This is a good confirmation of the standard cosmology, and a large triumph for science

Paul Richards

The results from a balloon-borne experiment, which peered back to a time shortly after the Big Bang, have provided strong evidence in support of the cosmologists' theories about "dark matter" and "dark energy".

The data was obtained through an international collaboration called the Millimeter Anisotropy eXperiment IMaging Array (Maxima), directed by the University of California, Berkeley.

The work supports and builds upon another experiment called Boomerang which last month produced data to show that the geometry of the Universe is flat.

Greater detail

The Maxima flight was made from the National Scientific Ballooning Facility in Palestine, Texas.

Maxima sees ripples in the early Universe

Launched at sunset, the project's balloon flew to about 40,000 metres (130,000 feet). Telescopes and sensors were returned to the ground by parachute.

The Boomerang data was performed in a similar way, but the Maxima results are much more detailed.

This means that Maxima has produced the highest resolution map yet of the so-called Cosmic Microwave Background (CMB) radiation.

Weak waves

The CMB stems from a time shortly after the Big Bang when the matter and radiation ceased to interact strongly and "decoupled". The matter went on to form stars and galaxies. The radiation just spread out into space - where it still is and can be detected as weak waves of radio frequency.

The CMB has a nearly uniform temperature across the entire sky: a very cold -270.45 deg Celsius - but mapping the tiniest of temperature fluctuations can enable astronomers can "see" the distribution of matter in the early Universe.

Maxima's CMB map, like Boomerang's, provides strong evidence that the Universe is flat - in other words, it follows the usual rules of Euclidean geometry where straight lines can be extended to infinity and the angles of a triangle add up to 180 degrees - and will continue to expand forever.

"This is a good confirmation of the standard cosmology, and a large triumph for science, because we are talking about predictions made well before the experiment, about something as hard to know as the very early Universe," said team leader Paul Richards, UC Berkeley professor of physics.

Good science

Although some members are common to both the Maxima and to the Boomerang teams, the two analyses were done completely independently.

New physics may be required to explain this

Shaul Hanany

"The fact that these independent experiments give such similar results is the best indication that we are both getting the science right," says Shaul Hanany, professor of physics at the University of Minnesota. "

Cosmologist Adrian Lee, from the Center for Particle Astrophysics and the Space Sciences Laboratory, both at UC Berkeley, added: "These are extremely difficult experiments, and yet the data from Maxima and Boomerang show spectacular agreement."

The tiny temperature fluctuations in the CMB images appear as spots. It is the size of these spots that tells cosmologists about the geometry of the Universe.

Inflationary theory

Both Maxima and Boomerang saw spots clustered in a size range of about one degree across - which indicates a flat Universe.

A future flight will attempt to measure the polarisation of the CMB

When combined with recent data on the Universe obtained from studies of distant supernovae, the data also support the inflationary theory of the Universe.

The calculations suggest that the amount of normal matter in the Universe should be about 5%; the amount of the mysterious dark matter in the Universe is about 30% and the amount of the even stranger dark energy is about 65%.

So if these observations are right, the Universe is mostly made of strange dark energy with normal matter, out of which we are made, being a minor contaminant.

Atom building

"That's probably the most interesting result of all these experiments," Hanany said. "New physics may be required to explain this."

Richards said that while the thermal map of the sky was a "pretty picture," most of the information came from a detailed statistical analysis of the sky data along with data at much larger angular scales obtained by the Cobe satellite in 1992.

Richards also noted that the number obtained for the fraction of the Universe made up of ordinary matter, called baryons, fits beautifully with entirely independent estimates that come from theories about atom building in stars.

"A lot of people are sceptical of cosmology, so when your results show this type of agreement, you have more confidence in your theories," he said.

New frontier

Maxima looked with finer resolution at an area representing 0.3% of the sky - a area 22 times broader than the full Moon - in a northern region of the sky near the constellation Draco.

Another mission, Maxima 2 flew in June 1999 and observed roughly twice the area that Maxima 1 observed. Maxima 3 will fly later this year and will attempt to measure the polarisation of the CMB, which has never been observed.

"That the radiation is polarised is another prediction of inflationary theories," Hanany said. "Polarisation measurements are the new frontier in cosmic microwave background research."