AFTER carefully studying the faint microwave echo of the big bang, three
teams of astrophysicists say that our Universe really did start out much smaller
than an atom and then expanded faster than light, exploding in size during its
first fraction of a second in existence. It鈥檚 the best evidence yet for what鈥檚
called 鈥渋nflation鈥� theory.
Last year experimenters working with Boomerang and Maxima, microwave
telescopes attached to high-altitude balloons, reported the most detailed images
yet of the cosmic microwave background. This is radiation from the big bang that
pervades all of space. The researchers found faint hot spots in the radiation
that were roughly an angular degree in size. These hot spots showed up as a
distinct peak in the 鈥減ower spectrum鈥� of ripple amplitude versus ripple
size.
The position of the peak showed that the total mass and energy of the
Universe exactly balances gravity, making the Universe 鈥渇lat鈥�. But inflation
also requires smaller ripples, one-half and one-third of a degree in size, and
they were not obvious in the data. 鈥淚f those peaks aren鈥檛 there, a lot of people
are going back to the drawing board,鈥� says John Carlstrom of the University of
Chicago.
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Now theorists can rest easy. Carlstrom and colleagues working with an
instrument at the South Pole called DASI announced at the American Physical
Society meeting in Washington DC this week that they have spotted the peaks in
data collected last year. The Boomerang and Maxima teams also said that they鈥檇
found the peaks after another look at their final data. 鈥淚t鈥檚 a huge result that
three independent and very difficult experiments produce what appear to be
statistically consistent results,鈥� says Paul Richards of the University of
California, Berkeley, a member of the Maxima team.
The ripples they spotted, varying by less than 0.0001 kelvin from the average
temperature of the radiation, are evidence of sound waves in the soup of
photons, atomic nuclei and dark matter that made up the early Universe. The
ripples in the microwave background are a snapshot of the waves roughly 400,000
years after the big bang, when hydrogen atoms formed and photons began to fly
through space unimpeded.
Researchers can use the relative sizes of the peaks in the power spectrum to
estimate how much ordinary and dark matter there is in the Universe. All three
groups found that ordinary matter accounts for only 5 per cent of the mass and
energy in the Universe, and dark matter only 30 per cent more. The rest must
come from some sort of 鈥渄ark energy鈥�.
The new results come as a relief to advocates of inflation, says Wayne Hu, a
cosmologist at the University of Chicago. 鈥淲e were a little concerned last year
when the peaks weren鈥檛 clearly seen,鈥� he says. 鈥淣ow, alternative explanations of
structure in the Universe are dead.鈥