Dr Jacqueline Mitton

Royal Astronomical Society

01223 564914
jmitton@dial.pipex.com

Cosmologists in Cambridge have been comparing and combining data from various kinds of cosmological observations made by different research teams in order to understand the universe better. They, and other cosmologists around the world, are generally finding excellent agreement between many different lines of research. In particular they find that the universe consists of roughly equal amounts of matter and the mysterious, self-repelling energy called ‘the cosmological constant’ or, more recently, ‘dark energy’. They also find that the universe is about 14 billion years old. More work is needed to iron out some remaining disgreements.

Many independent techniques are used to tackle basic questions about the universe, such as whether it will go on expanding for ever, but in recent years cosmologists have recognised that many of the answers are not going to come from any one method alone. The information from many different sources must be combined.

Comparing results from many independent approaches also helps to test whether assumptions routinely used by cosmologists are correct. The fact that there is such remarkable agreement is excellent news for the most popular theory – the ‘Big Bang’ followed by a period by a period of ‘inflation’, when the universe rapidly increased in size.

Work by the Cambridge team, consisting of PhD student Sarah Bridle, Dr Ofer Lahav, Dr Anthony Lasenby, and Dr Mike Hobson, is to be presented on Friday 11th August at a Symposium during the 24th General Assembly of the International Astronomical Union in Manchester. They have been paying particular attention to three cosmological quantities: the amount of matter in the universe, the present day speed of expansion of the universe, and the clumpiness of the universe.

By working closely with scientists working in different aspects of cosmology from Durham, Arizona, Hawaii, Jerusalem and Chicago they have been able to incorporate much more information than is often used for this type of work. They have brought together five different kinds of observations: the numbers of clusters of galaxies, the positions and distances of galaxies, ripples in the afterglow of the Big Bang, exploding stars (supernovae) in distant galaxies, and flow-like motion of galaxies through space caused by the clumpiness of the universe.

Checking how far these five different approaches agree with each other, they find good agreement between the first four. Combined together, they give the age of the universe as 14 billion years plus or minus 2 billion years – which is reassuringly older than the estimated ages of the oldest stars in our galaxy. Taking the last three types of observation together, there is still quite good agreement, but the age of the universe comes out as 13 billion years plus or minus 2 billion years. The team says there is more work to be done to understand why the results from counting numbers of clusters of galaxies do not quite agree with those from the flows of galaxies.

NOTE

Example of cosmic data fusion
A particularly powerful probe of the universe is the pattern of ripples in the afterglow of the Big Bang – the Cosmic Microwave Background radiation, so called because we can see it now as microwaves coming from the sky. Two recent experiments carried on high-flying balloon flights (BOOMERANG and MAXIMA) have shown that the universe is ‘flat’. This tells cosmologists that the sum of the amount of matter plus the amount of self-repelling energy is equal to a particular critical value. On their own, these experiments cannot tell us how much there is of each. However, it is possible to disentangle the the proportions of matter and energy by combining the data with results of another kind, such as the study of supernovae (exploding stars) of a particular type when they go off in distant galaxies. This technique measures the acceleration of the universe, which is determined by the difference between the gravitational attraction of matter tending to slow it down and the self-repulsion of the dark energy tending to make the universe expand more quickly. Supernovae tell us the amount of matter MINUS the amount of self-repelling energy. Ripples in the afterglow of the Big Bang tell us their SUM. Putting the two together means the equation can be solved and the amounts of matter and energy determined.

Notes for Editors

CONTACTS FOR THIS RELEASE:

Sarah Bridle
Cavendish Astrophysics, Cambridge University
Phone: +44 1223 766476
e-mail: s.bridle@mrao.cam.ac.uk
(At IAU 7-11 August)

Dr Ofer Lahav
Institute of Astronomy, Cambridge University
Phone: +44 1223 337540
e-mail: lahav@ast.cam.ac.uk
(At IAU 7-11 August)

Dr Anthony Lasenby
Cavendish Astrophysics, Cambridge University
Phone: +44 1223 337293
e-mail: A.N.Lasenby@mrao.cam.ac.uk
(At IAU 6-12 August)

Dr Mike Hobson
Cavendish Astrophysics, Cambridge University
Phone: +44 1223 337312
e-mail: mph@mrao.cam.ac.uk
(At IAU 7-9 August)

Meeting press room phones, 7 – 16 August

+44 (0)161 275 7832

+44 (0)161 275 9458

+44 (0)161 275 9499

Relevant research papers may be found at:
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