Lecture 9 | String Theory and M-Theory

[@euroroomer]

i am literally amazed such a university and such a professor of such caliber would offer this...for free. Tale about a commitment to education!

[@sherlockholmeslives.1605]

I didn't know that.

[@frankdimeglio8216]

@@sherlockholmeslives.1605 News flash ! Gravity IS ELECTROMAGNETISM/energy, AS E=MC2 IS F=MA. The Earth (A PLANET) is a MIDDLE DISTANCE form that is in BALANCED relation to the Sun AND the speed of light (c), AS the stars AND PLANETS are POINTS in the night sky; AS E=mc2 IS F=ma. By Frank DiMeglio

[@frankdimeglio8216]

Stanford University is knowingly and deceitfully lying about physics.

[@joabrosenberg2961]

Gravity in String theory; String on a surface 7:40; Ground state expectation value 16:00; Ricci flow 42:00; Einstein field equations 48:00; Compactification 54:00; Torus topology 1:20:00; Kaluza Klein particles 1:43:00; T (Torus) duality 1:54:00

[@frankdimeglio8216]

News flash ! Gravity IS ELECTROMAGNETISM/energy, AS E=MC2 IS F=MA. The Earth (A PLANET) is a MIDDLE DISTANCE form that is in BALANCED relation to the Sun AND the speed of light (c), AS the stars AND PLANETS are POINTS in the night sky; AS E=mc2 IS F=ma. By Frank DiMeglio

[@frankdimeglio8216]

Kiss...Keep it simple stupids.

[@PMaldeev]

"...it's a partial differential equation, partial differential equations are more difficult, but Partial was a very smart guy and he figured out how partial differential equations work"

[@isodoublet]

"Let him give the lecture, okay?" YES, thank you. That guy just won't shut up.

[@ZoeTheCat]

I think we were all grateful to hear that. Some people just love to hear themselves talk - despite not having anything to say. His stupid electronics clock analogy didn't even support what he was saying. Yeah, you can subdivide a clock, but it's still the same temporal metric.

[@isodoublet]

***** It's been like this every lecture in the series. Didn't anybody teach this guy that when you have a comment to make or a longer question you should leave it for after class?

[@ZoeTheCat]

gogerychwyrndrobwll Yeah I know, but this was his (our?) absolute worst moment. He's such a pompous idiot. It's the guy who gives him cookies right?

[@isodoublet]

***** Is it? I just assumed that was Susskind being eccentric. I mean, it's Lenny Susskind, he's allowed. That would however explain a lot. Lol, what a douchenozzle.

[@petergreen5337]

❤❤😂HAHAHA brilliant. That fellow is very IRRITATING and distracting. Bringing the cookies DOESN'T make YOU a teacher. JUST LISTEN like the REST OF US.😂😂

[@saikiranalvala502]

You sir...are a legend!!Thank you susskind sir...immense respect and thank you from India❤️❤️❤️

[@johnstfleur3987]

I AM HAPPY LEARNING FROM YOU. THANK YOU.

[@aristonxie6839]

OMG finally. After 9 lectures, something that's rigorous and mathematical.

[@johnstfleur3987]

THANK YOU PROFESSOR.

[@mik99D]

@UniversumExNihilo But M theory has to be able to describe all of the standard model as well. So it has to describe the colour force, which is Gell-Man's model. It also has to describe mass (Higg's field) and Gravity (Einstein's field theory but as a particle field). So regardless of who first came up with it. For string theory to ork it has to encompass all current theories and describe what we already observe.

[@DerMacDuff]

Sometimes I just watch these lectures because of Susskind, even if I don't understand what he is talking about.

[@crsohr]

I think they kind of unfairly dismissed that guy who was talking about two time dimensions. What's so crazy about two time dimensions compared to 25 space dimensions? Maybe the second time dimension is curled up so small that only small things can move forward in it, hence vacuum fluctuations!

[@tataltsal]

Initial value problems become ill posed

[@tataltsal]

@@jay.u ergo, the real world doesn't have 2 time dimensions

[@AnonYmous-spyonmepls]

​@@tataltsal Why not? It can be geometrically consistent, which a lot of our equations aren't and the whole point of string theory is to make everything geometrically consistent. Makes more sense than isolated logical constructs. 26 space is more logically consistent even with multiple time dimensions and in terms of logic spacial dimensions and time dimensions are identical. They are just mediums that every other dimension connect to. If a physical property has a function of time, that would just mean that there is one dimension we call time that the particular dimension connects to. If you boil it down the geometry clearly indicates that the concept of time is artificial. Anyway I found it difficult to put these ideas into words I hope you understand.

