Why doesn't NOT Hawking Radiation also radiate energy?
November 19, 2015 12:09 PM Subscribe
What happens to the Hawking Radiation particle and antiparticle AWAY from a black hole? Why does't the annihilation of the particle and antiparticle go BOOM?
I totally get how Hawking Radiation works, makes perfect sense. Here's a pic that shows how it works: link
What I don't get, however, is what happens to the particle and antiparticle AWAY from a black hole. If there's one thing I've learned from Scotty, it's that matter+antimatter=LOTS of energy (this has been verified by CERN or someone else sufficiently nerdy).
Hawking Radiation says that space is roiling and unstable, and creates a particle and a corresponding antiparticle, which subsequently annihilate one another leaving space where it started, empty. If that's the case, then where is the matter+antimatter release of energy? The only thing I can think of is some corresponding type of anti-energy that cancels out the regular energy, but matter/antimatter physics kind of prohibits that.
So, Steven, WTF?
I totally get how Hawking Radiation works, makes perfect sense. Here's a pic that shows how it works: link
What I don't get, however, is what happens to the particle and antiparticle AWAY from a black hole. If there's one thing I've learned from Scotty, it's that matter+antimatter=LOTS of energy (this has been verified by CERN or someone else sufficiently nerdy).
Hawking Radiation says that space is roiling and unstable, and creates a particle and a corresponding antiparticle, which subsequently annihilate one another leaving space where it started, empty. If that's the case, then where is the matter+antimatter release of energy? The only thing I can think of is some corresponding type of anti-energy that cancels out the regular energy, but matter/antimatter physics kind of prohibits that.
So, Steven, WTF?
the release of energy pays back the debt used to create the pair in the first place.
posted by andrewcooke at 12:35 PM on November 19, 2015 [1 favorite]
posted by andrewcooke at 12:35 PM on November 19, 2015 [1 favorite]
Also, matter + antimatter = a tiny amount of energy when you're in the realm of single particles. These aren't pool balls we're talking about here.
posted by pipeski at 12:51 PM on November 19, 2015 [1 favorite]
posted by pipeski at 12:51 PM on November 19, 2015 [1 favorite]
Response by poster: Thanks Huffy Puffy, I totally forgot about the energy required to create the particles in the first place. HOWEVER that also means that actual Hawking Radiation is an emission of particles and a net energy drop in the surrounding space. The particle "lost" inside the event horizon isn't technically lost per se, so wouldn't result in any net positive energy.
posted by skybolt at 5:06 PM on November 19, 2015
posted by skybolt at 5:06 PM on November 19, 2015
To start at the beginning, Hawking Radiation doesn't say that space creates particle/antiparticle pairs. This is a consequence of the Heisenberg Uncertainty Principle, which in one formulation reads ΔEΔt ≲ hbar/2. That equation says that an amount of energy (ΔE) can be created out of nothing, as long as it disappears back into nothing in an amount of time Δt, if and only if the amount of energy multiplied by the amount of time is less than a (really tiny) constant. This part is important: under traditional quantum mechanics, the particles have to annihilate again in a given amount of time. This can be roughly thought of as the universe won't notice the debt of energy if it's paid back quickly enough. This happens everywhere, all the time, and dealing with these 'virtual' particles popping in and out of existence is something particle physicists do a lot of.
Now, onto Hawking Radiation (I don't understand the maths from this point on, but I'll try my best to relate the metaphor). Imagine you're watching the event horizon of a black hole, and these particle/antiparticle pairs are popping in and out of existence, just like anywhere else. Occasionally, a pair will appear, that's positioned so that one partner will be dragged into the black hole whilst the other can just about escape. As an observer outside the black hole, it will appear that the black hole is radiating particles, which is the opposite of what you'd expect. There's also the issue of where the energy came from to create this particle, as it should have disappeared a long time ago according to Heisenberg. Well, in loose terms, the black hole's gravity had to do work to separate the particle/antiparticle pair, and this energy corresponds to the energy 'debt', so it all works out (as it loses a bit of energy, the black hole will shrink slightly).
It’s worth noting that virtual particles violate some things that are sometimes called laws of physics (conservation of energy, among other things), and black holes are the least understood objects in the universe, so a lot of arguments that would hold up in a different context, just aren't going to make sense here.
posted by Ned G at 6:05 AM on November 20, 2015 [1 favorite]
Now, onto Hawking Radiation (I don't understand the maths from this point on, but I'll try my best to relate the metaphor). Imagine you're watching the event horizon of a black hole, and these particle/antiparticle pairs are popping in and out of existence, just like anywhere else. Occasionally, a pair will appear, that's positioned so that one partner will be dragged into the black hole whilst the other can just about escape. As an observer outside the black hole, it will appear that the black hole is radiating particles, which is the opposite of what you'd expect. There's also the issue of where the energy came from to create this particle, as it should have disappeared a long time ago according to Heisenberg. Well, in loose terms, the black hole's gravity had to do work to separate the particle/antiparticle pair, and this energy corresponds to the energy 'debt', so it all works out (as it loses a bit of energy, the black hole will shrink slightly).
It’s worth noting that virtual particles violate some things that are sometimes called laws of physics (conservation of energy, among other things), and black holes are the least understood objects in the universe, so a lot of arguments that would hold up in a different context, just aren't going to make sense here.
posted by Ned G at 6:05 AM on November 20, 2015 [1 favorite]
« Older Is this 'Best Boss Ever' cake too obvious? | Post-apocalyptic fiction focused on rebuilding... Newer »
This thread is closed to new comments.
In Hawking radiation the black hole sucks up one particle, which takes a real amount of energy. So it "costs" something to change the virtual particles into real particles, two at a time (but we only see one).
posted by Huffy Puffy at 12:21 PM on November 19, 2015 [2 favorites]