Henry Maxfield

Theoretical physicist at Stanford University. My favourite things right now are quantum gravity, quantum field theory, and riding bicycles up big hills

[Henry Maxfield @henry_maxfield]

@Kaju_Nut My favourite idea is that the black hole interior inner product gets modified to lower rank (rank 1 at the end of evaporation) such that tracing it out transfers info to the radiation. A bit like final state, but with no modification to QM and perfectly unitary.

[Henry Maxfield @henry_maxfield]

@Kaju_Nut Right. A precise mechanism for transferring L-movers into R-moving radiation is the “poorly-understood” bit.

I’d worry that the same thing would obstruct HoI: eg, consider an operator that flips the sign of the left-moving part of f. Doesn’t that commute with all ops on \scri+?

[Henry Maxfield @henry_maxfield]

@Kaju_Nut The Ashtekar et el proposal is a remnant (infinitely many states with bounded energy). You can get away with that in 2D, but it’s not viable in higher D (uncontrolled pair production, etc). So would be interesting to know how much you can say without using that.

[Henry Maxfield @henry_maxfield]

@Kaju_Nut Exactly: using the island formula implicitly must allow extra ingredients (in particular, topology-change in the form of replica wormholes). That also modifies states, algebras of observables, dynamics etc (though exactly how is poorly-understood).

[Henry Maxfield @henry_maxfield]

@Kaju_Nut It looks like you’re studying algebras in CGHS, quantized in the usual way (without topology change or similar)? I’m worried it won’t teach you much because that model has info loss: no island formula, and (I think) no holography of information.

[Henry Maxfield @henry_maxfield]

@ZeroOne33408052 Science never deals with unequivocal evidence. A cosmological constant is the most parsimonious explanation for the data (galaxy/supernova surveys, CMB etc). But of course it’s not the only possible explanation!

[Henry Maxfield @henry_maxfield]

Despairing about accelerating expansion of the universe due to the eventual fate of ancestors in a trillion years may be premature. But some physicists despaired for another reason: it heralds the death of the dream of finding a single unique theory of nature! 🧵

[Dwarkesh Patel @dwarkesh_sp]

The day we discovered dark energy was "possibly the worst day in human history", says physicist Adam Brown.

This discovery inevitably consigns human civilization to heat death, unless we can change the way physics works.

And Adam's hope is that we can do exactly that.

[Henry Maxfield @henry_maxfield]

Perhaps finding the forces and constants of nature is more like measuring the solar system? Important, worthwhile, but less “fundamental”, more parochial. A positive spin: this frees us to explore the space of all possible laws, and imagine worlds beyond our own universe!

[Henry Maxfield @henry_maxfield]

These “anthropic” arguments are controversial and not without serious problems, but hard to dismiss entirely. Particularly given Weinberg’s prediction, not just some post-hoc explanation. It’s influenced the attitude of the generation of physicists that came after: including me!

[Henry Maxfield @henry_maxfield]

@maph1994 Supersymmetry in nature: (perturbative) quantum field theory, eg QED, can be formulated as a 1D quantum mechanics living on worldlines of particles (analogous to the 2D worldsheet of string theory). To describe fermions (eg, electron), that quantum mechanics is supersymmetric!

[Henry Maxfield @henry_maxfield]

@karch_andreas “…that is itself tethered to asymptotic infinity.” Surely not necessarily! Does it even work for our universe? It’s true for perturbation theory around empty Minkowski space (what they’re doing), but not around a nontrivial background (a better model for actual lab experiments).

[Henry Maxfield @henry_maxfield]

@karch_andreas Looks very nice, great to see explicit calculations of these things! Though I feel obliged to nitpick one phrase: “Seemingly local measurements are in truth nonlocal because they are defined relationally with respect to some other landmark…” so far so good…

[Henry Maxfield @henry_maxfield]

@WKCosmo @karch_andreas Yes exactly, there’s no such thing as truly local gauge-invariant operators in gravity.

This is timely as it’s closely related to our discussion on singularities: it’s hard to come up with a sharp question because there aren’t operators which directly probe the local physics!

[Henry Maxfield @henry_maxfield]

@WKCosmo @karch_andreas @vanoverbush I’m sure we’re not all that far apart here. I’m just trying to pin down why it falls short of a “full theory of quantum gravity”. Singularity resolution seems to be the shortcoming, but I’m making the point that you might be asking for too much (a satisfying answer may not exist)

[Henry Maxfield @henry_maxfield]

@WKCosmo @karch_andreas @vanoverbush I have a feeling that the Hamiltonian of a dual CFT would not satisfy you. It doesn’t really satisfy me either, but the fact is that there may be nothing better (even in principle), because local questions need not make sense when locality is emergent & approximate.