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Thought experiment proposed to reconcile psychological versus thermodynamic arrows of time:
A pair of physicists has proposed a thought experiment to help reconcile the seeming disparity between the psychological and thermodynamic arrows of time. In their paper published in the journal Physical Review E, Leonard Mlodinow and Todd Brun claim their thought experiment demonstrates that the two seemingly contradictory views of time, must always align.
When ordinary people think about time, they see the past as something that has come before and the future as a great unknown yet to come. We can remember the past, because it has happened already, but not the future, because it hasn't. Physicists, on the other hand see time as able to move either forward or backwards (towards greater entropy), which implies that we should be able to remember events in the future. So, why can't we?
It's because of the way our memories work the two say, and they've created a thought experiment to demonstrate what they mean. Imagine, they write, two chambers connected by an atomic sized tube with a turnstile in it. If there is gas in one of the chambers, individual atoms of it will move through the tube to the other chamber (towards higher entropy) tripping the turnstile as they go, in effect, counting the atoms as they pass by, until both sides have equal numbers of atoms-creating a state of equilibrium.
http://phys.org/news/2014-05-thought-psychological -thermodynamic-arrows.html
http://physics.aps.org/articles/v7/47
http://journals.aps.org/pre/abstract/10.1103/PhysR evE.89.052102
(Score: 2) by VLM on Tuesday May 06 2014, @03:34PM
On a more practical small scale you can get supporters of the "no arrow of time exists" crowd all wound up by showing them a dual slit QM experiment, randomly forcing particle or wave behavior, then asking to run time backwards and try to force the opposite behavior. You can also play some entanglement games first one time direction and then the other, but thats getting more esoteric.
All this "conservation of energy in a thrown baseball proves there's no arrow of time" stuff doesn't sound so cool when QM doesn't work that way, even if (some) physicists don't believe in chemistry, biochem, or engineering thermodynamics, they tend to believe in QM, so this gets them all worked up.
(Score: 2) by wantkitteh on Tuesday May 06 2014, @04:43PM
Funny, I understood that conservation of energy and arrow of time aren't mutually exclusive as reversing time also reverses entropy (and thus dissipation of heat through friction), effectively acting as a cue for all those seemingly independent actions that would need to happen "spontaneously" to satisfy all the prerequisites of time running backwards.
(Score: 1, Interesting) by Anonymous Coward on Tuesday May 06 2014, @05:01PM
However, this version of QM is more or less ruled out by now. (It would take a much longer post to lay out the case, but essentially experiments have shown larger and larger systems wherein superpositions can be maintained; there is no evidence for collapse kicking in at any particular timescale. Instead it appears that decoherence [wikipedia.org] theory is correct.) Modernly, the accepted version of QM (MWI [wikipedia.org] or similar) has no wavefunction collapse, and everything is microscopically reversible. So any QM experiment you can imagine (dual slit, etc.) can be time-reversed and will behave sensibly, as far as the physics are concerned. Of course if you time-reverse a entropy-increasing operation, then it will be entropy-decreasing (so there is always a thermodynamic arrow of time, defined by the direction of entropy increase); but nothing untoward (e.g. violation of a conservation law) happens.