====== Arrow of Time ======
{{tag>Inexplicable}}
A term coined in 1927 by the British astronomer //Arthur Eddington// to describe the //"one-way direction"// or //"asymmetry"// of time.

For most people, the notion that time passes only in one direction is a given. There are multiple reasons for taking this point of view : cause and effect, ageing etc etc. And on the cosmic scale, extensive and varied measurements have shown that the apparently expanding universe will irrevocably progress in the direction of more disorder. (Therefore, for //[[content:physics:cosmology:big_bang|Big Bang Theorists]]//, imagining backwards in time, the universe was previously more ordered)

But at the atomic and subatomic scale, quantum theory insists that particles can ‘travel’ either forwards or backwards in time with equal probability.

And further, //Albert Einstein’s// theories of relativity, incorporating Time as another dimension, insist that there is no single and special present - all moments are equally real.

//Quote from //[[http://www.newscientist.com/article/mg15621064.900-times-arrow.html|New Scientist]] Nov. 1997

>The past is gone, remembered perhaps, but unalterable. The future has yet to come into being, and is still open. Only the present moment is truly real. All this seems like common sense. Yet many scientists and philosophers are adamant that we have got it all wrong. They insist that time does not flow at all. "

More reference :[[http://en.wikipedia.org/wiki/Arrow_of_time|Wikipedia]]

One often overlooked factor is that disorder is (usually) more likely than order. If you drop a large handful of coins, the chance that they will all fall heads up ('ordered') is exactly the same as for any other possible combination. But they probably won't - simply because there are far more 'disordered' possibilities.

Also see : //'Physicists can’t agree on whether the flow of future to past is real or a mental construct//' an [[http://www.theatlantic.com/science/archive/2016/07/the-debate-over-times-place-in-the-universe/492464/?utm_source=atltw|Atlantic Magazine article]] July 2016, about the //Time in Cosmology// conference at the //Perimeter Institute for Theoretical Physics// in Waterloo, Canada.

//Note :// Although the effects of gravity can make the universe //more //ordered, cosmological theory currently insists that in the very very very long term, all matter will eventually evaporate and disintegrate - eventually ending up with all atomic particles having degraded into photons. At which point, according to Prof. Roger Penrose, 3-D space and Time itself will no longer exist //”[…] the universe has no way of 'building a clock' “  //See : [[content:physics:cosmology:conformal_cyclic_cosmology]]

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Also see :[[content:physics:cosmology:time_travel]]

~~stars>4/5~~