Wikipedia gives a pretty clear response to your question in its
article on the universe.
Wikipedia writes:
It may seem impossible that two galaxies on opposite sides can be separated by 93 billion light years after only 13 billion years, since special relativity states that matter cannot be accelerated to exceed the speed of light in a localized region of space-time. However, according to general relativity, space can expand with no intrinsic limit on its rate; thus, two galaxies can separate more quickly than the speed of light if the space between them grows. It is uncertain whether the size of the Universe is finite or infinite.
Keep in mind that 93 billion light years is the size of the
observable universe. We see the most distant galaxies, those that are maybe 12 or 13 billion light years distant, as they were 12 or 13 billion years ago, and in that time the expansion of space has carried them a much greater distance further away. When we look at these distant galaxies we're also looking far back in time, but cosmologists can calculate how far away they are today, and that turns out to be around 46 billion light years, which is the radius of the observable universe as opposed to its 93 billion light year diameter.
Wikipedia also has an
article on the observable universe that contains a section on
the size of the observable universe, so you might want to give that a look, too.
--Percy
Edited by Percy, : Grammar.
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