Watch this first! Advanced quantum field theory, Lecture 8

[@RaviSingh-on2qr]

THE UNDERTAKER, teaching qft.

[@vishalrao7010]

😁

[@javierrendon2194]

I've seen many amazing lectures on QFT (Coleman, Tong, etc), but this are the best I've seen on these topic of renormalization and other topics also. Lectures 8 and 9 on this course on QFT2 and the renormalization lecture in your QFT1 (don't remeber the number of that lecture) are the best material available. Thank You very much for sharing.

[@renzotamirovillazonscholer5666]

OMG! This lecture is pure gold. I remember taking a Harvard QFT course, I kept quiet and calculated, it went well. But I never understood what I was doing until seeing this video, finally! Thank you so much!

[@UnforsakenXII]

What a lucky scholar to take it at Harvard. I'm hoping that Berkeley lets me into their class this fall. : D

[@VPN14494]

the philosophy behind renormalisation was very elusive to me, at best I could do calculations... Now I understand better. Brilliant lecture. Thanks Tobias

[@Simonchongqing]

Amazingly clear presentation of the renormalization theory! Thx a lot!

[@oguzhanyucel6257]

Perfect Bro! But please try to use bigger letters. We can not see it. Just an humble idea: maybe you attach the corresponding notes below.

[@Mvu6]

Wow, you are doing important things! Thank you very much!

[@UnforsakenXII]

I just realized that this is a summer course. They don't offer summer grad courses at UCB unfortunately.

[@madhavestark3173]

This is weird. But I am thinking of attending physics grad school at UBC. Mind giving some advice?

[@UnforsakenXII]

@@madhavestark3173 UBC or UCB?

[@madhavestark3173]

@@UnforsakenXII my fault....I m dyslexic and read it as UBC

[@UnforsakenXII]

@@madhavestark3173 No problem. Good luck with your application nonetheless!

[@rafaelbendavid4041]

Dr. Osborne. I have a question: that integral I=2iC9sqr(k)/2 appears to be a complex function. is that problematic?

[@tobiasjosborne]

thankyou for your comment. I am not sure which integral you are referring to? (What is the time stamp?) If it is the integral I = 1/2(-i\lambda)^2 (i)^2 \int ... etc. then this is not a problem: this integral appears in an expression for a probability amplitude and hence may be complex. (The probability we get by taking the absolute value squared will be positive). I hope this helps; sincerely, Tobias Osborne

[@rafaelbendavid4041]

@@tobiasjosborne , 1:18-19 I=2iClog(k^2/2). Yes, that makes sense . Thank you!

You are doing this like a genius you know :-) tnx man

[@arjunkolli992]

I might be being stupid but isn’t the inverse temperature directly measurable because the temperature is directly measurable so it’s not a parameter? Excellent video btw

[@tobiasjosborne]

Many thanks for your comment. I would say that, for gapless scale-invariant systems, the temperature is measurable up to an overall scaling of the energy. (That is, the temperature is only defined once we've chosen an overall energy scale.) This is analogous to measuring energy where we can only measure differences: we need to set the zero point of the energy before we can measure energy. I hope this helps. Sincerely, Tobias Osborne

[@samreenzaman8112]

hi , can someone please recommend a good book/notes for more mathematical description of renormalization of phi cubed or phi four theory for someone self studying

[@MrMas9]

Useful QFT books I found are Ryder, Schwarz, Srednicki

[@mattmolewski7475]

Thank you so much for sharing these.

[@davidhand9721]

I generally like this line of reasoning and it's a good observation, but explanation is not strictly equal to compression. A compression would be a theory that describes and reproduces every data point you have - but that's the limit. It can't theoretically generate predictions, and predictions are a better metric of understanding.

[@nujuat]

Wow, I actually understand this now. Thanks :D

[@markkennedy9767]

This dude has some serious blackboard game. The philosophical prelude is interesting so far.

[@aueltis1894]

May I ask how did the differential equation in 1:27:30 arrive?

[@tobiasjosborne]

If I remember correctly, I believe one differentiates both sides of the equation for M wrt K_C. Since M is constant you get the DE.

[@wulphstein]

We should talk about the physics constants.

[@georgiossmyridis6145]

Absolute Legend. One question though, what does he exactly! mean by operational meaning of a variable.

[@tobiasjosborne]

thankyou for your comment. The definition of "operational interpretation" (or "meaning") I am using here is that there exists, at least in principle, an experiment that is capable of measuring the quantity or variable. E.g., a global phase in QM has no operational meaning or interpretation because there is no experiment which can measure it, even in principle. I hope this helps. Sincerely, Tobias Osborne

[@jonashartmann6687]

Great lectures. For some reason the video stutters for me which is a shame

[@tobiasjosborne]

Many thanks for your comment. The stuttering might be due to the quality settings overtaxing your computer. Try watching at a slightly lower quality to see if the problem persists. Sincerely, Tobias Osborne

[@kilianklaiber6367]

Great lecture, but the elaborate justification for "subtracting infinities" doesn't convince me.

[@shayangfkk7948]

wow amazing wish I have found you sooner

[@aeroscience9834]

1:20:00 I don’t see how this is correct. Taking s=0 leads to a divergence even with finite k_c, but that shouldn’t happen.

[@aeroscience9834]

Unless m is zero

[@magnuswootton6181]

REALLY GOOD LESSON!!!!

[@renormalization]

Fantastic!