The Day the Universe Changed - James Burke [73]
Descartes’ book was called The Discourse on Method, and just as Aristotelian logic had revolutionised the form of European argument four hundred years earlier, so now did Descartes’ ‘Method’. The book exhorted the reader to doubt everything. It advised him to take as false what was probable, to take as probable what was called certain, and to reject all else. The free-thinker should believe that it was possible to know everything and should relinquish doubt only on proof. The senses were to be doubted, initially, because they were also the source of hallucination. Even mathematics might be doubted, since God might make a man believe that two and two made five.
The only thing that was certain was thought. The fact that a man thought, whether falsely, madly or truthfully, proved that he existed. Descartes expressed this view in his famous dictum: ‘I think, therefore I am’ (cogito, ergo sum). Knowledge of things based only on experience might be alterable: like a honeycomb when the honey had been removed, which might look the same but would no longer be a honeycomb. Only the mind could be trusted because ‘all things that we conceive of very clearly and distinctly are true’.
Thought, in the form of critical doubt, was the only tool that the scientist could trust. In solving problems, the simplest possible solution should be examined first and after that the more complex. Straight lines should be postulated before curves. In thinking through a problem, Descartes used the analytical approach. He imagined the problem solved and looked at the consequences of the solution. In doing so he would quickly realise whether his solution had been right or wrong.
Descartes applied his ‘Cartesian doubt’ to the behaviour of the universe. In 1640 he wrote The Principles of Philosophy, in which he employed Kepler’s theory that the sun caused vortices, or whirlpools of force, which moved the planets. Descartes described a universe that would work without a vacuum and so without the need for attraction.
The universe as seen by Descartes, filled with whirlpools of matter. At the centre of each vortex is a sun: S, F, D, Y, and so on. The curved strip is the path of a comet moving from vortex to vortex.
There were, he said, three kinds of matter: solid matter, light emitted by the sun, and ether composed of particles of a luminous nature which filled space. The light streaming out from the sun as it rotated caused the particles to spin in a kind of solar whirlpool. As they did so, they caught each of the planets in a vortex, which spun as it carried the planet in orbit round the sun.
Gravity was explained as the effect of the particles as they swirled out from the sun, exerting a force on terrestrial objects to make them fall to earth and on planets to keep them in orbit. Descartes’ was an entirely mechanical universe, where nothing happened except as the result of impact between particles. ‘The world is a machine,’ said Descartes. Everything existed because of the effect of movement initiated by impact. When inert lifeless matter was impacted, it ‘felt’. This was why humans experienced sensory impressions.
With a bow towards the Church, Descartes prefaced his universal explanation by saying that while he accepted the biblical account of Creation, his was an alternative which would have worked. Descartes followed Benedetti in thinking that without the effect of the vortices, planets would be flung out in straight lines away from their orbits. But it was in his assumption of the inertness of matter that Descartes made the greatest advance. Matter had a tendency to do nothing until impacted: any object in motion moved as it did because its inert state had been altered by impact. Only Descartes’ rejection of Kepler’s idea that the planets attracted each other prevented the development of a full gravitational