[@while_coyote]

How can a string cross itself on that cylinder? (around 1:39:30) There is no height dimension to the surface of the torus/cylinder (he made a point to mention this), and the strings are literally one dimensional, so when they cross, they'd cut each other. Otherwise, how do you know which one is on top of the other? (I realize he cuts them later when he describes winding number, but how did they cross in the first place?)

[@Stopa42]

+Mason Glaves I guess it's because there was only one compactified dimension (and one infinite, so in total it was 2D). If you have more dimensions, there is quite a lot of space to wind a string around some dimension without it crossing itself.

[@aqwertgbvcxz]

Mr. Susskind knows physics very well.

[@MatthewSuffidy]

This compatification thinking is sort of weird because every particle has it's own universe it seems, instead of a global compatification, unless you saw there is this sort of tendency for a dimension to close globally. What is useful here is that there are some ideas and maybe some patterns are actually witnessed somewhere, so you say there may be a string connection. Wave like observations at a macroscopic level is the happiest result of wave like mechanisms. Also it is hard to say how these strings go from being sine waves to any sort of thing and not violate the equations. Also I don't know why exactly they don't act with other strings in strange manners, like interference, and complex connection. I was really hoping to see that quantization was the result of integer like building blocks that just come together a certain way. It is strange by an arbitrary formation how atomic structure is so well defined. I don't understand how say, kinetic energy interfaces, and gets stored in an object.

[@petergreen5337]

❤Thank you very much Professor and class

[@Cemselvi1988]

58:14 ..... "let him give the lecture, OK?" .... BURN!

[@saikiranalvala502]

Shoopaah yaaa..burnnnnn😍😍😍

[@Silhouette93]

When will the next lectures be published online? Been watching my iTunes subscription since 8th of march :(

[@Funtasmia]

Thank you!

[@ryanlafferty5948]

Actually your proper time would be just fine. Just add another minus sign to the Lorentz metric (-dTau^2 = dx^2+...dz^2-dt1^2-dt2). In fact, adding that minus sign will give you everything you need to work out the dynamics. Play with it.

[@KolasName]

It is a very smart comment. I think such an approach can produce some interesting mechanics with, say, a tilting of a rest mass or something else. But a human time isn't an imaginary dimension (or two, 3...) with basic vector. It is effectively a single scalar - the Entropy of the Universe. Not even a scalar field, but a number for the whole Universe due to the quantum entanglement.

[@drdca8263]

Hm, what if you start with a classical string on a sphere (which, should be consistent, right? I'm not certain.) and then try to quantize that, instead of taking the already quantized string which was arrived at in flat space, and trying to put it into a sphere? Alternatively, what if you try to change the radius of the sphere in such a way while you vary n_max , the radius increases to counteract the "as if the sphere was shrinking "?

[@drdca8263]

Ah, wait, that second option would have the curvature of it approach 0, so it would probably just end up like flat space?

[@jonnymahony9402]

a sphere is localy flat

[@drdca8263]

@@jonnymahony9402 the curvature of a sphere is inversely proportional to the radius? Also, Merry Christmas!

[@dabrownone]

Haha interupting-know-it-all finally got called out lol

[@lidan9805]

A plank energy thanks for Professor Susskind brings me to the world of theoretical physics. It really inspired me a lot. But I'm a bit disappointed when i learn the idea of dimension compactification, it may to description of 4d world in extreme cases, just can't be the correct general description of the 4d world.

[@diffidussocrates466]

Fantastic Lectures, however, I cant see how a torus can be cut to give a cylinder, since the inner radius of the torus is smaller than the outer radius. Also, for the same reason, I think that if the cylinder were cut, it would form a trapezium not a rectangle (with, for example, the base representing the large radius and the top representing the smaller toroid inner radius)?

[@cmfluteguy]

Two dimensions of time would mean that proper time is not a valid concept. There would be 2 proper time clocks that run at different rates. Then there would be no valid rest frame concept.

[@wtj11]

Where's that guy asking about time as 2 separate d? I mean that's really sounded good

[@loren-emmerich]

Strings explain the motion of energy and matter in space, therefor it's called m-theory. Got it.

