Public Lectures for the Session 2002-2003 held in Room E7 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

16 January 2003

''Simple Cosmology''

Professor Sir Francis Graham-Smith, FRS
(Former Director of Jodrell Bank and former Astronomer Royal)

There is apparently only one universe and we are in it. There are no comparisons to be made yet in the last four decades our understanding has increased enormously. Detailed observations of stars, galaxies, quasars and pulsars, using an ever-increasing number of instruments from the surface of the earth and from space and working at an ever-wider range of wavelengths, are showing us what the universe is really about.

Sir Francis emphasized that observations are what mattered; not just theoretical calculations, although these allowed increasingly detailed theoretical modelling. The expansion of the universe was predicted by Einstein and observed within a decade, by Edwin Hubble in the 1920s. Einstein also predicted gravitational lensing by massive objects, demonstrated by Arthur Eddington at the total solar eclipse in 1918. Gravitational lensing was first observed in intergalactic space only in the last two decades of the twentieth century. Georges Lemaître postulated the Big Bang eighty years ago and although Hoyle, Bondi and Gold suggested a steady-state model of the universe in 1948, this was short-lived. Background radiation from the Big bang, predicted by George Gamow at about the same time, was not discovered until some fifteen years later in the mid 1960s but confirmed the Big Bang theory that has remained unchallenged ever since.

Our universe can now be described in comparatively simple terms; from a Big Bang about 13 billion years ago that created Hydrogen, Helium and some Lithium, still by far the most common elements. Massive stars formed from this mixture and in evolving through to supernovae created the heavier elements seen in second and third generation stars like our own sun. Galaxies are also seen to have evolved throughout the age of the universe in line with theoretical predictions in which nearby galaxies are compared with the most distant and hence most primitive ones. Many of the latter show evidence of prodigious energy emission from massive quasi-stellar cores still visible from the most distant times.

Detailed measurements of slight temperature variation in the background radiation suggest irregularities and structure within the Big Bang itself. Recent computer models, in which the three-dimensional distribution of galaxies has been plotted, have shown very large-scale structures in the universe, great walls and voids of material, mainly galaxies, which may echo turbulence during the initial inflation.

Gravitational lensing has allowed better estimates of the amount of matter in galaxies and hence in the universe, to be calculated. Observations within the past ten years now support another idea originally postulated by Einstein, a repulsive force in the cosmos. This effect, hitherto passed over by theoretical cosmologists, seems to show that the expansion rate is actually increasing, contrary to Newtonian gravitational theory. This poses a theoretical problem that has yet to be explained. Non-baryonic matter is now thought to comprise 85-90% of the mass of the universe. Of this invisible mass, by far the largest part is in the form of dark energy that apparently drives the repulsive force.

There is more to learn but new observational techniques are increasingly validating our simplistic understanding of the cosmos.

Synopsis by Kevin J. Kilburn (Secretary)

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