MadSci Network: Physics

Re: if i ran into a bose einstine condensate

Date: Wed Jul 13 20:49:31 2005
Posted By: P Pathak, Grad student, Physics, Oklahoma State University
Area of science: Physics
ID: 1121172015.Ph

In wave propagation there are different kind of velocities like phase 
velocity another is group velocity. Phase velocity =c/n where c is 
velocity of light in vacuum and n is refractive index. The group velocity 
deals the propagation of an envelop (like pulse) through the medium and 
depends on the rate of change of refractive index of the medium with 
Now there is big field of research for manipulating group velocity in 
certain mediums. There are methods by using medium of certain atomic 
configuration and shining with proper lasers group velocity can be 
manipulated ( as has been done in BEC) in the medium.  Here I am avoiding 
more technical terms and details but you can read something on "Coherent 
Control" in quantum optics text books. The main point is that there are 
methods for manipulation of group velocity but phase velocity is same c/n 
and for Cerenkov radiation some charge particle has to move faster than 
phase velocity not the group velocity in the medium.

But if you say that you can carry some charge and can move faster than 
phase velocity in some medium result will be as you expect Cerenkov 
radiation from the medium and you will loose energy in charging the 

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