For the second time in three months, scientists confirm that the universe is expanding at an ever faster rate thanks to a mysterious repulsive force called "dark energy" that counters gravity. The findings this time come from observations of the orbiting U.S. Chandra x-ray telescope.
The latest batch of findings would probably have made renowned German physicist Albert Einstein exuberant were he still alive. He died in 1955 believing he had made a serious error in devising a concept he called the cosmological constant. He had created the notion in 1917 to explain why the universe did not collapse from the gravity exerted by all celestial bodies, including galaxies.
At the time, the universe was thought to be static. When astronomers realized the universe was actually expanding, Einstein discarded the concept, calling it his greatest blunder. However, astronomers resurrected it six years ago when they first discovered that the expansion of the universe was speeding up. Like Einstein, they needed a concept to explain what was defying gravity. This time, they called it dark energy.
Steve Allen works at the Institute of Astronomy in Cambridge, England. ?Einstein's cosmological constant is a good working model for dark energy,? he said.
He and an institute colleague are the latest to confirm the accelerating expansion of the universe, a discovery they say sheds light on dark energy. Another team did it in February by using the Hubble Space Telescope to measure distances to star explosions called supernovae. The British pair made the verification by using the U.S. Chandra x-ray telescope to observe the distances of 26 clusters of galaxies between one billion and eight billion light years away.
?What we find are that the distances to the clusters are all significantly larger than they would be if there were no dark energy,? he added. ?Moreover, we find that the distances are growing ever more rapidly as we move toward the present day. Dark energy is pushing the universe apart and accelerating the expansion.?
Yet so far, dark energy is just a concept, but no one knows what it is.
University of Chicago theorist Michael Turner is also looking into the theory.
?What is fair to say is that although we can give it a name, we are very, very much confused,? he said.
He added that dark energy is so elusive that it might not even exist.
?Maybe this is a really big clue, that there really is no dark energy out there and it's some new aspect of gravity,? he explained. ?That's why it's so exciting. The solution to this problem could come tomorrow, it could come in 10 years, it could come in 100 years. It's a big mystery.?
Mr. Turner said that the fate of the universe depends on how dense dark energy is. If it remains constant, then the universe will continue to expand at an accelerating rate. However, he believes that it is possible it is decreasing, losing its ability to counter gravity.
?If it decreases sufficiently, then the universe will slow down and can actually recollapse to a very spectacular Big Crunch,? he noted.
A third more radical outcome would occur if dark matter increases. The theorist says this would cause the universe to expand so rapidly as to fly apart.
Whatever the result, scientists say that each of these outcomes would take tens of billions of years to come about.
The good news is that the first option seems to be true. The results from Chandra seem to be consistent with a stable amount of dark energy and a smoothly accelerating universe. This is the same conclusion reached in February by the U.S. team using the Hubble Space Telescope, but even this outcome seems eerie, as Michael Turner explained.
?In a mere 100 billion years, the sky, instead of being filled with billions of galaxies we can study with our telescopes, will be down to a few hundred,? he said. ?It will be a very lonely place.?