# Evidence of expansion

1. Dec 2, 2009

### Calimero

Are there any evidence that universe is expanding other then redshifting of EM radiation?

2. Dec 2, 2009

### nicksauce

The existence of the CMB shows that the universe was once a lot hotter and denser, which is the conclusion you reach if the universe is expanding.

3. Dec 3, 2009

4. Dec 7, 2009

### Tyrgrendi

The redshift in the EM radiation from galaxies increases in proportion to their distance from us.

If interpreted as a Doppler shift, galaxies are rushing away from each other, matter inside galaxies remaining largely unaffected. This interpretation has lead to the Big Bang model, which has been so eagerly defended against evidence by postulating inflation, dark matter and dark energy.

It can also be interpreted as a successive shrinkage of space-time, if it is assumed that light is not shrunken. This leads to various models of the Universe that are dispreferred, mainly for non-scientific reasons.

Although some text-books say so, the redshift cannot be interpreted as due to an expansion of space as such. Such an expansion could not be observed, unless the light was not expanded on its way. But in this case, we would see a blueshift.