[ianhorn]

What blows my mind even more than that is the fact that the universe is apparently 93 billion light years in diameter despite being only 14 billion years old. Intuitively, I'd think that the radius of the universe would be smaller than the age of the universe. Stuff in the universe would go outward more slowly than light in the universe would go outward, because stuff moves slower than light. Apparently that's not the case. Space and time are weird.

[takk309]

My understanding is that the expansion of space/time can exceed the speed of light because space time is what light travels through. Nothing says that two points can't move apart faster than the speed of light, just that information between them can't be shared faster than the speed of light.

[ianhorn]

I don't understand what it means for points to move apart faster than the speed of light. I understand speed of a thing to be change with respect to space, so what does speed of space mean? Naively, I'd define it to be zero. If I stretch a ruler out, the 1ft mark hasn't moved with respect to the 1ft mark. I can say otherwise by comparing the ruler to what's around it. If the ruler is literally everything, we can only measure the ruler with respect to itself. I'd define measurement as with respect to the ruler (the ruler is spacetime). I know I'm wrong, but can't figure out why. Any help?

[mensetmanusman]

Look up the expanding balloon analogy.

[ianhorn]

With that analogy, the balloon would be the ruler in my analogy, which leads me back to the original questions. Using the balloon analogy, if you have a normal balloon in 3D euclidean space, you can measure/define the expansion easily. Without that, what can you do?

You could define some physical process on the balloon as distance and time, like light moving and atoms vibrating, and call that our ruler. Then measure intrinsic properties like curvature? If hypothetically the speed of light instantly dropped by 5% (with respect to existing objects' distances, I guess), do you just define those objects as instantly 5% further apart now, or do you you say something like the speed of light changed? Then there'd be similar questions about changes in how we define time. This is fun to think about.

[mrich]

When the universe has a size, what is outside of it?

[cthalupa]

Short answer: We don't know

Longer answer: Maybe nothing. Maybe it's nonsensical to think of something as being outside of the universe - as it expands, it creates space where there was none. Maybe a true vacuum that our universe is floating through. Maybe other universes. Maybe something else.

We might not be able to ever know the answer to this question - the laws of physics might prevent us from being able to decipher it.

[drran]

Chicken.