Why Doesn't the Moon Fall When Orbiting Earth?

[russ_watters]

Assuming the universe is finite, it has a center of mass, but we can't observe enough of the universe to determine where this center is.

That isn't necessarily true (the typical analogy is that the Earth's surface has no center) and isn't what cosmologist theorize the universe looks like.

 

[rcgldr]

Assuming the universe is finite, it has a center of mass.

That isn't necessarily true (the typical analogy is that the Earth's surface has no center) and isn't what cosmologist theorize the universe looks like.

The Earth's surface has a "center", just need to go up one dimension (from 2d to 3d) in order to find it. So if the universe is a 3d surface on a 4d bubble, there's probably a center, but we can't observe it since we're stuck in 3d mode.

 

[russ_watters]

The Earth's surface has a "center", just need to go up one dimension (from 2d to 3d) in order to find it. So if the universe is a 3d surface on a 4d bubble, there's probably a center, but we can't observe it since we're stuck in 3d mode.

If you need to go up a dimension to find the center, then the center isn't on the surface, is it? The surface has no center on it. I see what you are saying, but you are changing the question: the question is does the universe have a spatial (3d) center (or does the Earth have a center on its surface). And the answer is no. Whether there are extra dimensions in which a center can be found is a separate question.

Here is a very slick explanation/demonstration: http://www.exploratorium.edu/hubble/tools/center.html

 

[superweirdo]

no no no, the center still might be in our 3d but we just need a bigger look to find it. It is we are trapped in a glassic ball where we look, we find stars so there is no way to tell if there is a center b/c we are trapped, but a person outside that ball can easily tell.

 

[ZapperZ]

no no no, the center still might be in our 3d but we just need a bigger look to find it. It is we are trapped in a glassic ball where we look, we find stars so there is no way to tell if there is a center b/c we are trapped, but a person outside that ball can easily tell.

Then what you are guessing (it is not even a hypothesis) is NOT the Big Bang, but something else that is not defined. The BB is not something you can simply use whichever way you wish.

I will again ask you to re-read the PF guideline regarding speculative posting. If you wish to work out your own theory without basing it on existing physics, please do so in the IR forum.

Now, how this thing went from a simple classical mechanics problem to a center of the universe and the BB is a mindboggler.

Zz.

 

[superweirdo]

thats what my physics teacher told me so I was citing him, but I guess since he only took masters into it and he tells us that he his more interested in philosophy than physics, I guess I crossed the line, I apolozige.