The Day the Universe Changed - James Burke [144]
By this time the astronomical position of the earth in space had come to be seen as extremely complicated. The factors to be taken into consideration before any final position could be calculated were now known to include: the earth’s rotation on its axis, its revolution around the sun, its monthly inequality of period, the procession of the equinoxes, the wobble on its axis, the variation of its angle to the ecliptic, the variation of its point closest to the sun, perturbation of its movement by other planets, the sun-solar system wobble, the movement of the solar system in space, the two separately moving star streams of the Milky Way, and internal alterations of the earth’s shape. How many more factors might there be to consider before an absolute statement of position could be made?
This relativist view of the universe and the responsibility of science to explain it was expressed by a group of scientists and philosophers known as Positivists. Their leading figure was a Viennese physicist, psychologist, philosopher, physiologist and historian called Ernst Mach, who was opposed to absolutism in every form. Mach questioned the application of Newton’s laws to universal conditions, as he thought it was clear that no such conditions could ever be measured or identified. In terms of motion and inertia, if the position of the earth was not absolutely known the problem of whether or not the earth or the sun revolved was a false one.
All absolute statements about inertia, he said, could only be about all matter in the universe. Local statements were statements only about locally perceived phenomena, which might or might not be typical. All that could be described were personal, local, sensory experiences.
Mach shared George Berkeley’s instrumentalist view of nature that all theories and laws were no more than computational devices for describing and predicting phenomena. They were not explanations of reality. In his book The Science of Mechanics Mach attacked ‘the conceptual monstrosity of absolute space’as being ‘purely a thought thing that cannot be pointed to in experience.’The science of mechanics had come late in history, according to Mach, and so might well not be the definitive way to interpret nature. All that should be described by science was the way in which experiences related to each other:
We recognise what we call time and space only through certain phenomena… spatial and temporal determinations are achieved only by way of other phenomena… we define stars’positions in terms of time - and that is really in terms of the Earth’s position… the same is true of space… we conceive of position from what happens in the eye… against determination via other phenomena… every phenomenon is a function of other phenomena…. All masses and all velocities, and consequently forces, are relative. There is no decision about absolute and relative which we can possibly meet, to which we are forced, or from which we can obtain any intellectual or other advantage… the Ptolemaic or Copernican view is an interpretation, but both are equally actual.
This modern photograph of a bullet passing through the hot air above a candle shows the shock waves studied by Mach in the supersonic experiments during which he established the speed of sound-known today as Mach I.
Mach defined what became known as Mach’s Principle: ‘Every single body of the universe stands in some definite relation with every other body in the universe.’The problem was that the ‘other bodies’were distant star systems, beyond observation. In this case, all that science could attempt was to systematise experience and look