Universe 'proven flat'

The Boomerang balloon inflating just before launch

A high-flying balloon that soared over Antarctica has answered one of cosmology's greatest questions by revealing that the fabric of the Universe is "flat".

To astronomers, flat means that the usual rules of geometry are observed - light not being bent by gravity travels in straight lines, not curves. But since Albert Einstein proposed that the Universe may be "curved", the debate has been open.

It will mean rewriting the text books on the history of the Universe

Professor Peter Ade

Scientific opinion has moved towards a flat Universe and the latest data confirm this with greater certainty than ever before.

Another result of the study is the prediction that the Universe will continue its steady expansion, which started at the Big Bang, and will not collapse into a "Big Crunch".

"It's a tremendously exciting result - and one that will mean rewriting the text books on the history of the Universe," said one of the research team, Professor Peter Ade at Queen Mary College, University of London.

Faint heat

The new information is an exquisitely accurate map of the very faint afterglow of heat left behind by the Big Bang. This is called the Cosmic Microwave Background and is equivalent to the tiny warmth given off by something just a few degrees above absolute zero, -273 degC.

The detectors were cooled to -273 deg Celsius

Tiny temperature variations in the CMB, just 0.1% at most, allow scientists to test different models of how the Universe began and expanded.

The map paints a picture of the young Universe, just 300,000 years old - the cosmos is now over 12 billion years old. The chart was made by an international team led by Paulo de Bernardis of the University of Rome La Sapienza. He said: "It's really exciting to be able to see some of the fundamental structures of the Universe in their embryonic state.

The achievement, he said, was distinguishing the CMB from other interference: "The light we have detected has travelled across the entire Universe and we are perfectly able to distinguish it from the light generated in our own galaxy."

Sky high boomerang

The project to map the CMB was called Boomerang (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics).

On release, Bomerang soared skywards

The measurements were made using a very sensitive telescope suspended from a balloon 40,000 metres (131,000 feet) above Antarctica. The instrument flew around the frozen continent between 29 December 1998 and 8 January 1999.

It has taken since then to process the one billion measurements. The calculations alone would have taken six years to complete if run on a desktop computer. On the Cray T3E supercomputer at the Lawrence Berkeley National Laboratory, US, they took less than three weeks.

The fundamental cosmic parameters derived from the work are accurate to within just a few percent.

The research is published in the journal Nature and in an accompanying commentary, Wayne Hu, of the US School of Natural Sciences, New Jersey, said: "The Boomerang result supports a flat Universe. A perfectly flat Universe will keep on expanding forever, because there is not enough matter to make it recollapse in a 'Big Crunch'."

The research backs the inflation theory of the Universe put forward in 1980, which suggests that the whole of the cosmos expanded from a single tiny point at the Big Bang.

At that time, and for a short while after, space was curved because it was confined in a small region. However, the Universe's expansion has been so great that space has now been stretched to the point that it is essentially flat.