Sci Tues29"I awoke on Friday and because the universe is expanding it took me longer than usual to find my robe."
-- Woody Allen, in "Strung Out," the New Yorker, July 28, 2003
In a recent satiric article in the New Yorker magazine, Woody Allen makes a passing reference (a sexual one, of course) to dark energy. I suspect he knows -- though he does not say so -- that the universe is actually expanding at an accelerating pace, driven by this mysterious force.
So I figure Allen would be interested to know about a new study that provides important confirmation for the existence of dark energy, even if scientists remain baffled over what it is and how it works.
Whereas gravity attracts, dark energy repels (or sucks, depending on whether its viewed as an internal or external force relative to the universe). Theorists have no clue what's behind this antigravity, but they say it fuels an increased pace by which all galaxies in the universe recede from one another. The
end result, as best as they can figure, is a lonely universe in which folks in one galaxy can no longer see or hear from the folks in other galaxies because they're moving away at the speed of light. able -->  |
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 | History of expansion: A rough picture of how the universe's expansion decelerated, then began to accelerate. Fate is not known.
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Or perhaps, one fantastic theory posits, the acceleration will ultimately shred all matter in a
Big Rip.Observations of dark energy have so far been very indirect, limited to examining the light from distant supernovae to determine the state of the expansion at the time the light left the exploded stars.
The new study employed an entirely different method. Researchers compared millions of galaxies imaged by the Sloan Digital Sky Survey with a temperature map of the early universe
recently developed with data collected by NASA's Wilkinson Microwave Anisotropy Probe (WMAP).Dark energy's shadow
The researchers say they found dark energy's shadow on the cosmic microwave background radiation, a relic of the earliest epoch of the universe after the Big Bang that supposedly started it all.
Let's back up: The theorists theorized about what would happen to the microwave radiation over time, if there was dark energy and if there was not.
They determined that dark energy should leave a certain imprint, and it did.
Photons streaming from the cosmic microwave background, across time, pass through many concentrations of galaxies and dark matter, explained study team member Andrew Connolly of the University of Pittsburgh. As the photons fall into a gravitational well created by a large cluster of galaxies, they gain energy -- just like a ball rolling down a hill. As they come out they lose energy.
Photographic images of the microwaves become more blue (i.e. more energetic) as they fall in toward a well and become more red, or less energetic, as they climb away.
"In a universe consisting mostly of normal matter one would expect that the net effect of the red and blue shifts would cancel," said Albert Stebbins of the Fermi National Accelerator Laboratory. "However in recent years we are finding that most of the stuff in our universe is abnormal in that it is gravitationally repulsive rather than gravitationally attractive."
Welcome new data
The research, announced last month, shows that "dark energy, whatever it is, is something that is not attracted by gravity even on the large scales probed by the Sloan Digital Sky Survey," said David Spergel, a Princeton University cosmologist and a member of the WMAP science team. "This is an important hint for physicists trying to understand the mysterious dark energy."
John Blakeslee of Johns Hopkins University recently led a
separate study of two very distant supernovae that helped pin down the timing of a switch from deceleration to acceleration in the universe, which occurred about 6.3 billion years ago. (Yes, the universe has always been expanding, but not always at an accelerating rate.)Blakeslee told SPACE.com the Sloan result "provides an important consistency check" for assumptions about dark energy.
But are we sure now that dark energy exists as it has been described? "There still is some room for doubt," Blakeslee said.
If dark energy baffles the smartest scientists -- and it does -- then the rest of us can be excused for wondering what all this means to the evolution and fate of the universe. We can even be excused for not comprehending any of this. Woody Allen claims his grasp of general relativity and quantum mechanics "now equals Einstein's -- Einstein Moomjy, that is, the rug seller."
And Moomjy knows the source of dark energy just about as well as anyone.
All About Dark Energy
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