Expansion of the Universe

What exact is meant by the expansion of the universe? It is an expansion of the outer borders of the universe (if there is such a thing)? Or is it an expansion of every single point within the universe?

I’m curious because of the implications it would have on my layman’s understanding of the Big Bang, various natural laws in the universe, and black holes. Right now I’m working with the assumption that it expands from every point, please correct me if I’m wrong.

For example, if space is constantly expanding at every point, how does this effect the structure of an atom? Wouldn’t the space between the neutrons and protons continue to increase, to the point where eventually, the atoms couldn’t maintain it integrity? Same for the proton itself, wouldn’t the space between its quarks eventually become so great that it would eventually rip it apart?

Inside a black hole, wouldn’t the constant expansion of space eventually dissolve the black hole, as the gravitational forces became weaker?

Any help would be greatly appreciated?

First of all, where the expansion is happening will be useful to know:

Imagine a balloon with galaxies drawn all over it. If you put a little bit of air into the balloon, the galaxies will be close together. If you put more air into it, the galaxies will move away from each other. (You could measure the surface of the balloon to observe that.)

If you were a tiny person standing on the balloon, you’d see yourself standing in the middle of a circle (because you’d have a horizon). If you stood on one galaxy and looked at the surface you could see, you’d see galaxies all the way to the horizon. As the balloon expanded, it would look to you as if your galaxy were standing still and the horizon was rushing away from you, making the surface you could see bigger. The other galaxies you could see would be moving away from you, and further-out galaxies would be moving away faster. (If you draw dots on a balloon and pick a reference dot to be ‘your’ galaxy, you can again measure that the ones closer to your galaxy don’t fly outwards as fast.)

So where is the expansion? The balloon universe is a two-dimensional one: an expanding circle full of galaxies. The expansion is really taking place in a third dimension, since the circle gets bigger because the radius of the spherical balloon is getting bigger. The analogy is useful because you can then think of our spherical universe’s ‘edge’ as being a horizon, and maybe the real expansion is happening in a fourth dimension…

Anyways. As for the amount of expansion: on small distance scales it’s hardly noticeable. Galaxies far away from us appear to be flying away faster than nearby galaxies. Stuff in our own galaxy can’t even be detected to be receding from us. If it’s negligible on that kind of a size scale, it’s even more inconsequential to an object the size of a star or a black hole or a planet or especially an atom. The expansion inside them is so small that they just don’t notice.

Ok, you say that the effect of space expansion is hardly noticable on such a small scale such as stars, planets, and atoms. I’m assuming by this then, that there is still some actual increase of space between every point. And I’m thinking that although it may not be consequentual in terms of any real world application, it still may have effect on the longterm. Say eventually, something like 10^100 years from now, would those extremely small expansions add up to something rather significant, essentially ruling out interaction between particles?

No, because other forces are stronger. I.e., gravity, the electric force, the strong force, and the weak force can easilly hold an atom, a planet, or a galaxy together, despite the tiny expansion force. Think of galaxies as being stickers on the balloon being blown up. The stickers get farther apart due to the expansion of the balloon, but the stickers don’t get any bigger, because their internal cohesion is stronger than the expansion.