Another Saturday night and you ain't got nobody. It could be your aftershave, but more likely it's the cold fact that atoms and molecules make up a truly negligible, mind-bogglingly miniscule amount of the universe. According to cosmologists, the scientists who study the history of the universe, you and everyone else--- everything you have seen, are seeing, or will see here on Spaceship Earth--- is completely insignificant. This includes supermodels, Windows 95, and the new fall television lineup. This may be difficult to get used to, but then again, it puts high school in perspective.
Cosmology should not be confused with cosmetology, a science dedicated to hiding the truth rather than revealing it. Prominent cosmologists: P.J.E. Peebles of Princeton; Alan Guth of MIT; Steven Hawking of Cambridge. Prominent cosmetologists: Mary Kay, Merle Norman, Sy "Hair Club for Men" Sperling. Big difference.
Even so, cosmologists have feelings like the rest of us: anxieties, ambitions, bad hair days, and secret love affairs. It is a testament to their devotion to logic that they doggedly pursue the secrets of the universe, no matter how meaningless and wretchedly lonely it might make them feel. In fact, the only people I can think of who are more loyal to the precepts of logical deduction are Mr. Spock and Sherlock Holmes, and despite the advantages of being fictional they still had rotten love lives. Neither of them are accredited cosmologists, though Spock could probably get a master's degree in it through life experience credits.
Holmes, who between rampant misogyny and an equally rampant cocaine habit, didn't care much about getting a date, observed that when you have eliminated the impossible then whatever remains, however implausible, must be true. Of course Holmes also had suspects with wooden legs pegging through muddy gardens. Convenient. Cosmologists, luckily enough, also have suspects with wooden legs, and have searched the garden of the universe for their tracks.
The first prints are found in the signals of the Big Bang, the explosive birth of the universe some 15 billion years ago. The echo of that explosion is a faint background of microwave radiation so uniformly distributed that one theory, known as "inflation", predicts that Omega, a parameter describing the total density of matter in the universe, is equal to one.
In the Big Bang certain key elements---hydrogen, deuterium, helium, and that lithium you're reaching for to counteract your depression---were forged. But the measured proportions of those elements suggests that the contribution of ordinary matter---what scientists call "baryonic matter" and what you would call "the stuff around me"---to the density parameter Omega is only a few percent. At this point in the script Captain Kirk sings out, "Opinion, Spock?" and Spock opines, "Logic dictates that either (A) more than 90 percent of the universe is something unseen, exotic, and nonbaryonic; call it `dark matter;' or (B) something is wrong with the science.
Door "B" is a tempting option, but when the host swings it wide we are confronted by contrary facts. Unlike people, the attraction between the stars and galaxies is precisely calculable, thanks to Sir Isaac Newton---who died a virgin---and measurement of the motions of said stars and galaxies suggests gravitational pulls in the universe from much more than meets the eye.
In fact, by counting up the stars and galaxies we find that their contribution to the density parameter Omega is much less than even one percent. Therefore, logically, says Spock (who only got horny once every seven years, unless you count the underground sci-fi zines wherein he and Kirk are lovers), not only does the universe mostly consist of unseen "dark matter," there are at least two kinds of dark matter. The baryonic kind, like you and me, and the exotic, dominant, non-baryonic kind.
Any theoretical physicist worth her salt could before breakfast postulate at least six possibilities for dark matter. But two candidates are favored, named with acronyms that would've pricked Freud's ears: baryonic MACHOs (MAssive Compact Halo Objects) and nonbaryonic WIMPs (Weakly Interacting Massive Particles).
MACHOs, like their human counterparts, are fairly mundane: large planetoids, bigger than Jupiter but smaller than a star, that drift untethered through space. Astronomers have recently detected them as their gravity momentarily bends the light of distant stars.
WIMPs are the exotic manifestation of an abstruse and difficult mathematical theory (as opposed to those concrete and easy theories that led you to drop calculus) with the tongue-twisting name of "supersymmetry." Some physicists would normally consider supersymmetry little better than theology. But the conclusions of cosmology force physics agnostics to acknowledge the possibility that WIMPs may be the Silent Majority in the universe. So the search for WIMPs goes on in huge accelerators and cold, quiet detectors.
The story isn't finished. Detailed calculations of the structure of the universe suggest that WIMPs are only half of the nonbaryonic dark matter. The other half may be "massive neutrinos" or "axions" or.... You get the idea. Scientists like simplicity and begin to squirm at these particles-on-particles. They are reminiscent of Ptolemy and his awkward epicycles. But Ptolemy, champion of geo/ego-centrism, fell squarely into the cosmetology camp: making the universe look good so we don't feel so lonely.
I'd like to go on, but I have to run. I have a date.
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