Anonymous

It is expanding into EMPTY SPACE.

Anonymous

Space is expanding at a rate of 73.5 km/s per mega-parsec (approximately). That is if you take two points 1 million parsecs (3.26 million light years) apart they will be moving away from each other at 73.5 km/s.

Anonymous

Space is getting bigger, it is not going "into" any thing or anywhere.

Anonymous

The universe is not expanding at 4 km a second, or anything at all close to that. It's probably infinite, and when infinity expands it expands into itself. The actual speed of expansion for the VISIBLE universe (not the whole thing) is light speed.

Anonymous

We have no idea.

Anonymous

"What" is the universe. "What" is limited by the dimensions of the universe. Time and space are dimensions of the universe and they expand together. There is no "what" that's outside of the universe although the "what" gets bigger with time.

Anonymous

I don't think it's possible to know. If we knew what was beyond a certain boundary in space, that would also be part of the universe.

Anonymous

It may not be expanding into anything...

Anonymous

Nothing and then nothing.