3

Physicists have used math to calculate that gravitation separated from the 4 forces at 10^-36 seconds after the big bang, which is even before the inflationary period. The universe was still smaller than a pin head at this point, so what does it mean? Could it be better described that spacetime as we know it took shape? (regardless of if you are proponent of string theory or loop quantum gravity).

I have read this question, but I am really only concerned with gravitation and the formation of spacetime, so I am not looking at the other forces that separated later.

rob
  • 89,569
foolishmuse
  • 4,551

1 Answers1

2

This is really a long comment.

Lets see the concept of force:

One of the foundation concepts of physics, a force may be thought of as any influence which tends to change the motion of an object. Our present understanding is that there are four fundamental forces in the universe, the gravity force, the nuclear weak force, the electromagnetic force, and the nuclear strong force in ascending order of strength

So you are talking of fundamental forces .

Gravitation and electromagnetism were considered forces within the Newtonian classical mechanics formulation. The weak and strong belong to the quantum mechanical realm where, in the quantum field theoretical calculations for particles, force is the dp/dt the change in momentum in interactions of particles

When accepting there are four fundamental forces, including within this frame gravity one makes the assumption that quantization of gravity is a definite fact. This is not true, there are only effective theories for the quantization of gravity, used in cosmological models ad hoc to give the statement you make

Physicists have used math to calculate that gravitation separated from the 4 forces at $10^{-36}$ seconds after the big bang,

The three forces, weak, electromagnetism, strong can mathematically be extrapolated to the beginning of the big bang with Grand Unified Theories with mathematical rigor, they embed the standard model of particle physics.

Trying to include gravity for those high energies, as you also state, is a matter of models that are not yet mathematically rigorous in modeling gravity and embedding the standard model of particle physics., (as string theory and loop quantum gravity).

In my opinion, the grand unification epoch is still a hypothesis used to model the beginning times of the universe in a hand waving way, until and if a theory of everything is developed. The numbers are based on fitting cosmological observations with simple reasonable assumptions .

This essay might interest you.

hft
  • 19,536
anna v
  • 233,453
  • Thank for pointing out the essay. "Scientific descriptions of events earlier than a trillionth of the first second of time are only reverse extrapolations—regarded by scientists as better than religious dogma, philosophical musing, or science fiction, but how much better is frankly unknown" That says a lot. I'll read it carefully. – foolishmuse Apr 07 '22 at 19:18
  • I've read through the paper, but unfortunately it didn't provide an answer to my question. And the comments in the paper mirror you own: that no one knows what happened in the first fraction of a second. I guess I could rephrase my question as "at what point did the structure of spacetime as we know it appear?" – foolishmuse Apr 08 '22 at 15:30
  • @foolishmuse where the GUT theories can be rigorously extended, then one can assume that it is the spacetime of general relatvity unimpeded by complications of possible unification – anna v Apr 08 '22 at 16:43
  • So we might not have seen actual gravity in action until after the separation of the 4 forces? – foolishmuse Apr 08 '22 at 17:24
  • well, it is a hypothesis that the four forces can be unified in the same mathematical way that we know the rigorous mathematics for the three . gravity is not rigorously quantized. The known GUT theories for the three are our real limit. – anna v Apr 08 '22 at 19:49