Miércoles 22 de Marzo de 2006, Ip nº 145

Astronomers Find the Earliest Signs Yet of a Violent Baby Universe

Using data from a new map of the baby universe, astronomers said yesterday that they had seen deep into the Big Bang, and had gotten their first detailed hint of what was going on less than a trillionth of a second after time began.

The results, they said, validated a key prediction of the speculative but popular cosmic theory known as inflation about the distribution of matter and energy in the Big Bang. The theory holds that during its first moments, the universe, fueled by an antigravitational field, underwent a violent growth spurt, ballooning from submicroscopic to astronomical size in the blink of an eye.

"It amazes me that we can say anything about the universe in the first trillionth of a second," said Charles L. Bennett, a professor at the Johns Hopkins University and the leader of the group that reported the results yesterday. "It appears that the infant universe had the kind of growth spurt that would alarm any mom or dad." The map was produced by a NASA satellite known as the Wilkinson Microwave Anisotropy Probe that has been circling the Earth at a point on the other side of the Moon since 2001, recording faint emanations of microwaves thought to be the remnants of the Big Bang.

The microwaves paint a portrait of the 13.7-billion-year-old universe when it was only 380,000 years old, astronomers say. But in the details of that portrait are clues to processes that occurred when it was much younger.

Using the map, the Wilkinson team has been able to revise an earlier estimate of the time at which the first stars began to form and shine through the primordial murk that followed the cooling of the Big Bang. Those stars appeared when the universe was about 400 million years old, they said yesterday.

The previous estimate of 200 million years, based on earlier Wilkinson data, had been seen as surprisingly early by many cosmologists, and the new date is comfortably in line with mainstream theories.

Inflation theory, which was invented by Alan H. Guth of the Massachusetts Institute of Technology, has been the workhorse of Big Bang cosmology for the last 25 years. But astronomers and physicists admit that they still have no idea what caused inflation. As a result, there are a welter of models describing how it might have worked.

Although inflation is not yet conclusively confirmed, it is now in better shape than ever, many astronomers said, and many models can be eliminated.

"We've crossed a threshold," said David N. Spergel of Princeton University, a member of the research team. "We can now start to say something interesting about the physics of inflation."

Others not involved in the project tended to agree.

"If this holds up to the test of time, it's a real landmark," said Max Tegmark, a cosmologist at M.I.T.

Dr. Guth, who is at a conference in the Caribbean, was said to be walking around with a big smile.

The new map has been eagerly awaited by astronomers, who last heard from the Wilkinson group in 2003 when it released its first map. That map showed the cosmos speckled with faint hot and cool spots, the seeds of structures like galaxies.

Three years is a long time to go between baby pictures.

Dr. Bennett and his colleagues have spent the time taking a much more difficult measurement, in effect using spacecraft antennas to measure the polarization of the Big Bang microwaves. To make these measurements, which required 100 times the sensitivity of the previous heat measurements, the astronomers essentially had to recalibrate their entire spacecraft and the way they looked at the data.

"We had to rewrite the whole software pipeline — twice," Dr. Spergel said. The light waves from the Big Bang, they found, do not vibrate randomly in different directions as they travel from the distant past to us. Rather, they have a slight preference to line up in one plane.

Lyman Page, a Princeton physicist, compared it to the glare of sunlight bouncing off the hood of a car. The reflection causes the light waves to oscillate in a horizontal direction. In the case of the car, a person would wear sunglasses to eliminate the glare. In the case of the Big Bang microwaves, he said, "We measure the glare."

What plays the role of the hood of the car in this story, Dr. Page said, is a fog of electrons floating in space between the Earth and the Big Bang. This fog was produced, so the story goes, by radiation from the first stars ripping apart atoms in space and liberating their electrons.

Measuring the polarization more accurately allowed the Wilkinson team to refine its previous estimate of when the stars first turned on.

In turn, by correcting for the effects of this electron fog, the astronomers were able to measure fluctuations in the microwaves more accurately than they had before.

This allowed them to confront for the first time an important prediction of inflation theory. For 30 years, cosmologists had presumed that the waves and ripples in the early universe followed a simple pattern, namely that their brightness was independent of their size. But according to inflation theory, the brightness of the bumps should be slightly dependent on their apparent sizes in the sky. Smaller bumps should be slightly dimmer than big ones.

The reason, explained Dr. Spergel, is that the force driving inflation is falling as it proceeds. The smaller bumps would be produced later and so a little less forcefully than the bigger ones.

That, in fact, is what the Wilkinson probe has measured. Dr. Spergel said, "It's very consistent with the simplest inflation models, just what inflation models say we should see."

Michael Turner, a cosmologist at the University of Chicago, called the results, "the first smoking gun evidence for inflation."

But Paul Steinhardt, a physics professor at Princeton who has lately championed an alternative to inflation in which the universe begins and ends cyclically in a collision between two island universes, pointed out that the new data are also compatible with his theory.

Andrei Linde, a Stanford University physicist, noted that his favorite model was still in the running and exclaimed in an e-mail message, "Great day for cosmology!"

The stage is set for a race to achieve the next milestone, proof of inflation theory. If it is correct, there should be a separate, even fainter pattern of polarization, because of gravity waves, the roiling of space-time by the violent wrench of inflation.

Detecting those waves would confirm inflation. Dr. Spergel said that if those waves were there the Wilkinson probe might eventually be able to see them. Next year, the European Space Agency is scheduled to launch its Planck satellite, which will also search for gravitational waves. In the meantime, balloon- and ground-based telescopes will also take aim at the cosmic microwaves.

Dr. Steinhardt said, "If you want to know where you came from, and where you're going, that's the issue at stake."

  17/03/2006. The New York Times.