Lecture 3 | Quantum Entanglements, Part 1 (Stanford)

[4kx]

Could me some one tell me, what job is waiting for me, if I change my studies to theoretical physic? I'm now on mechanical engineering, is it worth to change the studies?

[alecbrady]

@4kx I can't tell you what job would be waiting for you; but I can tell you that - if that's the question you want to ask - you should stick with engineering. If you're going to change, do it because you love the subject, not because you can sell yourself at a higher price.

[4kx]

@alecbrady since I was a kid, I loved know how things works, how machines, electronics, toys works - very often I crashed them to see what is inside. The universe is the most complicated toy we can imagine, understanding how IT works probably is the most beautiful thing in it. However, does physicist are happy? Dealing with numbers, models make them happy trough whole live?

[alecbrady]

@4kx I wish I knew what could (reliably) make people happy. But, yes, I think this is a better question than "what job is waiting for me?".

[phuimath]

As a student who is first exposed to quantum mechanics, without a doubt this is an excellent series of lectures.

[seadarie]

I bought books on this topic but this is much better as an introduction. It's a help to understand the Schrodinger wave viewpoint before this imo as they are all related.

[grunder20]

complex and modified. hard to absorb.

[Aure217]

As a graduate in mathematics from Cambridge, I find the method-explaining parts to be irritatingly slow (but necessary for the intended audience - I don't dispute that). Even so, I'm still glad to see such an enjoyable series of lectures available for free.

[Boepyne]

@SuperWorldwide23 Well, I'm no expert, but to give you the gist of it; a quantum value, like spin, only obtains a particular value in the very act of measurement - so the rather abitary value that falls out when measuring one particle will be instantaneouly reflected in the other. Sorry I've not responded 'til now, I forgot all about this until my attention was drawn back by another response.

[Ferrus91]

@quaternionEM: It's frigging hilarious, some of the the audience in these videos really don't deserve to be taught by one of the founders of string theory.

[1989AndyL]

At 1h33m, should the x and y be the other way around?

[funkyiceman]

Does anyone else find Leonard Susskind hilarious?! It's so funny when he rubs out |a> and |b> and then immediately forgets which one was which! Don't get me wrong I love these lectures all the more for it! He's obviously so clever he's thinking about stuff other than a's and b's but the humanity of it makes me laugh, as with "Chocolate Chip"!

[1isaacmusic]

15:21 " chocolate chip " :)

[bubba5656]

did he muddle up his eigenvectors at 45:00 ish

[quantomic1106]

00:34 the guy asking a question sounds like Stephen Hawking. :)

[nejtilsvampe]

I'm alittle confused, why does the title say Part 1 ? I mean it's 2 hours long, is there a part 2 ? :P

[Kisa8092]

Goods

[tfy6600]

Does the fact that there is only 3 Pauli spin matrices (sigma 1, 2 & 3) means that there could only be 3 dimensions of space or at least 3 observable dimensions of space, i.e. the higher spatial dimensions, if exists, must be unobservable? It seems that if there is a 4th spatial dimension, then we need a sigma 4 for calculating the probability.

[matharoofmaths]

i loved the ending of this video

[QuaternionEM]

Good gravy!....lol @ the guy around 00:58 who has to explain to the whole

class that he knows the geometric interpretation......

[horrabletypoe]

Aw man, cis(theta) notation gets no love? :(

[dismember1349]

glad i took linear algebra

[luzzie9]

For Susskind doing a proof of orthogonality is as easy as me doing long division. Yes, I understand long division but I would probably make some mistakes in the process and I am sure some grade school kid could do it better.

[machobunny1]

What an incredible find. There is no way in the world to match the quality or value of the material being presented here - if you actually want to be conversant in quantum mechanics without spending your life. Given all that, does anyonw know which of these lectures actually gets into a discussion, definition, manipulation of entangled particles?

[Boepyne]

Suprisingly, he makes a real mess of the orthogonality proof at 1:04:50.

When he reverses 'a' and 'b' in the second equation, he's already conjugated, so he should have: (blMla)=B*(bla)

and not

(blMla)*=B*(bla)*, the B here standing for the eigenvalue, I can't type lamda.

Then all he needs to do is show that B*=B as B is real.

I hope this helps for anyone as confused as I was!

[Boepyne]

Ha! I just noticed that the corrected proof has appeared on the whiteboard after the break; someone must have pointed it out over coffee.

[fassterblade]

@Boepyne you are correct

[LennyLeonard85]

@Boepyne He makes the mess because he's influenced by the audience. If you're next to a blackboard (or whiteboard ;-) ) you lose the overview. I don't like it if people try to correct you who don't know what they're talkin' about. About the proof. I think you're not done after B*=B. What you really have to assume is that a/b is equal to b/a. This is true for real numbers. And than you are at the same point where he makes the fault. Maybe it's possible to show it for complex numbers too.

[TheLiberalSoup]

@Boepyne

ah, thank you for clearing that up.

[dojokonojo]

haha i love this, i dont go to stanford but i get to hear lectures from stanford professors, way awesome

[keggerous]

im so confused....fuck i wanna learn more math!!! i dont think im dumb but im not a genius i guess either.

[mephistophile33]

i know. its sooo hard to wrap my head round this maths. especially because there are so many names to learn.

[fuhongwei141]

This lecture series is great, but I can't watch this one.

An error occured, please try again!

Somebody fix it, please!

[AtomosNucleous]

just refresh

[fuhongwei141]

hmm, tried.

Dont' work!

[wrdeboise]

I like that this professor seems down-to-earth and makes this stuff accessible to normal people. I probably will now call any directional property in real space a "pointer" and any quantum state a "vectors". I won't confuse the issue by trying to figure out what these conceptual states represent, even though the professor explained them as having some sort of directionality i.e. up or down.

[eedahl]

What's good to remember is that mathematically, they're the same. They're all members of vector spaces (like a plane) over fields (like the real numbers), with respect to some basis (x,y) etc. It's really cool when you get into it. Get a book on linear algebra (like "linear algebra done right" and you'll see what I mean.

[davidwizard2006]

professor susskind is one of the most eminent professor that make the complex concept easy to understand

[Mazmatickz]

I see most students confuse quantum state vectors with spatial vectors. Quantum state vectors are abstract representations of states in a quantum system, spatial vectors define certain points in space, however quantum and spatial vectors share some mathematical definitions and thus can be manipulated in similar ways, but are conceptually distinct from each other.

[stratelite]

This guy eats a lot.