141 votes
Accepted

Would touching a black hole of a small mass (the mass of an apple) cause you to spiral in and get dead?

This is just a quick calculation that shows what would happen to a black hole with a mass equal to the mass of an apple: It is shown that not only the builder of this black hole but also the whole ...
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  • 4,408
77 votes

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

Congratulations on finding a method for baryogenesis that works! Indeed, it's true that if you have a bunch of black holes, then by random chance you'll get an imbalance. And this imbalance will ...
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  • 95.5k
53 votes

Would touching a black hole of a small mass (the mass of an apple) cause you to spiral in and get dead?

No. A black hole created from something like an apple will still have the gravitational pull of an apple, so it's not going to suck you into it. If you swiped it it would pass through your hand, ...
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  • 6,214
51 votes
Accepted

Why would a black hole explode?

The expression for the power emitted as Hawking radiation is $$ P = \frac{\hbar c^6}{15360 \pi G^2 M^2} = 3.6\times10^{32} M^{-2}\ \text{W} = -c^2 \frac{dM}{dt},$$ where the term on the far right hand ...
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  • 113k
48 votes
Accepted

Why is the information paradox restricted to black holes?

(The answers by Mark H and B.fox were posted while this one was being written. This answer says the same thing in different words, but I went ahead and posted it anyway because sometimes saying the ...
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41 votes
Accepted

Why do physicists trust black hole physics?

At first many people didn't care much for black holes. But later people showed that they were pretty unavoidable features of the theory of general relativity and that theory made other quite precise ...
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  • 24.7k
40 votes
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An explanation of Hawking Radiation

To answer this we need to talk a bit about how particles are described in quantum field theory. For every type of particle there is an associated quantum field. So for the electron there is an ...
32 votes

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

Locality The random walk would be expected to create different (opposing) asymetries in different regions, including regions that are distant enough to not affect each other. If this would be the ...
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  • 1,262
26 votes

Why do physicists trust black hole physics?

...why do we trust black hole physics? ... (physics which is derived by combining quantum mechanics and GR such as Hawking Radiation, things relating to the Information Paradox, etc. ) Formally, ...
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  • 24.7k
23 votes

An explanation of Hawking Radiation

@JohnDuffield: I can give you both a correct answer in simple terms and the fairy tale, together with references to an explanation how the fairy tale is related to the real thing! The dry facts are ...
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23 votes

Why doesn't Hawking radiation add to the mass of a black hole just as much as it subtracts from it?

The pop science picture of Hawking radiation as particles popping into existence near the event horizon is grossly oversimplified and in many respects misleading. See https://www.forbes.com/sites/...
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  • 6,214
22 votes

Why is the information paradox restricted to black holes?

When Dr. Hawking talks about information being destroyed, he is talking about the erasure of all evidence that the information ever existed. In the case of burning a written letter, you could track ...
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  • 21.7k
20 votes
Accepted

How does one correctly interpret the behavior of the heat capacity of a charged black hole?

The paper pointed out by Daniel's comment gave me a starting point to find more literature on this topic and do further research. After a while, it became clear to me that my question is actually an ...
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  • 15.8k
19 votes
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Is Hawking radiation real for a far away observer?

External observers and black hole formation The event horizon is simply the delineation between the part of spacetime from which light can escape and the part of spacetime from which it cannot. In ...
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16 votes

Is Hawking radiation really the same as Unruh radiation?

First, the Unruh and Hawking radiation aren't quite "the same thing". They have a similar origin and the Unruh radiation may be considered a flat space (large black hole) limit of the Hawking ...
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15 votes
Accepted

Are electrons just incompletely evaporated black holes?

Yes and no. Electrons - and all other elementary particles - may be viewed as microstates of very tiny black holes. As one considers increasingly heavy elementary particles (e.g. those in the ...
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15 votes

Why do larger black holes emit less Hawking Radiation than smaller black holes?

The Newtonian gravitational acceleration for an object of mass $M$ is given by the well known expression: $$ a = \frac{GM}{r^2} \tag{1} $$ And the radius of the event horizon of a black hole is ...
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15 votes

Could Hawking radiation have a lot of neutrinos and dark matter?

Yes. Hawking radiation is universal: the black hole is a modification of spacetime geometry, and the quantum fields, which manifest particles, are residents of that spacetime. Thus they are all ...
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15 votes

How can black holes evaporate into photons if they contain no anti-matter?

Hawking radiation is not only in the form of photons. Fermions, scalars, other spin-1 particles, and even gravitons also contribute (for example, see https://www.sciencedirect.com/science/article/pii/...
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  • 35.5k
14 votes

Can a Black Hole become a normal mass again?

Hawking radiation leads to a complete evaporation of black holes, whether there are remnants and the problems this creates is a matter of ongoing discussion.For example see here for a review. Forty ...
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  • 223k
13 votes
Accepted

Intensity of Hawking radiation for different observers relative to a black hole

This paper discusses these issues in a fairly comprehensible way. Faraway observers (like your observer A) see thermal Hawking radiation with an effective temperature given by the Hawking temperature ...
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  • 41.8k
13 votes
Accepted

Could Hawking radiation have a lot of neutrinos and dark matter?

Yes. From this paper (Hooper, Krnjaic, McDermott: Dark Radiation and Superheavy Dark Matter from Black Hole Domination): Unlike most other mechanisms for particle production, the process of ...
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  • 4,504
13 votes

Why can't the information inside a black hole be reconstructed from what's left outside?

I'll first give an anecdote exemplifying the issue, and later I'll give the problem in more technical terms. I'm doing it like this because I'm not sure of what pieces of Physics you are acquainted ...
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12 votes

Based on black hole thermodynamics, shouldn't empty space contain infinite energy?

Wouldn't this mean that empty space would have infinite energy? So ignoring quantum issues (and in the absence of a complete theory of quantum gravity we have no choice) and staying strictly with the ...
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11 votes
Accepted

Black hole area theorem and Hawking radiation

I'm surprised that Jacobson's notes, which are great by the way, failed to mention this explicitly, but the reason is that Hawking radiation indeed violates one of the theorems assumptions, namely a ...
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  • 2,424
11 votes

When we are talking about black hole evaporation - what exactly happens?

Does this mean that from some point in time black hole just will cease to be a black hole because it won't be massive enough? No, once a black hole forms there's no turning back. It can lose mass via ...
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  • 10.1k
10 votes
Accepted

Will a black hole eventually turn into a neutron star?

I think that once a black hole forms then that is it, because although its mass is finite, its density (in GR) becomes infinite at the central singularity. The loss of energy(mass) will then result in ...
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  • 113k
10 votes

Why is the intensity of Hawking radiation dependent on the size of the black hole it comes from?

Any non-mathematical answer is obviously going to be an oversimplification, but as long as you're happy with that here is my oversimplification. The temperature of a big black hole is lower than a ...
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10 votes
Accepted

Derivation for the temperature of Reissner-Nordström (charged) black hole

The temperature of a black hole is related to its surface gravity. For stationary black holes, the surface gravity is given by $$ \kappa^2 = - \frac{1}{2} D^a \xi^b D_a \xi_b \big|_{r=r_+} $$ where $\...
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