# Casimir effect

#### neila9876

I don't know what's exactly the Casimir effect. Some materials in web tells that it's "the phenomenon of the occurance of attractive force between two metalic panels which close to each other in very small distance".
If it is that, then someone who can explain why atoms can form that metalic panel can explain Casimir effect.

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#### topsquark

Forum Staff

I'm not quite sure what queston you are asking. Here's a link to it.

(The article mentions the zero point energy to help explain the process. I don't like anything that invokes the ZPE from the standpoint that any measurement of the ZPE that is not 0 is really a measure of our inability to correctly calculate it. I may have to eat those words if at some point someone experimentally measues it to be non-zero. But for now the question of a non-zero ZPE is an open one.)

-Dan

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#### neila9876

If the true cosmos is a 4D space, then what's the use with even complicated mathematical calculation in 3D space? "To discuss the gap between math and physics?"

#### topsquark

Forum Staff
If the true cosmos is a 4D space, then what's the use with even complicated mathematical calculation in 3D space? "To discuss the gap between math and physics?"

-Dan

Yes, sir.

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#### neila9876

Zpe

I heard that dragon talked about ZPE in the Lounge before. The abstract is:
"Now, in QFT we assume that the difference in the fields from point to point are linear (as in a Taylor approximation: This leads to approximating the field as a collection of little simple harmonic oscillators.
In QM the simple harmonic oscillator has a strange feature... The energy of the oscillators is ...
... that is to say that the vacuum contains an infinite amount of energy. This energy is what is called "zero point energy."
Clearly this is unacceptable. The best we can do is say, "Okay, all we care about is the measurement of changes in energy, so let's simply agree to subtract out the ZPE and Physics works fine again." When we need to hand wave like that it means something is desperately wrong with the calculation but no one knows how to fix it. For now we use what works and wait for the data to tell us what to do in the future."
The key point is "infinite amount of energy".
..........
What he talks about ZPE here is " I don't like anything that invokes the ZPE from the standpoint that any measurement of the ZPE that is not 0 is really a measure of our inability to correctly calculate it. "
The key point is "not 0".
..........
I feel a bit confused. With regard to the former one , namely the "infinite amount of energy", I would laugh my butt off...
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This semi - tramp just read a bit content of the "Casimir effect" in the scentificamerican site provided by Woody. Temporarily, wo questions worthy of discussion.
"To understand the Casimir Effect, one first has to understand something about a vacuum in space as it is viewed in quantum field theory. Far from being empty, modern physics assumes that a vacuum is full of fluctuating electromagnetic waves that can never be completely eliminated, ..."
1. "...full of fluctuating electromagnetic waves". The background microwave is well known thing, why say "assume"? If it's talking something else?
2. What's the exact concept of "vaccum" in physics? Traditionally, when the air in a glass bottle has been exhausted, it's a "vaccum"; but light can penetrates the glass bottle, so the glass bottle fills with light and light is matter too...So, the concept of "vaccum" should also exclude light/electricmagnetic wave?

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#### topsquark

Forum Staff
I feel a bit confused. With regard to the former one , namely the "infinite amount of energy", I would laugh my butt off...
That's what the calculation of the ZPE is. The current way to "calculate" it ends up giving us an infinite amount of energy in the vacuum. Laugh away! It's a ridiculous answer, which is why I don't like using it.

1. "...full of fluctuating electromagnetic waves". The background microwave is well known thing, why say "assume"? If it's talking something else?
2. What's the exact concept of "vaccum" in physics? Traditionally, when the air in a glass bottle has been exhausted, it's a "vaccum"; but light can penetrates the glass bottle, so the glass bottle fills with light and light is matter too...So, the concept of "vaccum" should also exclude light/electricmagnetic wave?
Think of the vacuum as an otherwise smooth sheet that has random "bumps" in it that move around. On layman's terms that's what the vacuum looks like, where the bumps are particles randomly popping in and out of the vacuum. This is true of not only the EM field, but the electron field, the neutrino field, etc. The bumps are the quanta of that particular field.

Classically we can get away fields without quanta and then we get the nice result that the vacuum is simply where there are no particles and no fields. We can't get away with that in QM.

-Dan

Addendum: Strictly speaking, light is not matter. It has no mass. It's better to say that light carries momentum. The Einstein equation predicts that E = pc.

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