I was reading a post on anyflower’s blog and she was telling us that she is having trouble understanding that the universe is expending into nothing and that dimensions were folded into themselves. I won’t say it’s quite simple, because well it isn’t and quite frankly it is unintuitive.
First, let us set some base, there are two answers that are helping me understand the expansion of the universe: everywhere and 13.7 billions years ago. Like 42 these don’t help mean much without the question those answers answer. Well the question are: where did the Big Bang occur, and When did it occur. It might sound strange to say that the Big Bang happened everywhere but let me walk you through the reason. This reasoning is quite simple, we observe that the universe is expending, since it is getting bigger in the future, we can safely say that it was smaller way in the past. And if you continue to look into the past at some point the dimensions of the universe are going to be zero, it’s gonna be a point. Now, this point containing all the matter and energy of the universe is the Big Bang, well no to be completely accurate this point is the result of the Big Bang, it comes into existence at instant 0, which can only exist simultaneously with the Big Bang.
Now, this point contains all the matter, energy AND space in the universe. So all the everywhere of the universe is contained in that point. Which means that in that everywhere the Big Bang happened. You might wonder why when we do not know where the Big Bang occurred, how can we know when. Well through the same process as we figured out the entire universe was in that point. You see the reversal of the expansion produce this point some time in the past, that why we know “when” the Big Bang occurred.
This existence of a when with nowhere (or with everywhere) helps us in the where does this universe expend into. You see nothing is not exactly the answer I would give. While it is true that the universe does not expend into any space (if their was space to expend into it would be part of the universe…). You see everywhere stays the same, but when changes, in a way the three-dimensional expansion we see are the result of the explosion of the Big Bang but in time instead of space. Each second the universe becomes older and this manifest as space being a little bigger.
Now, this ties in with the folded dimension idea. This idea comes from string theory, which basically says that the universe is the manifestation of vibrating object. One of the interesting prediction of this theory is that their exist an number of extra dimension that are too small to be observed by humanity (depending on the version of the theory you see it, it ca be as much as 22 extra dimension). Now we explain those hidden dimension as being folded over themselves to insane amongst. Now “before” the Big Bang every dimension was folded in this way. At the moment of the Big Bang, 3 spatial dimensions and one temporal dimension for some reason unfolded and created the space-time we observe.
This lead to another way to understand the expansion of the universe, the dimension of space have not yet finished to unfold and are slowly relaxing into their full size. Kinda like a t-shirt that would be folded and help by only one layer of the fold, it would quickly restore itself to its original size. But that doesn’t really answer the question of what it is unfolding into, and one again we much go back to the time answer I am usually giving.
So here I’d welcome questions about the expansion of the universe, tell me about what puzzles you and I will try to answer. Now I do not hold all the answer, in fact I don’t believe science as all the answers to that question figured out yet. However I will try to answer and explain to the best of my abilities.