- #1
davidbenari
- 466
- 18
I'm reading introductions about inflation and one thing they assume is that presently ##\ddot{a}<0## where ##a## is the parameter in our FRW metric.
We know that this is observationally false, since in fact ##\ddot{a}>0##.
But why do they assume this?
My guess is that in the big-bang model there is a period where radiation and matter dominates over the cosmological constant and it is in this regime that ##\ddot{a}<0##.
Another guess could be that theorists of the time didn't know that ##\ddot{a}>0##. But I don't think this is a good enough answer since people keep talking about inflation so there has to be some reasoning behind the assumption that ##\ddot{a}<0## after inflation.
So, what going on here?
Thanks.
We know that this is observationally false, since in fact ##\ddot{a}>0##.
But why do they assume this?
My guess is that in the big-bang model there is a period where radiation and matter dominates over the cosmological constant and it is in this regime that ##\ddot{a}<0##.
Another guess could be that theorists of the time didn't know that ##\ddot{a}>0##. But I don't think this is a good enough answer since people keep talking about inflation so there has to be some reasoning behind the assumption that ##\ddot{a}<0## after inflation.
So, what going on here?
Thanks.