Unruh Radiation

[Quetzalcoatl]

Hi All,

 

Looking again into the Casimir/Hawking/Unruh effects, made me think that:

 

1. Take any gravity source.

2. Use general relativity's gravity-acceleration equivalence principle.

3. The Unruh effect applies.

4. We get radiation in a similar way to Hawking radiation around a black hole?

 

So, are black holes special in that they give enough energy for virtual particles to emit as radiation, or does every massive object (meaning one with a nonzero stress-energy tensor) have a "Hawking" radiation? To be more specific, do the Earth or Sun produce radiation in a similar mechanism as does a black hole (in addition to their more conventional radiation spectrum)?

[imatfaal]

Casimir - surely you need some form of constraint limiting the standing waves that can arise.

Hawking - don't you need a horizon (rindler, event, etc.)?

Unruh - if you are accelerating yes if you are not no.

[ajb]

Yes, you get effects like particle creation in non-static space-times and other effects like Hawking radiation.

 

All these effects stem from the fact that without Poincare invariance (or at least translational invariance) no particular state that we can all agree is the vacuum is singled out. An empty state for one observer can look like a filled state for another observer.

[Quetzalcoatl]

Thanks ajb (and imatfaal for trying! i meant you're in constant orbit, so technically accelerating, yes). That's what I was expecting. And you added the clear connection to the non-agreed upon vacuum, which I liked. I was just struck by how this is not very much talked about, but yet is very mysterious, while Hawking radiation specifically from black holes is quite a popular topic, although it seemed to me a black hole wasn't really necessary.

 

Maybe the reason is that with just a regular sun/planet/etc there isn't the effect of having negative energy particles falling back down and evaporate the sun/planet/etc. Or is there? I wouldn't think so, but not sure.

Edited November 6, 2015 by Quetzalcoatl

[ajb]

I was just struck by how this is not very much talked about, but yet is very mysterious, while Hawking radiation specifically from black holes is quite a popular topic, although it seemed to me a black hole wasn't really necessary.

The main reason more general effects are not discussed in popular accounts is simply that it is very technical and require good knowledge of quantum field theory and general relativity. Moreover, you need to forget some of what you might have been told about Poincare invariant QFT.

 

There are some good reviews of this that can be found on the arXiv, but they are technical reviews.

Edited November 6, 2015 by ajb

[Quetzalcoatl]

you need to forget some of what you might have been told about Poincare invariant QFT.

What do you mean? Does the universe in QFT not look the same to different observers? Or is this a statement about the difference between SR and GR?

[ajb]

What do you mean? Does the universe in QFT not look the same to different observers? Or is this a statement about the difference between SR and GR?

When you lose Poincare invariance you really have to thing about QFT as exactly that: a quantum theory of fields and not really a theory of particles. Lots of the formalism of standard QFT on a flat space-time really makes use of the Poincare group, just it is often somewhat hidden.

[Quetzalcoatl]

ajb, thanks for replying! But now I'm not sure I understand. When you say standard QFT adheres to invariance under the Poincare group, do you just mean that standard QFT is a relativistic (tensorial) theory? and the tensors, mathematically "hide" the invariance stuff making the equations look neater?

 

I understand there is a problem combining GR with QFT in a fully satisfactory manner, but I didn't realize it was the relativistic Poincare invariance that was the problem. I thought it had more to do with the use of continuous manifolds. Can you please elaborate on this a bit? I thought I understood, but I'm not sure I follow anymore. You are definitely more technical than I am, but I'll try to keep up! (I kind of enjoy the understanding that comes with the technical stuff)

Edited November 10, 2015 by Quetzalcoatl