The Story of Least Action and the Double Slit

[jedishrfu]

TL;DR

The video presents some history on the concept of least action in Classical Physics and how it came to dominate all of physics.

 

[pines-demon]

Some people have argued that the anomalous dot in the laser experience is just due to laser leakage.

 

[jedishrfu]

How would that get resolved? Is there a different way to run the test?

 

[pines-demon]

How would that get resolved? Is there a different way to run the test?

Better laser

 

[jedishrfu]

That's true. In the video, he turned off the light, and the laser was just dangling by a string. Initially, I thought the laser was somehow aimed at that area.

 

[pines-demon]

The other problem with this video is that there is no quantum physics involved. The demo can be clearly explained using classical waves. He would have to perform it using electrons or single photons.

 

[jedishrfu]

I imagine every video has some defect in it.

I was really amazed at how the idea of least action from Mapertuis to today have shaped and reshaped physics. In college, either I missed it or just didn't appreciate its use in quantum mechanics. In my junior year, I was formally introduced to least action and liked how it cut through the headache of using forces so elegantly.

Susskind in his CM book from the Theoretical Minimum series shows how classical least action can be used to derive the F=ma law cementing its use as a favored method for any CM problem. I often wondered why we didn't learn it in introductory courses.

 

[Demystifier]

What is the question? What is this thread about?

 

[jedishrfu]

Its a discussion of the Least Action principle as described in the video.

 

[jedishrfu]

Tough crowd here. I thought the video was quite good. It gave me the big picture something I missed when I took CM and QM in the 1970s in physics.

Of course, I missed a lot of things and lived the uncertainty principle in other aspects of just growing up. Ahh, the relativity of it all.

 

[vela]

I was really amazed at how the idea of least action from Mapertuis to today have shaped and reshaped physics. In college, either I missed it or just didn't appreciate its use in quantum mechanics. In my junior year, I was formally introduced to least action and liked how it cut through the headache of using forces so elegantly.

I suspect you never saw the Lagrangian in the context of quantum mechanics in college. When I took quantum mechanics, we only used the Hamiltonian, and I don't recall the Feynman formulation of non-relativistic quantum mechanics ever being taught. Those of us who knew about it had read about it on our own. The Lagrangian reappeared in QFT in grad school.

 

[jedishrfu]

Yes, you're probably right. We used Schiff as our book on QM. The professors would talk about Rojansky's QM book, but we never used that one.

For CM we used Marion not Goldstein.

This was in the 1970s.

 

[lightlightsup]

Please let me know if this experiment is 'legit'.

Can leakage or something else other than "light considers all paths" explain this phenomenon?

 

[lightlightsup]

Better laser

I am surprised that this test is not being replicated with low-leakage lasers.

 

[jack action]

Tough crowd here. I thought the video was quite good. It gave me the big picture something I missed when I took CM and QM in the 1970s in physics.

I just posted about the first video of this series that explains how we came to the principle of least action and I was also amazed. Then I find out about this second video. I appreciate you posted it.

 

[TensorCalculus]

There's another quite comprehensive video by Physics With Elliot on a similar topic (in my eyes, it's a bit more mathematically rigorous, though Veritasium's videos, aimed at a wider audience, are wonderful - I'm a huge fan):
It's a very interesting topic!

 

[lightlightsup]

Does anyone have a link or reference to the Feynman lecture video that this Veritasium video uses?

I'd rather hear this from the horse's mouth.

 

[lightlightsup]

Some people have argued that the anomalous dot in the laser experience is just due to laser leakage.

The guy in this thread seems to have limited the laser leakage, except, I can't tell how long his cardboard goes on for, relative to the starting point of the laser light.

 

[lightlightsup]

https://www.patreon.com/posts/least-action-q-126148989

It seems that they're aware that this laser experiment should be repeated with more exacting instrumentation.

I am surprised that there is no one on YouTube with a repetition of this experiment.

 

[pines-demon]

https://www.patreon.com/posts/least-action-q-126148989

It seems that they're aware that this laser experiment should be repeated with more exacting instrumentation.

I am surprised that there is no one on YouTube with a repetition of this experiment.

Well there is also this: