Take two beakers of water and use a spoon to stir water clockwise in one beaker and counterclockwise in the other beaker. Observe the beakers after a sufficiently long time when the water flow has slowed down.

Is it possible to determine the original direction of water flow after 1 hour? 1 day? 1 week?

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    $\begingroup$ Is this a legitimate physics question, or more of a lateral-thinking question? $\endgroup$ – Hugh Feb 22 '19 at 8:53
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    $\begingroup$ It's not much of a puzzle. It looks to me more like a physics problem. Maybe it should be asked in physics.stackexchange.com $\endgroup$ – rhsquared Feb 22 '19 at 9:06
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    $\begingroup$ @KameliaSavova if it's an ongoing competition, this topic should be close as site's policy doesn't allow this :/ $\endgroup$ – Flying_whale Feb 22 '19 at 9:09
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    $\begingroup$ Is this from an ongoing competition? As Flying_whale says, if it's ongoing, we sadly don't allow that. $\endgroup$ – Hugh Feb 22 '19 at 9:33
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    $\begingroup$ From a physics perspective, physicists spend a lot of time isolating a system so they can measure what they are interested in. In a model system, the information would be lost as @hugh says. In practice, it would depend on details. For example, the surface under the breakers might show slight scuff marks which under an electron microscope might show the original direction essentially indefinitely. We would normally assume that the stirring was adiabatic and therefore not enough to do this, but the details would be important $\endgroup$ – Dr Xorile Feb 23 '19 at 17:23

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