# Tag Info

28

I'm going to give you an intuitive answer. Keep in mind, this is not the "actual" answer, as the Hawking radiation is quite a bit more complex than the typical pop-sci explanation with virtual particles. But some intuitive justification is possible nevertheless. I don't see how this event contributes to evaporation of the black hole (, since the ...

14

I thought that the anti-particle was annihilating with "normal" mass inside the black hole? No? No. First, both particles and anti-particles have "normal" mass (should they have mass in the first place) and "normal" (positive) energy. The distinction between them is either a matter of convention or a question of which type is more common in the universe. ...

9

These lecture notes address the issues to some degree, especially on slides 33-35. Because in the strongly warped spacetime near the horizon, virtual particles made from vacuum fluctuations turn out to have negative energy density. Energy density = energy per unit volume. These particles indeed have positive mass -- look at the one that ...

8

the candidate star is an "average" 5 solar mass star, and the black hole is a 5 solar mass black hole Then their gravity is identical. Black holes don't have magic powers. A 5 M☉ star and a 5 M☉ black hole exert the same attraction from the same distance. The only difference is that the black hole would be much, MUCH smaller (about 30 km diameter in this ...

7

Andy Gould proposed a classical derivation of Hawking radiation in a somewhat obscure paper from 1987. The essential argument is that a black hole must have a finite, non-zero entropy (otherwise you could violate the second law of thermodynamics with a black hole). Moreover, the entropy of the black hole must depend only on its area (otherwise you could ...

6

I've asked this question to a couple of physicists a few days ago. Great minds think alike, huh? First, bear in mind that Hawking radiation is only hypothetical. It is not theory. If we trust that hypothesis, this is what we can get. In general relativity, black holes can be described through a number of approximations. For example, the Schwarzschild ...

4

Black holes can "eat" Hawking radiation, but the radiation has to be directed towards the black hole before it can be "eaten". Black holes are pretty small, and space is very very very big. So as a black hole evaporates, and gives off" Hawking radiation, some may eventually fall into another black hole, but most will not. It will just travel out into space, ...

4

An infalling observer cannot remain stationary inside the event horizon of a black hole. According to them, there is a short period of proper time before they meet whatever lies at the centre of the black hole (a singularity in GR). If the observer looks back, they do not see an infinite amount of time pass by in the outside universe. In fact for the type ...

4

In a shrinking, roughly 3-spherical universe with only a black hole, Hawking radiation should follow a geodesic line and return to the black hole, without excerting radiation pressure to the universe as a whole. Therefore it's hard to see, how Hawking radiation should establish an equilibrium with gravity. More feasible seems, that the shrinking universe ...

4

The escape velocity is c at the event horizon of a black hole. Above the event horizon the escape velocity is below c. Escaping particles of the Hawking radiation form above the event horizon; that's why they can escape, if they are pointing towards a sufficiently narrow angle to vertical upward, and if they are sufficiently energetic. Escaping particles ...

3

First, I'd like to point out and commend @user83692435's reply which came first and is correct. Expanding on it: The image of a virtual particle/anti-particle pair being created and then one of the pair being swallowed by the event horizon leaving the other as real is an analogy which provides a picture of what is happening, but is definitely not correct. ...

3

An analogy in the settings of the question would be a deceleration down to an expansion rate, such that eventually light from anywhere in the universe can reach us, meaning the cosmic horizon can vanish. A constant expansion rate of the universe above the speed of light would be the analogy of a black hole of fixed mass. In an infinite universe this would ...

3

The space itself is falling into the black hole. Below the event horizon - in the timelike zone - an observer is falling towards the singularity, together with the space. Seen from this falling observer, space looks like vacuum outside the black hole. Close to the singularity tidal forces become an increasing problem. But for a sufficiently large and "...

3

Hawking radiation is the black body radiation that black holes emit. It is a well established theoretical result but it has never been observed. For all currently known astrophysical black holes it will be totally insignificant and will never be observed. The reason for this is that the equivalent temperature of the black body is inversely proportional to ...

