Physicists from the Universities of Cambridge and Manchester and the
Instituto de Astrofisica de Canarias in Tenerife have released the first
results of new high-precision observations of the relic radiation from the
Big Bang, often called the cosmic microwave background or CMB. These
observations have been made with a novel radio telescope called the Very
Small Array (VSA) situated on the Mount Teide in Tenerife. The images show
the beginnings of the formation of structure in the early Universe. From the
properties of the image, scientists can obtain vital information on just
what happened in the early universe and distinguish between competing
cosmological theories.

Radiation from the Big Bang fireball has been travelling across the
universe, cooling as space expands. Today, we see the faint relic radiation
in all directions on the sky at a temperature of just 3 degrees centigrade
above absolute zero, giving a picture of the universe when it was less than
one 50,000th of its present age. Because galaxies must have formed out of
the primeval fireball, astrophysicists have predicted that they will have
left imprints in the radiation. Across the sky, there should be tiny
variations in the temperature of the relic radiation. However, these ripples
are very weak—only one 10,000th of a degree C.

During its first year of operation the VSA has observed three patches of
sky, each some 8 x 8 degrees across. It can see detail down to one third of
a degree, well matched to the typical size of interesting temperature
variations. The VSA has 14 aerials, each somewhat akin to a satellite TV
dish but only 15 cm across. The signals from each aerial are combined,
forming an interferometric array – a technique pioneered by Cambridge
physicists. The array is able to filter out unwanted terrestrial and
atmospheric radiation allowing the the extremely faint CMB sky signal common
to all the aerials to be detected. This approach allows high precision
observations to be made at modest cost – the capital cost of the VSA was 2.6
million GBP. The performance of the VSA also results from using advanced
receivers built at Manchester University and from the outstanding
atmospheric conditions at the 2.4 km high Teide Observatory on Tenerife. The
VSA can therefore measure specific, individual structures in the relic
radiation with great precision.

A small number of other experiments have made similar observations. The
different experiments work in different ways and face different challenges
and sources of error; a key advantage of this diversity is that if their
results agree, one can be confident that they are correct. One special
strength of the VSA is that it is an interferometer array; another is that
it is able to robustly remove the contaminating radiation from radiogalaxies
and quasars that lie between us and the CMB relic radiation. The VSA results
provide amazing confirmation of the current picture of the Universe.

The VSA observations of the CMB released today reveal the following
properties of our Universe:

1) The curvature of space is close to zero — we live in a spatially ‘flat’
universe.

2) The material in the universe is dominated by dark matter.

3) There is direct evidence for ‘vacuum dark energy’ which is currently not
well understood, but is causing the universe to accelerate.

4) There are multiple peaks in the CMB power spectrum. This is direct
evidence that all the structure in the universe today is due to microscopic
quantum-mechanical fluctuations, inflated to astronomical size in the very
early universe.

Notes for Editors

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Images and Web Sites

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Images and captions, and links to the scientific papers, are available from
the Cavendish Laboratory website at

http://www.mrao.cam.ac.uk/ telescopes/vsa

See also:

Press release in both English and Spanish at the Instituto de Astrofisica
de
Canarias website:

http://www.iac.es/gabinete/noticias/2002/m05d23.htm

Press release and images at the University of Manchester JBO website:

The Jodrell Bank website:

http://www.jb.man.ac.uk/news/vsa/

The PPARC website:

http://www.pparc.ac.uk/Cnt/CM.asp

The VSA is a collaborative project between the Astrophysics Group at
Cambridge University’s Cavendish Laboratory, Manchester Spaersity’s Jodrell
Bank Observatory, and the Instituto de Astrofi’sica de Canarias (IAC) in
Tenerife. The project is funded by the UK Particle Physics and Astronomy
Research Council and the IAC.

Background notes

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The cosmic microwave background

The cosmic microwave background radiation was discovered in 1965 by American
physicists Arno Penzias and Robert Wilson (who received the Nobel Prize for
the work). It is a faint radio radiation which fills the entire universe,
and thus appears to come from all directions in the sky. It is believed to
be the relic of the hot Big Bang phase of the universe, when the entire
universe was roughly the temperature of the surface of the Sun. The
expansion of the universe has since cooled the radiation down to a
temperature of just under 3 degrees above absolute zero (ie -270 deg C).
There are tiny variations in this temperature, of a few parts in 100,000,
which were first discovered by the NASA satellite COBE in 1992. These are
due the tiny fluctuations in density of the universe which have since
collapsed under gravity to form all the structures (galaxies and stars) in
the universe. These density fluctuations are believed to be quantum
fluctuations, blown up to astronomical size by a process in the very early
universe called ‘inflation’.

