Stanford News


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Sun's motion may explain cosmic axis

Two Stanford scientists are proposing a less than controversial explanation for a recent study that suggests all directions in space are not created equal.

The new study, which was published in the April 21 issue of Physical Review Letters reported the discovery of a pattern of polarized radio waves from distant galaxies which suggests that the universe has an axis pointing in the direction of the constellation Sextans. The scientists ­ Borge Nodland of the University of Rochester and John P. Ralston of the University of Kansas ­ reported that the amount the radio waves were polarized varied depending on how far the source galaxy lies from this apparent axis. They had no explanation for these variations.

Now, two emeritus professors of electrical engineering at Stanford ­ Ronald N. Bracewell and Von R. Eshleman ­ think they know what could cause the effect: the sun's cosmological motion.

The fact that the sun appears to be traveling at an absolute velocity of about 300 kilometers per second relative to the universe as a whole was discovered by Bracewell and Edward K. Conklin of FORTH Inc. in 1969. Not only does the sun's motion create an axis that points in about the same direction as that found by the new study, but the manner in which polarization varies is consistent with a velocity-related origin, Bracewell and Eshleman point out

"The velocity effect is centered on nearly the same direction as the newly discovered radio polarization effect and it has the same pattern of dependence with direction. So, if the new effect is real, it is most likely a different manifestation of the same phenomenon," Bracewell says. He and Eshleman make this argument in an article that they have submitted to Physical Review Letters (available in full at

Bracewell and Conklin found evidence for the sun's cosmological motion in minute variations in the cosmic background radiation, an extremely weak but exceptionally uniform microwave signal that scientists think is a remnant left over from the Big Bang origin of the universe. This clearly contravened Einstein's postulate that the universe has no preferred frame or direction.

The variation in the brightness or temperature of the signal, which amounts to only three one-thousandths of a degree, has been explained satisfactorily by well-established causes, one of which is the Doppler effect. The same effect that causes a train whistle to sound higher in pitch when approaching an observer and when moving away also explains the fact that cosmic background radiation appears minutely hotter in the direction the sun is traveling and minutely cooler in the opposite portion of the sky. The effect is fully consistent with observed variations in the cosmic background when it is modified by two other more esoteric factors caused by the sun's motion: stellar aberration, a change in the apparent direction and size of stellar images, and a relativistic intensification of radio waves.

Bracewell and Eshleman point out that the authors of the new study did not take the sun's motion into account when they analyzed the polarized radio patterns from distant galaxies.

The similarity between the pattern reported by Nodland and Ralston and the solar velocity effect is too great to be coincidental, the Stanford scientists maintain. First, the axis of the velocity effect lies within 30 degrees of that calculated by Nodland and Ralston, an angle well within their margin of error. Second, the amount of polarization they found varies over the sky in the same way as does the temperature variation caused by the velocity effect. Both observations vary in proportion to the cosine of the angle from the axis.

"Nodland and Ralston don't have any reason why the polarization should vary as the cosine," says Eshleman, "but if it is due to velocity it just comes naturally, and sidesteps the requirement for a second axis."

Exactly how the sun's motion could produce the observed polarization shifts is not immediately evident, the Stanford scientists admit, but they are exploring several ways by which such coupling could arise. Taken individually, these effects appear to be too small to explain Nodland and Ralston's observations, Bracewell and Eshleman acknowledge. But they maintain that individual effects could interact in a way that produces such unexpected polarization shifts. At the least, that seems more likely than the two-axis alternative, the scientists maintain.

"What is the likelihood of two cosmologically significant axes lying in nearly the same direction? Pretty darned small," says Eshleman.


By David F. Salisbury