Finite Or Infinite Nature of Universe

It’s an existential question most of us have probably pondered at some point: is space infinite? It’s tricky to answer because there’s not just one kind of infinity to consider. Even if the universe goes on forever, it may not be infinitely large. It could be bounded like the surface of the Earth, allowing you to travel indefinitely without ever finding an edge.

The universe may be infinite, but we can only see a finite section of it due to the finite speed of light. We can only see those parts from which light has had time to reach us since the beginning of the universe - which means we can (in theory) see a spherical universe with radius of about 47 billion light years. If I gave you some time to think about that I’m sure that you would come up with the following conclusion - “that means that the universe must have expanded faster than the speed of light at some point”, which appears to violate special relativity. In fact that is what is thought to have happened, during a period called “inflation”, and it does not violate special relativity since it is not a spatial motion, but the expansion of space itself.

In our human words, this means 13.8 billion light-years in all directions, the Universe doesn’t repeat. Light has been travelling towards us for 13.8 billion years this way, and 13.8 billion years that way, and 13.8 billion years that way; and that’s just when the light left those regions. The expansion of the Universe has carried them from 47.5 billion light years away. Based on this, our Universe is 93 billion light-years across. That’s an “at least” figure. It could be 100 billion light-years, or it could be a trillion light-years. We don’t know. Possibly, we can’t know. And it just might be infinite.

If the Universe is truly infinite, well then we get a very interesting outcome; something that I guarantee will break your brain for the entire day. Consider this. In a cubic meter (or yard) of space. Alright, in a box of space about yay big (show with hands), there’s a finite number of particles that can possibly exist in that region, and those particles can have a finite number of configurations considering their spin, charge, position, velocity and so on.

There are only 1080 particles in the observable Universe, so that’s much less than the possible configurations of matter in a cubic meter. If the Universe is truly infinite, if you travel outwards from Earth, eventually you will reach a place where there’s a duplicate cubic meter of space. The further you go, the more duplicates you’ll find.

In fact, hopefully you’ll absorb the powers of an immortal version of you, because if you keep going you’ll find an infinite number of yours. you’ll eventually find entire duplicate observable universes with more yours also collecting other yours. And at least one of them is going to have a beard.