Causality and Propagators in Free Klein-Gordon QFT

[@tillerbrady6624]

At 10:00, the change of variables V shouldn’t have a square on it for (x-x_0)^2.

[@NickHeumannUniversity]

You are correct! Thank you for noticing! I'll pin this for future reference

[@quantumworld9434]

I've watched many lecture series on qft but your video lectures gave me proper understanding of qft.

[@NickHeumannUniversity]

Thank you! I do my best to make the lectures easy to follow

[@RobertBabani]

The best introduction to Quantum Field theory I have ever seen, you have implemented what I have been wanting to see for 61 years, using Bob’s Baby step approach to derive the propagator for the Klein Gordon Equation, thank you so much, if you are ever in Albuquerque New Mexico, let’s meet at the Olive Garden and I’ll have my favorite, fettucine alfredo with broccoli, you totally rock, thank you, thank you

[@NickHeumannUniversity]

Thank you for the kind comment! I'm glad you enjoyed the lecture! Unfortunately, I'm half a world away, but I am honored by the offer!

[@billdicklechips]

You good sir are underappreciated. This helped immensely with my QFT homework.

[@nirajangupta7406]

Finally, Nick sir remembered his channel's password😉😉. Anyway, I am so happy you uploaded a QFT video after such a long time.

[@kevinowens1]

You were born to teach Physics my friend. Please keep going. You saved my neck in Electrodynamics. I wish you had taught other chapters like 3, 4 and 5. What you gave was priceless! it helped me understand it, not just work problems. Thank you

[@NickHeumannUniversity]

Thank you so much! I'm glad I was able to help!

[@erikstephens6370]

50:53-51:40, Keep in mind, this transformation is only possible if x-y is a spacelike vector and not a timelike one. This makes our commutator go to zero for x, y that are too far apart to "communicate" according to special relativity. Doing the integral for the timelike case does not give zero (it doesn't converge interestingly enough).

[@jasonpalin4521]

Glad to see you back - and for QFT!

[@dondada2096]

Thank you so much for uploading again!

[@HansTube1]

Thank you Nick. Hopefully we wont wait another 8 months for the next video 😄

[@kevinowens1]

Thanks!

[@NickHeumannUniversity]

Thank you!

[@zanxder7536]

I recently had my QFT exam's it would have been great if it was uploaded earlier.

[@zanxder7536]

thanks for the awesome QFT content though.

[@NickHeumannUniversity]

My apologies. It's been a tough year, and a lot of things hindered me from making videos. I will do my best to stay on track now!

[@petershotts8571]

Thank you so much for all your videos. I really appreciate your clarity and detail. I am confused, however, when you consider the case of D(x-y) when x0-y0=t whilst xi-yi=0. I follow the maths when you show that as t tends to infinity x0-y0 is finite. However I do not see what the problem is. If the zero component of x is the time component why shouldn't there still be a non-zero value for x0-y0 as t tends to infinity? Given that the particle remains in the same place, why does this contradict causality? Peter

[@harshit3602]

Plz upload full qft

[@luisbielmillan8467]

very very useful. My teacher just presents the conclusion with barely any explanation ...

[@Dirac_0]

how do you find the exponential decrease for time like case. When you let t goes to infinity. Is there some kind of derivation ?

[@Dirac_0]

i found it :)

[@SagnikSaha-cj6nl]

Thank you very helpful

[@onnilattu9138]

Awesome videos but brother PLEASE go back to the dark background lmao

[@tillerbrady6624]

Why do you always say “propagate in an arbitrarily short period of time”? Is there a reason you add the arbitrarily short?

[@NickHeumannUniversity]

It means "in any short amount of time", meaning that there is no limit, and thus, that it can surpass the speed of causality (speed of light)

[@youtubesucks1885]

Will you do some vidoes about Yang-Mills theory and interacting QFTs? As far as I am aware every video until now was about the trivial free case.