Hawking (1988: 77-8):
Up to 1956 it was believed that the laws of physics obeyed each of three separate symmetries called C, P, and T. …The symmetry T means that if you reverse the direction of motion of all particles and antiparticles, the system should go back to what it was at earlier times; in other words, the laws are the same in the forward and backward directions of time. …
There is a mathematical theorem that says that any theory that obeys quantum mechanics and relativity must always obey the combined symmetry CPT. In other words, the universe would have to behave the same if one replaced particles by antiparticles, took the mirror image, and also reversed the direction of time. But Cronin and Fitch showed that if one replaces particles by antiparticles and takes the mirror image, but does not reverse the direction of time, then the universe does not behave the same. The laws of physics, therefore, must change if one reverses the direction of time— they do not obey the symmetry T. Certainly the early universe does not obey the symmetry T: as time runs forward the universe expands — if it ran backward, the universe would be contracting.
Blogger Comments:
From the perspective of Systemic Functional Linguistic Theory, the universe does not obey physical models of it, just as a landscape does not obey a map. Like a landscape, the universe is a construal of experience as meaning, and, like a map of a landscape, a physical model of the universe is a reconstrual of meaning.
Importantly, (conceptually) reversing the direction of motion of particles through space does not reverse the direction of time. This is because time is the dimension of the unfolding of processes, and this is independent of the direction of motion through space. The locomotion of particles only occurs along spatial dimensions, not through time; time is a measurement of location and extent of the unfolding of the process of locomotion. A process extends from one location on the time dimension to another.
Moreover, the mistaken notion of time "running" forward or backward arises from confusing the circumstantial dimension (time) with the process that is used as the standard of measurement (the ticking of a clock).
In this interpretation, time does not run either forward or backward, whether the spatial intervals of the universe are expanding or contracting.
Importantly, (conceptually) reversing the direction of motion of particles through space does not reverse the direction of time. This is because time is the dimension of the unfolding of processes, and this is independent of the direction of motion through space. The locomotion of particles only occurs along spatial dimensions, not through time; time is a measurement of location and extent of the unfolding of the process of locomotion. A process extends from one location on the time dimension to another.
Moreover, the mistaken notion of time "running" forward or backward arises from confusing the circumstantial dimension (time) with the process that is used as the standard of measurement (the ticking of a clock).
In this interpretation, time does not run either forward or backward, whether the spatial intervals of the universe are expanding or contracting.
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