What is the size of the universe?

Because nothing can go *through* space faster than light. Space itself can, and does, expand as fast as it wants. The expansion has been going on for 13.7 billion years. So stuff that started out much closer is NOW 40+ billion light years away. It was much closer when the light we're seeing started our way. Yes the observable universe is 40 something billion LY in any direction, so 90 something in diameter. It is believed to be *at least* 2 to 3 times larger than that. Although experiments done with WMAP indicate, though don't fully "prove", that the universe is probably infinite in size.

I'm afraid the others are wrong. The observable universe is 90ish billion LY in *diameter*. Since it's us observing it we are at the center. Not at the center of the universe obviously since there is no such thing. Just at the center of what we can see. Which is 40+ billion LY in every direction. Again though, the light we're seeing is from objects that are NOW 40+ billion LY away. They were 13ish billion LY away when the light started this way.

"What is the size of the universe?"

It depends on your definition of size.

http://www.astro.ucla.edu/~wright/cosmo_02.htm#MD

Since we can never interact with anything outside our Rindler horizon, it does not really matter.

"How can the size be 93 billion light years in diameter if nothing can go faster than the speed of light?"

Place an ant on a balloon. Pick the fastest ant, and make that speed c. Now inflate the balloon, and the fastest ant separates from other ants faster still, but no ant energy was expended in getting faster (well, it is just an analogy).

"How can we know anything exists past 13.7 billion light years if we can't see the light?"

13.7 "left" and 13.7 "right", and no pattern on the "left" matches patterns on the "right" (we have looked), and you have "greater than 27.4", you agree?

"How can there be a diameter if there is no center of the universe and everything is moving away when viewed from any point in the universe, as I have read?"

If you are confined to the surface of a balloon (the instant *now* is that surface), and you know the radius of the balloon is 13.7 billion light years...

"It all seems counter-intuitive. I realize there's probably not a simple answer to this."

Intuition describes journeys already made, so you don't have to think about them again. You are entering a new place. Welcome. There are no masters here, or certainly not me.

Try this, in 4 parts. Also review the FAQ.

http://www.astro.ucla.edu/~wright/cosmo_01.htm

The 93 billion light-year figure refers to the universe's circumference, not its diameter. The diameter of the universe (if it has one) would exist in a hyperspatial region that may or may not actually exist physically.

"Surface Volume of the Universe:

The estimated circumference of the universe is about 90 billion light-years. This gives it a radius along a hyperspatial axis of about 14,323,944,878.271 light-years. The formula for the surface volume of a hypersphere is 2(π^2)(r^3), giving the universe a total volume of about 58,011,976,756,995, 849,887,758,131,749,274 (or 5.8 * 10^31) cubic light-years, or 11,785,418,756, 431,253,168,329,368,104,103,000,000,000, 000,000,000,000,000,000,000,000,000,000 (or 1.17855 * 10^70) cubic miles."

"How can the size be 93 billion light years in diameter if nothing can go faster than the speed of light?"

Nothing can travel faster than the speed of light, but "speed" isn't a concept that applies to the expansion of the universe. There's no reason the circumference of the universe cannot increase more than 186,282 miles per second, because there isn't any "travel" involved.

George Patton's answer is a very good one. However, many cosmologists would dispute the total size of the Universe. Most put it at several orders of magnitude larger than the Observable Universe.