This is my first post - saw the opportunity to ask questions to professional astronomers and I've had this one on the back of my mind for a while.
I understand that the distances of stars are calculated from their redshift - that is, since the Universe is expanding at faster speeds the farther away from Earth you look, the more pronounced redshift would indicate a more distant star/galaxy.
My question is: how can we be so sure? Isn't that a big generalization? What if:
- the redshift isn't caused by a doppler-like effect? or
- the expansion of the Universe isn't constant in all directions? or
- the expansion of the Universe isn't constant at all distances?
I also read something about a class of variable stars that is used to 'calibrate' these redshift calculations - the reasoning being that since they basically always have the same brightness you can ascertain their distance from how bright they look... What if... their brightness wasn't constant across the Universe?
Seems to me like a kind of circular reasoning... What is it that breaks the circle and makes everyone so sure about redshifts and distances? (there must be something, it's just me who don't know what it is - therefore my question.)
Lisbon - Portugal