The uniform accelerated observer sees isotropic thermal radiation with no net energy flux.(Gerlach, Ulrich H. 1983 as an example) However, people naturally believe Hawking radiation causes blackhole evaporation, assuming non-vanishing energy flux for an outside observer. The only difference is blackholes do not have a uniform gravity field, but I cannot see why it causes anisotropic radiation.
By the way, even if there is some correction causing anisotropic radiation, can we still observe some thermal radiation moving from infinity to the blackhole, which is implied by the Unruh effect?
Too many non-sequiturs.
Hawking radiation is an example of the Unruh effect.
Radiation carries energy, which contributes to the evaporation process since, as energy is transferred to radiation, this means the black hole loses energy, i.e. mass and, given the relation between mass and radius of a black hole, this means the radius decreases and the black hole ``evaporates" when the radius vanishes.
One issue with this reasoning is that the Unruh effect can be consistently descrubed when the spacetime doesn’t change ``too fast", which, certainly, breaks down as the black hole becomes ``too small".
That's why Hawking radiation (and the Unruh effect) can't describe black hole evaporation, since that occurs under circumstances that aren't consistent with the assumptions of Hawking radiation and/or the Unruh effect.
So it's necessary to go beyond the adiabaticity assumption, when the size of the black hole becomes of the order of the Planck length. How to do so isn't, yet, known.
Libo Jiang Firstly let me make the point that Hawking radiation has never been observed so there is considerable doubt that it exists as a real phenomenon.
Looking at the Wikipedia page for Hawking Radiation in the section on emission process: “An accelerating observer sees a thermal bath of particles that pop out of the local acceleration horizon, turn around, and free fall back in.”
So Hawking Radiation seems to depend on the vacuum of empty space containing particles that pop in and out of existence. This also has not been observed and is contrary to the General Relativity description of empty space.
So I would take the view that Hawking Radiation does not exist.
Richard
The reason Hawking radiation from astrophysical black holes hasn't been observed and can't be observed is quantitative: The Hawking temperature is given by the expression
T/μK=0.12M_Sun/M_BH
which means that it is so low that it is drowned out.
Once more: Hawking radiation from a black hole, of size much larger than the Planck length, is consistent; its observation is, simply, not possible, which is why there's a considerable effort in so-called ``analog gravity'' contexts, where the same equations describe fluid flow. The problem there is how to describe the singularity.
In a curved spacetime the vacuum can't be uniquely defined, that's what Unruh noticed. The statement about ``particles that pop in and out of existence'' is, unfortunately, wrong.
Hawking radiation is an inevitable property of curved spacetime; it, just, can't describe black hole evaporation, which is something completely different.
- Badges
- Science topic
- Similar topics
- Organizational Psychology
- Training