Is the Universe Infinite?
4-minute read

Traditionally when it comes to clickbait articles, it is common to frame the headline as a provocative question whose answer, all said and done, is “Nope, nothing to see here!” Happily, this article is not clickbait, and the answer to the titular question is most likely “Yes!”

The question of whether the Universe is finite or not is an interesting one, because despite there being only two possibilities, neither answer really seems satisfactory. When I was a kid, I used to wonder: (a) if the Universe is infinite, how could it possibly go on forever? (b) if the Universe is finite, what happens at the edge? Today, while I can make the question sound smarter with physics jargon thrown in (like “spacetime”), the essential point remains the same and the question is still open.

So here’s a fundamental problem: science ultimately relies on experiment to validate its hypotheses; with the acceptance of Einstein’s theories of relativity, we now know that the “observable” universe is about 93 billion light years across, and anything outside this bubble is beyond our reach forever (and in fact, cannot influence events in our part of the Universe at all). So from an experimental standpoint, we’re stuck, and may need to take a more Aristotlean approach to the problem. (Aristotle famously believed that women had fewer teeth than men…and didn’t bother to check.) So if we started from first principles and simple logic, should the Universe be finite or infinite?

In modern times, the question of whether spacetime is finite or not can be answered with an excellent trick. Let’s assume that there are only a hundred billion galaxies in all. Is spacetime finite or infinite? Answer: it is both, in a manner of speaking. Yes, it is finite, but no, you will never reach the edge. Consider the analogy of the surface of the Earth - the surface is finite but you can keep walking around forever (or until you drop). Now extend this analogy to spacetime as a whole. Can’t visualize it? Sorry, that’s the way it goes.

But are there a hundred billion galaxies in all, or more, or…even more? No one knows, but, we can switch our perspective to consider time instead. If the Universe has existed forever, and has been creating galaxies all along, there must be an infinite amount of stuff lying around. So has the Universe been around forever? Here, we may be tempted to seek out one of the many philosophies that claim that time is cyclic, and that if you go back to the distant past you end up in the future. Roger Penrose has a far more scientific-sounding but no less mystic version of this philosophy posited as a hypothesis. But there is a simpler version of this idea: certain conditions are conducive to the creation of fields, that evolve relative to other fields, and we perceive these fields as quantized packets under the right observational conditions. The relative evolution generates the notion of time we understand on a day-to-day basis, so you can think of time as a “local” concept. Meanwhile, there is a sense in which all of this has been happening “forever”, where “forever” is not in terms of the conventional and local notion of time mentioned earlier. And so the bottomline is, we have stuff being created on a continual basis (assuming, reasonably so, that the Big Bang is not a once-in-a-Universe event), and that implies there cannot be a beginning or end to this process. And this, finally, leaves us with an infinite amount of stuff, and an infinite Universe.