The Surrey U3A Network’s November study day on cosmology encompassed everything we know about the creation of the universe as well as things we can still only guess at, writes Mike Thurner
The day was split into four lecture sessions – all taken by Dr Roger Luther, Teaching Fellow (Mathematics) at the University of Sussex – interspersed with coffee and lunch breaks. The topics were ‘What we know’, ‘What we think we know’, ‘What we’re not at all sure of’ and a ‘Conclusion’.
It started with an indication of the age and size of the universe, a timeline of events following the assumed Big Bang start of space and time, and the life cycle of a star (including our sun). Some of the numbers are hard to imagine if your world is founded on perceived reality. Only mathematicians are unfettered by this intuitive understanding of objects and events. The universe is unimaginably large and the time scales for early events unimaginably short.
It is thought that from a very dense, very hot state at the time of the Big Bang, where only elementary particles of high energy existed, a very brief period of inflation was followed by the four natural forces (gravity, electromagnetism and the two nuclear forces) unravelling from an initial combined super-force. It is thought that there was almost as much anti-matter as matter, and much mutual annihilation took place, leaving only a small residue of normal matter. Elementary particles (quarks) combined to form protons and neutrons (the nuclei of atoms of hydrogen and helium) in a hot plasma which was opaque to light. After some time, as the universe cooled, these nuclei captured electrons to form atoms and the universe became translucent (the cosmic dawn) so that scientists can now study this early light as the Cosmic Microwave Background. Gravity acted on irregularities in the distribution of the early matter, forming clusters leading to galaxies and, as the atoms heated up on compression, nuclear fusion started and the early stars were born.
The life cycle of a star involves its conversion, by nuclear fusion, of hydrogen into helium, with the release of much energy (the heat and light we receive from the sun). When all the helium is used up fusion continues to create higher elements, up to iron; but eventually a star of sufficient size collapses and then explodes as a supernova, releasing huge amounts of energy sufficient to create the full range of elements above iron. The planet we live on today, and we ourselves, include these elements, and it is sobering to realise that they were created in a cosmic explosion. We are made of star dust!
It is thought that only 4% of the total energy (mass and force) in the universe is detected as bright stars. The remainder is supposed to comprise dark matter (23%) and dark energy/vacuum energy (73%). The dark matter is suspected to include dark bodies such as planets, comets, black holes, cosmic dust and other undetected matter. It is used to explain the way stars revolve around galaxies. Science has so far no idea what dark energy is, but it is used to explain the perceived continued expansion of the universe.
The future of life on our planet will be dictated by the eruption of a super-volcano (eg, Yellowstone) or the impact of a comet or asteroid. Such events have, in the past, led to mass extinctions of life. The future of our planet and solar system depends on the life of our star (sun), which will probably swell into a ‘red giant’, boiling our water and melting our rock before engulfing us. In the far distant future it is thought that our galaxy will pass through another galaxy (Andromeda). In the end the universe will run out of hydrogen and the last star will go out.