Physicists at the University of Rochester and the University of Kansas have found evidence that flies in the face of the long-held belief that space is the same in all directions (isotropic). In fact, measurements indicate something seldom considered by physicists: that the universe has an orientation. The unexpected finding, determined by measuring the polarization of light as it travels to Earth from the far reaches of the universe, is the subject of a paper in the April 21 issue of Physical Review Letters.
The work, which may be one of the most fundamental findings about the universe in recent years, could affect physicists' views about the birth of the universe and suggests that scientists will need to explore how Einstein's theory of relativity and the theory of electromagnetism might explain the finding. That's quite an impact from an effect so tiny that it's betrayed only by light traveling across most of the observable universe, from 15 billion years ago. Physicists have dubbed the effect the "corkscrew effect" for the way it twists light crossing the heavens.
"The big news is that perhaps not all space is equal, for as far back as we can peer in time," says Borge Nodland of the University of Rochester.
Adds co-investigator John Ralston of the University of Kansas: "The shocking thing about our result is that there seems to be an absolute axis, a kind of cosmological north star that orients the universe. We don't really know yet what this axis represents."
This axis of orientation is not a physical entity but rather defines a direction of space that somehow determines how light travels through the universe. In effect, Ralston and Nodland have discovered a direction in space that is out of the ordinary or different from all other directions. The idea that any direction of space is in any way "special" has long been taboo among astrophysicists.
"This work defies the notion that there is no 'up' or 'down' in space," says Nodland, research fellow at Rochester's Theory Center for Optical Science and Engineering.
From Earth, the axis of this orientation runs toward the constellation Sextans, roughly in the direction of Leo and Gemini and high in the southern evening sky this time of year. The other end of the axis points toward the constellations Aquila and Equuleus. (Stargazers, of course, will see nothing special when they look in that direction.) Nodland and Ralston, a professor of physics and astronomy at Kansas, say the axis might have several interpretations: It could be an intrinsic property of the universe, or it might indicate that an undiscovered particle, such as the long- theorized axion, is at work.
The team made the finding by studying the polarization (orientation of electric fields) of radio waves from 160 distant galaxies as measured in previous experiments by astronomers around the world. Nodland and Ralston found that the plane of polarization of the light rotates like a corkscrew as the light travels through space, and that the orientation of the universal axis that they've discovered is key to the amount of rotation. The rotation of polarization depends on the angle at which the light moves relative to the axis and on the distance the light travels before being measured. The effect is crudely analogous to that of a crystal that twists light depending on the direction light is traveling through the crystal.
Astronomers have long known about a somewhat similar effect called the Faraday effect, which is caused by magnetic fields between galaxies and causes the plane of polarization of light to rotate as the light travels through space. The newly discovered effect is in addition to the Faraday effect.
Though the cause of the corkscrew effect remains unknown, in their paper the team constructs a mathematical theory that explains the observations. The data indicate that light actually travels through space at two slightly different speeds. Such a mismatch in speeds would cause the polarization plane to rotate in a well known manner, in a way that physics students see when they pass light through corn syrup and look at the light with polarizing filters. This corkscrew effect is far more subtle, though: Light traveling across the heavens undergoes one full rotation of its plane of polarization about once in a billion years.
Whatever the cause, the work could have widespread implications. Scientists have long theorized that the Big Bang was completely symmetric. Says Nodland: "Perhaps it was not a perfect Big Bang, but a Big Bang with a twist to space and time." Such a twist would be seen today as a ripple of non-uniformity, perhaps as the axis (an "axis of anisotropy") represents.
Much more speculatively, the work may provide some of the first experimental evidence for physicists who have theorized the existence of other universes. If our universe was asymmetric at creation, and symmetry in the cosmos is maintained as many physicists believe, it raises the possibility of the simultaneous creation of another universe with an opposite twist.
The work also seems to run counter to the notions that all space is uniform and that the speed of light in a vacuum is always precisely the same, key assumptions of the theory of special relativity.
Though the researchers say there's only a few chances in a thousand that the result comes from statistical fluctuations, they stress the need for other scientists to confirm their results.
Questions about the universe and our role in it have fascinated Nodland ever since he can remember, filling his mind as he took long hikes while growing up in his native Norway.
"I've always had a passionate interest in the universe and its origins," he says. "We're on a little planet going around some burning mass that we call a sun, in a certain region of space. What is this space, and why are we here? The universe is amazing, and I want to know the most I can about it."
The team's work is funded by the U.S. Department of Energy, the National Science Foundation, the New York State Energy Research and Development Authority, and the Kansas Science and Technology Advanced Research (KSTAR) program.