The Secrets of Feynman Diagrams

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Feynman’s path integral shows us that, to properly calculate the probability of a particle traveling from point A to point B, we need to add up the contributions from all conceivable paths between those points – including the impossible paths! In fact we can go even further: according to Feynman’s approach, every conceivable happening that leads from a measured initial state to a measured final state DOES in a sense happen. To calculate the probability of any quantum system evolving from one state into any other state we need to sum over every conceivable intermediate state. This is impossible because there are infinite possible intermediate states.

Written and Hosted by Matt O’Dowd
Produced by Rusty Ward
Graphics by Kurt Ross
Assistant Editing and Sound Design by Mike Petrow

Comments answer by Matt:

Superphilipp

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Myrmidon
Sure people love Star Wars. But I think they missed a golden opportunity to call the project Ronald Ray-gun.

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[RealStuntPanda]

I love the story about Feynman's wife, Gwyneth Howarth, driving the Dodge Tradesman van with Feynman diagrams all over it and some CalTech physics students were shocked so asked her why she had Feynman diagrams on her van. Her response was something like, "Because my husband invented them."

[flymypg]

OMFG! I was exposed to Feynman Diagrams in 1983, toward the end of a very intensive 2-year undergraduate physics sequence. Back then, I learned the math, turned the crank, and passed the exams.

Only today, 34 years later, did the light bulb light, the "Eureka!" get shouted, and the Zen-like state of the "Wonder of the Universe Explained" inhabit my mind.

Matt, thanks so much for communicating so extraordinary well! I think it was the "rotations of a single vertex diagram" that broke my mental block.

I knocked out the challenges in literally 10 minutes, delighting and amazing myself in the process. But I won't submit them, since, ideally, I really should have been able to do them 34 years ago.

I've already got my prize. Thanks!

[dabebop]

I'd get a Feynman Diagram tattoo if i wasn't so unsure about getting one.

[gorog]

This is amazing. This is basically a free semi-formal lecture with sharp and engaging production value -- I am really getting a lot out of this. Thank you!

[LamirLakantry]

I'm getting the impression that this Feynmen guy was kind of a smart guy.

[romajimamulo]

you should make a "I am made of particles of questionable reality" shirt

[akshatsaxena]

I got really excited when he said that we're going to do some quantum field theory ourselves

[ArturdeSousaRocha]

How come a popular science channel just gave a more in-depth and clearer explanation of Feynman Diagrams than what I got at the university where I majored in physics? I watch your videos from time to time because I've been working in a different area for the last two decades and I often discover stuff here that wasn't even known at the time (plus astrophysics was just one optional lecture — one I took and liked). Now I got a new appreciation of the quality of the work you do!

[yoskkdkdk]

"you can make your quantum field theories yourself" *throws glitter in the air*

[walts]

This video is especially good. Discussion of the six orientations of the basic vertex is quite clear and usually muddled in most field theory textbooks. Great job!

[TimmacTR]

I just wanted to stop and say that we live in an incredible time, where we have direct interaction, not with our anti-particle, but with experts in the field that can explain to us in simple and entertaining terms how the fundamental mechanics of existance work..

My brain interacted with this information and the result was a blown brain...

[ToastedFanArt]

I'm super high stumbling through YouTube and this comes up new. Great timing...

[CrownedMeadow]

I just looked up a bio on Dr. Matt and found out that he writes all of these scripts himself. Just when I thought that talent might have been left to someone else.

(Nope. Apparently he has ALL of the talents. I really enjoy every SpaceTime video. I’m a complete layperson with a new interest in physics for personal reasons, and this channel is practically all I watch anymore.)

[hoogmonster]

Two things I regret; not continuing physics study being secondary school and not learning maths to a more advanced level too. But PBS Space-time perfectly feeds my continuing lay curiosity in these fields. Maybe when i retire I'll take some evening courses in physics and maths just for the fun of it. Meanwhile channels like this are a real treasure and joy to watch.

[EugeneKhutoryansky]

The "questionable reality" of virtual particles should make us all very nervous. Our only measure for evaluating a theory is how precise its predictions are, and in this respect QED is the most successful theory in history, but this unfortunately still doesn’t tell us if it is an accurate description of reality. Some have the point of view that science is "only" about making accurate predictions. But the reason for getting interested in science, at least for me, is wanting to know what is actually going on.

[deeponjitbose]

I am a Undergrad Physics Major student. Wish I have been learning physics from professors like you. So well and smartly explained sir. Many Many thanks Professor Matt for explaining these stuffs so simply and interestingly

[jacksonburek]

Wow. Kind of reminds me of control systems diagrams, and how they can be converted to the system diff EQs

[ttul]

I don't always understand everything that you say. but you do, and it's very comforting.

[AtlasReburdened]

What did one approaching electron say to the other?




I only want a photonic relationship.

[ayoobewonders]

Quantum mechanics joke:

"A photon walks into the bars."