"When theorists see something like that, that indicates something suspicious. It looks like a coincidence," said Egan. Various efforts have been made to explain this coincidence problem over the years, but none of the ideas raised have gained widespread acceptance. Now Egan and Lineweaver have taken a pragmatic approach, reasoning that the only time in the history of the universe that it would be possible for us to exist is around now -- when stars have been formed, galaxies coalesced and planets have evolved for us to live on. "It struck us that it's kind of silly to think that observers could have occurred anywhere during the whole history of the universe," said Egan. "If we are tied to terrestrial planets then we could not possibly have observed the radiation era, and when the universe gets large and diffuse and so on then we could not possible observe that late future either." In an earlier paper, the researchers tested whether that principle was strong enough to make the coincidence problem go away under the very simplest model of dark energy. "It was," said Egan. Now they have shown that the effect is so strong that the coincidence problem vanishes for any of the various explanations scientists have proposed for dark energy. "The results are important for the direction of dark energy research," Egan said. "It means we can focus on other problematic aspects of dark energy with some confidence that there is a reasonable explanation for the coincidence problem, regardless of what dark energy turns out to be." Related Links: |
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