# Helium, ZPE, and Casimir Effect

1. Jun 23, 2007

### Blitz Kurt

I'm currently doing a coursework in A2 Physics, on Zero Point Energy, and Casimir effect, and why doesn't Helium freeze at atmospheric pressure within micro-degrees of absolute zero. I've researched and I found out that only ZPE can account for the source of energy that prevents helium from freezing at atmospheric pressure.

I know that absolute zero can never be reached due to the third law of thermodynamics, (basically absolute zero can never be reached within a finite number of steps), but I'm unsure of the Casimir effect has anything to do with that.

I've read on Quantum Harmonic Oscillator and how it has been predicted and modelled due to experimental evidence and theory that, if you had an electron on a frictionless spring suspended in a total vacuum, it would continue to vibrate even if the temperature of the vacuum was reduced to absolute zero.
(Tom Valone.)

However, I am unsure if that effect is caused by the Casimir effect. Could it be that, within micro-degrees of absolute zero, the source of the ZPE is the Casimir Effect? My understanding of the Casimir effect isn't complete; I have tried to read and understand many sources; but after a few attempts, due to the density of information and depth (that my coursework does not require, as my teacher has told me), I could not completely understand what the Casimir Effect is.

I would appreciate it if my doubts were clarified, and since I'm doing physics at A-Levels, I would very much appreciate a simplified, yet explained version of the Casimir Effect.

2. Jun 23, 2007

Blitz Kurt,

The Casimir effect took me a while to understand, too, but after much conceptualising, I finally got it!

Picture this setup:
A vessel in which there is a vacuum, no matter (air) and no energy. Inside this vessel, two metal plates are brought into very close proximity (micrometers - nanometers apart).

What happens:

In a vacuum, there is MUCH 'vacuum energy' due to the random electromagnetic oscillations in space. This is caused by spontaneous generation of pairs of virtual particles (matter -antimatter pair) which almost instantly annihilate one another, producing energy as radiation (photons), according to E = mc^2. So really, you have many photons shooting around this 'empty' vessel.

The narrow gap between the metal plates limits the wavelength of the photons that can physically fit between them. Radiation of a smaller wavelength can fit between the plates, that of a larger wavelength cannot.

The net result is an overall greater amount of energy (small and large wavelength photons) surrounding the plates compared to between the plates (only small wavelength photons). This creates a light 'pressure' gradient, which forces the plates together.

This is fascinating because in a vessel devoid of matter and energy... energy still exists, even in a state which we can call 'zero'. It is even more fascinating because between the plates in Casimir's experiment, we have an energy state that goes below 'zero'!

Hope this helps. I can draw pictures if you like :)

3. Jun 23, 2007

### Blitz Kurt

I understand more than I did a few days ago, about the Casimir effect, thank you very much. However, I dod not udnerstand how a negative (below zero energy) would exist in such a set up... Everything else was alright and understood, do you mind explaining that to me? I completely understood that there's more energy forcing the plates towards one another than energy between the plates away from one another; but how can the energy between the plates be less than zero?

4. Jun 23, 2007

### turbo

Blitz, in a vacuum at minimal temperature, QT says that virtual-particle pairs arising and self-annihilating within the limits of the Heisenberg uncertainty principle will suffuse that vacuum. If you have a pair of plates in such a cold vacuum, and put them close together so that they suppress the formation of VP pairs that have wavelengths too long to exist between the plates, the vacuum surrounding the plates will exert a force on the plates that is larger than the force between the plates. This is the Casimir Effect, and although it is sometimes expressed as an attractive force between two plates, it is more properly considered as the result of a more "refined" vacuum being produced by the proximity of the plates, forbidding the formation of longer wavelength virtual pairs that are allowed outside that gap.

5. Jun 23, 2007

### Blitz Kurt

I'm grateful to the both of you; thank you very much- That cleared up all of my doubts.

6. Jun 23, 2007

### Chronos

7. Jun 24, 2007

Good work with the wording, turbo-1.

So there you go Blitz, it's all relative!

8. Jun 24, 2007

### jambaugh

It always helped me to think of the vacuum as fill with a "gas" of these zero-point excitations with a corresponding pressure. Then objects by suppressing nearby ZP excitations effectively create a pressure gradient around themselves. Hence two objects are attracted by each other's contribution to this pressure gradient.

9. Jun 30, 2007

### Chronos

Interesting, but inconsistent with observational evidence.

10. Jul 1, 2007

In what way?