John D Barrow’s new book, The Book of Universes, has so far proved to be a fascinating read – I’m only about a third the way through. The book starts the story way back in Aristotle’s time, whereas the talk he gave at the Royal Institution started much later with Einstein on gravitation.
He quoted the “Groucho Marx Effect”, applying “I wouldn’t want to belong to any club that would accept me as a member” to cosmology as “A universe simple enough to be understood is too simple to produce a mind capable of understanding it.”
A talk that works through the developments in cosmological theory could have been dry, but because of the digressive anecdotes which came thick and fast, this one was never dull.
Einstein thought there could only be static universes, but realised that he had made a mathematical mistake; Desitter showed the universe could be expanding; Friedmann developed the three types of expanding universe – open, critical (a ‘British compromise universe’, expanding forever while doing the least amount of work needed), and closed. Hubble & Humason produced observational evidence of expansion; Eddington showed that a static universe would be unstable; Lemaître established the idea of the Big Bang (he also introduced the cosmological constant into the Einstein-Desitter universe to produce the best description of the universe as known today).
The next idea covered was that of the cyclic universe, Richard Tolman applying the Second Law of Thermodynamics to the cycles. Something bizarre that I didn’t know before was that universes have zero energy – if the positive energy of expansion and masses are added to the negative energy of gravity, within Einstein’s equations they always equate to zero; this answers questions about conservation of energy. The lambda force stops an infinity of future cycles. All these universes are expanding spherically.
Moving on to anisotropic universes, Kasner found the first one, Bianci classified all possible geometries, and Taub found the universes that matched the geometries in a systematic way; this produced universes that are different in different directions but the same in every place.
Kurt Gödel found rotating universe that didn’t expand, and topologies which allowed time travel to occur while obeying all the laws of physics.
Universes that differ from place to place were next, including the Einstein-Strauss (or Swiss Cheese) Universe, and the possibility of a universe where different places expand at different rates, meaning one could look back and see the end of the universe somewhere else.
The mid-1950sto mid-1960s were glossed over – magnetic universes, anti-matter, chaotic universes, strange topologies, ones where gravity would change over time, and Steady State universes
1965 brought evidence of super-dense hot past in the CMB, giving information about the shape and structure of the history of the universe. The temperature is equal in all directions (showing the universe is spherical), and the idea of inflation explains not only why the universe is so close to the compromise universe, but also where do the inhomogeneities come from.
The accelerated expansion in the universe’s early history produces a region 15 billion light years across (with a split second of inflation) from one 10-25cm across – light moves across this several times and therefore smooths it out, and quantum uncertainties cause little statistical fluctuations which became irregularities which caused galaxies etc.
The idea of eternal inflation yields the Multiverse (i.e. the whole universe, rather than ‘our’ visible universe), a foam in which it can be shown that there were 10 to the power 1077 of ‘by-product’ universes leading to the production of our patch of universe.
Lastly we have found ourselves in a universe with inflation followed by deceleration, and then acceleration starting again, and so Dark Energy has raised its head – probably equivalent to Einstein’s Lambda force or the Cosmological Constant; it is hoped that the LHC will find new particles to help our understanding of this.
Barrow usually manages to give extremely interesting talks, he’s an excellent communicator, and this lecture at the Ri was just about fully booked, the fullest I’ve seen the theatre for a while. He often gives public lectures as Gresham Professor of Geometry (he’s lecturing again on this subject on the 1st of March).