A challenge for 21st-century physics is to answer two questions.
"Our" big bang could be just one island of space-time in an unbounded cosmic archipelago.
So the aftermath of "our" big bang could encompass a stupendous volume. And it may be some consolation that when we make a bad decision, there’s another one of us, far beyond our horizon, who has made a better one. Far beyond the horizon, we could all have avatars. If space stretched far enough, then all combinatorial possibilities would be repeated. But we expect far more galaxies lying beyond. There are billions of galaxies within our horizon. But this shell has no more physical significance than the circle that delineates your horizon if you're in the middle of the ocean. However powerful our telescopes are, our vision is bounded by a horizon: a shell around us, delineating the distance light can have travelled since the big bang.
Is space finite but unbounded Patch#
Physical reality could be hugely more extensive than the patch of space and time traditionally called "the universe." Our cosmic environment could be richly textured, but on scales so vast that our astronomical purview is restricted to a tiny fraction: we’re not aware of the "grand design," any more than a plancton whose "universe" was a spoonful of water would be aware of the world’s topography and biosphere. An astonishing concept has entered mainstream cosmological thought: it deserves to be more widely known.
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