Big Bang Birthday: gravitational waves (Introduction)

by David Turell , Thursday, April 03, 2014, 19:45 (3887 days ago) @ David Turell

More theoretical discussion:-http://blogs.scientificamerican.com/critical-opalescence/2014/04/03/gravitational-waves-reveal-the-universe-before-the-big-bang-an-interview-with-physicist-gabriele-veneziano/-It is going to need a solution to quantum gravity:-"GM: What about the theorems that say there had to be a singularity—a beginning to time?
 
"GV: You can always talk about the hypothetical big bang that should be there if you use general relativity all the way, but the fact you need to apply quantum mechanics to the theory of general relativity invalidates the arguments that there must have been a singularity. I'm not saying you can prove there was no beginning; this is still something which people have not been able to settle. What went on before inflation—if there was a singularity, if there was a beginning of time—is up in the air. There is a certain amount of fine-tuning needed for inflation, and these initial conditions are really still very mysterious.
 
"GM: So, you're saying that we should mark the end of inflation as the big bang?
 
"GV: I would define the big bang as the moment when the temperature reaches it maximum value, right after the end of inflation. Inflation cools down the universe, but then inflation ends and the energy in the inflaton field immediately converts into heat—so-called reheating. And then the expansion makes the temperature decrease it again. So, presumably the temperature went down and up and down again. If I had to identify a special moment, I'd look at when the temperature reached its maximum value and call that the big bang.