Ordinary Meeting, 2009 March 25

Cosmology and the Expanding Universe

Mr Boles presented a pictorial overview of the development of cosmology in the twentieth century, beginning with the first observations, made in the 1920s, which had produced truly compelling evidence that the 'spiral nebulae' discovered by the Herschels were in fact vast systems of stars which lay outside the Milky Way, known today as galaxies. He went on to outline the experiments performed by Vesto Slipher in 1921 to measure the rotation speeds of these nebulae, explaining that Slipher's measurements had revealed that these objects rotated at phenomenally fast speeds – moving hundreds of kilometres each second – implying that they must also be startlingly large and distant in order to have nonetheless appeared static throughout the ages. Mr Boles then followed the story through Edwin Hubble's discovery in the 1930s of the apparent expansion of the Universe, to the discovery of the cosmic microwave background by Arno Penzias and Robert Wilson in 1964. He discussed the earliest evidence for the existence of dark matter, which had arisen from observations of the rotation velocities of galaxies made in the mid-1970s, and described how modern observations of gravitational lenses and the X-ray emission of galaxy clusters had corroborated the early evidence.

To close, Mr Boles described in detail how recent observations of the cosmic microwave background, made by a wide range of instruments including most notably the WMAP satellite, had allowed many of the parameters in modern cosmological models to be determined with remarkable precision.

Following the applause, the President apologised for the late running of the meeting, and invited Mr Nick James to present his Sky Notes.