&gt;Our direction of time is defined by the observation that entropy (or &quot;chaoticness&quot;) always increases with time. If you mix orange juice with water, you will not see the result unmix itself again, even though the interactions between the individual molecules are perfectly reversible.<p>Perhaps in zero-g, under the effect of no acceleration and&#x2F;or gravity. But I&#x27;ve seen all (most of) the non-water bits settle in the bottom of a bottle left alone for a long time.<p>That doesn&#x27;t detract from your overall point about entropy, but it&#x27;s probably to use an example based on the quality of energy (try to generate electricity from the heat that leeches from the walls of your cabin in winter).