Some of the physics students I tutor recently asked me to explain the Casimir Effect in simple conceptual terms, so here it is...

The Casimir Effect can be noticed if you take two plates separated by a very small distance in a vacuum; there will be a mysterious force that causes the plates to be attracted to each other.

The cause of this effect is analogous and similar to having two plates in a medium, like water; If you apply sound waves to the water with a wavelength greater than the distance of the separation of the plates you will notice the plates will attract. This is because the waves are too big to enter the space between the plates and as such they exert a force on the outside faces of the plates and none on the inside faces, causing them to attract.

However with the Casimir Effect the plates are in a vacuum, and the waves come from quantum fluctuations rather than traditional mechanical waves. As we know from quantum mechanics everything can be represented as waves. We also know that at very small dimensions we witness a "quantum foam", essentially particles and energy constantly flashing in and out of existence. These particles and energy are essentially the source of the waves in a vacuum. If the plates are sufficiently close then only particles and energy of sufficiently small wavelength will occur between the plates, while larger wavelengths would be free to form in the space outside the plates. As such a similar effect as our water example occurs where there are more waves to exert a force on the outside faces of the plates than on the inside faces. As such the two plates are again attracted to each other.

https://en.wikipedia.org/wiki/File:Water_wave_analogue_of_Casimir_effect.ogv

#Science #Physics #QM #Quantum #QuantumMechanics #wave #Waves

@freemo
A bit of an aside, but is there a limit to the wavelength that can be generated spontaneously in quantum foam?

If no, then that would mean that the Casmir Effect would take place at any distance.

@Demosthenes Well not exactly a limit per say, but as wavelengths get larger they become less likely. so particularly large wavelengths while not entirely impossible would be so rare that you may not see a single instance of one occur spontaneously during the entire lifetime of the universe.

So in theory there is no hard upper limit but in practice, there is.

@freemo
I've always heard that there is a disconnect between macro and micro physics. Could this quantum force that causes everything to attract (with the strength of that attraction varying considerably based on the distance between two particles) explain this discrepancy? Do you know if it is accounted for in current models?

@Demosthenes Depends on which discrepancy you are talking about specifically. Usually when people talk about any such discrepancy they are probably talking about gravity.