Some of us remember when superCool string theory — just around the corner — was going to give us the multiverse that would prove all naturalist concepts right — and then some!
But if you go by this at Ars Technica:
After 50 years of work on a theory of everything, we’re left with approximate theories that seem so tantalizingly close to explaining all of physics… and yet always out of reach. Work continues on finding the underlying dualities that link the different versions of string theory, trying to suss out the mysterious M-theory that might underlie them all. Improvements to perturbation theory and approximation schemes provide some hope for making a breakthrough to link the dimensional structure of the extra dimensions to predictable physics. Routes around the damage caused by the LHC’s lack of evidence for supersymmetry continue to be laid.
In response to our inability to choose which Calabi-Yau manifold corresponds to our Universe—and more importantly, why our Universe has that manifold rather than any of the other ones—some string theorists appeal to what you might call the landscape. They argue that all possible configurations of compact dimensions are realized, each one with its own unique universe and set of physical laws, and we happen to live in this one because life would be impossible in most or all of the others. That’s not the strongest argument to come out of physics, but I’ll save a dissection of the idea for another day.
We don’t have a string theory, so we can’t test it. But it might be possible to perform experiments on string theory-adjacent ideas, and there’s been some progress on that front. Perhaps the event of inflation, which occurred immediately after the Big Bang, can teach us about string theory (or the formation of Universe-spanning cosmic strings). And perhaps there’s more to the dualities than we initially thought.
Paul Sutter, “Requiem for a string: Charting the rise and fall of a theory of everything” at Ars Technica (January 27, 2023)
But just because string theory can’t be tested, is that a reason it should be abandoned, when it gives so much comfort to naturalists? Look at what else they accept in defiance of evidence…
You may also wish to read: Post-modern physics: String theory gets over the need for evidence