Word: though
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Dates: during 2000-2000
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Some argue conservatively that time travelers don't change the past; they were always part of it. On the other hand, paradoxical though this sounds, a version of the many-worlds theory of quantum mechanics (see "Will We Discover Another Universe?" in this issue) devised by Oxford physicist David Deutsch might allow such history-changing visits. In this picture, there are many interlacing world histories, so that if you went back in time and killed your grandmother when she was a young girl, this would simply cause space-time to branch off into a new parallel universe that doesn...
...ultimate fate, though, remains in doubt, in part because the jury is still out on whether the expansion or gravity will triumph in the end. Most observations point toward the former, but many uncertainties persist. One is the galling "dark matter" issue. Studies of how galaxies are moving around indicate that there's lots of extra gravity out there, suggesting that the stars and nebulae we can see constitute only 1% to 10% of the matter in the universe. The rest is invisible; it emits no light. Nobody yet knows what this dark matter is. One possibility is that...
Instead, the perpetuals have become more sophisticated. Most (though not all) now admit their machines are using outside energy--usually via new theories of physics that physicists don't grasp yet. Joseph Newman, for example, a Mississippi inventor, promoted an "Energy Machine" in the 1980s that operated via "gyroscopic particles." More recently, New Jersey inventor Randell Mills has been pushing power from "hydrinos." Still others claim they're tapping the "zero-point energy" that fills all space. The first two are considered nonsensical, and while zero-point energy has a basis in science, using it to run a machine does...
Forget it, though. You'll never go that fast. Albert Einstein said so. His special theory of relativity had at its heart an astonishing claim: the speed of light in a vacuum is always the same, for all observers. Shine a flashlight out into space and the light goes at 186,000 m.p.s. Jump into a spaceship and chase the beam at 185,000 m.p.s. and it recedes from you not at 1,000 m.p.s. but at 186,000 m.p.s. If you head in the opposite direction at 185,000 m.p.s., the light beam still moves away at...you guessed...
...million apiece - some reports say $60 million - the planes were considered a risky investment by many. Some critics cited shaky safety records as reason enough to sideline the project: Before Saturday night, the craft's record included one fatal and one nonfatal crash during test flights. This record, though, was considered unremarkable; more often it was the program's cost that came under attack...