Science a GoGo's Home Page Forums General Discussion Physics Forum Post Big Bang gravity

At what point, after the big bang, did gravity become a significant force in the Universe?

Have to get in a first answer (before the experts arrive) to that irresistable question

The Planck Epoch - up to 10 to the minus 43 sec - is unknown territory, but at that time there may have been a single fundamental force. On the other hand, some argue, that may not have been the case and gravity may have been a distinct force even at that instant after the Big Bang.

According to generally accepted theory, however, there followed the Grand Unification Epoch. This, again, was an unfathomably tiny instant, by the end of which, it's generally agreed, gravity certainly existed.

At whichever point it came into existence during in that first moment of time, I imagine it was very significant to the entire subsequent evolution of the cosmos.

To add to red's reply, the answer also depends on what you mean by "significant". Gravity is a weak force, relative to the three others, but it is has the greatest capacity to act over long distances. So even in the early universe, when it existed as a separate force (with the caveats red described), it would have been a minor force in comparison to the strong/weak forces and electromagnatism. As the density of matter decreased, gravity would have had a larger and larger role, compared to those other forces.

Bryan

If gravity manifests as the curvature of spacetime, and at the moment of the Big Bang, spacetime was "infinitely" curved, would this not mean that gravity was infinitely strong at that point?

Well, that is one of the places where modern physics breaks down. Nobody knows what was going on at the first instant of the big bang. The problem is that GR says that the universe was an infinitely small point. But physicists don't like infinities, because there is no way to handle them. QM makes other predictions, but it doesn't work well when you mix it with GR, since it was developed assuming that the force of gravity was small enough in comparison with the forces at work in the atom that it was negligible. There is no clearly defined way to figure out what was going on at that time. In fact, off of the top of my head there is nothing there to cause the big bang. After all we know that black holes are quite stable, other than the very slow Hawking radiation. So what would seem to have been the ultimate black hole shouldn't have been blowing up. At least that is how it seems to me. However, there was something that was causing the universe to start expanding, probably dark energy. But of course, other than the name we don't have any idea just exactly what dark energy is.

Bill

Absolutely, and I suggest that its existence even in the Grand Unification Epoch may be considered significant if one considers how it's related to spacetime, and bears in mind the butterfly-effect.

This is one of the things I find a little frustrating. Sometimes it seems as though infinities are unpopular and unmanageable unless they can be used to support a particular argument.

If the curvature of spacetime was infinite at the time of the BB, how could it have become finite?

We should keep in mind that in mathematics division of by 0 is disallowed. That type of calculation winds up as being undefined. It is the most common case in which we meet an infinity. In physics we want to be able to say what will happen if we do a certain thing. When we find out that according to the math that works wonderfully in most cases in this case gives us an undefined answer we just have to say, "I don't think that anything in the universe is really undefined". And then we say we don't understand how the universe works under these conditions and go back to looking for a new idea that will work. To a large extent it is a matter of going back to the concept of 'effective theories'. These are theories that work over a certain range of conditions. For example Newton's theories work wonderfully, if we don't try to work with high speeds or large masses. SR and GR work wonderfully, if we don't try to get too small. But in a black hole, or at the start of the big bang we get answers that don't make sense, so we have to look for a better theory.

Bill Gill

I hate gravity force.
Division of by 0 will just give you some sort of things like complex infinity.You won't like that.

Gravitons in string theory and the general relativity (GR) is not theories that explained well. Something is missing inside it, and some of it is just boasting around.

Any of you believe on gravitons which can travel through different dimension of space-time?

Any of you figure out why general relativity says that gravity is just space-time curve which comes complex while you change your reference frame? Just imagine, you are standing under the curve, what will the curve looks like? A hyperboloid? Or a hanging cloth?

Is that the same as the idea that gravity might leak through higher dimensions into other universes? I believe that has been suggested as a reason why gravity is so weak.

I have a couple of problems with that.
1. If it leaks out, why should it not also leak in?
2. If it leaks out, that would seem to suggest that it is leaking to an area of weaker gravity, so it would not explain the strength of gravity in general.