00:00If you traveled far enough, in a perfectly straight line through the universe,
00:04you might come back to exactly where you started,
00:07and never once feel the curve.
00:11The universe may be shaped like a torus, a cosmic donut,
00:15space that loops back on itself in every direction.
00:19The physics allows it.
00:21General relativity doesn't care what shape the universe is,
00:25only what it does locally.
00:27And here's the part that should unsettle you.
00:30The light we see from distant galaxies could be our own galaxy,
00:34ancient, unrecognizable, staring back at us across the loop.
00:40We can't see past our observable horizon,
00:43so the loop, if it exists, is invisible by definition.
00:48The universe could be finite, folded, endlessly repeating.
00:54The universe was over at the beginning.
00:54We'll see...
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