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Friday, 28 April, 2000, 18:21 GMT 19:21 UK
Pictures of the early Universe
Boomerang
Scientists have produced the best evidence yet to show that the Universe is "flat".

This means the usual rules of Euclidean geometry taught in schools are observed in the cosmos: straight lines can be extended to infinity, the angles of a triangle add up to 180 degrees and the circumference of a circle is equal to 2pi times the radius, etc.

The precise geometry has been the subject of much debate since Albert Einstein suggested that the Universe might actually be "curved". Some cosmologists have championed spherical and even hyperbolic (saddle-like) models.

In the former, for example, the angles of a triangle would add up to greater than 180 degrees.

Boomerang

Enormous structures in the early Universe which are invisible to the unaided eye become apparent when observed using a telescope sensitive to light with millimetre wavelengths. This image is of approximately 1,800 square degrees of the southern sky (the apparent size of the Moon is indicated). It shows the Universe as it makes its transition from a glowing 2,700 deg C plasma to a perfectly transparent gas, a mere 300,000 years after the Big Bang. The enhanced colours show up the tiny temperature variations in the primordial plasma.

But the researchers who have been flying a balloon-borne telescope in Antarctica seem to have saved us from any mind-bending alternatives.

They have produced highly accurate maps of the Cosmic Microwave Background (CMB) radiation, which has its origins in the very early stages of the Universe.

Immediately after the Big Bang, the Universe was a hot, dense "soup" in which sub atomic particles interacted strongly with radiation. But there came a time - about 300,000 years after the Big Bang - when the matter and radiation "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. This is the CMB and it has a nearly uniform temperature across the entire sky: a very cold -270.45 deg Celsius.

But by mapping the tiniest of temperature fluctuations in the CMB, first done by the Cobe satellite in 1991, astronomers can "see" the distribution of matter in the early Universe. The CMB gives us clues as to how stars and galaxies might have evolved from that matter.

It can also tell us about the rate of expansion and age of Universe - and the ultimate fate of the Universe.

Boomerang

By observing the characteristic size of hot and cold spots in the Boomerang images, the geometry of space can be determined. Cosmological simulations predict that if our Universe has a flat geometry then the images should be dominated by hot and cold spots of around 1 degree in size (bottom centre). Any other geometry (bottom right and left) would distort the images. Comparison with the Boomerang image (top) indicates that space is very nearly flat.

The team working on the Boomerang (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) telescope have measured the temperature fluctuations in the CMB with a sensitivity of better than one ten thousandth of a degree. This gives a map that is over 40 times more detailed than the one produced by Cobe.

The team say their analysis of the data strongly indicates that the geometry of the Universe is flat, and not curved.

This result is in agreement with a fundamental prediction of the "inflationary" theory of the Universe. This theory hypothesises that the entire Universe grew from a tiny subatomic region during a period of violent expansion that occurred a split second after the Big Bang.

The enormous expansion would have stretched the geometry of space until it was flat.

The data from Boomerang, published in the journal Nature, imply that the Universe will go on expanding forever and will not, as one theory predicts, collapse back into a "Big Crunch".

In the main picture on this page, an image of the Cosmic Background Radiation has been overlaid on to the sky above Antarctica to indicate the size of the fluctuations as they would appear if a standard 35mm camera were sensitive to microwave light. The colours have been chosen to match aesthetically the rest of the picture. The Boomerang team are preparing for a flight in the foreground.

All images are courtesy of Boomerang

 WATCH/LISTEN
 ON THIS STORY
Dr Phillip Maufkopf
"Space is not curved"
Professor Carlos Frenk
"An ultrasound of the baby universe"
The BBC's Christine McGourty
"The Universe is flat and will probably expand forever"
See also:

26 Apr 00 | Science/Nature
05 Nov 99 | Science/Nature
26 May 99 | Science/Nature
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