# Quantum Particle Question

As I understand it, outer space is full of quantum particles that pop in and out of existence and annihilate each other almost instantly. So, as “Space” is expanding faster than the speed of light, (so I understand) Where do these particles come from? Are they traveling faster than light also?

Regarding the energy, the phrase I think you are looking for is dark energy.

Regarding going faster than light: space is not expanding faster than light. Space is expanding everywhere by a tiny, tiny, tiny rate. But over large distances it adds up. For example, between the earth and the moon, the expansion is less than half a nanometer per second. Between the earth and the sun, the expansion amounts to about a tenth of a micrometer per second. But the longer the distance, the more it adds up. Between the Milky Way Galaxy and the Andromeda Galaxy, the expansion amounts to about 24 kilometers per second. Go just a bit further, and the expansion is faster than the speed of light. That just means that for galaxies that are far apart from each other, they are effectively moving relative to each other faster than the speed of light, even though measured locally, they aren’t actually moving very fast.

And sometimes, if the particles arise in close proximity to a black hole, they can get separated before they have a chance to cancel each other out. One falls down the gravity well, and the other escapes. This is what’s known as Hawking Radiation. As far as I know, there’s been no suggestion that the escaping particle would exceed light speed.

But, if a particle falls Into a black hole, isn’t it adding to the mass of the black hole?

Only if the particle has positive energy, which these particles can’t.

Personally, though, I prefer to describe Hawking radiation in terms of thermodynamics. Black holes are pretty much the ultimate in end states, and so they must have considerable entropy. If they have entropy, then they must have temperature. And if they have temperature, then they must radiate. Perfectly simple, and if you formalize the argument right, it gives you exactly the same answer as the virtual-particle explanation.

Yes. So I would suggest that you avoid taking too seriously the heuristic description of Hawking radiation given by Snerky Snerk. What is really happening is a bit more complicated than that, and no one completely agrees yet on the physical description of the process. One issue is that an in-falling observer doesn’t see a horizon, nor any hawking radiation at all. You only see the radiation if you go far from the black hole or accelerate against its pull. And if you do any of these things, then you will not see anything fall into the black hole – in-falling matter will be frozen on the boundary. So from your perspective the Hawking radiation can be coming from the massive boundary of the black hole just outside the event horizon, rather than from the inside. In any case, there are a number of ways of looking at it. From the “pair-production” viewpoint from a far away observer, you can try to picture the pair being produced through an interaction across the boundary of the black hole, so that the particle that escapes takes away energy, but if you do this you have to worry about whether it is OK to have a virtual particle exchange across the horizon of a black hole. Another, simpler way to view it is simply as a quantum mechanical tunneling process.