[FRIAM] Watch "The Most Important Idea in Physics: The Principle of Least Action - Ask a Spaceman!" on YouTube

Barry MacKichan barry.mackichan at mackichan.com
Mon Jul 10 14:00:45 EDT 2023

This is late since another ISP cut my fiber connection a week ago. 
Living with only cell service plus $15 per gigabyte is not pleasant.

Some comments.
1. I believe that the fact that photons travel on geodesics (least 
distance betwee2 points on a surface (manifold)) gives a fingerhold on 
trying to grasp least action.
2. I read the wikipedia artice, and it hints that the application to 
electromagnetism and quantum physics requires some tweaks, so it is not 
as straightforward as the video implied.
3. Granted that Newton’s laws are simpler, my understanding is that 
problems involving constraints are easier to set up than integrating the 
constraints into the setup of the equations.

Just sayin’


On 3 Jul 2023, at 2:51, Pieter Steenekamp wrote:

> Hi Nick,
> Exercise caution when attempting to grasp the principle of least 
> action,
> particularly if you desire an intuitive comprehension of it.
> It is essential to recognize the significance of the principle of 
> least
> action, as it applies to various areas of physics and could 
> potentially
> hold a closer answer to the "why" question than Newtonian physics 
> regarding
> the laws of motion.
> However, based on our current knowledge, the best explanation for why 
> the
> principle of least action holds true is that it aligns with the
> observations and experiments conducted in the real world. Although a
> breakthrough might be on the horizon, a consensus has not yet been 
> reached
> regarding the "why" question.
> Therefore, at present, the following points can be made:
> a) When applied to the laws of motion, the principle of least action 
> and
> Newton's laws of motion are equivalent.
> b) The reason for their acceptance lies in their agreement with 
> empirical
> evidence and experimental results.
> c) The principle of least action carries more depth as it applies 
> across
> several other fields of physics, such as electromagnetism and quantum
> physics.
> d) The fundamental formulation of the principle of least action is 
> also
> simpler than that of Newtonian physics.
> However, if you are aiming to develop an intuitive understanding of 
> the
> motion of objects in the real world, it is advisable to adhere to 
> Newtonian
> physics. The principle of least action lacks inherent intuitiveness. 
> Let me
> rephrase that: I have personally constructed an intuitive 
> understanding
> that I find useful, but I cannot present it as the definitive answer.
> Perhaps someone else has a compelling intuitive explanation? I am open 
> to
> hearing different perspectives.
> Moreover, for practical mechanical engineering calculations involving
> forces and motion in the real world, Newtonian physics surpasses the
> principle of least action.
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