Does the Cosmos Have a Direction?
An alignment in the cosmos? The
red line running between the constellations Aquila
and Sextans, with Earth at its center, indicates a
special direction in space. The polarization of
radio waves emitted by galaxy A, which lies nearly
parallel to this axis, rotates more (green
corkscrew) on the journey toward Earth than does
the polarization of radio waves from galaxy B
(blue), which lies in a nearly perpendicular
East side, west side, all around the cosmos: No matter
which way an observer looks, the vast reaches of space
appear the same. Indeed, direction is meaningless in the
simplest version of the Big Bang model, which holds that
the primordial universe expanded uniformly, like a
perfectly spherical balloon.
A controversial report now challenges that long-held
tenet. An analysis of the polarization of radio waves
emitted by distant galaxies suggests that the universe may
have a preferred direction after all.
"This work defies the notion that there is no up
or down in space," says Borge Nodland of the
University of Rochester (N.Y.). He and John P. Ralston of
the University of Kansas in Lawrence describe their
analysis in the April 21 Physical
The results of the study, if verified, could have
startling consequences. One possibility is that the Big
Bang gave rise to a nonuniform distribution of matter and
a somewhat lopsided expansion. Alternatively, the
interaction of electromagnetic radiation with some kind of
exotic, unknown elementary particle might produce a
preferred direction in space.
Several cosmologists dismiss the study out of hand.
They argue that the report represents a premature effort
by two theorists searching for a subtle effect among a
disparate set of observations gathered in the 1970s and
1980s by radio astronomers using a variety of telescopes.
Many of the observations predate high-resolution,
multiple-array radio telescopes. However, Philipp P.
Kronberg of the University of Toronto, who studies
polarization and some years ago disproved a similar claim
about the universe (SN: 8/7/82, p. 84), says that the new
work appears to be on a sound footing.
In their study, theoretical physicists Nodland and
Ralston reviewed the measured polarization of radio waves
emitted by 160 distant galaxies. The original observations
were designed to measure Faraday rotation, a
well-documented effect in which intergalactic magnetic
fields rotate the angle of polarization of waves traveling
through them. But the physicists say they have found an
Galaxies that lie along a particular direction in space
show significantly greater polarization of their radio
waves than do galaxies in any other direction.
From Earth, this axis runs toward the constellation
Sextans in one direction and the constellation Aquila in
the other. The effect is more pronounced among the more
distant galaxies in the sample, the researchers note.
"I really think this is much ado about
nothing," says cosmologist Michael S. Turner of the
University of Chicago and the Fermi National Accelerator
Laboratory in Batavia, Ill. "The number one rule in
astronomy is that you can't reanalyze someone else's data
to look for an effect that [the observations] were not
designed to measure."
Kronberg disagrees. "They have seen a
statistically significant effect, and it raises a flag
that there is something of fundamental interest here, and
it ought to be rechecked, as they say in their
Turner emphasizes that the existence of a special
direction in space does not violate Einstein's theory of
general relativity, which allows for a multitude of
nonuniform universes. David N. Spergel of Princeton
University says the finding appears to be at odds with
measurements of the cosmic microwave background, the
whisper of radiation left over from the Big Bang. The tiny
fluctuations in that uniform background would seem to be
inconsistent with a lopsided cosmos, he says.