The power spectrum of the cosmic microwave background

Astronomers describe the fluctuations in the cosmic microwave background by
its power spectrum. This is a graph of the strength of the fluctuations
versus their angular size. Theories of the universe can predict the shape of
this graph in detail, and the theories are tested by comparing the observed
power spectrum to the predictions. An important prediction of the favoured
class of theories, based on the theory of inflation, is that the power
spectrum should show multiple peaks. These are due to coherent oscillations
(sound waves) in the hot plasma of the early universe, driven by quantum
fluctuations that had been vastly enlarged by the process of inflation.

Flatness of the Universe

Einstein proposed in his General Theory of Relativity in 1915 that matter
and energy cause space to become curved. In curved space geometry works
differently to normal flat (Euclidean) geometry: the angles of a triangle
don’t add up to 180 degrees. Einstein showed that the curvature of the
entire universe depends on the amount of matter and energy in it. If there
is relatively little matter/energy, the universe is negatively curved (like
the surface of the bell of a trumpet or the stem of a wine glass). If there
is a lot of matter/energy, space is positively curved (like the surface of a
ball) – this also means the universe is finite in size. If the amount of
matter/energy is just right, space is flat, and traditional school geometry
does apply. Observations of the the CMB measure the curvature of space by
effectively constructing a triangle between the observer and the edge of the
observable universe, and measuring its angles. These measurements are
showing that space is indeed flat.

Dark Matter and Dark Energy

Astronomers have long known that there must be another type of matter in the
universe besides the ordinary matter that the stars and planets are made of.
This matter is detected by its gravitational effects, but what form it takes
is a mystery; some type of new heavy subatomic particle is usually assumed,
and given the name dark matter. Einstein’s General Theory of Relativity also
allows for the existence of dark energy (also called the Cosmological
Constant). This is a property of empty space that causes the universe to
expand more and more rapidly. Long thought to be a mathematical curiosity,
it now turns out that the dark energy is real; the accelerating expansion
was discovered in the last few years by observations of distant supernovae.
Now the observations of the CMB have confirmed this. Both dark matter and
dark energy contribute to the flatness of the universe, but the amount of
dark matter can also be measured by combining the CMB measurements with
measurements of the Hubble Constant (the expansion rate of the universe).
There is not enough dark matter to make the universe flat, so there must be
a contribution from dark energy too. The nature of the dark energy is not at
all understood.

Contact details

For more information please contact any of these staff or research students

  • Dr Keith Grainge (Cambridge, +44 1223 337298, kjbg1@mrao.cam.ac.uk)
  • Dr Richard Davis (Manchester, +44 1477 571321, rjd@jb.man.ac.uk)
  • Prof Rafael Rebolo (IAC, +34 922 605273, rrl@ll.iac.es)
  • Dr Mike Hobson (Cambridge, +44 1223 339992, mph@mrao.cam.ac.uk)
  • Prof Rod Davies (Manchester, +44 1477 571321, rdd@jb.man.ac.uk)
  • Dr Mike Jones (Cambridge, +44 1223 337363, mike@mrao.cam.ac.uk)
  • Jose Alberto Rubino-Martin (IAC, +34 922 605370, jalberto@ll.iac.es)
  • Dr Richard Saunders (Cambridge, +44 1223 337301, rdes@mrao.cam.ac.uk)
  • Clive Dickinson (Manchester, +44 1477 571321, cdickins@jb.man.ac.uk)
  • Dr Bob Watson (Manchester, working at IAC, +34 922 605276 raw@ll.iac.es)
  • Rich Savage (Cambridge, +44 1223 337234, rss21@mrao.cam.ac.uk)
  • Anze Slosar (Cambridge, +44 1223 337278, anze@mrao.cam.ac.uk)
  • Angela Taylor (Cambridge, +44 1223 337234, act21@mrao.cam.ac.uk)
  • Prof Anthony Lasenby (Cambridge, +44 1223 337293, anthony@mrao.cam.ac.uk)
  • Dr Paul Scott(Cambridge, +44 1223 337306, paul@mrao.cam.ac.uk)
  • Klaus Maisinger (Cambridge, German speaker, +44 1223 337366,
    maising@mrao.cam.ac.uk)

  • Dr Ruediger Kneissl (Cambridge, German speaker, +44 1223 337298,
    rkneissl@mrao.cam.ac.uk)

  • Kieran Cleary (Manchester, +44 1477 571321, kcleary@jb.man.ac.uk)
  • Ian Morison (+44 1477 571321, im@jb.man.ac.uk)