactions for fermion masses, and by minimizing entanglement entropy for the CKM and PMNS matrixes. The W and Z boson masses aren't independent of each other. There have been several proposals to explain the Higgs boson mass in approaches along these lines. One possibility is that these values are the result of some dynamical processes (a bit like the way muon g-2 takes it value). This would just be a subtle tweak extending the existing SM. It wouldn't necessarily involve anything as grand as a typical TOE or GUT. Maybe it is possible to got deeper still, maybe it isn't. But it is unlikely that anything more than the most subtle and unimportant BSM physics would result from a deeper "within the SM" theory that explains its features in a more reductionist and profound way.
Quantum gravity would be nice, is probably possible, and may be necessary (although there are credible proposals to reconcile the Standard Model and GR without quantum gravity).
Verlinde's Emergent Gravity, while it didn't work out quite right exactly as proposed, would be a particularly wonderful step towards a TOE if it could be made to work, as it would make GR emergent from the SM in a non-obvious way, rather than being a fundamental force at all.
Deur's resort to non-perturbative gravitational effects to explain dark matter and dark energy still hasn't been rigorously vetted despite one inadequate critique that uses only perturbative methods, and would answer the lion's share of gravitational/cosmology questions that have any observational motivation. Non-perturbative gravitational effects also look promising as the key trick to finally coming up with a quantum gravity theory that works.
Concepts like mirror cosmology, while ultimately somewhat speculative and perhaps even beyond the scope of any direct observational test, would eliminate the motivation for a lot of BSM physics proposals.