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<b>Astral Arcs</b><br>Star trails over the Canada-France-Hawaii Telescope, one of Mauna Kea's thirteen observatories. <br><i>Photo by Richard J. Wainscoat / Photo Resource Hawaii</i>
Vol. 13, no. 3
June/July 2010


View from the Top (Page 8)



The Great Force: Dark Energy


Photo: Canada-France-Hawaii Telescope
Dark matter is not the only vast mystery. Perhaps it should come as no surprise that the universe is full of “dark energy,” too. We can’t see it, we can’t feel it, but it’s “the biggest constituent of the universe,” says Armandroff. “And we didn’t know about it twelve years ago.”


The detection of dark energy traces to Edwin Hubble’s groundbreaking work in the 1920s that helped to prove the universe was expanding and galaxies were moving away from each other. The next questions were inevitable. If the energy from the Big Bang were still pushing the universe outward, astronomers wondered, how would that expansion proceed in the future as the energy waned? Would it slow down? Stop? Would the universe eventually begin to contract?


To answer those questions, astronomers sought to determine the rate at which the universe was expanding. They discovered they could measure the rate of expansion by finding “fixed points”: a class of supernovae that had an intrinsic, unchanging brightness. They dubbed these supernovae “standard candles” and at the end of 1990s initiated a systematic search for them using, on Mauna Kea, the low-resolution spectrograph at Keck and the wide-field telescopes of Subaru and CFHT, as well as the Hubble Space Telescope and other telescopes around the world.


What they found astonished everyone. The expansion of the universe was not slowing down but rather accelerating. “It’s completely counterintuitive and one of the most exciting detections in modern astronomy,” says Kudritzki. “There must be a source of energy in the universe that’s driving this. We call it ‘dark’ because we can’t see it and we don’t know what’s behind it. The basic idea is that there must be elementary particles of energy in the universe that form the basis of it, but we don’t know what they are.”


“It’s incredibly exciting,” says Armandroff, “and really mind-boggling. Something has to drive this. You can’t get an acceleration from nothing. The biggest skeptics say it’s an artifice. No one can put their hands on it or measure it in any other way except for these astronomy experiments that show these accelerations. But it has since been confirmed with objects other than supernovae. This is a force that’s all around us. One of Einstein’s pioneering concepts is that mass and energy are equivalent. And astronomers have a pretty good idea of how much mass there is in the universe: stars, planets, gases. And all mass pales in comparison to the amount of dark energy. That’s amazing!”