Olber's paradox: If the universe is infinite, and there are an infinite number of stars, how come when we look up at night, it isn't ALL stars. Every possible direction we could look in would hit a star eventually, so it ought to be solid star, everywhere you look. Someone suggested that dust got in the way so we don't see all the stars. But this doesn't work, if the dust and us are both surrounded by stars in every direction, then everything inside, dust and everything heats up to the temperature (and brightness) of a star. Flaw in Olber's paradox: it assumes the lifetime of the Universe has been infinite and that the universe is generally static. Neither is true. So we don't see an infinite number of stars for two reasons: 1) The light from the most distant stars hasn't got here yet. Looking into space is looking back into time - in the background we see the very early universe - beyond which we cannot see. But where we see early universe, there must actually be stars whose light hasn't reached us yet. 2) The universe is expanding. This means that the light of stars beyond a certain distance can never reach us, as the distance it has to travel increases faster than it can cover it.