B Unruh & Hawkins Radiation: A Comparative Analysis

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Unruh radiation and Hawking radiation are related but not identical phenomena, both influenced by observer perspective. Unruh radiation is observer-dependent, with accelerated observers detecting more photons due to an apparent event horizon, while Hawking radiation is detectable by all observers, including those in free fall. The equivalence principle connects the two, yet acceleration and gravitational fields are not the same, leading to different observable effects. In Hawking's original model, free-falling observers do not perceive Hawking radiation, though newer models suggest they might see something, albeit not identical to what accelerated observers detect. The resolution of these differences likely hinges on the black hole information paradox.
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Are Unruh radiation and Hawkins radiation manifestations of the same basic phenomenon?
 
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backward said:
Are Unruh radiation and Hawkins radiation manifestations of the same basic phenomenon?
They're similar, for sure. But not completely identical.

The phenomenon of Unruh radiation shows that the number of photons is an observer-dependent feature of the universe: accelerated observers see more radiation. The additional photons can be viewed as stemming from the apparent event horizon that arises in the space-time of an accelerated observer, which makes them very similar to Hawking Radiation.

The difference is that Hawking radiation is visible to all observers, not just accelerated ones.
 
They are related by the equivalence principle, but an acceleration does not equal a gravitational field; they only imply the same physical effects locally in spacetime.
 
Chalnoth said:
The difference is that Hawking radiation is visible to all observers, not just accelerated ones.

Actually we don't know whether that is true. In Hawking's original model, it wasn't; an observer free-falling into a black hole would see no Hawking radiation. There are other more recent models in which the free-falling observer does see something, but it still isn't always the same as what the accelerated observer sees. This question probably won't be resolved until the black hole information paradox is resolved.
 
Abstract The Event Horizon Telescope (EHT) has significantly advanced our ability to study black holes, achieving unprecedented spatial resolution and revealing horizon-scale structures. Notably, these observations feature a distinctive dark shadow—primarily arising from faint jet emissions—surrounded by a bright photon ring. Anticipated upgrades of the EHT promise substantial improvements in dynamic range, enabling deeper exploration of low-background regions, particularly the inner shadow...
https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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