If the Universe is only 10 billion years old, why isn the most distant object we can see 5 billion light years away?
This question makes some hidden assumptions about space and time which are not consistent with all definitions of distance and time. One assumes that all the galaxies left from a single point at the Big Bang, and the most distant one traveled away from us for half the age of the Universe at almost the speed of light, and then emitted light which came back to us at the speed of light. By assuming constant velocities, we must ignore gravity, so this would only happen in a nearly empty Universe. In the empty Universe, one of the many possible definitions of distance does agree with the assumptions in this question: the angular size distance, and it does reach a maximum value of the speed of light times one half the age of the Universe. See Part 2 of the cosmology tutorial for a discussion of the other kinds of distances which go to infinity in the empty Universe model since this gives an unbounded Universe. Back to top. If the Universe is only 10 billion years old, how can we see objects
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