Paul Davies, Entropy, the Universe and Noise

I was lucky enough today to listen to a collquium on the subject of Gravitational entropy and cosmology given by Paul Davies (also his old
Adelaide University pages). Along with being a theoretical physicist Paul Davies is an excellent science communicator. I read a number of his books while in high school and without doubt they strongly contributed to my decision to study theoretical physics and mathematics at university.In fact, I strongly considered attending Adelaide University because he held a professorship there.

Interestingly enough, the reason given by Davies for moving to Adelaide from his native Britain was that he was tired of Margaret Thatcher’s constant funding cuts to the sciences (sadly repeated here by the present government). He credits Thatcher, once a chemist (not pharmacist!), with stimulating his interest in the sciences when, while at school, she presented him with a book on science.

I found the colloquium quite fascinating. Davies started off by demonstrating how gravity appears to contradict the second law of thermodynamics. The second law states that entropy (disorder) always increases in the universe, yet gravity seems to clump things together. For instance, this solar system was once a cloud of dust, yet ended up as discrete lumps in the form of planets, asteroids and the Sun – this is a more stable state for the solar system than the dust cloud.

Most especially, Davies discussed black holes, seemingly the greatest sink for entropy. These incredibly dense objects would appear to “suck” entropy right out of the universe, concentrating, rather than dispersing, matter and energy. However, it turns out that the size of the black hole’s event horizon (the distance from the centre of the hole at which it would be necessary to travel at the speed of light in order to escape) seems to be related to its entropy. The event horizon enlarges as matter falls into the black hole. It can also shrink as energy is “extracted” from the hole through a process known as Hawking Radiation. Furthermore the universe itself may have event horizons through which entropy is transferred.

It was so refreshing to sit through a lecture at the ATNF with mathematical proofs and theoretical constructs. The standard astronomical colloquium is naturally about real observations, or the difficulties in making them. Almost all experimental physics (including astronomy) is more about the study of noise and interference more than anything else these days. Most of the easy measurements have been made already and the challenge now is to make incredibly fine measurements of events. However, the more sensitive a measurement, the greater the chance that it will be hidden by noise. So the experimental physicist is a detective, hunting down sources of interference, eliminating the unwanted noise to find the signal they are after.

A theoretical physicist can usually assume away the noise and attempt to develop models of the underlying process, hopefully giving leads to the experimental physicist to look for certain phenomena or explanations of the causes behind observed events.

There are many who do both theory and experiment, but I find myself attracted to the former. Today’s talk made me wish I were involved in it now.

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