[@LLorfa]

The energy momentum of cookies. Yum yum

[@ryanlafferty5948]

Don't get me started. Well for one, E8 does contain U(1)xSU(2)xSU(3) as a subgroup. But it is huge! Its smallest irreducible rep is 248 dimensional. I suspect it is indeed more than a theory of everything: its a theory of anything.

[@zoltankurti]

You mean faithful representation. 1 with multiplication is a representation of every group, and it has certainly less than 248 dimensions.

[@johnstfleur3987]

I AM THE PROFESSOR.

[@msq7041]

Just wondering if anyone who understands this better then i do reads this, wouldnt that 1. Predict timeless particles which stand still in our 3 dimensions 2. Allow for extra dimensions which are not degrees of freedom but are only accessed by the angular offset of a compactified dimension

[@markell1172]

Maybe you rn dont mind it or already have answer, but 1) actually yes, and they have a name: "instaton". 2) if im not wrong thats the reason why a torus isnt the best compactification.

[@msq7041]

@@markell1172 thank you for the anwer! Im looking forward to learn more about this.

[@markell1172]

@@msq7041 you're welcome :)

[@superok4luv2u]

@Engravingsful string theory is not superstition it can be falsified by falsifying quantum theory or general relativity

[@rhainegraves7235]

Any resemblance s to one(s) static or nonstatic, living and or nonliving is a quantum coincidence. Earthly sol366 discernment and discretion advised.

[@gordanpoljak1897]

haha that look when he wants to go home but has to explain smth else 1:49:41

[@crsohr]

KZbin discussions are ALWAYS a bad idea, so don't feel obligued to respond. :P But you may be right, though I don't think it is as silly a case as was implied. Everything's 'obvious' until someone finds a better 'obvious' thing, like time being a vector with different components. Proper time would be unchanged, but the time time-like coordinate would not. Not saying it's right, just not silly.

[@whispermason8052]

So playing Asteroids the 1980's coin op is played on a topologically speaking toroidal surface. See Mom, told ya it wasn't a waste of time.

[@johnstfleur3987]

I AM THE PROFESSOR...

[@superok4luv2u]

@Engravingsful no it's not

[@johnstfleur3987]

5.

[@anthonydavolio981]

"let him give the lecture ok"

[@csmcmillion]

"and take it, to the limit, one more time."

[@Urdatorn]

Cue Scarface theme “Take it to the limit”

[@Jotun184]

This definitely doesn't djent

[@stevenparada5284]

the grad student read that in our paper and asked it to sound smart UCSD

[@AdrewFilms]

"If you want to know the future history of it..."

[@ДмитрийВербицкий-у7д]

Gonzalez Donald Davis Frank Martinez Maria

[@luizgustavolgss]

I was understanding general relativity and the geometry of the universe but this string theory i just gave up.

[@angelmorales2241]

Mire ha mi y tengo algo ke exponer sobre. Hoyente y su idioma lo construye con linias corta y linia larga y exsiste dos semi sircunfersia () coresponde a SEMILLA o CIRCULO o entra en anbito de paresido o o akello e in igualdad o paralelo de confiuso

[@angelmorales2241]

Mire ha mi y tengo ke exponer halgo sobre Hoyente a distansia local Juakin y Enxe y la otra exi ke falta mas los Primo (entran tanbien pero son contaminado ) SI TANBIEN pero meno por motivo porpula o anunsio no espiritu materia union no gana perdida

[@WarrenEden-u8c]

Anderson Jessica Harris Kevin Moore Timothy

[@brickowscki]

as ideia man

[@Dilaton100]

Prof. Susskind seems not to be a fan of his colleagues doing F-theory, they have 10 space and 2 time (alltogether 12 !) dimensions LOL :-D ...

[@johnstfleur3987]

I LOVE JEHOVAH.

[@johnstfleur3987]

I AM L.

[@aqwertgbvcxz]

Thumbs up if you understand.

[@johnstfleur3987]

I AM GOD.

[@johnstfleur3987]

HUMBLY SPEAKING

[@johnstfleur3987]

I AM THE GOD OF PEACE; JESUS CHRIST. JOHN 10:34.

[@johnstfleur3987]

STEPHEN CURRY IS GOING TO WIN.

[@naimulhaq9626]

Taking imagination to almost an intolerable level. Could be the greatest of Hawking's failures to expect the theory to explain everything although it explains nothing verifiable !?

[@ibreakkidslegs]

So the only geometries in which a string has a proper limit are the ones in which there are no strings? Wonderful

[@grunder20]

Really didnt understand what M theory is.