Solving the Impossible in Quantum Field Theory

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Previous Episode:
Feynman’s Infinite Quantum Paths

The equations of quantum field theory allow us to calculate the behaviour of subatomic particles by expressing them as vibrations in quantum fields. But even the most elegant and complete formulations of quantum physics – like the Dirac equation or Feynman’s path integral - become impossibly complicated when we try to use them on anything but the most simple systems. But physicists tend to interpret “that’s impossible” as “I dare you to try!” And try they did. First they expressed these impossible equations in approximate but solvable forms. Then they tackled the pesky infinities that kept appearing in these new, approximate equations. Finally, the entire mess was ordered into a system that mere humans could deal using the famous Feynman diagrams.

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

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[markchadwick]

This series keeps getting better. Finally, a lecture that isn't afraid to put up equations, but also doesn't use them exclusively for describing real interactions (like my Physics professors did).

[antoniolewis]

Kudos to you for wrapping up multiple Nobel Prize concepts into 15 minutes. That is badass!

[yolanankaine]

Matt : “But if you try calculate the self energy correction to an electrons mass using QED, you get that the electron has infinite extra mass. Ammm...This sounds like a problem”
Haha I don’t know why this amuses me so much. Just picturing the physicists working on this calculation then getting infinity as the answer. Then all of them just sitting there, staring at each other like “ahh.. crud”

[zjr]

Your guys work to make this type of information available to anyone willing to follow your videos is outstanding. I'm sure these lessons will go on to change lives of countless people. Thank you for all of your work and dedication.

[jona]

This is pretty amazing. To think you're actually making QFT videos for laymen.

I didn't think it was possible. It's by far the toughest topic I have ever studied.

[karstent]

Matt, you have the best tone, mood, wording, and rhythm for explaining these things I have heard up until now, Thank you (~8

[TheRogueWolf]

Man, I'm glad these weird quantum mechanics rules don't govern regular physics. Imagine just going to a friend's house:
"Hey, sorry I'm late. The Interstate was closed so I had to take a shortcut."
"That's okay. Did you take Vine Street, Route 44 or the old dirt road?"
"Yes."

[nachannachle]

Oh, I'm glad I caught this series now, rather than from its beginning. Quantum mechanics are absolutely FASCINATING. Bear in mind that this statement is coming from a non-physicist, non-mathematician, non-scientist, non-engineer person.

I stumbled upon PBS spacetime while trying to dig into Einstein's "E=mc²". It has been a year and I'm still determined to absorb every bit of the discipline, from Classical mechanics through to Cosmology.

Simply put, this channel is brilliant at popularising core concepts, while providing relevant links to explore the subject in detail.
I have to say, Feynman's path integral is giving me the hardest time because it is both extremely logical and complex yet extremely unassuming and abstract. It's hard to believe that someone could manage to tidy up the QM mess in such elegant ways.

Essentially, I've got more exploration to do...while waiting for the next episode of the QM series on PBS Spacetime! :)

[markchadwick]

I’ve subscribed to this channel for years. This video is still my favorite one.

[donttouchmycoffee]

Matt, I love what you and the folks at Space Time are doing and have watched all of the videos dealing with QM, QED, and Special Relativity. I've watched them over and over, since I am a middle aged man with no background in higher maths or physics. I wouldn't want the episodes dumbed-down; I just with I could understand the maths and the very weird QM concepts more.

[Locedamius]

Quantum Physics: If it makes sense, you're doing it wrong.
Gotta love it! :)

[spacebread]

Can we please all agree to call Feynman Diagramms Feynman-Doodles from now on? :)

[sansvoir]

Hey, Space Time, loving this recent series on the quantum realm. I really appreciate the deeper looks than you normally get with pop-science, while keeping it firmly within layperson's land.

[while_coyote]

Could you go more in depth about how fields couple someday? This stuff is fascinating, never stop!

[EvulDali]

These videos are just right for me. Not too dumbed down to make them fail describing complicated phenomena but still not too technical that a non physicist like myself cant understand anything. Fantastic!

[JoshuaHillerup]

Now that you're covering the Standard Model, and you've already gone over a lot about General Relativity, will you do a video about some of the details of the problems that come from combining the two?

[BrendanSteffens]

You guys are doing a fantastic job in particular with these QFT videos, in my opinion. I do hope that at some point in the future you will address the Feynman "antiparticles traveling backward in time" interpretation, and what came of that, historically speaking.

[RobCod]

Never has there been a faster video click time than when I saw the new Space Time video. I love your work mate, I wish I could have a personal conversation with you face to face matt, keep up the good work you bloody tank Cx

[Sam_on_YouTube]

Feynman's sum over histories is among the most underrated discoveries in physics. I used it in my philosophy thesis in college to show how even if you believe that only the present exists now, you can still take thw past as real because every past that COULD lead to the present actually DID happen. Though for macroscopic events, there aren't really important distinctions between one history and another.

[ristopaasivirta]

"You are a hack!"
"Oh my, thank you very much."