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Time...Quantum mechanics presents a more complex picture of time. Particularly in field theory, where particles are created and annihilated with only a delayed adherence to conservation of energy, things become fuzzy. The path integral formulation of quantum mechanics defines the most direct confrontation with the classical picture. It states that the behavior of a particle is as if it traveled along every possible path from the point of origination to the point of interaction. This is a notion of simultaneity that violates classical notions of causality. Field theory has formalized the study of symmetry to a degree not possible before its invention. In its formalism, the laws of physics are constrained to be unchanged under a symmetry known as CPT. This is not an intuitive notion: it holds that, if we change a particle into its anti-particle (charge inversion), invert the spatial axes (parity inversion), and reverse time (T), the resulting equations are still a valid description of reality. CPT is a very strong principle, based upon general arguments regarding causality. Classically, each of three principles (C, P and T) holds separately. However, early in the study of the weak interactions, it was obvious that parity is not conserved. While CP appears to be conserved in the equations, more detailed studies have shown that CP is violated. By implication, time reversal must contain a compensating violation. This is useful in the theory of the Big Bang. It provides a mechanism to explain the preponderance of matter in the universe. This is happy: matter and anti-matter participate in a violent annihilation whenever they get together. In all likelihood, there wouldn't be physicists (or anyone else, for that matter) if it weren't for time reversal violation. But this still doesn't explain the asymmetry between space and time. If fact, in a theory of composition, in which space-time is constructed from simpler primitives, it would seem to be sensible to consider that physics should be possible in the reduced 1- and 2-dimensional realities. This suggests that there should be a time dimension for every spatial dimension. |
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