Physics and observable magnitudes

Physics and observable magnitudes

17 Şubat 2013, 04:54

By the year 1926 Einstein had already abandoned his Machian positivistic views - the idea that all quantities that enetred a physical theory must have 'operational definitions' in terms of measuring instruments - which characterized the analysis leading to special theory. Heisenberg who did not know that Einstein had abandoned this position many years earlier when he was seeking his final formulation of the theory of gravitation, was astounded when Einstein asked, 'But you don't seriously believe that none but observable magnitudes must go into a physical theory?' To which Heisenber answered, with some surprise, "Isn't that precisely what you have done with relativity? After all you did stress the fact that it is impermissible to speak of absolute time, simply because absolute time cannot be observed; that only clock readings, be it in the moving reference system or the system at rest, are relevant to the determination of time'. As Heisenberg recalls, Einstein replied, "Possibly I did use this kind of reasoning but it is nonsense all the same. Perhaps I could put it more diplomatically by saying that it may be heuristically useful to keep in mind what one has actually observed. But on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality the very opposite happens. It is theory which decides what can be observed..."