00:00Imagine being born into a civilization that can never know where it came from.
00:05Right now, we can prove the universe is expanding.
00:09We see other galaxies flying away from us.
00:11We can detect the faint afterglow of the Big Bang, the cosmic microwave background.
00:17But that won't last.
00:19In about 100 billion years, the expansion of space will be so extreme
00:25that every other galaxy will have been pushed beyond the cosmic horizon.
00:30Their light will never reach us again.
00:33At the same time, the afterglow of the Big Bang will be stretched so thin, so red,
00:39it will become completely undetectable.
00:42So picture an astronomer born in that distant future.
00:46They will look up at the night sky and see nothing,
00:50just empty blackness with their own galaxy floating alone.
00:55They will have no evidence that other galaxies exist,
00:58no evidence that the universe is expanding,
01:01no evidence that the Big Bang ever happened.
01:04They will conclude their galaxy is the entire universe.
01:09And they will be wrong.
01:11We are living in the only window in cosmic history where the truth is still visible.
