We believe that certain symmetries apply to the laws of physics.  For example, we believe that the laws of physics are independent of the observer&#x27;s position.  I mean, look (visualize me stepping sideways here).  So we can demonstrate that one pretty easily.  And they&#x27;re independent of rotation.  Again, look (visualize me turning 90 degrees here).  And exchanging left and right.  I mean, look... (visualize me pausing with a confused look on my face as I try to figure out how to exchange left and right).<p>I can&#x27;t actually do that experiment.  And it turns out, when we got deep enough, we found out that things actually behaved differently (parity non-conservation).<p>When it comes to time reversal, we can&#x27;t actually do the experiment, either, so we don&#x27;t really know whether physics behaves the same when time is reversed.  We expect, philosophically, that it will, but we don&#x27;t <i>know</i>.  But it seems to me, given how relativity mixes time and space, if physics is not the same with left and right reversed, then it can&#x27;t be the same with time reversed either.