A-level Physics/Cosmology/Structure of the universe

Olbers' Paradox
Heinrich Olbers showed that in an infinite and uniform universe the sky at night would be exceedingly bright, whereas we know perfectly well that this is not the case. This contradiction, that the universe must be infinite otherwise it would collapse under its own gravitational forces, yet cannot be infinite otherwise the sky would be bright at night - is now known widely as Olbers' Paradox.

To be included in this section:
 * Cosmological Principle
 * Hubble's Law (and why it can't be used accurately at the moment to estimate the age of the Universe)
 * Significance of the 3 K microwave radiation that we can detect

from A level OCR Physics A specification