Lecture 4 | Topics in String Theory

[@freesoul6122]

Simply it's wonderful to hear this great man speaking, KZbin is a bless, thanks Stanford KZbin team.

[@joabrosenberg2961]

Sometimes a cigar is just a cigar :-) 15:00; BH Singularity 41:00; Past Horizon 50:00; Penrose diagram 1:05:00; BH Penrose diagram 1:15:00; How are BH made? 1:23:30; Birkhof theorem 1:25:00

[@Dexteritye]

I wish i was in this Class because you can't have the actual feeling in this class with this video, and it gives people a feeling to learn much more.

[@PMaldeev]

"So once Alices' feet are behind the horizon she has two alternatives: falling with them, no problem, nothing unusual, or stay out of the black hole and she will be deFEETed" 40:14

[@BerikVisschers]

From the era wherein dad jokes didn’t exist yet 😂

[@erwinmarschall2465]

007:10 "bifurcate" from latin: bi (two), furca (fork)

[@SalvatoreIndelicato]

Una bella lezione chiara e scorrevole

[@GunsNRosesbitches]

@x1x2x3ct He wore that because he was invited at a TED event at Caltech. he spoke about Feynman

[@jreedmcu1]

thank you!!!! i have told people that when we see something we are viewing it in the past relative to the person.... i just wish i knew the math to explain it...

[@SimonJackson13]

electric charge and reverse effect. Not orbits, but electron repulstion. Like charges attract in revesre, so orbit structure is different.

[@eligraham55]

Great lecture.

[@snjsilvan]

It seams time invariant equations would mean that if a thing happens, then (time being one dimension) to go backwards would simply be to undo (and unlearn) what had happened. Alice comes out, but neither of them remember her going in to begin with. No? Sorry if I'm just stupid and/or confused :n)

[@Shockszzbyyous]

I must ask, what is the difference between propper and normal, like propper distance and normal distance, propper time and normal time ...

[@Stopa42]

+Shockszzbyyous there is nothing like "normal" time or distance. However, in relativity there is distinction between coordinate time/distance (which is just some made-up quantity which itself doesn't have any true meaning) and proper time/distance (which is actualy something you can directly measure, hence it is a physical concept). The reason for this distinction looking strange is simple: In non-relativistic case proper time/distance and (usual) coordinate time/distance are the same.

[@josephlau13d77]

proper time is a Lorentz scalar, invariant in coordinate systems, it is the proper time interval between events in a world line/timelike separated events. Worldsheet was actually coined by Susskind in explaining string theory.

[@Dyslexic-Artist-Theory-on-Time]

Could quantum mechanics represent the passage or Arrow of Time? This theory is based on just two postulates, 1.The first is that the quantum wave particle function explained by Schrödinger’s wave equation represents the forward passage of time or Arrow of Time itself photon by photon, quanta by quanta or moment by moment. 2. The second is that Heisenberg’s Uncertainty Principle that is formed by the wave function is the same uncertainty we have with any future event.

[@longalexislong]

No, It doesn't. The ever increasing amount of entropy represents the arrow of time, all other physical processes work the same both backwards and forwards in time.

[@Carn1feX616]

@grunder20 The thing Sheldon Cooper is always talking about :P

[@mmartin5816]

Wait, shouldn't the event horizon of the black hole be represented as a cylinder? The way he's got it drawn (as a two cones), doesn't that imply the event horizon is expanding at the speed of light?

[@crazyumesh]

+M Martinski The even horizon of a black hole is a lightlike surface - it's not like an ordinary surface. And as you correctly observed, it is expanding outward at the speed of light.

[@grunder20]

what is string theory

[@ruchi9917]

A theory about strings

[@cloffff]

@mccdotedu Feynman has been dead since the 1980s.

[@Dyslexic-Artist-Theory-on-Time]

@sn1pe352 That is good because I am on KZbin trying to promote my theory on the dynamics of light and time (Quantum Atom Theory) so I need to be seen!

[@aqwertgbvcxz]

Yeah, you will be wondering for a looooong looooong time. lol

[@jreedmcu1]

you make me wanna cookie...