I understand the evidence for the big bang (expansion, background radiation, etc), but how do we know that it was the start of the universe? Why couldn't it have occurred in an existing, but very ...
I read in an article announcing the detection of gravitational waves by LIGO that it will be possible to detect them from the Big Bang. Is this true?
We know that the universe is approximately 13.7 billion years old. What methods did we use to discover this? How sure are we about its accuracy?