In a tour de force of ultra-sensitive technology, astronomers have obtained the first detailed images of the universe as it was nearly 15 billion years ago, long before stars or galaxies had begun to form.
An international team of scientists used balloon-borne detectors 40 times more sensitive than anything ever employed before and trained them on primordial background radiation that has pervaded space since shortly after the Big Bang. In that way, the researchers were able to see previously invisible, super-faint ripples that were the first seeds of the structure of the cosmos.
These are the first clear images of the embryonic universe,
said Andrew Lange of the California Institute of Technology, co-leader
of the international project with Paolo de Bernardis of the University
The images provide some of the best evidence yet for why the
universe—which began as a uniform fireball—has such an
uneven distribution of matter today. In addition, the specific pattern
of the ripples indicates that the cosmos contains precisely the right
amount of matter and energy so that the fundamental geometry of space
is not curved, but
That is, two light rays that leave Earth traveling parallel will
remain parallel forever. They will neither converge nor diverge, as
they would if space were bent by greater or lesser contents. A flat
universe has exactly the
critical density so that it will
neither curve back upon itself in a cataclysmic
big crunch or
expand so drastically that it thins out to nothingness.
The finding also supports the so-called inflation theory about the universe, a once-outlandish hypothesis that when the universe was only a billionth of a trillionth of a trillionth of a second old, it underwent an explosive accelerating expansion.
Our boldest and most promising theory of the earliest moments
of the cosmos
has passed its first important test, said
University of Chicago theorist Michael Turner.
This new result is an unprecedented picture of the afterglow from
the Big Bang that created the cosmos, said astrophysicist Charles
L. Bennett of NASA's Goddard Space Flight Center.
The stage is
now set for experiments that have the ultimate goal of a precision map
of the entire sky to reveal the shape, content, past and future of the
The new data, announced yesterday at NASA headquarters and reported in today's issue of the journal Nature, were produced by measuring tiny variations in a faint remnant glimmer in the sky called the Cosmic Microwave Background (CMB).
The CMB formed about 300,000 years after the Big Bang that created everything, when the fiery young universe—then about 1/1,000th its present size—suddenly became transparent. Before then, the cosmos consisted of a sizzling incandescent fog of disconnected particles and radiation. As it expanded, it cooled. When it finally reached a temperature about half that of the surface of the sun, particles combined into atoms, leaving open space for bits of light, called photons, to travel unimpeded.
Some 15 billion years later, those same photons (now terribly enfeebled and stretched by the expanding cosmos to wavelengths in the range known as microwaves) are still detectable from every direction in the sky. Slight discrepancies in their temperature from place to place reveal the earliest detectable ripples in the density of the universe.
Those deviations, astronomers believe, provided the seeds of agglomerations of matter that would eventually grow to become stars, galaxies and clusters of galaxies.
The CMB was discovered in 1965, and for a quarter of a century appeared to be exactly identical in intensity in every part of the sky. But the present-day universe is lumpy in some places and empty in others, a condition that must have been caused by very small fluctuations when the universe was very young. Those differences, astronomers believe, should be reflected in a slight variation in the temperature in the CMB photons.
But throughout the 1970s and '80s, every measurement of the CBM showed it to be perfectly even. Finally, in 1992, the Cosmic Background Explorer (COBE) satellite produced data that showed temperature differences from one place to another.
The COBE data, however, were taken from a very wide swath of the sky. And theory predicted that the telltale early ripples should appear at scales not much wider than 1 degree. That is the range at which the new data show the biggest difference in photon energy—which in turn indicates the biggest difference in primordial density.
There are plenty of the CMB photons around; in fact, they make up about 1 percent of the static noise picked up by a home TV antenna. But they are extremely faint, equivalent to the radiation that would be emitted by an object less than 3 degrees above absolute zero.
A few years ago, a U.S.-Italian-Canadian-British consortium called
balloon observations of millimetric extragalactic
radiation and geomagnetics) set out to see if it could detect
energy differences between adjacent parts of a 3 percent slice of the
sky. Those variations amount to about 1/10,000th of a degree Celsius
and would not have been detectable without the exquisitely sensitive
detectors developed at Caltech and the University of Rome, which can
measure temperature differences 40 times smaller than the COBE
Millimeter CMB waves are readily absorbed by water vapor in the air. So in late 1998, the 36-member Boomerang team launched its two-ton detector beneath a helium-filled balloon into the extremely dry, thin air of Antarctica. Over 10* days, it traveled 5,000 miles at an altitude of 23 miles.
The Boomerang findings appear to confirm research by Saul Perlmutter
of the Lawrence Berkeley National Laboratory and colleagues, who
recently astonished scientists with evidence that the universal
expansion is accelerating, thanks to a still-mysterious
energy that acts like gravity in reverse.
Perlmutter's group studied data from far-off exploding stars
Maybe what we're seeing today is that all
these different techniques are starting to agree with each other,