So I’ve been going through the dangerous rabbit hole of wondering how everything came to be and, obviously, the leading theory is the big bang theory. Where an infinitely dense spot of matter exploded and created every single thing in existence, including the ever-expanding universe. So, if the ever-expanding universe started expanding from an infinitely dense spot that exploded, wouldn’t that spot be the “center of the universe”, since it’s the starting point of said expansion?
In: 7
My answer: the big bang.
Imagine a sphere that is expanding in size, like a balloon being inflated. Note that the surface of the balloon is flat, i.e. two-dimensional. Now imagine a tiny 2D creature living on that surface, like a flat ant crawling on the surface of a beach ball.
Now consider how this world looks to the ant, compared to how it looks to us.
The ant says:
* My world is flat and two-dimensional. I define X as forward/backward and Y as left/right, but I have no concept of any other spatial direction.
* My world is unbounded, there’s no edge, but it has a finite amount of space, and that amount is expanding over time
* My world has no center, every spot is just like every other, so your question is meaningless
From our 3D perspective, we would say:
* Your world does indeed have two spatial dimensions, X and Y, but I can see that it’s curved through a radial spatial dimension, R, which is orthogonal at all points to X and Y
* What you call “expanding through time” is what I call “increasing distance R”. What you call the past is what I would call inward, and what you call the future is what I would call the same value of X and Y but a larger value of R.
* There is no “center” **on** the 2D surface at any particular value of R, but your world does have a center in 3D space: the origin point, what you would call t=0 and I would call R=0. It’s clearly the center, because at any value of R, that point is equidistant from every point on the 2D surface of your world.
* You might find it interesting that at that point, X=Y=R=0, the 2D surface you occupy is infinitely small and dense
Hopefully it’s clear that the point of this analogy is to suggest that our universe is similar, but with one extra spatial dimension. We would say:
* Our world has three spatial dimensions, X, Y and Z, and moves forward through time
* The volume of our universe is unbounded, but it is finite and increasing
* There is no “center” of the universe, as described in every other answer here
But you can imagine an alien who might say:
* I, from my 4D perspective, can see that your world is curved through a 4th spatial dimension R which is orthogonal to X, Y, and Z
* You experience this dimension as time; what you call “the future” I call “larger values of R”
* There is no center on the 3D “surface” of your universe, but viewed in 4 spatial dimensions it’s clear that the center is the origin point, what you’d call t=0 and I call R=0, the point at which your 3D world is infinitely small and dense: the big bang.
NB: this explanation is more thought-provoking than useful; it’s just an analogy, and AFAIK you can’t use this perspective to solve any previously unsolved question. It’s just a good way to visualize how a 3D surface can be limitless but still finite, and what “center” might mean in different dimensions. I hope you find it interesting (and that this thread isn’t too old for some real physicists to come along and tear it to shreds 🙂 ).
My answer: the big bang.
Imagine a sphere that is expanding in size, like a balloon being inflated. Note that the surface of the balloon is flat, i.e. two-dimensional. Now imagine a tiny 2D creature living on that surface, like a flat ant crawling on the surface of a beach ball.
Now consider how this world looks to the ant, compared to how it looks to us.
The ant says:
* My world is flat and two-dimensional. I define X as forward/backward and Y as left/right, but I have no concept of any other spatial direction.
* My world is unbounded, there’s no edge, but it has a finite amount of space, and that amount is expanding over time
* My world has no center, every spot is just like every other, so your question is meaningless
From our 3D perspective, we would say:
* Your world does indeed have two spatial dimensions, X and Y, but I can see that it’s curved through a radial spatial dimension, R, which is orthogonal at all points to X and Y
* What you call “expanding through time” is what I call “increasing distance R”. What you call the past is what I would call inward, and what you call the future is what I would call the same value of X and Y but a larger value of R.
* There is no “center” **on** the 2D surface at any particular value of R, but your world does have a center in 3D space: the origin point, what you would call t=0 and I would call R=0. It’s clearly the center, because at any value of R, that point is equidistant from every point on the 2D surface of your world.
* You might find it interesting that at that point, X=Y=R=0, the 2D surface you occupy is infinitely small and dense
Hopefully it’s clear that the point of this analogy is to suggest that our universe is similar, but with one extra spatial dimension. We would say:
* Our world has three spatial dimensions, X, Y and Z, and moves forward through time
* The volume of our universe is unbounded, but it is finite and increasing
* There is no “center” of the universe, as described in every other answer here
But you can imagine an alien who might say:
* I, from my 4D perspective, can see that your world is curved through a 4th spatial dimension R which is orthogonal to X, Y, and Z
* You experience this dimension as time; what you call “the future” I call “larger values of R”
* There is no center on the 3D “surface” of your universe, but viewed in 4 spatial dimensions it’s clear that the center is the origin point, what you’d call t=0 and I call R=0, the point at which your 3D world is infinitely small and dense: the big bang.
NB: this explanation is more thought-provoking than useful; it’s just an analogy, and AFAIK you can’t use this perspective to solve any previously unsolved question. It’s just a good way to visualize how a 3D surface can be limitless but still finite, and what “center” might mean in different dimensions. I hope you find it interesting (and that this thread isn’t too old for some real physicists to come along and tear it to shreds 🙂 ).
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