<!DOCTYPE html><html><head><title></title><style type="text/css">p.MsoNormal,p.MsoNoSpacing{margin:0}</style></head><body><div style="font-family:Arial;">everyone knows that balls can read minds—especially that of the thrower. So it knows the intended end point. Any deviance from that is just willful disobedience. Least action is just the ball's laziness.</div><div style="font-family:Arial;"><br></div><div style="font-family:Arial;">davew<br></div><div style="font-family:Arial;"><br></div><div style="font-family:Arial;"><br></div><div>On Wed, Mar 12, 2025, at 10:44 AM, Pieter Steenekamp wrote:<br></div><blockquote type="cite" id="qt" style=""><div dir="ltr"><div>There's a *"nice"* layman’s explanation of the principle of *least action* (<a href="https://www.youtube.com/watch?v=qJZ1Ez28C-A)">https://www.youtube.com/watch?v=qJZ1Ez28C-A)</a>—though I don’t quite agree with it. (It does, however, include a rather neat explanation of quantum mechanics that I find useful—but that’s another discussion.) <br></div><div><br></div><div>Back in engineering school, when calculating trajectories, we relied entirely on Newtonian mechanics, applying it so relentlessly in problem-solving that it became second nature. Later, I encountered the principle of *least action* and its claim to be more fundamental than Newton’s laws. <br></div><div><br></div><div>A common example used to illustrate this principle goes like this: <br></div><div>If someone throws a ball from point A to point B, the ball *evaluates* all possible paths and then follows the one of least action. <br></div><div><br></div><div>This framing presents a problem. Here’s my perspective: <br></div><div>If a person throws a ball from point A and it *happens* to land at point B, a post-mortem analysis will confirm that it followed the path of least action. But that’s an observation, not a mechanism. <br></div><div><br></div><div>The distinction is subtle but important. In both cases, when the ball leaves the thrower’s hand, it has no knowledge of where it will land. Throw a thousand balls with slightly different angles and velocities, and they’ll land in a distribution around B. Yet the layman’s explanation suggests that each ball somehow *knows* its endpoint in advance and selects the least-action trajectory accordingly. <br></div><div><br></div><div>I don’t buy that. <br></div><div><br></div><div>My view (and I welcome correction) is that the ball simply follows Newton’s laws (or the least action laws) step by step. It doesn’t *choose* a trajectory—it merely responds to the local forces acting on it at every instant. Once it reaches its final position, we can look back and confirm that it followed the least-action path, but that’s a retrospective conclusion, not a guiding principle. <br></div><div><br></div><div>Ultimately, in this context, Newton’s laws and the least-action principle are equivalent descriptions of the same physics—neither requires the system to "know" its endpoint in advance.<br></div><div><br></div><div><br></div></div><div>.- .-.. .-.. / ..-. --- --- - . .-. ... / .- .-. . / .-- .-. --- -. --. / ... --- -- . / .- .-. . / ..- ... . ..-. ..- .-..<br></div><div>FRIAM Applied Complexity Group listserv<br></div><div>Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom <a href="https://bit.ly/virtualfriam">https://bit.ly/virtualfriam</a><br></div><div>to (un)subscribe <a href="http://redfish.com/mailman/listinfo/friam_redfish.com">http://redfish.com/mailman/listinfo/friam_redfish.com</a><br></div><div>FRIAM-COMIC <a href="http://friam-comic.blogspot.com/">http://friam-comic.blogspot.com/</a><br></div><div>archives: 5/2017 thru present <a href="https://redfish.com/pipermail/friam_redfish.com/">https://redfish.com/pipermail/friam_redfish.com/</a><br></div><div> 1/2003 thru 6/2021 <a href="http://friam.383.s1.nabble.com/">http://friam.383.s1.nabble.com/</a><br></div><div><br></div></blockquote><div style="font-family:Arial;"><br></div></body></html>