how is empty space expanding?

Originally posted by @lemon-lime
I'm not saying there is, but...

if there was a center of the universe, then.....


where would it be?

for the universe to have a center, it would have to have some kind of definable boundaries (which it doesn't ) else how can you define the meaning of 'its center'?

Originally posted by @menace71
I'm sure no analogy is perfect but I've always heard the expansion of the universe is kinda like a balloon or it's a good way to show kids anyway... Draw your galaxies on the surface of the balloon then blow it up and you see them moving away and the universe expanding outward. Of course this doesn't explain why?

Manny

the problem with the balloon analogy is that it is impossible to visualize it without space inside it and without space outside it and the balloon expanding 'through' that 3D space and yet there is no analogous equivalent in physical reality of that space inside it and space outside it and the balloon expanding 'through' that 3D space. It is this that makes the balloon analogy cause much layperson misunderstanding and confusion.

Makes sense

Manny

Originally posted by @humy
all of what you suspect is totally unintelligent nonsense and only in part because there is no center of the universe.

" there is no center of the universe."

I assume you have proof of this? If not, why are you wasting our time with your unintelligent nonsense?

Originally posted by @humy
for the universe to have a center, it would have to have some kind of definable boundaries (which it doesn't ) else how can you define the meaning of 'its center'?

...that we know of.

Just because you cannot see something does not rule out the possibility it is there.
By your flawed logic the assertion that dark energy exists is unintelligent nonsense......so why do people keep talking about it?

Originally posted by @metal-brain
...that we know of.

And by the principle of Occam's razor, we should assume no (to be more precise, assign an arbitrarily very 'low' probability of) boundaries to the universe until if or when we have evidence to the contrary; that is just how science works.

By your flawed logic the assertion that dark energy exists is unintelligent nonsense

wrong; we have evidence of dark matter (observable gravitational effect in the way galaxies rotate that cannot currently be adequately fully explained by any other known means) ; we have no evidence of 'boundaries' to the universe. That is the critical difference between those two cases. Occam's razor applies to the first case because of no evidence (for or against) for the first case. Occam's razor doesn't apply to the second case because of evidence (for or against) for the second case.

Originally posted by @ogb
what's the best guess as to why space is expanding? ...

Is it? Naked apes near the bottom of a gravity well. We have a handle? I tell myself to not confuse math with reality.

I

Originally posted by @apathist
Is it?

you do know it is a scientific fact that space is expanding, right?
Just checking.

Originally posted by @humy
for the universe to have a center, it would have to have some kind of definable boundaries (which it doesn't ) else how can you define the meaning of 'its center'?

If the universe began from a single point and expanded ouwards from that point, it should be possible (not practically, but in theory) to reverse engineer the expansion back to that one single point. By itself that point cannot be located, because without surrounding reverence points the concept of location wouldn't exist.

So I'm suggesting it could be theoretically possible to locate where the point was within (not outside, but within) the universe as it exists now. The only sticking point with this idea is if what you say about the universe having no boundary is true. But if you're defining boundary as a line separating two distinct areas, without taking into account the limitations of a finite universe, then perhaps 'boundary' isn't the correct word to be using here.
It would be better (imho) to focus on the concepts and ideas expressed by the words we use, rather than on the limiting (and often arbitrarily assigned) definitions of the words themselves.

Originally posted by @humy
you do know it is a scientific fact that space is expanding, right?
Just checking.

No. Stuff is moving away from each other, yes. (Generally speaking.) Space is not a substance, and isn't doing anything. Which, if you think about it, is exactly what nothing does.

The layman explanation of einstein gravity is a stretched rubber sheet. Put a bowling ball on the sheet and roll in some ping-pong balls, and look how accurate it all is! Clearly mass distorts space!

If we presume the existence of the phenomenon we mean to explain, things are easy. Illogical, but easy. Anyone not see the illogic?

Originally posted by @apathist
The layman explanation of einstein gravity is a stretched rubber sheet. Put a bowling ball on the sheet and roll in some ping-pong balls, and look how accurate it all is! Clearly mass distorts space!

If we presume the existence of the phenomenon we mean to explain, things are easy. Illogical, but easy. Anyone not see the illogic?

If we presume the existence of the phenomenon we mean to explain...

In order for that stretched rubber sheet illustration to actually work (using a real rubber sheet and ping pong balls) you would have to take into account that a real force of gravity is needed. Otherwise the stretched sheet would remain stretched.

You could put on 'heavy' rocks instead of ping pong balls and still nothing would happen, because without the actual unseen force of gravity working to show how an illustration of gravty is achieved, the illustration would fail to show what gravity is. It can show what gravity does, but not without a real force of gravity to do it.

An attempt to 'explain' gravity with this sort of illustration is like using a particular word in a definition of that very same word, so the illustration seems to be somewhat (for lack of a better word) incestuous.

Originally posted by @lemon-lime
[b]If we presume the existence of the phenomenon we mean to explain...

In order for that stretched rubber sheet illustration to actually work (using a real rubber sheet and ping pong balls) you would have to take into account that a real force of gravity is needed. Otherwise the stretched sheet would remain stretched.

You could put on 'heavy' r ...[text shortened]... me word, so the illustration seems to be somewhat (for lack of a better word) incestuous.[/b]

It illustrates the curved space nature of gravity, that is it bends space and it LOOKS like a force to us but it really is just tipping the sheet a bit to make things roll on the sheet.

Originally posted by @lemon-lime
...
An attempt to 'explain' gravity with this sort of illustration is like using a particular word in a definition of that very same word, so the illustration seems to be somewhat (for lack of a better word) incestuous.

It is called 'begging the question', an informal logical fallacy. Glad to know I'm not alone in seeing this.