Alan M. MacRobert Sky and Telescope
 Maps
of sky fields observed by the Degree Angular Scale Interferometer
(DASI), one of the experiments imaging the cosmic microwave background
radiation. Each 3.4°-wide field shows temperature differences
of roughly 0.0001° Kelvin in the universal glow left over
from the Big Bang. The resolution is as sharp as 1/3°. Courtesy
DASI team.
Cosmology,
the study of the whole universe and its origin, is looking in
mighty good shape these days. Last weekend three research teams
announced new results that dramatically strengthen the new "concordance
model" of the universe — in which the cosmos contains
exactly enough matter and energy to render space flat. Only 4
or 5 percent of this stuff is ordinary matter, a larger amount
is some kind of exotic dark matter, and the rest is the newly
discovered, mysterious "dark energy" causing space to
expand at an accelerating rate. The new findings are also a powerful
vindication of the 21-year-old inflation theory of how the Big
Bang was powered into being during its first 10–32 second
of existence.
The new studies
measured tiny temperature fluctuations in the cosmic background
radiation. This weak radio glow, which covers the whole sky, dates
from 300,000 to 500,000 years after the Big Bang, when the hot
gas of the universe first became transparent to its own radiation.
The minute irregularities in its temperature (measured in parts
per million) reveal very slight density ripples in the otherwise
smooth substance of the universe that emerged from the inflationary
moment. According to the mind-boggling theory, these irregularities
began as microscopic, random quantum fluctuations on the scale
of elementary particles, then ballooned so vastly during inflation
that they became the clusters of galaxies populating the universe
on the largest scales today.
The exact
sizes and strengths of the irregularities should tell volumes.
Many astronomers are busily seeking to measure their intensities
at different angular sizes on the sky. The full inflationary-universe
theory predicts that the resulting graph of their strength should
be complex, showing several peaks at certain angular sizes —
"like overtones in a musical instrument," describes
cosmologist Wayne Hu (University of Chicago). From the exact sizes
and shapes of these overtones, cosmologists should be able to
read much about the origin of the universe, its shape, its history,
and its contents.
The first
peak was discovered last year. Its size and placement (at an angular
size of just under 1°) proved that space is flat — in
other words, that the early cosmos had exactly the right matter-and-energy
budget to balance perfectly between recollapsing and expanding.
Last weekend, researchers from three experiments in Antarctica
— the balloon-borne BOOMERANG and MAXIMA instruments and
the ground-based Degree Angular Scale Interferometer (DASI) —
jointly announced that they had found the much-anticipated second
peak as well as signs of a third. These and subsequent peaks were
predicted to arise from blobs of early material falling together
under the action of gravity, rebounding outward because of radiation
pressure, and falling together yet again.
Cosmologists
heaved a sigh of relief at the discovery of the second peak. Last
year, preliminary analysis of the BOOMERANG and MAXIMA data hinted
that the second peak was weak or missing. This would have implied
that as much as 7 percent of the stuff of the universe consists
of baryons — protons and neutrons, the main building blocks
of atoms and therefore all the ordinary matter we know. The nuclear
physics of the early Big Bang predicts that baryonic matter should
instead add up to only 4 or 5 percent of creation. The second
peak announced last weekend squarely matches that prediction.
It was a triumphant convergence of two totally different ways
of measuring the amount of ordinary matter that emerged from the
Big Bang.
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