Dark Energy Could Be Einstein’s Cosmological Constant

Dark energy, which forms almost three-quarters of the universe, is the most mysterious stuff known to man. A new set of Chandra X-Ray Observatory data, however, has given scientists good information on what dark energy might actually be.

Turns out, it looks suspiciously like Einstein’s cosmological constant, a factor he added to his theory of general relativity. He once considered it his greatest blunder.

“Putting all of this data together gives us the strongest evidence yet that dark energy is the cosmological constant, or in other words, that ‘nothing weighs something,'” said lead researcher, Alexey Vikhlinin of the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, in a press release. “A lot more testing is needed, but so far Einstein’s theory is looking as good as ever.”

Einstein’s general relativity equations famously described the curvature of space-time as the mechanism for gravity. In the original theory, Einstein added a “cosmological constant” that acted as an expulsive force to counteract gravity. That stabilized the universe so it didn’t collapse in on itself, but Einstein abandoned the idea when further astronomical observations showed the universe was accelerating and not static, as the great physicist had thought.

For years, the cosmological constant remained just a blunder, but mounting evidence for dark energy in recent years, a mysterious expulsive force, revived interest in the idea.

Previous work on the nature of dark energy had focused on the speed at which the universe was flying apart, which requires enormous amounts of energy counteracting the contractive force of gravity. The new data from the X-Ray Chandra Observatory provides astrophysicists with another data point: Dark energy is slowing down the formation of galaxy clusters by stretching space-time. Combining the two sets of observations allows scientists to make the mysterious dark energy a little bit smaller and more well-defined.

“What’s remarkable is that these two different methods — distance and structure — are giving the same answer,” said David Spergel, a theoretical astrophysicist at Princeton University who was not involved with the new research.

Now scientists know that dark energy has remained constant through time, an important factor in figuring out the ultimate fate of the universe. Vikhlinin said it appeared that the universe won’t stop expanding anytime soon, but won’t be torn apart in what some theoretical physicists had called “The Big Rip.”

“The acceleration of the universe will proceed forever, but it will probably not be torn apart,” Vikhlinin said.

The scientists also have a pretty good idea that dark energy — responsible for these large-scale structural changes of the universe — is generated at the smallest scales we know of.

“The quantum fluctuations in the vacuum have some tiny energy,” Spergel said. “Even nothing, empty space, weighs something. And because in our universe, we’ve got a lot of nothing, it has a major effect on our evolution and causes space to expand.”

Now, scientists will focus on pinning down these energies, which, as seen in the diagram at right, drive the expansion of the universe. Vikhlinin’s co-investigator, William Forman, compared dark energy to “springs” driving matter apart at high speeds.

“We’re now confident in the existence of the springs,” said Forman, an astrophysicist at the Smithsonian Astrophysical Observatory. “Now our goal is to understand the nature of the springs.”

Image: Two images, the left taken in the optical section of the spectrum, the other taken in the X-ray. In the X-ray part of the spectrum, galaxy clusters become far more obvious /NASA. Schematic: X-Ray Chandra Observatory.

Aby.T.Joseph

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