As most people are aware, our universe is expanding. Scientists noticed that all of the galaxies that they were able to measure in the night sky were moving away from us. They were able to determine this by a phenomenon known as the Doppler shift, which measures the difference between the expected color spectrum of an object and the actual color spectrum. Just like the sound of a train coming towards you sounds higher in pitch than a train going away from you, so too, the actual light of an object that is moving towards you has a slight shift towards the violet end of the spectrum, and if the object is moving away from you, the shift is towards the red end. It was when they discovered that the galaxies were all moving away from us at different speeds, and that the galaxies furthest away were moving away the fastest, that the concept of the "Big Bang" was born. Imagine for a moment the miniature "Big Bang" that occurs when a fire work goes off in the sky. If one of the sparks were the Milky Way, then all the sparks that are close to it would be moving away from it much more slowly compared to a spark on the opposite side of the fire work explosion.
One of the most interesting things to think about the universe is the question of whether it will continue to expand forever, or if it will one day stop expanding and then begin to contract until there is a "Big Crunch". It all boils down to whether there is sufficient mass to slow down the expansion. The scientists' latest theories suggest that there isn't. Both scenarios hold interesting possibilities.
The more popular view, that the universe will expand indefinitely, suggests a beginning with no end. The first thing that I would want to know, then, is where did all that mass come from to make the "Big Bang"? Bear in mind that I am just a guy doing a little light thinking here, and by no stretch of the imagination do I remotely resemble a theoretical physicist, and yet I have a hard time imagining a universe being born in a"Big Bang" without all that matter coming from somewhere. I would like to propose one possible solution.
Imagine we are out in empty space, outside of our universe. When we look at it we see a faint, hazy ball that's slowly expanding. What I propose, however, is that in every direction that one looks, there are additional balls of every imaginable size, with the newly born, small and intensely bright,and the largest nearly invisible. In order to explain the source of the matter that caused our "Big Bang", we would have to imagine that occasionally the universes would expand to the point where they overlapped, with gravity taking over and condensing matter to the point were a "Big Bang" event would occur. There is no creation, matter and energy is what there is, and it has always been that way.
The other scenario is where our universe is sufficiently massive enough to eventually stop expanding, and then contract in a final "Big Crunch". The distressing thing for me is not that everything will eventually get crunched, but that this type of universe wouldn't necessarily need any other outside universe for it to exist. It could be part of my imagined multiverse, but it doesn't have to be. It could be all there is, completely self contained. Somehow, that bothers me. I guess I'd rather not have a part of my reality, no matter how distant it might be in space and time, to be limited in any way.