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As a non-physicist, I've always been hung up on a much simpler paradox: how does radiation escape from a black hole? I thought even light could not escape? Is t

As a non-physicist, I've always been hung up on a much simpler paradox: how does radiation escape from a black hole? I thought even light could not escape? Is there an explanation to that?

whimsicalism 6y ago
Basically.. and this is somewhat lay: in quantum mechanics, there is fundamental randomness. Part of that randomness means that in space, virtual pairs of particles can be formed right at the barrier between being able to escape and not escape. Normally, these particles annihilate each other - however if one crosses the threshold and is not able to escape, it can't annihilate the other particle and that escapes as radiation.
- colejohnson66 6y ago
  So similar to “anti particles”?
  - db48x 6y ago
    No, even anti-matter particles have positive mass. Thus they make a black hole larger when they are absorbed.
  - saagarjha 6y ago
    Well, the pair created can be thought of as as a particle and an antiparticle, one of which falls in.
deleted 6y ago
[deleted]
adzm 6y ago
This is Hawking radiation, which I'm sure wikipedia can explain better than me: https://en.wikipedia.org/wiki/Hawking_radiation https://en.wikipedia.org/wiki/Hawking_radiation > A pair of virtual waves/particles arises just beyond the event horizon due to ordinary quantum effects. Very close to the event horizon, these always manifest as a pair of photons. It may happen that one of these photons passes beyond the event horizon, while the other escapes into the wider universe ("to infinity"). A close analysis shows that the exponential redshifting effect of extreme gravity very close to the event horizon almost tears the escaping photon apart, and in addition very slightly amplifies it. The amplification gives rise to a "partner wave", which carries negative energy and passes through the event horizon, where it remains trapped, reducing the total energy of the black hole. The escaping photon adds an equal amount of positive energy to the wider universe outside the black hole. In this way, no matter or energy ever actually leaves the black hole itself. A conservation law exists for the partner wave, which in theory shows that the emissions comprise an exact black body spectrum, bearing no information about the interior conditions.
- tzs 6y ago
  > The amplification gives rise to a "partner wave", which carries negative energy and passes through the event horizon, where it remains trapped, reducing the total energy of the black hole Is that the same kind of negative energy that comes up in talk of stabilizing wormholes and building Alcubierre drives?
- PeterisP 6y ago
  The big question to me is whether Hawking radiation is actually a real thing? I mean, the hypothesis is interesting and the math seems to work out, but at least according to that page there is no experimental evidence yet of it actually existing; we have some experiments that might provide some data about the existence of Hawking radiation in the future, but as of now it seems just an unfalsifiable hypothesis. Is there any observational data that requires Hawking radiation to explain it? It's not my field, so I really don't know and I'd be happy to be proven wrong. Does it make sense to worry about paradoxes created by black holes evaporating, if we have no evidence that they actually do evaporate in our physical reality?
- deleted 6y ago
  [deleted]
saiya-jin 6y ago
Yes its about matter-antimatter (or different spin?) particles forming spontaneously from energy on the edge of event horizon, one falling in and another escaping. At least that's my super-layman recollection, a lot of space to be wrong in that 1 sentence.
BobbyJo 6y ago
It kind of doesn't. Stuff doesn't actually 'escape' a black hole to form Hawking radiation, rather, negative stuff goes in. Photon pairs form in the vacuum all the time. When a pair forms at the event horizon of a black hole, it rips the pair apart. Half falls in, and half shoots out into space. The half the falls in, through the effect that rips the pair apart, winds up with negative energy, lowering the energy level of the black hole.
acqq 6y ago
I suggest reading https://www.forbes.com/sites/startswithabang/2018/11/03/ask-ethan-how-do-black-holes-actually-evaporate/ https://www.forbes.com/sites/startswithabang/2018/11/03/ask-... Most importantly, he argues that Hawking's own popular explanation (often repeated across the media, about the particle-antiparticle pair) is too simple to be correct: "It's not right, though, in a number of ways. First off, this visualization is not for real particles, but virtual ones. We are trying to describe the quantum vacuum, but these are not actual particles that you can scoop up or collide with. The particle-antiparticle pairs from quantum field theory are calculational tools only, not physically observable entities. Second, the Hawking radiation that leaves a black hole is almost exclusively photons, not matter or antimatter particles. And third, most of the Hawking radiation doesn't come from the edge of the event horizon, but from a very large region surrounding the black hole." Additionally, the article also writes enough to explain the whole context and gives enough details for those who are interested to learn more.
- flubert 6y ago
  I wonder how charge evaporates from a charged black hole? And does it do so at a rate that is different from the mass? i.e. does most of the mass evaporate away, and then the charge?
  - tzs 6y ago
    That seems to be an open question. Hawking radiation is not charged, but it also turns out that there is a maximum amount of charge a black hole of a given mass can have, and the lower the mass the lower the maximum allowed charge. So it would seem that a charged black hole would evaporate by Hawking radiation until it reached the point where any further mass loss would put it over the charge limit. Physicists don’t think it is then simply going to stop radiating, and so what happens then is I believe still quite open. There was an article in Quanta a few months ago on this: https://www.quantamagazine.org/black-hole-paradoxes-reveal-a-fundamental-link-between-energy-and-order-20200528/ https://www.quantamagazine.org/black-hole-paradoxes-reveal-a...
    - 6y ago

