The theory of general relativity: It works. OK, it's not exactly Earth-shattering news that Albert Einstein's century-old idea works in real life. That's been shown over and over. But what had been difficult for researchers to do until now was verify the theory on truly massive scales beyond the solar system, that of whole galaxies and clusters of galaxies. This week in Nature, Reinabelle Reyes and colleagues report that they did it, and that Einstein was proven correct once more.
While the find is a nice coup for Reyes' team, its importance goes beyond just reaffirming the great scientists of yesteryear with yet another "Einstein was right" story. The existence of dark matter and dark energy is based on the assumption that Einstein's gravity is affecting galaxies billions of light-years from Earth in the same way that it affects objects in our solar system.
However, if the study had shown that general relativity needed a slight adjustment at vast distances (like the nudge Einstein himself provided to Newton's physics), that could have altered prevailing ideas about dark matter and energy. This research indicates those pesky ideas may be here to stay.
Reyes' approach combined the study of galaxies' gravitational lensing (how much they bend the light from surrounding galaxies), their velocities, and how and where they formed clusters. All of these measurements combined created a system to test theories of gravity independent of particular parameters theories.. What they found closely matched what you'd predict under general relativity. They tested two alternative gravitational theories, too. One, called tensor-vector-scalar (TeVeS), gave results beyond the study's margin of error. Another, called f(R), didn't work as well as general relativity. But it fell within the margin of error, so the scientists say it will take more research to disprove it.
Meanwhile, as the spirit of general relativity is reaffirmed in the pages of Nature, the pages upon which Einstein formulated the theory are going on display in Jerusalem. Elsa, his wife, gave the pages to Hebrew University, and they are currently part of 50th anniversary festivities at the Israel Academy of Sciences and Humanities. Each of the 46 pages, labored over between November 1915 and their publication in May 1916, has its own case, each lighted dimly in a room that has been darkened to protect the paper. There on Page 1 is the now familiar title in German: "The Foundation of the General Theory of Relativity."
However, if you need more Einstein and can't make the trip to Israel, check out his mustachioed mug on the cover of the April DISCOVER issue, on newsstands this week.
By Andrew Moseman
Reprinted with permission from Discover