A (VERY) BRIEF HISTORY OF COSMOLOGY

... By Andy Young

If you have read Steven Hawking’s "A Brief History Of Time" you may remember his anecdote where a distinguished scientist, possibly Bertrand Russell or Thomas Huxley, gave a public lecture in which he described how the earth orbits the sun & how the sun orbits the centre of a vast collection of stars called the galaxy. At the end of the lecture a little old lady at the back of the room got up & said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying: "What is the tortoise standing on?" "You’re very clever, young man, very clever" said the old lady "But it’s turtles all the way down"

The turtle theory apparently originated with a Hindu myth; as an attempt to explain the nature of the Universe it may strike us as eccentric, but the concept of scientific investigation - observation, leading to theory, leading to predictions about further observations - was then unknown. In the beginning it was inevitable that ideas about the nature of the world, the sky & the objects contained within it would be speculative & highly imaginative, since extracting patterns of behaviour from a tangle of natural phenomena must have been difficult. The apparently capricious occurrences of fire, flood, storms, famine & drought would look much more like the doings of some moody being with superhuman abilities. However, the sky would have provided the best examples of order & continuity in an unpredictable world. After the regular daytime transit of the sun, night would bring the moon & stars, rewarding observation with gradually more distinct patterns of behaviour, thus the beginnings of cosmology took shape Without exception early theories invoked gods as the moving force behind the changing face of the night sky; our relationship to these beings was more important to earlier civilisations than the more utilitarian view that we take today, but eventually such considerations - how we use astronomy for navigation, timekeeping & so on - took precedence. It could be said that we began to take less interest in who was running things & more in simply how they ran.

One of the biggest forces changing our attitude was the improvement in technology. In many ways the history of mankind is the history of technology; changes in weapons, travel, communications, farming, medicine etc. etc. have all impacted on every society in the world & these changes are increasing exponentially - they are building on themselves. It is worth reflecting that the reason we seem so clever compared to our ancestors is that we are standing on a great pile of knowledge, which is available to more & more of us. In astronomy the manufacture of lenses, increasingly more powerful & accurate, led to better observations & the heavens rapidly became an ever more intriguing & fruitful subject for investigation. This obviously led to greatly improved cosmological models, as the various theories could be tested against new & more detailed observations. So, here are a (very) few landmarks in the history of cosmology.

In the last 40 years advances in all technologies - computing, electronics, metallurgy, photography, to name a few - have accelerated enormously, often feeding off each other, leading to huge advances in astronomy & an ability to analyse not just the light from the heavens, but the full range of the electromagnetic spectrum pouring in on us . Even better, with telescopes in space the masking & distorting effects of our atmosphere are removed. Paradoxically, this welter of information has led to even more competing theories about the Universe; as can be seen above there used to be plenty of time for ideas & observations to interact, nowadays cosmology & astronomy are playing an accelerating game of catch-up - in the last few weeks Mr. Hawking has revised his ideas about just how black black holes are. Nevertheless the essential big bang, ever expanding Universe has had no serious competition, all observations seem to confirm it, the doubts arise at more fundamental levels.

One of the most interesting examples of astronomy dramatically changing cosmology was the discovery of red shift in the spectra of stars in other galaxies. When light from a star is broken down into its different wavelengths it produces a pattern typical for that type of star, with absorption lines corresponding to particular elements. It strikes me that it looks rather like a DNA pattern, & in the same way identifies the star family it belongs to. What was surprising was that the patterns were identical to known types, but all shifted to lower frequencies - red shifted. It was also found that the further away the galaxy the more the red shift. The simplest explanation (& science always takes the simplest explanation!) is provided by the Doppler effect, which implies that all galaxies are moving apart & the further apart they were the faster they were separating; a good way to imagine this is to think of a spotty balloon being inflated & visualise what happens to the spots. Thus the idea of an ever expanding Universe took root, which led directly to the big bang model we use today.

The important thing to remember is that all cosmological theories are just that & no more. They are all dependent on astronomical observations & if the observation is accurate & consistent & contradicts the theory, then out goes the theory. In practice what happens is that the best theories survive in their broad outline, approximating to the better, more detailed theories that supplant them.

Now suppose the turtles were invisible …..