Irreversible process can be reversed

From a discussion on embryophysics

http://groups.google.com/group/embryophysics/t/419d3c1fec30e3b5

29.02.2012 22:57 Steve McGrew:

Lots of experiments have been done in which seemingly irreversible processes can be reversed. In those cases, it is clear that the *information* needed to specify the original state is transformed, but not lost. Reversing the transformation restores the original state. Although it *looks* like entropy has increased when the transformation is first done, it turns out that it really hasn’t.

02.03.2012 00:36 Steve McGrew:

You asked for an example of a real experiment in which seemingly irreversible processes can be reversed. Spin echo and photon echo experiments are real examples. Here is a good one involving viscous liquid flow: http://www.youtube.com/watch?v=p08_KlTKP50. In the photon& spin echo experiments, the 180 degree phase reversal pulse serves essentially the same purpose as reversing the direction of rotation in the viscous liquid experiment.

02.03.2012 20:39 Evgenii Rudnyi:

The video is nice, thanks a lot. Yet, at the end one sees that dissipation does happen even in this case. If you have meant something like this, then why not.


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