Last week brought exciting news — of the successful parachute retrieval of material scooped off the surface of an asteroid. As usual, those in the P.R. department made the standard announcement that this “will teach us about the origin of the solar system.” In actuality, all but 44 meteorites in the hands of researchers and collectors (which came from the Moon or Mars) are asteroids and asteroid fragments. So we already have over 100,000 in hand (I own two myself) and thoroughly know their composition. It was nice to go out and grab a pristine sample, but still, realistically, meteorites are extraterrestrial materials obtained “without the commute.”
So if asteroid make-up is not really a mystery, what is? Of course, there are awfully big ones lurking out there. The very biggest? Well, the former publisher of Encyclopedia Britannica told me his number one was the origin of awareness, since consciousness lies at the heart of everything we can ever know, yet doesn’t arise by any known process. (No one has figured out how brain tissue might create the personal feeling of ‘experience.’) But since that puzzle always sounds mystical and woo-woo, let’s choose another – one that’s appropriate now in early fall, when the Milky Way hovers overhead.
A century ago, many believed that our galaxy, which is that Milky Way as we view it from our worm’s-eye perspective, constitutes the entire cosmos. Now we know that our galaxy is just one of hundreds of billions that make up the universe.
Okay, so what about “the universe?” Surely its nature constitutes the deepest of all mysteries. What is it? Is there one cosmos?
These days most people have heard of the multiverse idea, implying many universes, each presumably existing in a different dimension. But since there’s no evidence for other dimensions, some may be surprised to learn that instead of one universe or else multiverses, the accepted astrophysical reality is that there are precisely TWO universes.
Since galaxy clusters rush away from us with increasing speed (going 13 miles per second faster for each million light years farther away they happen to be) the situation produces a cut-off, a blackness that lies 13.8 billion light-years away, which is the distance at which galaxies race away at the speed of light. If we also include galaxies whose light will someday arrive here, then the observable universe extends all the way out to 46 billion light-years from where you now sit.
We cannot see anything beyond that because light from there will never arrive. There is thus a specific edge to the visible universe. The observable cosmos therefore comprises everything nearer than that. It contains a measurable mass whose total number of atomic particles is expressed by a one followed by 88 zeroes.
The universe beyond that must forever remain a complete mystery.
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