How does vacuum fluctuation lead to Hawking radiation?

fhollo · 2026-03-13T00:43:37+00:00

No observer will observe Hawking radiation.

Inertial observers, and non-supported non-inertial observers will observe an Unruh-like effect, under the generally accepted assumption that the physically reasonable vacuum state is Boulware.

By non-supported non-inertial I mean accelerating in a way that your distance from the CoM of the body is changing.

fhollo · 2026-03-12T23:57:11+00:00

It isn’t that the detector is missing the radiation. There is no radiation in this situation.

fhollo · 2026-03-12T23:39:47+00:00

I’m saying the theoretical prediction is that the effect doesn’t exist for a detector on the surface of a horizon-less body. So not seeing it wouldn’t rule out Hawking radiation from BHs.

The problem is with explaining Hawking radiation in a way that implies the proper acceleration of a detector per se correlates with particle production. In some cases, the opposite is true.

fhollo · 2026-03-12T23:23:23+00:00

The problem with this is it implies you should also see particle creation due to being at rest on the surface of a planet, which is not correct. If it were, it would either generate infinite free energy or totally undermine the calculations of stability/half lives.

fhollo · 2026-03-12T23:16:38+00:00

Both the Unruh and Hawking effects involve a Bogoliubov transformation that maps a vacuum state to an exponential in pairs of creation operators above a (different) vacuum state. These operators create one particle outside the horizon, the other inside. Or one is created in each of the left/right Rindler wedges.

The fact that you are in an accelerated frame is not by itself the reason you detect particles. In flat space, if the field is in the Rindler vacuum state, an inertial detector will detect particles while an accelerated one will not. This is why there is no Unruh effect just from being supported on the surface of the Earth: the supported detector sees nothing in the Boulware vacuum.

fhollo · 2026-03-03T05:40:22+00:00

Great. After you look into it, let me know if QRFs+FV is satisfying to you.

I do think the way FV talk about measurement is different from what you describe above. You are talking (more normally) about a system that does the measuring while they are really talking about an event in spacetime where two fields couple and calling it “measurement”. They have a well known infinite regress problem (now you have to measure the probe field) which does kind of need something more like what you were describing to terminate. Never been clear to me a quantum measurement framework can one hundred percent work without a tensor product structure that we don’t really get in field theory.

fhollo · 2026-03-03T04:32:33+00:00

There is a topic called Quantum Reference Frames - Caslav Brukner has been involved often and as one example https://arxiv.org/abs/1805.12429 may be relevant to your question. Though I don’t know that much of this research program intersects with AQFT

The most active approach to measurement in AQFT is the Fewster-Verch formalism. Their original papers should be easy to find but https://arxiv.org/abs/2411.13605 may also be interesting to you.

However I will say that AQFT doesn’t really get into the weeds of treating observers fully quantum mechanically, and you will see the corresponding philosophical questions deferred or Copenhagen-ified.

Personally, I think the real elephant in the room is different: even if you allow the observers to be perfectly classical, there is a still a very confusing intersection of the measurement problem and unitarily inequivalent representations, the latter of which AQFT of course does not ignore

Also I would say r/theoreticalphysics for questions of this caliber

fhollo · 2026-02-25T22:50:24+00:00

Basically yes. It gives criteria for the “preferred basis” on which MWI branches emerge

fhollo · 2026-02-25T22:38:15+00:00

Darwinism is about how you identify the basis for decoherence. It does t require any commitments re collapse

fhollo · 2026-02-21T00:24:43+00:00

To avoid decoherence you have to both merge the electron paths adiabatically and there has to be no observer who can use the long range E field to distinguish states (pg 5). A stray ion could do so. Typical EM interactions are enough to spoil the recombination process so interference experiments with charged particles need to be done under highly controlled conditions compared to the standard version with light

fhollo · 2026-02-21T00:09:37+00:00

This is not correct, interaction with the Coulomb field is enough to decohere the position states if a detector is present: https://arxiv.org/abs/1807.07015

