Werner Heisenberg (1901-1976) propounded (as applicable to quantum mechanics) his Uncertainty principle in 1927. It stated that there is a fundamental limit to the precision with which certain paired properties of subatomic particles can be known simultaneously. Two such properties are position and momentum.
In the original formulation, Heisenberg seemed to be saying that the act of measurement distorted the position or momentum of an electron. Many students of his work took this to mean that the problem had to do with imprecision in our measuring equipment and/or techniques, which introduced error that would be mitigated as we refined our laboratory procedures.
But subsequent clarifications indicated that the uncertainty in quantum systems is inherent in the wave behavior(of all energy and matter) known to co-exist with the particle behavior. It has nothing to do with limits to human knowledge or with the effect of an observer on the quantum system, although these factors may be seen to play a role.
A full treatment of this dichotomy quickly gets into Hilbert spaces, with infinite dimensions, in which the uncertainty relationship between position and momentum is described by Fourier transformability. It is not possible to simultaneously and precisely localize a function other than zero and its Fourier transform.
The realm of the very large, described by Albert Einstein’s relativity, and the realm of the very small, described by Heisenberg’s quantum mechanics, both surfaced in the first half of the twentieth century. The two knowledge systems stand in contrast to the everyday reality of classical physics.
Moreover, since the two concepts were formulated, things have become progressively stranger. At the macro level, we have string theory, multiple worlds and cosmic inflation. At the other end of the size scale, there are virtual particles, first postulated by Heisenberg in 1932, quarks and elementary particles that move backwards in time. At present it is impossible to reconcile these otherwise successful visions of the very large and the very small, nor has it become clear how gravity fits in.
Einstein, Heisenberg and Max Planck frequently got together to play music. Who among us can follow that act?
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