case western reserve university

Page Expired


The page you are attempting to view may be out-of-date.

The page in question has not been verified by its author in quite some time.

If the information provided on the page is time sensitive, it is possible that it is no longer accurate. To ensure that you receive the most current information, we recommend you contact the page's author. He or she can verify whether the information is correct and/or direct you to a more up-to-date page.

Continue to the requested page.

hing is clear: It is pressuring space to expand. That makes dark energy stand apart from everything else in the universe because every other form of matter or energy gravitationally tugs on other matter.

Dark energy’s peculiar feature is that it seems to fill any void or vacuum, including those created by the universe’s expansion. Even a patch of empty space that had been eradicated of all known forms of matter and energy still contains dark energy, Starkman says.

“So if you have twice as much vacuum as you had before, then you have twice as much of that energy,” he says. “That’s really peculiar. If you take a box and stretch it, you get something for free. That’s the property that accounts for the ability of the vacuum to expand at an accelerating rate. The more you expand it, the more of the [dark energy] you have, and the more that it pushes.”

If dark energy seems confusing, that’s because it is, Starkman says. The greatest minds in physics are baffled. Dark energy is one of the most perplexing unsolved mysteries in science today, and scientists’ best guess for what lies at the heart of dark energy and the cosmological constant lies in quantum physics, Starkman says.

Quantum theory predicts that empty space will wiggle with low-level vibrations, even when all the energy in that space is depleted. It says that the simplest kind of motion conceivable, subatomic particles moving back and forth like miniature springs, will be present even when no other energy is present and they will never not move. Imagine a universe filled with simple quantum particles. Now rob the universe of every ounce of energy it contains. What quantum theory says is that, powered by nothing whatsoever, the universe will still vibrate with what is sometimes called “vacuum energy” or “zero-point energy.”

Quantum vacuum energy is “the simplest explanation for the origin of [dark] energy,” Starkman says. But the explanation remains murky. Starkman holds out hope that in Geneva, Switzerland, the CERN laboratory’s Large Hadron Collider, the world’s most powerful particle accelerator, may uncover precious clues about dark energy. The accelerator, which began operating in September, will allow scientists to analyze high-energy beam collisions and possibly reveal a new world of unknown particles.

The experiments could ultimately explain why those particles exist and behave as they do. They could reveal the origins of mass, shed light on dark matter, uncover hidden symmetries of the universe, and possibly find extra dimensions of space.

In the meantime, the observed existence of dark energy—whatever its origins—is producing real consequences for the universe’s future.

The Universe’s Beginning and End

In 1999, Starkman co-authored a paper with fellow Case Western Reserve physicist Tanmay Vachaspati, Ph.D., and Mark Trodden, Ph.D., of Syracuse University. The research, which appeared in Astrophysical Journal, linked cosmic acceleration to a decidedly bleak future. The universe had entered an extended period of rapid growth, they said, and, eventually, the objects in it would move away so rapidly from our world that they would fall away from view.

The evidence came from observations of supernovae, they said, which measurements showed were not only moving away, but moving away at ever faster speeds. Traditional Big Bang theory runs counter to this notion. It predicts that cosmic expansion will slow or even halt over time. Think of a fireworks explosion: an initial blast, streamers shooting out from the core at great speed, then a gradual slowing until the lights of the fireworks collapse and fade.

If the universe’s expansion continues to speed up, not slow down, then light from distant galaxies will fade for a different reason: It eventually will be unable to keep up. “We realized that things were going to start disappearing,” Starkman says. “The longer you wait, the less you’ll see.”

However, he adds, it will take scores of billions of years to lose sight of the universe’s landscape as we know it. Today, the universe is just a teenager, a spry 14 billion years young. The cosmic end-state comes when the universe nears 100 billion years old.

As that faraway birthday approaches, cosmic expansion will have created vast stretches of void between galaxies. Today’s visible universe, with its hundreds of billions of galaxies stretchingfar into the great beyond, will have sunk below the Earth’s horizon. Our sun and solar system will be long gone, having fizzled somewhere near the 19 billion-year mark.

If civilizations exist in other galaxies at such a late date, their conclusions about the universe will be incomplete. Light from neighboring galaxies will be unable to reach them because the expansion of space will have quickened beyond the lowly photon’s ability to keep up. Cosmology, particularly the study of the universe’s origins, will by then have reached an end. The science launched by Einstein’s notion of a cosmological constant will be destroyed by that very same constant.

But scientists are not only considering questions of the past; they are also considering future prospects for life in the universe.

In 1979, physicist Freeman Dyson, Ph.D., of the Institute for Advanced Study at Princeton University published a paper in the journal Reviews of Modern Physics that argued life could survive indefinitely in a universe that also expanded indefinitely. In Dyson’s view, biology could ultimately win the battle with a hostile universe.

Of course, appearing 19 years before the discovery of accelerating cosmic expansion, Dyson’s paper did not consider dark energy or a cosmological constant. In 2004, Starkman co-wrote another paper with Lawrence Krauss that delivered the bad news: Life is eventually doomed. Einstein’s greatest blunder ultimately, after hundreds of billions of years, wrenches the universe apart. And with it goes the prospect for biology.

“The universe is going to have a long, slow end,” Starkman says. “It will first begin with ignorance. And if we are right, it will end with death.”

Kinney, of the University at Buffalo, expands on that argument. In a paper written with physicist Katherine Freese, Ph.D., of the University of Michigan, Kinney points out that no one knows for certain whether the cosmological constant is, in fact, constant. It could be that the acceleration of the universe’s expansion will change over time. In some scenarios, in which the amount of dark energy exponentially diminishes over time, they find that doom and gloom may not prevail. Under such circumstances, the universe and biological processes in it could, theoretically at least, continue far into the future.

The question is, how far into the future?

“We all agree that life can last longer if the cosmological constant isn’t constant,” Starkman says. “What we’re arguing over here is how long. The evidence doesn’t seem to suggest that it will last forever. But maybe the certainty of our continued existence isn’t the most important thing—maybe it’s the understanding that we gain while we’re here.”

Share bookmark or share

[an error occurred while processing this directive]