Word: 20th
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...reaching Mars is doing it smart and doing it cheap. In 1989, during the 20th anniversary of the Apollo 11 lunar landing, President Bush challenged NASA to figure out how to put human beings on Mars. The space agency came back with an elephantine 30-year plan that involved construction bays and fuel depots in low-Earth orbit and carried a jaw-dropping price tag of $450 billion...
...grander dream--of contacting extraintelligent E.T.s like those canal-building Martians imagined by the early 20th century astronomer Percival Lowell--lives on in the radio and optical searches underwritten by private outfits like Drake's SETI Institute and the Planetary Society. And even scientists dubious of success don't want to be spoilsports. They agree on the importance of continuing the quest, not just for microbes on Mars or Europa but also for those faint signals from some remote world--if only to underscore the preciousness of life and the importance of protecting perhaps its lone example. Admits Drake: "Even...
...20th century was quite a time for physicists. By the mid-1970s we had in hand the so-called standard model, a theory that accurately describes all the forces and particles we observe in our laboratories and provides a basis for understanding virtually everything else in physical science...
Things don't look much more certain in the second type of alternate universe, which comes not from quantum mechanics but from the other great physics revolution of the 20th century, Einstein's general theory of relativity. According to Einstein, objects with extremely large mass or high density stretch the fabric of space-time. Find something whose density approaches infinity--a black hole, for example--and that stretch can become a tear...
...that's just what makes me suspicious of it. The great lesson of scientific cosmology is that the universe does not usually conform to our time-honored ways of thinking--that to understand it, we need to think in new ways. Integral to modern cosmology are mind-bending 20th century concepts like Einstein's curved space, Heisenberg's uncertainty principle and the realization that exotic subatomic particles sail through our bodies by the trillions without laying a glove on us, and I see no reason to suppose that doors won't open onto even stranger notions in the century...