Science Seen Time One author Colin Gillespie helps you understand the physics of your world.

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Lemaitre, Penrose and the Original Order of the Universe

Life is all about order. Life forms use energy to organize themselves. Their often-exquisite order is created at the expense of disorder which they dump somewhere else. The net effect is always a decrease in total order of the universe. It’s basic physics (the Second Law of Thermodynamics, if you care).

The Second Law says nothing special about life forms. It applies to any isolated system, meaning one for which we can track all the loss and gain of order. In particular, it applies to the system called the universe. And therein lies a tale of two cities, Louvain and London, and two physicists, Georges Lemaître and Roger Penrose, whom I have had occasion to mention separately. What they share is an obsession with the order of the infant universe.

Lemaître starts out with Einstein’s then-new theory of general relativity. He finds a solution to its equations for the entire universe. He says the universe must be expanding. Einstein says Lemaître’s calculations are correct but his physics is abominable. This is 1927. Two years later American astronomer Edwin Hubble shows Lemaître’s physics is dead right. Feed ‘Father of the Big Bang’ into Google and you’ll get Lemaître.

Lemaître is left protesting to anyone who’d listen to a physicist who also is a priest talk about how the universe must have begun. He says about ‘ten thousand million years ago’ the universe must have been very small. A ‘single quantum’, he suggests, or a ‘primeval atom’. Unfortunately he thinks this quantum/atom must hold all the matter of the universe. His most telling argument is little noticed. He says that the universe gets always more disordered over time so, in its infancy, it must have been in a state of ‘minimum disorder’.

Fast forward fifty years. Penrose comes to the same conclusion. It gets a chapter in his classic volume on the laws of the universe. He says that, in its origin, the universe ‘must have had an absurdly low entropy’, physics-speak that means it had few choices of ways to be. His frustration that most physicists don’t understand this fact is manifest.

Maybe this frustration drove him to the Big-Bounce views he now espouses. Too bad the two physicists in their two cities never got together. They might have synthesized a simple solution: The universe began as a single quantum, not of matter, but of space. It has no choices. By definition it’s a state of perfect order. This makes them both right.

Further reading:

Georges Lemaître (1946), L’Hypothese de L’Atome Primitif, Paris: Dunod; Betty H. Korff & Serge A. Korff (trs.), (1950), The Primeval Atom, New York: D. van Nostrand Company, Inc.; http://www.scribd.com/doc/99059242/Lemaitre-The-Primeval-Atom-o

Roger Penrose (2004), A Road to Reality: A Complete Guide to the Laws of the Universe, London: Vintage Books, pp. 686 to 734; http://staff.washington.edu/freitz/penrose.pdf

Wikipedia article on entropy (accessed 21 February 2014): http://en.wikipedia.org/wiki/Entropy

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