Casimir Tricks

Most recent answer: 06/29/2009

Q:
greetings, as i understood that the casimir effect is a result of pressure of large infinity of wavelengths on small infinity of wavelengths which is the distance between the 2 neutral conducting plates which results to the attraction of the 2 plates...(i could have understood wrong) so how did scientists reverse the effect to make the 2 plates repel and hence achieve levitation? did they introduce various and many wavelengths between the plates so that the the wavelengths between the plates have higher pressure than wavelenths outside the plate (between plates and the area of the vacuum)? and i have a fuuny question... can i make at home my own vacuum by whatever means and replace 2 conducting plates and demonstrate the casimir effect? :)
- youssef (age 18)
Cairo,Maadi,egypt
A:
Those are great questions. I'll try rough answers and then go back and fix them up if I find better information.

Your basic description is essentially right.  There's a bit of a complication, however, The net force points in the direction to lower the total energy of the vacuum around the pieces of metal.  The changes in energy have two terms. The first is that as the plates get closer together, more and more low-frequency vacuum modes are lost for the space between them. That lowers the energy. However, the space between them, with lowered energy density, is replaced with space outside them, with normal energy density. That raises the energy. It turns out that the balance between these opposite terms depends on the dielectric properties of the surfaces and of the space between them. With some surfaces immersed in fluids, the force can end up being repulsive.

The  second question is also hard. I don't know whether you have access to a decent vacuum pump. The sorts of very cheap vacuum pumps easily available for home use are driven by water flow, and don't reach vacuums less than the vapor pressure of liquid water. Since the force becomes very small unless the pieces of metal are very close to touching, this is not an easy experiment to perform at home.
As often happens, there's a good Wikipedia article available:
.

Mike W.

(published on 06/29/2009)