Prof. Michael Berry talked about his work and the future of quantum mechanics in an interview during his recent visit to ICTS-TIFR for the ‘A Hundred Years of Quantum Mechanics’ program. Some excerpts:
Q: What is the status of the foundational questions in quantum mechanics now?
A: I have no idea, I don’t work on them. [...] Transport the question back to classical mechanics. Two points. Is Newton’s equation more fundamental than Hamiltonian’s? Philosophers could argue about it. In fact, Newton’s equations are more general, that’s another matter.
This refers to work by Berry and others on curl forces: position-dependent forces that cannot be written as the gradient of a potential. Curl forces have many peculiar properties - symmetries do not imply conservation laws, the dynamics are non-conservative yet non-dissipative, and in many cases they cannot be generated by a Hamiltonian. I first heard about this fascinating topic when Berry gave a colloquium at NTU in 2016. There has been quite a bit of work on this topic since then, including a recent generalization to quantum curl force dynamics.
Q: Do you have any advice for people who work in this field or who aspire to work in this field?
A: Yes. I have two contradictory pieces of advice for people who ask me for career advice.
The first piece of advice is: don’t take advice.
But, if pressed, I would say that if I were starting out, I would probably work on quantum information. Probably, though I can’t tell — this is what philosophers call counterfactual history. So I would say: work on quantum information. There are so many riches to be uncovered there to do with these big Hilbert spaces, even with a modest number of particles. So that’s what I would say.
For context, Berry's main contributions to physics relate to the "simple" case of linear wave equations and single particle quantum mechanics - well-established theories that nevertheless held numerous surprises and emergent behaviour in their singular limits and asymptotic phenomena. We've only scratched the surface when it comes to exploring these effects in complex many-body quantum systems.
The full text of the interview can be found here.