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Time-symmetric systems and fundamental physics - sorry, no sources (maybe I'll try to find them later, if I can bypass the captcha)
The '''arrow of time''' is how the passage of time is always associated with an overall increase in disorder, or [[entropy]]. Hence time is not symmetric, like space, but is directional.
The '''arrow of time''' is how the passage of time is always associated with an overall increase in disorder, or [[entropy]]. Hence time is not symmetric, like space, but is directional.
== Time-symmetric systems ==
Physical systems with a few degrees of freedom usually are time-symmetric; for example, analysing the breakup of a binary asteroid with the capture of one of them as a planet's satellite yields equations where the time can be reversed: the analysis can be made for the event where a rogue asteroid captures a planet's satellite.
When the freedom degrees increase, it becomes improbable that the time can be reversed: a rogue star that passes close to a solar system and disrupts the nice orbits of the planets might be seen as the inverse process where a rogue star "fixes" the disrupted orbits, but this scenario is very improbable.
== Fundamental physics ==
It's usually believed (and backed by experiments) that most "forces" in nature ([[gravitation]], [[electromagnetism]], [[strong nuclear force]]) are time-symmetric, at least in the microscropic level. The possible exception is the [[weak nuclear force]], that is not time-symmetric but has [[CPT symmetry]] (CPT stands for "charge", "parity" and "time" - if we reverse time, the only way to have a realistic process is by reversing charge and parity).
[[Category:physics]]
[[Category:physics]]
[[Category:philosophy]]
[[Category:philosophy]]