Lecture 2: Symmetries and Conservation Laws

MIT 8.323 Relativistic Quantum Field Theory I, Spring 2023
Instructor: Hong Liu

Definition of symmetries, different types of symmetries, statement of Noether’s theorem that connects continuous global symmetries with conservation laws and its proof, concept of quantum fields

License: Creative Commons BY-NC-SA

[brianchoi]

@21:50: Noether's Theorem in high school. Great.

[Arevilov]

This is great! I was recently looking for video lectures on QFT and then I saw this uploaded here just 2 weeks ago!

[carlesv]

Thank you for this lecture, professor Liu. You are stating very clearly what the transition from CM to QM and then from QM to SR+QM=RQM=QFT implies and which conceptual key points we must keep in mind. Good job and thank you again

[naghdezartoshtian]

@mitocw Could you please also record QFT II and QFT III?
that would be really great

[KipIngram]

This is great stuff. I think my big problem in the past has been trying to consume QFT materials with the Schrodinger picture in mind. My eyes wind up glazed over. I can see I need to go back and get more familiar with the Heisenberg picture.

[DitDitDitDahDahDahDitDitDit]

The camera operator is ruining these videos by panning back and forth and by bad framing of the scene: the scene consists of both the lecturer and the contents on the boards. To be more explicit, we get blurring when the camera swings back and forth (maybe image processing can fix this), and then, in the close ups, we see the lecturer pointing to equations that are outside the frame. And explaining derivations requires that one is able to see the equations that lead up to a conclusion. If you go back and look at Gilbert Strang’s videos, this problem was solved by using a wider camera angle. These videos require a different sensibility than one might use in filming a movie.

[LydellAaron]

1:17:39 I don't fully comprehend infinitely negative interpretation.
That equation looks like more of a circle if you treat the p and m as oscillating states, p=cos(..) and m=sin(...) then they are on a unit circle if you apply r=sqrt(cos^2(theta) + sin^2(theta)). r is a radius energy level E. The +/- being more of a conjugate for a reflection.

[hr]

@30:05 is this assuming measure does not transform?

[J_Lau]

@mitocw can problem sets and notes be used openly anywhere?

[opkimo]

OK. It’s interesting. But I totally have no idea about those equations and what’s their meaning if there is any.

[yliuos]

How long is a lecture in MIT? Prof Liu always stopped at an odd time lol

[J_Lau]

also what year is this course generally aimed for (eg grad)?

[EricPham-grpg]

How we compare matter and space in symetry or balance ? So negative goemetry or antimater is real

[gihf]

Damn so MIT grad students also act dumb as fuck questions (no problem with that, just good to know they’re normal)