added 12/18/2008, with comments in red and italics by Rydin

Mysterious `Dark Energy' Not as Ominous as Thought

By John Achenbach, Washington Post Staff Writer
And ASSOCIATED PRESS
December 17, 2008

 

New observations offer evidence that astronomers are not simply imagining that there is a mysterious essence they call "dark energy" that is causing the universe to expand at an ever accelerating pace. Dark energy is still a relatively new idea that came out a decade ago when measurements of star supernovae showed the universe was surprisingly expanding. One way to explain the expansion - building on idea Einstein first broached and called his biggest mistake - is that another force in the universe is essentially fighting gravity. That force is dark energy. As discussed in another section, the theoretical interpretation of the data supporting dark energy assumes that the general relativity model of the universe is correct, and thus compares measured redshift data against the Big Bang model to come to the conclusion that the data systematically lie above the expected Hubble curve. This was the sole basis for concluding there was an expanding universe! If the Big Bang model is wrong, so is this interpretation.

In justifying the idea, astronomers came up with more evidence that Albert Einstein's theory of gravity works even at the grandest, most cosmic scale. And in confirming, with a new technique, an earlier measurement of dark energy, they found that there is little reason to fear that dark energy will eventually cause a "big rip" that will tear apart everything we see and blow up the smithereens. Their research supports the hard-to-fathom concept of dark energy as a potent force that governs the growth of the universe. This is an attempt to provide a second experimental underpinning to the idea of dark energy.

In findings announced yesterday, astronomers at the Harvard-Smithsonian Center for Astrophysics said they measured the effects of dark energy using NASA's Chandra X-ray Observatory, and the results echo the earlier observations of supernovas made by the Hubble Space Telescope. Chandra observed dozens of galactic clusters - aggregations of galaxies that constitute the largest observed structures in the universe. Some of the clusters were about 5.5 billion light-years away, meaning their radiation (in the form of X-rays) was 5.5 billion years old by the time it reached Chandra. Other clusters were relatively nearby. This gave a past-and-present view of galactic clusters and showed that they are not forming as easily as they did 5.5 billion years ago. As Eric Lerner (1) has pointed out, 5 billion years is too little time to form galactic clusters. The age of the universe has to be much bigger, like 100 billion years to form such structures from an assumed uniform and isotropic universe.

Whatever dark energy is, it seems to be inhibiting the clusters' growth. "What we find is that the growth of structure has slowed down during the last 5.5 billion years, and this is unmistakably a signature of dark energy," said Alexey Vikhlinin, lead author of one of the new reports, to be published in the Astrophysical Journal. Without dark energy, these giant clusters would keep forming, getting denser and bigger because of gravity. But in the last few billion years that hasn't happened, said Vikhlinin, a scientist at the Harvard Smithsonian Astrophysical Observatory in Cambridge, Mass. He looked at when 86 such clusters formed and saw the slowdown in girth, starting about 5.5 billion years ago. The logical cause: dark energy. "They're put on a diet, a permanent diet," Vikhlinin said in a telephone interview. It is very difficult to measure the rate of change of structure growth, especially over such a small time interval relative to the time it might take to form such structures. Many assumptions about uniformity have to be made to make such a comparison, and the errors would be large when differences are taken to get derivatives, especially when you do not know exactly how old these structures really are.

In addition to offering a new line of sight on this mysterious phenomenon, the research supports the interpretation of dark energy as a "cosmological constant," a force that permeates empty space and, bizarrely, has precisely the opposite effect of gravity. At the human scale, dark energy is imperceptibly weak. But even the weakest of forces can add up to something powerful when the scale becomes cosmic, and all that vast, empty space between the galaxies is thrown into the mix. "Even nothing, even empty spare, 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 itself to accelerate," said David Spergel, an astrophysicist at Princeton University. It also means Albert Einstein's century-old theory of general relativity passes another crucial, but not conclusive, real-world test. Again, there is an assumption that General Relativity governs the motion of the universe, which is at odds with the spherically symmetric periodic data on galaxy distributions about an origin near Virgo.

