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

Mon Jul 3 13:03:19 EDT 2023

Nick,

Two points, first an answer to your request to share my intuition, then
maybe a possible source for you to learn more:

My understanding of the concept of least action in physics is that it
involves the principle that objects in the universe exhibit a tendency to
minimize the transfer of energies between kinetic and potential energies as
they move through space. In other words, objects are "lazy" in the sense
that they prefer paths that require the least amount of energy exchange.
To elaborate on this intuition, consider a body in motion with both kinetic
and potential energies. The total sum of these energies remains constant
because energy cannot be created or destroyed. However, as the body moves
through space, there can be a transfer of energy between the kinetic and
potential forms. In line with the idea that objects in the universe tend to
be lazy, the transfer of energies between kinetic and potential forms is
minimized during the body's movement.
>From this perspective, the concept of least action can be understood as
minimizing the sum of the differences between kinetic and potential
energies along the path taken by the body. By minimizing this quantity, we
capture the "laziness" or preference of objects to follow paths that
require minimal energy exchange as they move from one point to another in
space.

Now, the second point, there is a nice book on the bare minimum you need to
understand to start doing physics, written for people without a math or
physics background wanting to really understand physics. It is "The
Theoretical Minimum. What You Need to Know to Start Doing Physics". By
Leonord Susskind and George Hrabovsky. (Available from Amazon at
https://www.amazon.com/Theoretical-Minimum-Start-Doing-Physics/dp/0465075681
)
You can just watch the video lectures at
https://theoreticalminimum.com/courses/classical-mechanics/2011/fall
Specifically the concept of least action is covered in lecture three of the
series at
https://theoreticalminimum.com/courses/classical-mechanics/2011/fall/lecture-3

On Mon, 3 Jul 2023 at 17:01, Nicholas Thompson <thompnickson2 at gmail.com>
wrote:

> Thank you Peter for that helpful answer.
>
> You seem to endorse what I am calling "Roberts's Maxim": "*He who would
> try to understand fluid dynamics will never understand fluid dynamics*."
> Still, I would like to know what your intuitive answer is, even though it
> will probably be beyond me.
>
> My fascination with this stuff dates from my childhood and arises from the
> hurricanes, blizzards, and tornado that afflicted Massachusetts in late
> 40's and early 50's..  Thus, I have been a meteorologist for far longer
> than I have been a psychologist.  I think there is an odd similarity
> between  two domains:  each has an old theory with an old language that
> everbody falls back on, but basically both fields consist of empirical odds
> and ends, rules of thumb, and dramatic tales barely held together by the
> fact that whatever else can be said about them, the public has a strong
> interest and opinions . I have been working on a short essay for 20 years
> whose working title is, "Shall we name a storm?"
>
> A subfascination within this general area concerns the manner in which
> physicists use psychological language  which they instantaneously disclaim
> as "metaphorical".  Now to me, a  rapt Darwinian, metaphors are everywhere
> in science.  Models,  we call them. Thus, this disclaimer seems profoundly
> dishonest.  I owe my interest in least action to my long-time mentor,
> Stephen Guerin.  He has learned to be very careful around me, but I can
> tell that in his own private modeling -- the kind I urge you to tell me
> about above -- he believes that the lightening bolt internally models all
> the possible routes to ground and then *chooses the least action path.  *One
> of my favorite Friam members, Hywel White, a particle physicist, used to
> attribute motives to particles, and every time he did it, I would
> congratulate him on his insight that psychology is the mother science.  As
> a behaviorist, I'm perfectly willing to entertain panpsychism, but only if
> you are willing to own it, work out its implications, and test it.   One
> cannot use psychological terms as a bench language, and then disclaim that
> their functioning as models in yo one's thinking.  That's an intellectual
> foul.
>
> Thank you again for your honest and inspiring response.  Now, it has
> stopped raining and I must return to to the garden.
>
> Nick
>
> On Mon, Jul 3, 2023 at 2:50 AM Pieter Steenekamp <
> pieters at randcontrols.co.za> 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.
>>
>>
>> On Mon, 3 Jul 2023 at 05:12, Nicholas Thompson <thompnickson2 at gmail.com>
>> wrote:
>>
>>> So the difference is at a positive max when the ball hits the ground and
>>> at a negative maximum when the ball reaches its highest altitude?  So how
>>> am I to understand positive and negative?    vectors?
>>>
>>> Instantaneious Action is at a minimum when the two terms are equal?
>>>
>>> I have no intuitive sense of what is going on here.
>>>
>>> But thanks for trying, Frank.
>>>
>>> N
>>>
>>>
>>>
>>> N
>>>
>>> On Sun, Jul 2, 2023 at 12:27 PM Nicholas Thompson <
>>> thompnickson2 at gmail.com> wrote:
>>>
>>>> Frank,
>>>>
>>>> Thanks SO  MUCH for forwarding this to me.  To any other defrocked
>>>> english majors on Friam, who have listened to these guys blather on about
>>>> LaGrangians for all these years,  I highly, HIGHLY recommend the video.
>>>> Pretty short, AND, you might possibly, conceivably understand Steve Guerin
>>>> when you  get to the end.   Yeah.  Really.
>>>>
>>>> Nick
>>>>
>>>> ---------- Forwarded message ---------
>>>> From: Frank Wimberly <wimberly3 at gmail.com>
>>>> Date: Thu, Jun 29, 2023 at 2:53 PM
>>>> Subject: Fwd: Watch "The Most Important Idea in Physics: The Principle
>>>> of Least Action - Ask a Spaceman!" on YouTube
>>>> To: Nicholas Thompson <thompnickson2 at gmail.com>
>>>>
>>>>
>>>>
>>>>
>>>> ---
>>>> Frank C. Wimberly
>>>> 140 Calle Ojo Feliz,
>>>> Santa Fe, NM 87505
>>>>
>>>> 505 670-9918
>>>> Santa Fe, NM
>>>>
>>>> ---------- Forwarded message ---------
>>>> From: Frank Wimberly <wimberly3 at gmail.com>
>>>> Date: Thu, Jun 29, 2023, 12:51 PM
>>>> Subject: Watch "The Most Important Idea in Physics: The Principle of
>>>> Least Action - Ask a Spaceman!" on YouTube
>>>> To: Thompson, Nicholas <nickthompson at earthlink.net>, Barry MacKichan <
>>>> barry.mackichan at mackichan.com>
>>>>
>>>>
>>>> https://youtu.be/UuqpCBZoX3M
>>>>
>>>> ---
>>>> Frank C. Wimberly
>>>> 140 Calle Ojo Feliz,
>>>> Santa Fe, NM 87505
>>>>
>>>> 505 670-9918
>>>> Santa Fe, NM
>>>>
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