As a non-physicist, I've always been hung up on a much simpler paradox: how does radiation escape from a black hole? I thought even light could not escape? Is there an explanation to that?

whimsicalism 6y ago

Basically.. and this is somewhat lay: in quantum mechanics, there is fundamental randomness. Part of that randomness means that in space, virtual pairs of particles can be formed right at the barrier between being able to escape and not escape. Normally, these particles annihilate each other - however if one crosses the threshold and is not able to escape, it can't annihilate the other particle and that escapes as radiation.

colejohnson66 6y ago
So similar to “anti particles”?
- db48x 6y ago
  No, even anti-matter particles have positive mass. Thus they make a black hole larger when they are absorbed.
- saagarjha 6y ago
  Well, the pair created can be thought of as as a particle and an antiparticle, one of which falls in.

deleted 6y ago

[deleted]

adzm 6y ago

This is Hawking radiation, which I'm sure wikipedia can explain better than me: https://en.wikipedia.org/wiki/Hawking_radiation https://en.wikipedia.org/wiki/Hawking_radiation > A pair of virtual waves/particles arises just beyond the event horizon due to ordinary quantum effects. Very close to the event horizon, these always manifest as a pair of photons. It may happen that one of these photons passes beyond the event horizon, while the other escapes into the wider universe ("to infinity"). A close analysis shows that the exponential redshifting effect of extreme gravity very close to the event horizon almost tears the escaping photon apart, and in addition very slightly amplifies it. The amplification gives rise to a "partner wave", which carries negative energy and passes through the event horizon, where it remains trapped, reducing the total energy of the black hole. The escaping photon adds an equal amount of positive energy to the wider universe outside the black hole. In this way, no matter or energy ever actually leaves the black hole itself. A conservation law exists for the partner wave, which in theory shows that the emissions comprise an exact black body spectrum, bearing no information about the interior conditions.

tzs 6y ago
> The amplification gives rise to a "partner wave", which carries negative energy and passes through the event horizon, where it remains trapped, reducing the total energy of the black hole Is that the same kind of negative energy that comes up in talk of stabilizing wormholes and building Alcubierre drives?
PeterisP 6y ago
The big question to me is whether Hawking radiation is actually a real thing? I mean, the hypothesis is interesting and the math seems to work out, but at least according to that page there is no experimental evidence yet of it actually existing; we have some experiments that might provide some data about the existence of Hawking radiation in the future, but as of now it seems just an unfalsifiable hypothesis. Is there any observational data that requires Hawking radiation to explain it? It's not my field, so I really don't know and I'd be happy to be proven wrong. Does it make sense to worry about paradoxes created by black holes evaporating, if we have no evidence that they actually do evaporate in our physical reality?
deleted 6y ago
[deleted]

saiya-jin 6y ago

Yes its about matter-antimatter (or different spin?) particles forming spontaneously from energy on the edge of event horizon, one falling in and another escaping. At least that's my super-layman recollection, a lot of space to be wrong in that 1 sentence.

BobbyJo 6y ago

It kind of doesn't. Stuff doesn't actually 'escape' a black hole to form Hawking radiation, rather, negative stuff goes in. Photon pairs form in the vacuum all the time. When a pair forms at the event horizon of a black hole, it rips the pair apart. Half falls in, and half shoots out into space. The half the falls in, through the effect that rips the pair apart, winds up with negative energy, lowering the energy level of the black hole.

acqq 6y ago

I suggest reading https://www.forbes.com/sites/startswithabang/2018/11/03/ask-ethan-how-do-black-holes-actually-evaporate/ https://www.forbes.com/sites/startswithabang/2018/11/03/ask-... Most importantly, he argues that Hawking's own popular explanation (often repeated across the media, about the particle-antiparticle pair) is too simple to be correct: "It's not right, though, in a number of ways. First off, this visualization is not for real particles, but virtual ones. We are trying to describe the quantum vacuum, but these are not actual particles that you can scoop up or collide with. The particle-antiparticle pairs from quantum field theory are calculational tools only, not physically observable entities. Second, the Hawking radiation that leaves a black hole is almost exclusively photons, not matter or antimatter particles. And third, most of the Hawking radiation doesn't come from the edge of the event horizon, but from a very large region surrounding the black hole." Additionally, the article also writes enough to explain the whole context and gives enough details for those who are interested to learn more.

flubert 6y ago
I wonder how charge evaporates from a charged black hole? And does it do so at a rate that is different from the mass? i.e. does most of the mass evaporate away, and then the charge?
- tzs 6y ago
  That seems to be an open question. Hawking radiation is not charged, but it also turns out that there is a maximum amount of charge a black hole of a given mass can have, and the lower the mass the lower the maximum allowed charge. So it would seem that a charged black hole would evaporate by Hawking radiation until it reached the point where any further mass loss would put it over the charge limit. Physicists don’t think it is then simply going to stop radiating, and so what happens then is I believe still quite open. There was an article in Quanta a few months ago on this: https://www.quantamagazine.org/black-hole-paradoxes-reveal-a-fundamental-link-between-energy-and-order-20200528/ https://www.quantamagazine.org/black-hole-paradoxes-reveal-a...
  - 6y ago