30 December 2022

Age of Wonder

Every now and then, I like to renew my sense of wonder by contemplating the extent of all that exists (at least in this universe). 

Although there are some anomalies, it seems fairly certain that the region of the Big-Bang universe (excluding any consideration of a "Multiverse") within the so-called "cosmic light horizon," in other words, the "observable universe," is only a small fraction of the entire universe. Indeed, the majority view among cosmologists is that the universe beyond the cosmic light horizon is at least many hundreds of times larger than the region inside it, and it cannot even be ruled out that the entire universe is actually infinite. It does, however, seem more likely that it is a curved multi-dimensional torus, unbounded (like the surface of a sphere is unbounded), but finite. But really, really big. The observable universe is approximately 92 billion light years across, and expanding at faster than the speed of light, frontier vs. frontier. (This is possible, and, in fact, well, fact, even though the Big-Bang universe is 13.7 billion years old, because space is expanding, so regions that were once closer are now exponentially further away, a process that with the unchanging limit of the speed of light will eventually actually shrink the cosmic light horizon in terms of what is visible, so that observers at any given location will see less and less of the universe as a whole). 

The observable portion of the universe contains approximately the same number of large galaxies (as large as or larger than the Milky Way's companion galaxies visible in the southern skies, the Large and Small Clouds of Magellan) as there are stars in the Milky Way Galaxy... about 200 billion. That's about 17 galaxies for every man, woman and child on Earth. And that's just the part of the universe we could, in principle, see. Beyond that, far more, maybe an incredibly large factor more. The large scale structure is inhomogeneous on a pretty large scale: there are large voids, up to a billion light years in diameter, where there are few galaxies, and there are tendrils and filaments where they are more concentrated, somewhat like suds or froth, but on the very largest scales, including the vast extent beyond the cosmic light horizon, it is believed to be essentially homogeneous, approximately the same in every direction. I wanted to say "as far as the eye can see," but, actually, it's much, much farther than the eye can see. To quote a line from my favorite speculative fiction author, Jack Vance, "and to think some believe the Age of Wonder to be past and gone!" 

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