The Sum over Paths Theory - A Level Physics

[@DrPhysicsA]

Thanks for kind comments. I'm not a great fan of the phasor approach. I didn't do a video till it was requested. It rather oversimplifies what, as you say, is a much more complex approach, and in my view causes more confusion than enlightenment at this level.

[@fabulusinvictus2198]

How could Feynman prove that the other paths exist if all they cancel before reach an observable point? (I talk in the mirror example)

[@Eva_sings]

They don't all cancel, one path remains. That is why you see your reflection in the mirror. It is is because one path in the entire sum remains.

[@spiros1994]

you should sell the papers you draw in e-bay. A way to donate you for giving us so much free and correct knowledge!

[@pikiwiki]

Oddly enough, I think i understood most of it. Lack of clear definition of terms at the end had be a bit fuddled, but, was holding on all the way through!! Nice, simple explanation

[@dectillion]

excellent, very informative, and much appreciated, keep em coming PLEASEEEEE

[@DrPhysicsA]

I guess its because the imperfections are not sufficiently serious to wreck the basic principle. You'll recall that the phasors from all other routes don't fully cancel out but are negligible in their contribution. As long as the imperfections don't seriously impede the image, all is well.

[@comprehensiveboycomprehens8786]

DrPhysicsA Does this approach indicate that 'miraculous' phenomena are not impossible but just very rare?

[@daratash1]

No it means what some might call "miraculous" is just "a run of the mill" rare event that fits and is governed by the theory.

[@michaeltebele3305]

I'm pretty sure that if the amplitude of the arrow cancels out than the event is impossible to occur, all remaining possibilities occur probabilistically, with a distribution of events that correspond to the probabilities

[@CAPITALISTRASH]

Thank you. I am in the middle of reading A brief history of time which mentioned Feynman’s sum of histories..which you indeed explained superbly 😊

[@henriquecsouza]

Thank you professor. Your explanations are clear and amazingly comprehensible.

[@comprehensiveboy]

As a non physicist I recently read that book and found it very interesting. How precisely did they botch it in your view?

[@aroubm.5265]

i swear doc u can never imagine how much thankful i am for ur help that enabled me to achieve what i always dreamed of u are a damn hero

[@defensegeneral9893]

your phasor graph @ 5:00, some how I don't understand why the arrows are pointing opposite to each other on the first half cycle but on the second half cycle they are all pointing down the same way

[@iMasterchris]

Agreed. You are amazing, and I would very much love the ability to support you.

[@fareshalasah7983]

I have a question, when a quantum cancels the other as a trough meets a crest where does the photons energy goes?

[@rxwop3698]

the quantum is not destroyed at that point, only the wavefunction of the quantum is. The quantum still can be observed at any point where the wave exists. So there is no destruction of photons in the interference

[@MrSmith2718]

Thanks for your great videos! You said that the various paths through a lense to the focal point take the same amount of time and therefore all phases in the focal point are the same and add to a maximum amplitude, which square is the intensity. But real lenses are not perfect: A variation of the thickness of the lense in the middle of just 10^-6 m causes a phasedifference of about 2 Pi (by green light with lamda=530nm) Nevertheless real lenses work, why? Thanks for all answers!

[@lambda4931]

Thank you!

[@jimdogma9890]

Great vid Doc, please do more of this phasor stuff. I think this is what that joker Brian Cox was trying to use to explain QM in his recent book, "The quantum universe," but he botches the whole approach...that book SUCKS! You explain it alot better. Also, do the phasors have to do with the complex conjugate wave function thing that gets canceled out by mutiplying it by the real wave function, [psi*psi]^2. Or is that something else?

[@JakeVS]

Very helpful :)

[@jigsmg]

thank you so much

[@cameronmorrison4100]

one question, how can the probability be greater than one?

[@JoeHinkle11]

Cameron Morrison I think it’s supposed to be out of 100. I could be wrong though...

[@eileens9848]

thanks doc.

[@jochemvanderspek5168]

Thanks for the video, but it's a bit weird that you don't explain the idea of a 'phaser' before using it, it makes the explanation rather unintelligible to me.

[@theblackhole1]

shortest path is not the quickest paath doc

[@michaeltebele3305]

yes it is. unless acceleration is involved in the picture, in which case the answer is the brachistochrone