Lecture 7 | String Theory and M-Theory

(November 1, 2010) Leonard Susskind discusses the specifics of strings including Feynman diagrams and mapping particles.
String theory (with its close relative, M-theory) is the basis for the most ambitious theories of the physical world. It has profoundly influenced our understanding of gravity, cosmology, and particle physics. In this course we will develop the basic theoretical and mathematical ideas, including the string-theoretic origin of gravity, the theory of extra dimensions of space, the connection between strings and black holes, the "landscape" of string theory, and the holographic principle.
This course was originally presented in Stanford's Continuing Studies program.
Stanford University:
www.stanford.edu/
Stanford Continuing Studies Program:
csp.stanford.edu/
Stanford University Channel on KZbin:
/ stanford

[@stanford]

@esy87 Glad you're enjoying our videos.

[@joabrosenberg2961]

The propagator (Feynman path Integral); Renormalization 10:30; String worldsheet and worldtube action 21:00; Invariances of the Lagrangian 38:00; Laplace equation 42:00; Conformal mappings 51:00; Joining strings 1:00:00

[@qwadratix]

I am once more amazed at just how good this guy is at teaching. His explanation of Laplace's equation and Conformal Mapping is just masterful.

[@HughesMath1]

He was the advisor of Dr. Amanda Peet. She talks about String Theory too.

[@slyy4096]

masterbution it is

[@PMaldeev]

"...and then you integrate it over all possible surfaces. I'm not gonna try to draw a complicated surface. Well, I tried, I failed" "...or you can do what a physicist would do and say: "Analitically continue!" Analitical continue - last refuge of scoundrels. And we are going to be scoundrels" "...the other form is sometimes called the Polyakov action though it has nothing to do with Polyakov, it was invented by me...which Polyakov keeps constantly keeps telling people"

[@user-gj7vp6wk3e]

GOOD JOB, PROFFESSOR LEONARD SUSSKIND.🖖✌️👌🤙👍

[@nullgeodetic]

There must be a commandment somewhere along the lines of: 'Thou shalt never take credit for your own actions' :-) I cannot thank you enough, Stanford and Prof. Susskind, for posting your lectures.

[@cliffhanger625]

Excellent job Stanford and Prof. Susskind. A lot comes together in lect. 7.

[@SalvatoreIndelicato]

Magnifica impostazione mediante l'analogia tra fisica classica, quantistica e teoria delle stringhe. In nessun libro o corso ho trovato una presentazione così efficace quanto semplice e profonda

[@while_coyote]

I really wish people would wait until the end to make comments or ask questions, I've been watching dozens of these and they keep throwing him off just as he's getting on with the lecture and it takes forever to be back on track. Go faster!

[@esy87]

You guys are awsome. So is Mr.Susskind. Thanks for uploading.

[@Unidentifying]

I love these! He makes it so easy

[@slyy4096]

thats a lie detection video for intelligence test

[@randymartin5500]

Also known as the Wick rotation at 19:00 to flip real time to imaginary time to deal with the UV divergence

[@grunder20]

Now getting the hang of the theory.

[@user-fc8xw4fi5v]

yeaaahhh man, the analytic continuation stuff at the beginning really starts putting it all into perspective.. it also justifies the tachyonic condensation (the 26 dimensions) technique discussed back near the beginning of the series!

[@sb123sunil]

the doubts the students ask are not audible so sometimes its confusing that what are you answering to.

[@otonanoC]

Why is he covering this material in the 7th lecture? I was expecting these principles at the beginning.

[@jayejayeee]

i enjoyed this vid

[@perjespersen4746]

3:00 Action principle

[@PMaldeev]

"...and the whole exponential magically looses its eye" ))

[@Dilaton100]

@nullgeodetic Good joke, LOL :-) Maybe one can then not be blamed for one`s actions too, but for those of others ;-) ...? Watching thise lectures is my favorite hobby at the moment :-))) Good to know that there's a follow up course after this one, called "Topics in String Theory". The "trick* to make the path and worldsheet integrals convergent is called Wick rotation I think.

[@ericbradshaw888]

I have been following these lectures and some of your other physics lectures for some time now, well doing the mathematical and other leg work... I can safely say now "I know Kung Fu" Many thanks for this

[@sb123sunil]

plz repeat the doubts that the students asked and then answer

[@RohanArora]

I'm 13 I love the science but wish I could understand the math

[@isodoublet]

The math really isn't that sophisticated. Up until this point he has only used some basic ideas of calculus with a passing mention to special functions. This is accessible to you if you try to learn it on your own. The "hard" part is really the physics: he has been assuming that you have quantum mechanics ideas down pat, which you could also learn if you were so interested but it's spread out over a lot of books. You could take a look at Griffiths' for an introduction, it's very fun to read. Good luck in your studies!

[@TheHeretiCan]

you just have to try to understand. it isnt that complicated. dont just listen. try to understand what he means. try to visualize it.

[@jxchtajxbt53]

One of the problems with Lenny's lectures is he repeats himself and goes slowly often times making simple mistakes. This breaks the continuity of his discourse as he keeps going back and forth. You definitely need to learn differential, integral and vector calculus before you can really follow the math. But there are much better videos to learn those concepts from. These math techniques are most easily understood in the context of basic classical mechanics and electromagnetism.

[@brainoutyakabrainout]

So how do you feel now, 3 years later? When I don't understand something, it's usually because the vocabulary is strange, so I just listen over and over even sleeping to the words. That's how we learned as babies, too. But how do YOU feel about it now?

[@lucasthompson1650]

I'm curious how you feel about it now as well. When I was 13-14 I spent the better part of a summer and many a weekend with library books (this was the mid-1980s) on subjects like vector calculus and tensor mechanics just so I could do the math to understand more about black holes, relativity, QM, and string theory (which was HUGE in the mid-80s). It was difficult, but my curiosity kept me stubborn. As a bonus, it provided me with skills that allowed me to skip grades in high school math and physics like stones across a pond, but I'm also still branded as a "math guy" among my friends - I am not, nor have I ever been, a "math guy", I simply took the time to learn a little more math than other people.

[@HughesMath1]

21 minutes in. What does this mean, "Turning time on its side.'

[@BerikVisschers]

I’m no expert, so excuse me if incorrect. This means you multiply by i, which is mathematically the same as a 90 degree rotation.

[@theultimatereductionist7592]

Please: SHOW US WHAT HOMEWORK PROBLEMS YOU GIVE YOUR STUDENTS! NOBODY can learn WITHOUT DOING. You have to DO the homework exercises by the bazillions to understand this stuff.

[@Mehlsack93]

36:45 Lenny, Joseph Liouville died in 1882, when Einstein was already alive!

[@VsauceInspired]

WHY is there DISLIKES?!

[@joefromzohra]

string cookies

[@miloyakavetta4898]

m theory creates space and time.

[@stevenmarshall1119]

guitar-string theory and m-theory are wrong