What remains unclear is what dark energy is, exactly. "We've discovered this incredible dark energy; we don't understand what the hell it is," said Lawrence M. Krauss, a physicist at Arizona State University. The universe as we know it is believed to have sparked into existence about 13.7 billion years ago. From that initial big bang onward, it expanded, but until about 5 billion years ago gravity dominated the show, gradually slowing the expansion. Then dark energy became the more powerful actor, and the expansion began to accelerate as surely as if someone had put pedal to the metal. Lawrence Krauss also does not understand the Earth's motion with respect to the Cosmic Microwave Background frame, i.e., the Dipole Anomaly, and its Large Scale Drift. Krauss (2) says, “This situation has caused a great deal of confusion. Are we falling toward Virgo or are we not? Is our local motion due to the gravitational pull of nearby objects, or is it due to some primordial ‘kick’ ; which would be very difficult to explain at present ? " The universe is also surely much older than 13.7 billion years.

All manner of theories, some involving hidden dimensions and exotic particles, have been tossed around to account for dark energy. One possible solution would be to revise, or even toss out, Einstein's general theory of relativity. The theory holds that gravity is a function of the geometry of four dimensional "space-time." Matter, as physicists like to say, tells space-time how to curve, and space-time tells matter how to move. The theory is so well established that GPS navigation devices have to account for the curvature of space-time to remain accurate. First of all, neither Special Relativity nor General Relativity is used to correct GPS clocks, because they give different and incorrect answers. There are other arguments against space-time, including those of Peter Erickson (3) and Reginald Cahill (4).

But although general relativity is used all the time in modern cosmology, there have been suggestions that it breaks down at the cosmic scale. "It's never been proved right on the scale of the observable universe," Spergel said. The most famous confirmation of the theory came in 1919 when, during an eclipse, astronomers measured the way the sun bent the light from a star behind it. If the classical laws of physics developed by Sir Isaac Newton were correct, the sun 's gravity should have deflected the starlight to a small but predictable degree. Einstein, with his tale of curved space, predicted twice as much deflection. When astronomers showed that Einstein was right, he became an instant global icon. The new findings, by bolstering general relativity once again, suggest it will be a while before Einstein's universe is revised the way he revised the Newtonian universe. As discussed in another section, the minimal data taken in 1919 were inconclusive as to which theory was correct, but Eddington pronounced Einstein the winner. The perhelion of Mercury should be remeasured using modern techniques.

Hovering over the new research is the minor matter of the fate of the universe. If the universe continues to expand at an accelerating rate, Krauss has estimated, in about 100 billion to 1 trillion years, almost all the galaxies we see will be so far away they will vanish from sight. It will be a much darker universe. But what will not happen, apparently, is the cosmic apocalypse that scientists call the big rip. That would occur if dark energy was strong enough to rend asunder all the stars, planets, moons, rocks, dust and even atomic nuclei, as well as any and all innocent bystanders. The new measurement shows dark energy at a level that will permit our immediate surroundings and galactic environment to survive. "The accelerated expansion will proceed forever," Vikhlinin said, "but will probably not result in a big rip." Maybe none of this will happen at all.

Three outside experts praised the new study, which will be in February's Astrophysical Journal, as important to understanding a concept that is counterintuitive but crucial to figuring out the evolution of the universe. The history of the universe has been a battle between "the two dark titans, dark matter and dark energy", said University of Chicago Astrophysicist Michael Turner. "This is the first time you've seen the effect of dark energy taking over," he said. "It's much more important and abundant in the evolution of the universe than the atoms that make us up," said Princeton theoretical astrophysicist David Spergal. As discussed in another section, dark matter may not exist either if Cahill's (5) experimentally supported new theory of gravity, with an extra term proportional to the fine structure constant, holds up.

References

1) Eric Lerner, The Big Bang Never Happened: A Startling Refutation of the Dominate Theory of the Origin of the Universe, 1991.

2) Lawrence Krauss, Quintessence, the Mystery of Missing Mass in the Universe, Basic Books, Parts II-IV, pp. 82 - 85, New York, NY, 2000.

3) Peter F. Erickson, Absolute Space, Absolute Time, & Absolute Motion, Xlibris Corporation, 2006.

4) Reginald T. Cahill, "Unravelling Lorentz Covariance and the Spacetime Formalism", Progress in Physics , Vol. 4, pp. 19 - 24, October 2008.

5) Reginald T. Cahill, "Black Holes in Elliptical and Spiral Galaxies and in Globular Clusters", Progress in Physics, Vol. 3, pp. 51 - 56, October 2005.