What is the size and age of the universe?
Though the exact figure remains open to debate, most astronomers agree that the observable universe is somewhere between 12 billion and 15 billion years old, based on tracing the universe's current rate of expansion back to its beginnings in the Big Bang. For any observer, then, the apparent size of the universe is dictated by the speed of light traveling for those 12 to 15 billion years, and thus the farthest point we could see (or gain any sort of information from) lies 12 billion to 15 billion light-years away.
Astronomers using Hubble Space Telescope to observe 18 nearby galaxies put the age of the universe at about 13.7 billion years. In particular, they looked at pulsating stars inside the galaxies. By measuring how fast the stars pulse, the astronomers determined their true brightness, which, in turn, revealed their distance. Observations by another spacecraft, which measured tiny "ripples" in the very early universe, agree with the Hubble estimates.
The true spatial dimensions of the universe are a somewhat different matter altogether and vary depending on the values of certain cosmological quantities, including the overall density of the universe and its expansion rate. If our universe is "open," meaning it will continue to expand throughout its lifetime, its current physical size is infinite; a "closed" universe -- destined to collapse in on itself -- could be as much as 100 billion light-years in circumference. Note that this latter scenario does not imply the universe has an "edge" -- in the bizarre world of multidimensional space-time geometries, the "edges" are all smoothly joined together.
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