How uniform is the expansion of the universe?

[Notvacka]

The universe is known to be expanding. There is no centre of expanision, since it's space itself that is expanding, rather than galaxies speeding away from us through space.

But if the expansion is uniform, wouldn't the space between molecules expand as well as the space between galaxies? If this were the case, one would think that the expansion would go unnoticed. The proportions within a picture remains the same when the picture is enlarged and in the popular balloon illustration of expansion, it's not only the distance between the marks on the surface of the balloon that increases, but the size of the marks as well.

 

[zomgwtf]

The universe is known to be expanding. There is no centre of expanision, since it's space itself that is expanding, rather than galaxies speeding away from us through space.

But if the expansion is uniform, wouldn't the space between molecules expand as well as the space between galaxies? If this were the case, one would think that the expansion would go unnoticed. The proportions within a picture remains the same when the picture is enlarged and in the popular balloon illustration of expansion, it's not only the distance between the marks on the surface of the balloon that increases, but the size of the marks as well.

What you suggest would be true, however the force of expansion is miniscule compared even to that of gravity. So at small distances nothing is happening because the force to expand is being well over-powered by various forces. Think gravity, electro static interactions, gravity, magneticism. These forces are very strong relative to expansion, at great distances however expansion still holds on while the other forces dwindle away.

 

[IceMan815]

The universe is known to be expanding. There is no centre of expanision, since it's space itself that is expanding, rather than galaxies speeding away from us through space.

But if the expansion is uniform, wouldn't the space between molecules expand as well as the space between galaxies? If this were the case, one would think that the expansion would go unnoticed. The proportions within a picture remains the same when the picture is enlarged and in the popular balloon illustration of expansion, it's not only the distance between the marks on the surface of the balloon that increases, but the size of the marks as well.

Well the space between molecules won't expand because its hold by electrostatic energy and gravity, also for example The milky way and Andromeda won't go away from each other because we are gravitationally bound in the local group of galaxies. Thats why molecules won't expand, solar systems won't expand, galaxies and galaxy clusters! the expansion is about distant galaxies that are far enough from each other that gravity is much less strong then the dark energy! It's all relative, to us every galaxy is moving away from us except a few of them that are in our gravitation field, relative to other galaxy clusters we are moving away from them!

 

[Notvacka]

Then I guess that if gravity can curve space, it can also stretch space. In the balloon analogy, the markings would be replaced by pieces of adhesive tape. These would increase the tension in the surrounding surface, by not allowing the taped parts of the balloon to stretch as much when the balloon expands.

This means that the other forces mentioned, like electro static interactions, also deform space, at least to some extent, I suppose.

 

[Passionflower]

The universe is known to be expanding. There is no centre of expanision, since it's space itself that is expanding, rather than galaxies speeding away from us through space.

That is true but space expansion is not the only way that gives that effect. See for instance the Milne model, every object here is also in the center of the universe while it starts with a point.