Research News

Award-winning essay predicts dark energy will be the death of cosmology

Fast forward to a civilization about three trillion years in the future. Astronomers at that time equipped with instruments equal to those of today would likely come to a much different conclusion about the basic nature of the universe, one that harks back to static models that were popular at the turn of the century.

That is the conclusion advanced by theoretical physicists Robert J. Scherrer and Lawrence Krauss in an article, “The Return of the Static Universe and the End of Cosmology,” that has received one of the top awards in an annual essay competition by the Gravity Research Foundation. Previous winners include Stephen Hawking, Roger Penrose and George Smoot. Scherrer is a professor of physics at Vanderbilt and Krauss – the Ambrose Swasey Professor of Physics and Astronomy at Case Western Reserve University – is a visiting faculty member at Vanderbilt for the year.

The current view of the cosmos is a dynamic one. The universe appears to have begun 13.7 billion years ago in a fiery Big Bang explosion. A fraction of a second later, it went through a brief period of exponential growth, called cosmic inflation. Since then it has been expanding at a slower but ever-increasing rate, driven by a mysterious repulsive force called dark energy. However, all the evidence for its dynamic nature has come from observations that have been made in the last three-quarters of a century. Before that the existing astronomical observations allowed prominent figures like British astronomer Fred Hoyle and Dutch astronomer Willem de Sitter to argue convincingly for a steady-state universe with a basic structure that is eternal and unchanging.

Ironically, if the universe continues to expand at an ever-increasing rate, Krauss and Scherrer calculate that it will eventually erase not only all the evidence of the expansion itself, but also all the evidence of the universe’s explosive origin, leaving future astronomers with an observable universe that appears to be consistent with the now discredited static theories.

This process of cosmic erasure occurs as the universe expands because the most distant objects recede at the highest velocity. The faster an object recedes, the more that the light coming from it is “red-shifted” to longer wavelengths. When its recessional velocity reaches light speed, it simply disappears because it is moving away faster than the speed of the light that it emits or reflects. The net effect is to gradually shrink the size of the observable universe. After a few trillion years, only our local cluster of galaxies will be visible and this is too small a group to reveal the effects of dark energy, the physicists argue.

Similarly, the strongest evidence of the Big Bang – a phenomenon called the cosmic background radiation (CBR) – will disappear. The CBR is a microwave signal that comes from every direction in the universe. It is considered to be fossil radiation left over from the period when the universe was about 300,000 years old and much hotter and denser than it is today. Over the eons, the expansion of the universe has red-shifted the CBR from white-hot visible light to cold, invisible microwave radiation. As the expansion continues, the CBR will essentially be red-shifted to longer and longer wavelengths until it becomes undetectable.

“We live in a special time in the evolution of the universe: The only time at which we can observationally verify that we live in a very special time in the evolution of the universe,” the researchers quip.

The paper will be published in the October issue of the Journal of Relativity and Gravitation.

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