These galaxies are part of the aftermath of our own big bang. Not even the most conservative astronomer would deny that these never-observable galaxies (which, as I’ve already mentioned, could hugely outnumber those we can see) are part of physical reality. For instance, (unless we are in some special central position and our universe has an "edge" just beyond the present horizon) there will be some galaxies lying beyond our horizon-and if the cosmic acceleration continues they will remain beyond forever. But it’s hard to defend that hard-line view. Some claim that unobservable entities aren’t part of science. Its seemingly designed or fine-tuned features wouldn't be surprising. Ours would belong to the unusual subset where there was a "lucky draw" of cosmic numbers conducive to the emergence of complexity and consciousness. We therefore wouldn’t expect to find ourselves in a typical universe. Even though it makes some physicists foam at the mouth, we then can’t avoid the A-word-“anthropic." Many domains could be still-born or sterile: the laws prevailing in them might not allow any kind of complexity. But what we’ve traditionally called the laws of nature will be just local bylaws. If the answer to this latter question is "yes" there will still be overarching laws governing the multiverse-maybe a version of string theory. First, are there many "big bangs" rather than just one? Second-and this is even more interesting-if there are many, are they all governed by the same physics? Or is there a huge number of different vacuum states-each the arena for different microphysics, and therefore offering differing propensities for spawning life? 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.
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.