It both amuses and exasperates me to hear people say that the universe is limitless and infinite. Where do people get such a notion from, I haven’t the slightest idea. There is no evidence to support this belief, but there is much evidence to support the fact that the universe is finite.
When I say “people,” I obviously do not mean scientists because they know better than to say that the universe is infinite. No, I mean lay people. And do I expect lay people to know that the universe is not infinitely large? Yes, I do. They don’t need to know much science to infer that the universe does not have a limitless size. To these people I would not use science to “prove” that the universe has a finite size. I’m not going to mention the Doppler effect or talk about Hubble’s constant. I’ll just use logic.
The first proof is in the night sky. If the universe were infinite, it would have an infinite amount of energy. This energy would be in the form of electromagnetic radiation, one of which is visible light. The universe would be bathed in this infinite amount of energy and this would kill us. At the very least, there would be an infinite amount of light, not only because of the infinite amount of energy, but an infinite universe could very well also have an infinite number of stars. The result would be a universe filled with light; our nights would be full of light and there would never be darkness. But look at the night sky. It’s dark. Meaning that the universe has a limited amount of energy. Meaning it has limits: a limited size and a limited mass.
Then, there is the philosophical point of view. We cannot say that the universe is infinite because if it is, then there would be nothing outside of it. Including nothing. Let me explain.
If the universe is infinite, then the universe is all that there is. There is nothing other than the universe. All of existence is the universe and all the universe is all that exists. Meaning, “nothingness” can never exist. Because if “nothingness” exists, it will create a “hole” in the universe and the universe would become smaller by the amount of space that that “hole” occupies. But if the universe were infinite, it could not become smaller. Meaning, if the universe were infinite, “nothingness” could never exist. (Didn’t I say that already?)
But we know that “nothingness” exists, don’t we? We have concept of it, don’t we? We understand nothingness as the absence of something. May I suggest to you the corollary: that “somethingness” is also the absence of “nothingness”? “Something” and “nothing” are dual opposites that must exist together. “Nothing” can not be anything if there is no “something” to compare it with. On the other hand, “something” has no meaning unless there is “nothing” to compare it with.
So while there is a universe (“something”) there must also “exist” a nothingness. And that nothingness exists outside the universe. The boundary where “something” and “nothing” meet define the physical limit of the universe.
Finally, I’d like to ask those people who say that the universe if infinite: Where is the evidence that says so? I think some say that the universe is infinite only because somebody once said it, and somebody else believed it and said it to someone else who also believed it, and it went on from there. One thing’s for sure: There is no scientific basis for believing that the universe is infinitely large. But there is a lot of evidence that says that it is of a finite size.