How is the universe expanding?
The idea that the universe is expanding comes from the observation that the redshift of light from distant galaxies is proportional to the magnitude of the light, i.e. how far away a galaxy is. Taking this redshift to be a Doppler Effect means that the further away a galaxy is, the faster it is moving away from us, hence expansion. There is, however, evidence to suggest that there may be non-Doppler causes of redshift which would cast doubt on the expansion theory. Quasars have large redshifts that suggest they are as far away as distant galaxies, but their light doesn’t share the same redshift/magnitude relationship as galaxies. Some quasars with very high redshifts appear to be interacting with neighbouring galaxies that have lesser redshifts, which would suggest that quasars have an intrinsic redshift. Here’s a good documentary about it… http://www.youtube.com/watch?v=1yTfRy0LT…<
