RE: What does the universe expand into?
November 6, 2014 at 7:15 pm
(This post was last modified: November 6, 2014 at 7:37 pm by Alex K.)
There is a pretty definitive answer in a sense. If you look at the theory (of general relativity and of the friedmann lemaître robertson walker scenario of cosmology in particular) it becomes somewhat clear why the notion of a space into which the universe expands is not necessary.
I don't even want to go into the discussion of whether the universe is finite at all, and it may well be infinite, or whether it has boundaries (it can be finite and without boundaries, if it leads back onto itself like a three dimensional torus or sphere).
If you look at the maths, you see that the expansion comes from the dynamics of a field called the metric, which is the mathematical object which is used to calculate distances in spacetime. The universal expansion occurs because this field gets larger and larger values, such that the distance between objects at two different fixed coordinates is measured larger and larger as time proceeds. It's really more like a shrinking of the univeral measuring rod, and less like something expanding into something. There does not need to be an embedding of our universe into a bigger space for this to occur, merely our local metric field changes its value and becomes larger. That's how it works in general relativity.
I don't even want to go into the discussion of whether the universe is finite at all, and it may well be infinite, or whether it has boundaries (it can be finite and without boundaries, if it leads back onto itself like a three dimensional torus or sphere).
If you look at the maths, you see that the expansion comes from the dynamics of a field called the metric, which is the mathematical object which is used to calculate distances in spacetime. The universal expansion occurs because this field gets larger and larger values, such that the distance between objects at two different fixed coordinates is measured larger and larger as time proceeds. It's really more like a shrinking of the univeral measuring rod, and less like something expanding into something. There does not need to be an embedding of our universe into a bigger space for this to occur, merely our local metric field changes its value and becomes larger. That's how it works in general relativity.
The fool hath said in his heart, There is a God. They are corrupt, they have done abominable works, there is none that doeth good.
Psalm 14, KJV revised edition
