Major new cosmic background (CMB) measurements uphold the idea of
an early "inflationary" era during which the observable universe
expanded with superluminal speed and tiny quantum fluctuations in the
density of matter were amplified into much larger structures. These
structures are imprinted in the CMB as faint variations in the temperature
across the microwave sky. The CMB, the curtain of photons set free when
the expanding universe became cool enough to permit the existence of
neutral atoms, is the earliest, largest, and furthest observable thing
in all of science.
The best way to extract cosmological information from the CMB is to
plot the observed microwave power as a function of the angular size
of regions contributing to the CMB. The inflation model predicts that
this spectrum should feature a number of peaks. The first peak, at an
angular size of about 1 degree (about twice the angular size of the
Moon), corresponds to the largest blobs of matter in the primordial
plasma at the time of the CMB (about 400,000 years after the big bang).
Subsequent peaks should correspond to blobs that had come together under
the action of gravity but had then rebounded outward because of radiation
pressure, and later still had condensed for a second or third time,
A year ago the Boomerang collaboration, which used a balloon-based
detector floating over Antarctica, provided a detailed map (Update
481) of the first peak which, besides falling at the 1-degree size
predicted by inflation, also determined that the overall curvature of
the universe was zero. But Boomerang, and another detector group, Maxima,
saw scant evidence of any other peaks, and this puzzled astronomers.
All this changed earlier in the week at the American Physical Society
(APS) meeting in Washington, DC, where the Degree Angular Scale Interferometer
(DASI) collaboration, which parks its microwave detector on the roof
of NSF's South Pole station, presented solid evidence for a second and
third peak. The DASI results (John Carlstrom, University of Chicago,
773-834-0269) were largely in concert with Boomerang's presentation
at the meeting (Barth Netterfield, Univ Toronto, 416-946-5465); Boomerang
used a new type of analysis and reported 14 times more data than last
The microwave spectra for the two groups were similar (see figures
as were the values of various cosmological parameters. For example,
the position of the first peak yields the total energy of the universe
(a parameter, denoted by the letter omega, expressed as a fraction of
the critical density needed for halting the cosmological expansion).
Boomerang and DASI found values of 1.03 and 1.04, respectively, with
about a 6% uncertainty. Comparing the height of the first and second
peaks, one can calculate the expected percentage of all energy in the
universe that exists in the form of ordinary matter (baryons). This
turns out to be about 5% for both groups, a fact that agrees well with
predictions made by the independent "big bang nucleosynthesis"
It is harder to nail down other cosmological parameters, such as the
percentage of energy in the form of dark matter or dark energy (energy
lurking in the vacuum and responsible for the newly discovered net acceleration
in the cosmological expansion). The new CMB measurements suggest values
of about 30% and 65%, respectively, again in keeping with recent expectations.
New Maxima results (Shaul Hanany, Univ Minnesota, 612-626-8929) presented
at the meeting did not have nearly the statistical weight of the other
two groups, but were generally consistent; the three-way agreement brought
a great round of applause from the audience of astronomers eager to
unravel the mysteries of the early universe.
Noted cosmologist Michael Turner (Univ Chicago, 773-702-7974) observed
that last year's discovery of the first microwave peak constituted the
first great vindication for the Inflation model and that this new discovery
of secondary peaks was the second great vindication. The third type
of evidence, Turner said, would be the detection of gravity waves from
before the time of the CMB.
(Recently posted preprints on the Los
Alamos server include the following: Maxima astro-ph/014459; Boomerang
astro-ph/0104460; and DASI astro-ph/0104488, 89, and 90.)