The echo of the Big Bang bathes our universe in a steady afterglow
of microwaves that extends evenly in all directions. Various space
telescopes have measured the distribution of the so-called cosmic
microwave background with fantastic accuracy, the most recent being
the WMAP spacecraft.
We’ve long known that the temperature of these microwaves is 2.7 K but WMAP established that this varies by no more than about 10^-5 across
the entire sky. That fits exactly with our vision of the Big Bang as
an entirely homogeneous event–there ought to be no “preferred”
directions in spacetime
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But in 2004, astronomers found a region of the cosmic microwave
background in the southern hemisphere in the direction of the
constellation of Eridanus that is significantly colder than the rest
by about 70 microkelvin. Such a cold spot should not exist if the Big
Bang really were a well behaved, even event.
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Since then astronomers, have puzzled long and hard over the origin of this cold spot, suggesting
variously that it is caused by a supervoid, that it is a remnant of
an early phase transition in the universe and, most controversial of
all, that it is a window into a parallel universe.
Now Ray Zhang and Dragan Huterer at the University of Michigan in
Ann Arbor say that the cold spot is simply an artifact of the
statistical method–called Spherical Mexican Hat Wavelets–used to
analyse the WMAP data. Use a different method of analysis and the cold spot
disappears (or at least is no colder than expected). They say:
“We trace this apparent discrepancy to the fact that
WMAP cold spot’s temperature profile just happens to favor the
particular profile given by the wavelet.”
And they conclude:
“We find no compelling
evidence for the anomalously cold spot in WMAP at scales between 2
and 8 degrees.”
That may resolve the mystery but it makes a damp squib out of what
once seemed one of the most exciting discoveries in astrophysics.
Shame!
