So all the mass in the universe is compressed into small insanely dense “ball”. Something happens, it explodes with enough force to escape it’s own huge gravity pull. Matter is sent out into a vacuum. So what slows all this new matter down enough for the particles to coalesce and form objects?
If singularity exploded with enough force to escape it’s own gravity, wouldn’t the particles themselves be going to fast for their own gravity to pull other particles together and form objects?
A tangent question: Since space is a vacuum does that mean we are all still traveling at the same speed as we did right after the Big Bang?
The simple answer is that gravity slowed them down. Now there appears there may also be a cosmological constant (an anti-gravity force) which is speeding things up as well, but that is irrelevant to this answer.
Think of shooting a gun straight up. The bullet flies up, but gravity slows it down untill eventually it falls back to earth. If you shoot it fast enough (about 7 miles per second as I recall) then it’s going fast enough that gravity will never slow it to a stop.
The big bang was like this – we know how fast things are flying apart (using Doppler red shifts). If we know how how much total mass there is in the universe, we can tell if it’s enough to slow the expansion down to a stop or not. (Unfortunately we don’t really know that, and that’s one of the questions cosmologists worry about. There are various theories now that there is a lot of dark matter/energy which we cannot see.
But thats the part I cant wrap my little head around. The initial explosion of the big bang had to be strong enough so that gravity wouldn’t pull everything back again. But shouldn’t that same force been strong enough that the particles expelled would have been moving to fast and far from each other for gravity to work on them?
You misunderstand the nature of the Big Bang. Nothing exploded in the sense that you think. The Universe popped into being and started expanding and energy filled the empty space. So it is wall to wall hot. Just energy that does not interact with itself much. As the Universe gets bigger things get less hot, until finally mass starts to fall out of the energy. Once that happens, gravity occurs. Some of that energy is still there, spread out over the whole of the Universe - the Cosmic Background Radiation. The mass eventually started forming atoms, and we get to see the stars etc.
So things (and not matter) did not explode out, they just filled an increasing volume that is now everything. And everything is still moving away from everything else as the Universe expands.
First, the universe isn’t made of a big ball of stuff that exploded and expanded into a big empty nothing. The “empty space” itself is also expanding. Google “Hubble’s Constant” for more info. Don’t think of it in terms of simple Newtonian physics.
Second, just because two particles are zipping away from everything else doesn’t necessarily mean that they are zipping away from each other. Draw two dots next to each other on a balloon and inflate the balloon. The dots don’t expand away from each other as much as they expand away from the other side of the balloon. Therefore, the two dots could be pulled together by their own gravitational pull and form a clump. The clump is still moving outward. The particles don’t have to stop or slow down to start clumping together.
Third, gravity still affects everything in the universe. One of three things can happen. Either the expansion isn’t big enough to overcome gravity, and the universe’s expansion will eventually slow down and reverse, and everything will start moving back towards each other and end in the Big Crunch. Or, the expansion of the universe will be big enough to overcome gravity, and everything will spread out thinner and thinner forever. Or, the third possibility is an exact balance is hit so that the universe expands out to a particular point and stops.
Scientists have been arguing over which possibility is actually occurring for quite some time. In the last decade or so, careful measurements indicate that the rate at which the universe is expanding is actually accelerating, which has really thrown a wrench into the works. Come up with a good explanation for it all and you might end up with a Nobel prize.
Not quite. It’s easy to misunderstand the balance case. In such a case, the universe would still expand infinitely, and there is no scale factor which it would not eventually reach, but it would do so at a speed asymptotically approaching zero.
And we are still going at the same speed we were at the Big Bang: Zero. At least, in our frame of reference. In this frame, everything else is moving away from us, but we’re sitting still. So we can say that the location of the Big Bang was right exactly here. Meanwhile, of course, an observer anywhere else in the Universe can say the exact same thing, so the Big Bang occured exactly right there, too. Or in other words, the Bang happened everywhere at once.