What we can see of a space is only a tiny fraction of what is there. With powerful telescope, intensely bright clusters of stars or galaxies called quasars can be seen 13 billion light-years across.
So if there are quasars equally far away in all directions, the universe must be at least 26 billion light-years across. The light of some stars, when see through a telescope, may be thousands or even millions of light-years away.
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