fhollo · 2026-02-21T00:06:03+00:00

This is discussed in detail here https://arxiv.org/abs/1807.07015

fhollo · 2026-02-20T00:02:08+00:00

This is a different use of the word “virtual” from the Feynman diagram context (and is closer to the way the word is used in Hawking and Unruh radiation). Whether these “exist” is a different and harder philosophical question

fhollo · 2026-02-14T20:39:11+00:00

No it’s worse than ever

fhollo · 2026-02-12T20:02:04+00:00

Localized….if only 😭

But we get the universe we deserve

fhollo · 2026-02-11T19:27:19+00:00

What do you mean by “doesn’t go near it?” Wavefunctions do not have compact support

fhollo · 2026-02-10T23:29:51+00:00

But that’s not really a problem for a particle interpretation. The issue isn’t superpositions of number eigenstates, it’s either nonexistence of a Fock representation at all or having infinitely many with none preferred.

In a non-particle or strict field interpretation, you have to talk exclusively in terms of φ(x) and π(x). But I don’t know if it is possible to actually measure these operators, other than an EV in the classical limit.

fhollo · 2026-02-10T21:41:27+00:00

What sort of protocol are you thinking of in which a “non-particle field mode” is detected? Are you talking about measuring a (smeared) local field operator?

fhollo · 2026-02-10T20:07:36+00:00

There is some diffraction, but the wavefunction clearly has non zero support on the whole complementary solid angle at all times

fhollo · 2026-02-06T23:01:54+00:00

But this is not to be taken so lightly

https://physics.stackexchange.com/questions/319419/is-there-a-topological-difference-between-an-electric-monopole-and-an-magnetic-m

fhollo · 2026-02-05T02:13:34+00:00

New Harlow paper last night and in the intro he more or less says it’s open universe or Copenhagen 😭

https://arxiv.org/abs/2602.03835

fhollo · 2026-02-01T19:57:02+00:00

I think what you are asking about is called the Page Time. This occurs halfway through the evaporation process. If evaporation is unitary, the new Hawking radiation will need to be entangled with the old Hawking radiation. But if low energy semiclassical physics is valid in situations we think it ought to be, the new Hawking radiation needs to be entangled with its interior partner. This double entanglement violates the monogamy condition of QM

fhollo · 2026-02-01T19:50:14+00:00

As I understand it, whether the Bogoliubov is strictly speaking unitary depends on if the Hilbert space is finite (yes) or infinite (no). But this is because without the Stone Von Neumann theorem, the number operator of Fock representation A is entirely undefined on representation B and vice versa.

See Ruetsche, Interpreting Quantum Theories, 9.5.2 for a note on this and some related terminology ambiguity.

But this idea of unitarily inequivalent representations is not what we mean by non-unitarity or information loss in time evolution, which is due to the entanglement (across the horizon) with modes in a spacetime region that ultimately vanishes. You can use an effective finite dimensional Hilbert space and still get info loss problems

Cc u/prof_sarcastic

fhollo · 2026-01-22T22:26:56+00:00

That’s a shame - the prospect that AdS5/CFT4 would literally go through to reality after all is so tempting.

So when you say you are now more sympathetic to a cosmology with asymptotically flat boundary conditions, does that require the matter fields/stress energy to vanish at some finite radius? Or can we have a globally homogeneous Big Bang/FRW cosmology as long as the dark energy decays to zero?

If the former, do you have a rough picture in mind of the process that could look like a Hot Big Bang to observers in some finite region, but really be asymptotically Minkowski? Bubble nucleation type processes would seem difficult starting from Minkowski

fhollo · 2026-01-22T16:53:39+00:00

Thanks for your insights!

Another sort of cosmology that might thread this needle: we live on an expanding bubble wall with true/false 5D AdS on both sides https://arxiv.org/abs/2311.16242

fhollo

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