In an earlier thread--What is space?--a few people indicated that only a part of our universe is observable: Because space is expanding, photons from distant parts of the of the universe haven't had time to get here yet. So that's my next question. Is our entire universe observable? My thinking--based on what I've read, of course--is that we can observe all of our universe. When we look out into space, we're also looking back in time, so when we see the very earliest galaxies--which we do--we're looking back about 10 or 12 billion years, and (I think) when we observe the cosmic microwave background radiation, we're looking back even further in time; in fact, we're listening to the "noise" from the Big Bang. Put another way, our universe began with the Big Bang about 13.7 billion years ago. Since then, it has expanded--and the expansion is getting even more rapid--but it can't have expanded to infinite size because that would require that the rate of expansion also be infinite. We've measured the rate of expansion, and it is increasing, but it's not infinite. At some time in the distant future, our universe will have expanded enough so that we won't be able to observe distant galaxies; in fact, we'll be able to see only our local galactic cluster. But we're not there yet. Since we can look back almost as far as the Big Bang, we can observe everything in our universe. Am I even close on this one?