4 ms·

Without a gravity well whose escape velocity exceeds c, how are they supposing hawking radiation happens in this scenario? Both virtual particles-antiparticles

Without a gravity well whose escape velocity exceeds c, how are they supposing hawking radiation happens in this scenario? Both virtual particles-antiparticles survive (and promptly disappear because one didn't just cross an event horizon).

Sharlin 1y ago
That one's a big white lie of how Hawking radiation works. It's not even an approximation, just a far-fetched metaphor that Hawking made up, presumably to satisfy science journalists.
- raattgift 1y ago
  Hawking 1974, "Black hole explosions?" (Nature paywall) <https://www.nature.com/articles/248030a0 https://www.nature.com/articles/248030a0> (sci-hub antipaywall) <https://sci-hub.se/https://www.nature.com/articles/248030a0 https://sci-hub.se/https://www.nature.com/articles/248030a0> ("... the time dependence of the metric during the collapse will cause a certain amount of mixing of positive and negative frequencies [...] Part of this wave will be scattered by the curvature of the static Schwarzschild solution outside the black hole ... Another part of the wave will propagate backwards into the star") was certainly not for science journalists and is not at all "far-fetched". The only missing piece here is possibly discussion of his particular approach to second-quantization of the matter fields and how one might interpret that; Hawking's peers fifty years ago did not need assistance there. This was followed in detail by Hawking 1975 (open access via Project Euclid) <https://projecteuclid.org/journals/communications-in-mathematical-physics/volume-43/issue-3/Particle-creation-by-black-holes/cmp/1103899181.full https://projecteuclid.org/journals/communications-in-mathema...> where the most relevant bit surrounds eqns (2.27-28) and there is nothing wrong with talking about signed "contributions to the probability flux into the collapsing body" (as opposed to identifying those contributions as particles). Hawking himself wrote simpler pop-sci explanations in a number of places, including his book, where a reader would not be expected to understand how canonicalizations of wave functions in other than position space and directly-measured particles differ. However none of those works is the equivalent of the brief "explosions?" letter and its follow-on.
EA-3167 1y ago
You have to remember the "one particle in the pair fails to escape the event horizon" explanation is a simplification of the alleged reality, which is the scattering of particles (or fields) in the presence of an event horizon. As far as I know there is no intuitive, non-mathematical way to describe this accurately, so science communicators of all stripes tend to approximate it in ways that can mislead the audience. The man himself (Hawking) said: "One might picture this negative energy flux in the following way. Just outside the event horizon there will be virtual pairs of particles, one with negative energy and one with positive energy. It should be emphasized that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally."
- gruturo 1y ago
  Thanks! I just learned something!
  - pixl97 1y ago
    Arvin Ash just did an episode on exactly this effect. The modern way we understand it is much to simplified. https://www.youtube.com/watch?v=UxVssUb0MsA https://www.youtube.com/watch?v=UxVssUb0MsA
    - coolcase 1y ago
      Now I am confused as what he says at the end seems to agree with the paper "Hawking radiation doesn't just come from black holes but from any collapsed star"
- bryan0 1y ago
  Not a physicist, but the more accurate “intuitive” explanation I read is that an accelerating observer sees thermal radiation in a vacuum. This is called the Unruh effect [0]. And since a black hole requires an accelerated observer to not be pulled in you will always have thermal radiation coming from the black hole UNLESS you are free falling into it. Physicists please correct me where I’m wrong! [0]: https://en.m.wikipedia.org/wiki/Unruh_effect https://en.m.wikipedia.org/wiki/Unruh_effect

Sharlin 1y ago

That one's a big white lie of how Hawking radiation works. It's not even an approximation, just a far-fetched metaphor that Hawking made up, presumably to satisfy science journalists.

raattgift 1y ago
Hawking 1974, "Black hole explosions?" (Nature paywall) <https://www.nature.com/articles/248030a0 https://www.nature.com/articles/248030a0> (sci-hub antipaywall) <https://sci-hub.se/https://www.nature.com/articles/248030a0 https://sci-hub.se/https://www.nature.com/articles/248030a0> ("... the time dependence of the metric during the collapse will cause a certain amount of mixing of positive and negative frequencies [...] Part of this wave will be scattered by the curvature of the static Schwarzschild solution outside the black hole ... Another part of the wave will propagate backwards into the star") was certainly not for science journalists and is not at all "far-fetched". The only missing piece here is possibly discussion of his particular approach to second-quantization of the matter fields and how one might interpret that; Hawking's peers fifty years ago did not need assistance there. This was followed in detail by Hawking 1975 (open access via Project Euclid) <https://projecteuclid.org/journals/communications-in-mathematical-physics/volume-43/issue-3/Particle-creation-by-black-holes/cmp/1103899181.full https://projecteuclid.org/journals/communications-in-mathema...> where the most relevant bit surrounds eqns (2.27-28) and there is nothing wrong with talking about signed "contributions to the probability flux into the collapsing body" (as opposed to identifying those contributions as particles). Hawking himself wrote simpler pop-sci explanations in a number of places, including his book, where a reader would not be expected to understand how canonicalizations of wave functions in other than position space and directly-measured particles differ. However none of those works is the equivalent of the brief "explosions?" letter and its follow-on.

EA-3167 1y ago

You have to remember the "one particle in the pair fails to escape the event horizon" explanation is a simplification of the alleged reality, which is the scattering of particles (or fields) in the presence of an event horizon. As far as I know there is no intuitive, non-mathematical way to describe this accurately, so science communicators of all stripes tend to approximate it in ways that can mislead the audience. The man himself (Hawking) said: "One might picture this negative energy flux in the following way. Just outside the event horizon there will be virtual pairs of particles, one with negative energy and one with positive energy. It should be emphasized that these pictures of the mechanism responsible for the thermal emission and area decrease are heuristic only and should not be taken too literally."

gruturo 1y ago
Thanks! I just learned something!
- pixl97 1y ago
  Arvin Ash just did an episode on exactly this effect. The modern way we understand it is much to simplified. https://www.youtube.com/watch?v=UxVssUb0MsA https://www.youtube.com/watch?v=UxVssUb0MsA
  - coolcase 1y ago
    Now I am confused as what he says at the end seems to agree with the paper "Hawking radiation doesn't just come from black holes but from any collapsed star"
bryan0 1y ago
Not a physicist, but the more accurate “intuitive” explanation I read is that an accelerating observer sees thermal radiation in a vacuum. This is called the Unruh effect [0]. And since a black hole requires an accelerated observer to not be pulled in you will always have thermal radiation coming from the black hole UNLESS you are free falling into it. Physicists please correct me where I’m wrong! [0]: https://en.m.wikipedia.org/wiki/Unruh_effect https://en.m.wikipedia.org/wiki/Unruh_effect