Such as cosmic background radiation. The faint light we see in all directions, is the same light emitted when the universe is several hundred thousand years old.
Photons from cosmic background radiation may be about 13 billion years old, but they come from where we are now about 46 billion light years away.
“As soon as humans perceive the expansion of the universe, we also begin to think about the distance from where the signal was received based on how the universe expanded in the past,” said Fairbairn.
That distance is called the cosmic horizon and will get further away as the universe ages. If civilized life remains in the solar system after a billion years, it is very likely that future humans will discover new galaxies and stars when their last light reaches Earth.
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