well i am an atheist and i should say when people ask me who and how is the universe is created and i just say them the big bang made everything and there are some people who ask what is before big bang and this is for yo people the big band dint just legit come out of my pocket..now im gonna give a stright up answer,
The universe is likely infinite. The presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model.
If something is infinite, then it must have always been infinite. You can not have something finite, and make it infinite without adding something that is infinite to it, and if we are talking about the universe then there's nothing else to add, so the universe is infinite and has always been infinite.
If we look at all the stars in other galaxies no matter how far away they are and measure how they are moving we see that the galaxies are all moving away from us, and they are going faster and faster. That doesn't mean that we are in the middle, because they are all moving away from each other as well. If you were standing on any other planet you would still see that every other galaxy is moving away from you.
Which means that yesterday every galaxy was closer to us than today. And a year ago they were even closer. And if you go back long enough (which we now know is around 13,72 billion years), they will be so close to us that we are practically in the same spot. This is called a singularity and time stops running here, similar to what happens inside black holes. But as we know, I am explaining it in reverse; so in reality time actually started here.
Remember, the universe is still infinite because it has always been infinite. At the moment of the big bang the universe was still infinite.
I'm going to add something to this that may be hard to grasp for someone who's not used to thinking about the universe in grand scales. When you look at something, you don't see it instantly. You only see it after the light from it has had the time to reach your eyes.
So when you are speaking to your mother, you don't see her instantly - because it takes time for light to reach your eyes. But light is ridiculously fast. It is the absolutely fastest thing that can travel through space. So you won't really notice it here on earth when talking to your mother or catching a ball that's moving that light has a speed, everything here just seems instant.
But when you look at the moon, you are not looking at the moon as it is right now but as it was 1,3 seconds ago. And if you feel the warmth of the sun on your body, that energy has been travelling through space from the sun to you for about 8 minutes! That also means that if you look at the sun, you are watching what happened 8 minutes ago. No matter what you do, you can't change what happens on the sun in 4 minutes if you start now to plan something. Because you can't travel faster than this speed of light.
Now think about the universe that is infinite. Do you think you can see the whole universe? No you can't, because it takes time for light to reach you. If something is billion billion billion billion billion billion billion light years away then it will take billion billion billion billion billion billion light years to get here, and the universe just isn't old enough for light to have reached all that way.
So if you look around you into space, there is a limit to how far you can see, until you can't see further. We call this the "observable universe", which is simply how far we can yet see. Our observable universe is like a huge bubble around us, and it contains everything that we can see.
But all that was once closer together, at the big bang. It was so close together that it was just condensed in a tiny little dot. Our whole observable universe was once just a dot. And around that dot there was even more stuff. We don't know what it was, but we assume that it was just like the stuff that our 'dot' has.
So there you have it. An infinite universe that was infinitely dense and time was stopped. Then for some reason expansion started, it happened incredibly fast, so fast that space expanded faster than the speed of light and now there are parts of the universe we actually just can't see.
Then the expansion slowed down, but later it picked up speed and is now going faster and faster. Eventually, physicists think, other galaxies will be moving away from us faster than the speed of light - which means we won't be able to see them any more.
That also means that any future alien civilizations will not be able to see other galaxies move away from each other, and they are just going to have a completely wrong picture of the universe because they don't know how it all started. The only reason we do is because we can observe galaxies moving away from us faster and faster. And this is the only time in the history of the universe that we are able to do that. So we are pretty lucky to be living in the time where we can know this for sure, because this information will be lost forever to everyone else who will be isolated in their galaxy in billions of years.