Expert: Jane Tang - 8/11/2006

Question
Hi--

Years ago I read that the universe is homogeneous and isotropic? I seem to remember that isotropism implies homogeneousness, but that homgeneousness does not necessarily imply isotroism. (i.e., the universe may be both, but we can't conclude that it is isotropic simply becasue it is homogeneous).

Why not?

Many thanks,

Steve  

Answer
Hi there!
   There is a good example that explains why. Image a universe in which all the particles are moving at the same speed and to the same direction. This universe is homogeneous. But it is not isotropic because it has a preferred direction ------ the direction of the particle movements. So if you rotate the universe by a random angle, the universe will look differently.

   Cheers,
       jane