Word: schmidts
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Dates: during 2000-2009
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...astrophysicists tried another approach: determine whether the expansion was slowing down, and by how much. That's what Brian Schmidt, a young astronomer at the Mount Stromlo Observatory in Australia, set out to do in 1995. Along with a team of colleagues, he wanted to measure the cosmic slowdown, known formally as the "deceleration parameter." The idea was straightforward: look at the nearby universe and measure how fast it is expanding. Then do the same for the distant universe, whose light is just now reaching us, having been emitted when the cosmos was young. Then compare...
...Schmidt's group and a rival team led by Saul Perlmutter, of Lawrence Berkeley Laboratory in California, used very similar techniques to make the measurements. They looked for a kind of explosion called a Type Ia supernova, occurring when an aging star destroys itself in a gigantic thermonuclear blast. Type Ia's are so bright that they can be seen all the way across the universe and are uniform enough to have their distance from Earth accurately calculated...
That's key: since the whole universe is expanding at a given rate at any one time, more distant galaxies are flying away from us faster than nearby ones. So Schmidt's and Perlmutter's teams simply measured the distance to these supernovas (deduced from their brightness) and their speed of recession (deduced by the reddening of their light, a phenomenon affecting all moving bodies, known to physicists as the Doppler shift). Combining these two pieces of information gave them the expansion rate, both now and in the past...
...shown up as distant supernovas, looking brighter than you would expect compared with closer ones. But, in fact, they were dimmer--as if the expansion was speeding up. "I kept running the numbers through the computer," recalls Adam Riess, a Space Telescope Science Institute astronomer analyzing the data from Schmidt's group, "and the answers made no sense. I was sure there was a bug in the program." Perlmutter's group, meanwhile, spent the better part of the year trying to figure out what could be producing its own crazy results...
Aside from that detail, the Einstein connection made the idea of dark energy, or antigravity, seem somewhat less nutty when Schmidt and Perlmutter weighed in. Of course, some astrophysicists had lingering doubts. Maybe the observers didn't really have the supernovas' brightness right; perhaps the light from faraway stellar explosions was dimmed by some sort of dust. The unique properties of a cosmological constant, moreover, would make the universe slow down early on, then accelerate. That's because dark energy grows as a function of space. There wasn't much space in the young, small universe, so back then...