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# Two mirrors watch

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1. (Original post by AntiMagicMan)
Er, it isn't misleading at all. The electromagnetic field has an energy density. Waves are not the only possible way for energy to exist in the electromagnetic field.

Consider a fixed point charge, it creates an electric field, the energy density of the electric field is given by 1/2 (epsilon nought) times the magnitude of the electric field vector squared. And a similar expression exists for the magnetic field. Even waves store their energy in the electric and magnetic fields anyway, so your comment is a bit misleading.
But any energy stored in the electromagnetic field is surely acompanied by charges in that field. I guess it is merely a question of how you chose to look at things. Einstein would probably say that the energy comes from a slight decrese in the mass of the mirror system (this reminds me of that old question whether a spring gets heavier when you stretch it).
2. Yes, but there is energy nonetheless in the electromagnetic field. Come on this is basic electrostatics, you must have learnt the equations to calculate energy density??

And I really don't think you can claim the energy is coming from a decrease in the mass of the plates, we aren't talking about relativity here.
3. but it's not the em field, it's the virtual particles appearing! The EM field is misleading!
4. No. To understand pair creation you first have to understand how the electromagnetic field behaves on a quantum scale.

The field itself fluctuates always and everywhere. It hovers around a mean value. When the fluctuation gets so big that the energy density at some point is such that mass can be created, then that mass sometimes is created.

So it is the fluctuation of the EM field that causes particle pair creation, not particle pair creation that causes fluctuation of the EM field.
5. (Original post by AntiMagicMan)
So it is the fluctuation of the EM field that causes particle pair creation, not particle pair creation that causes fluctuation of the EM field.
Chicken vs egg
6. I suppose yes... if you consider that the EM field on a quantum scale consists of photons.
7. It's called the Casimir effect, and it doesn't have to be mirrors per se. I believe the typical apparatus is "metal sheets".

Ollie
8. (Original post by DesertBeagle)
It's called the Casimir effect, and it doesn't have to be mirrors per se. I believe the typical apparatus is "metal sheets".

Ollie
A mirror IS simply a metal sheet. Most modern mirrors are made out of silver or lead behind a protective layer of glass. Lead is less and less common due to environmental concerns.
9. sorry, When I posted this it looked like there were only the first 2 posts. But still. Calling them mirrors implies any sort of reflectance, which isn't necessary. In fact, this effect happens with anything over short distances. On the macroscopic scale a similar effect can be observed between two large boats (thats why you should never swim between large boats that are near each other). It's a bad analogy as in this case it actually is pressure causing the effect. But energy can be extracted from the "potential waves/particles" field that permeates space. It in fact exhibits itself perticularly nicely as Hawking Radiation.

Ollie
10. (Original post by DesertBeagle)
When I posted this it looked like there were only the first 2 posts.
I mentioned it in the first reply
11. (Original post by AntiMagicMan)
No. To understand pair creation you first have to understand how the electromagnetic field behaves on a quantum scale.

The field itself fluctuates always and everywhere. It hovers around a mean value. When the fluctuation gets so big that the energy density at some point is such that mass can be created, then that mass sometimes is created.

So it is the fluctuation of the EM field that causes particle pair creation, not particle pair creation that causes fluctuation of the EM field.

In a way, are you saying that the "pop" really isn't coming from nothing? I just want to make sure I understand this.

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