3

There's an existing FAQ for these sorts of questions: http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/fall_in.html For this particular question, the answer is no.

2

As it has been mentioned in a comment by @zephyr, the infinite time issue is actually a non-issue. As you move closer to a black hole, the relative time to your point of view doesn't change in the same way that it does from a different reference frame. Looking at your own situation, everything would happen in "real time" however, everything observed about ...

2

The black hole loses mass in order to generate the Hawking radiation. The energy carried by the radiation is exactly proportional to the mass lost by the black hole according to Einstein's formula E = mc^2 No new mass is brought into the Universe this way. EDIT: (Keep in mind the explanation below is not rigorous. As Stephen Hawking himself has said, this ...

2

The lifetime of a black hole to evaporation by Hawking radiation scales as the cube of its mass. If sufficiently low-mass black holes are created then they can evaporate on a timescale shorter than the age of the universe. As they do so, their mass decreases and their evaporation timescale shortens - hence the rate at which they evaporate increases ...

2

In principle, yes. The main sticking point is that the emission of Hawking radiation become weaker for bigger black holes. Black holes from the collapse of stars always have masses of at least a few solar masses. At these masses Hawking radiation is so weak that we have no hope measuring it. However, it is also possible for black holes of almost any mass ...

2

No. Problems: Hawking radiation would have very small temperature of $10^{-6} M_{sun}/M_{BH}$ Kelvins. Primordial black holes below 1kg already did evaporate, so there would be no sources from small black holes. The only hope is artificial black holes created by CERN. Falling matter inside black hole would expirience enormous amount of acceleration leading ...

2

tldr; extremely little. Space is big, even biggest black holes are ridiculously tiny in physical size The amount of starlight absorbed by black holes is really minuscule. A black hole is not going to be sucking light in: it can be fairly well approximated to be an absolutely black object around the size of its event horizon (or photon sphere, does not ...

1

Hawking radiation isn't some special kind of radiation. It's perfectly ordinary "thermal" radiation, mainly photons, with a few neutrinos and electrons and positrons if the temperature is high enough. Black holes shrink when they emit it, not when the absorb it. So aiming simulated Hawking radiation (or any other kind of radiation) into a black hole just ...

1

I don't know if the experts will agree with this description, but here is how I understand it: Both space and the event horizon are in constant quantum fluctuation. Essentially, the event horizon has tiny ripples. At points where the event horizon ripples up (above the average radius of the black hole), it has an above average amount of local energy. The ...

1

How exactly can Hawking's Radiation carry the information? It does not, if you mean information about the interior of the black hole. The relevant theorem is the No Hair Theorem. Basically you can only get gross statistical properties of black holes, nothing else and no information about the interior structure (meaning any info inside stored in any way, ...

1

There is quite a nice explanation on this web page. A key passage is this: in curved spacetime there aren't these "best" co-ordinate systems, the inertial ones. So even very reasonable different choices of co-ordinates can give disagreements about particles vs antiparticles, or what's the vacuum. These disagreements don't mean that "everything is ...

1

This assumes that when a pair particle-antiparticle is created, a bias towards antiparticles being captured and particles escaping must exist. No such assumption or bias exists. As far as we know the universe treats anti-particles just like particles with different properties (e.g. charge is opposite compared to the corresponding particle). Otherwise, ...

1

With respect to "eternally collapsing", they are probably referrring to the fact that in the reference frame of an external observer, gravitational time dilation prohibits matter from ever reaching the event horizon (the "surface") of the black hole. Denoting the radius of the event horizon $r_\mathrm{S}$ (for "Schwarzschild radius"), time runs slower by a ...

1

The real explanation for Hawking Radiation does not concern virtual particles. My simplified version of the real explanation is that curved space-time has a different minimum energy amount for a moving object than normal "flat" space. Therefore, energy flows outward from the warped area. Because of this explanation, it has been determined that smaller ...

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