Lecture 5 | Modern Physics: Quantum Mechanics (Stanford)

[anakmudajaman]

I Love The Video Lecture 5 of Leonard Susskind's Modern Physics course concentrating on Quantum Mechanics It Can Increase My Knowledge

[imegatrone]

I Really Like The Video Modern Physics course concentrating on Quantum Mechanics From Your

[system0system0]

Why is he so smart ? Has he been genetecaly modified.

[arthurmee]

This series gets a great thumbs up from me. To be able to access such a valuable for free is something i shall forever be grateful for. I love this man's style and his accent. I'm European, so is this a New York accent?

[jamma246]

There is something that I don't understand:

When he is looking at polarisation, he states that a particle polarised at 45 degrees is |x>+|y> / (root2). But following the logic before, wouldn't this be the mixed state that would be equal probability of being one state OR the other? Shouldn't you technically create a new state which is 100% certain of being at 45 degrees to remain consistent?

[loopantenna]

@jamma246 In fact the photon has equal probability of being detected along x and along y, which is 1/2. The probability to detect it along 45 is certain. Any possible state can be represented in any possible base. A base is formed with orthogonal eigen vectors.

[jamma246]

I want him to be my dad.

[Emiffe]

I wish I attended Stanford. :(

[cowlicks666]

It'd be nice if these were organized by content

[dalcde]

0:35:00 Is the Psi(k) just an approximation because k will never be continuous?

[PanZajko]

Please, do I see this thing right?

The polarization along different perpendicular axes ( the x,y and their 45 degree rotated images, the 15,105 degrees and so on) is sort of an analogue to the momentum and position, right ?

Then, what corresponds to the NOT-polarized state??

OR

Do electric and magnetic fields of a photon oscillate ONLY in one plane each perpendicular to each other?

Does that mean that mean that at any given time a particle "shows" fields in ONLY one dimension?

[realCevra]

@PanZajko all transverse waves have a polarization (p.). it might be simple (linear, in on plane) or complex (2d, circular as mentioned in this lecture).

em-waves are mostly 2d-transverse, longitudinal em waves (plasma waves, without any p.) are rather a specialty and cannot be seen in free space for long.

[alecbrady]

@PanZajko

The polarization along x and y are mutually exclusive - if it's x, then it isn't y. But if it's x, then it might or might not be 45deg - prob (x'|x)=cos(x-x'), where x-x' is the angle between the two directions.

The NOT-polarized state doesn't exist for individual photons - it's just what happens when you have a beam of light whose photons are polarized in random directions.

HTH

[FlamingPope]

View count decreasing at geometric rate throughout lectures. lol

Seriously - Susskind is the best QM teacher ever >_<! Just goes to show how confusing QM still is.

[bhigr]

The polarization example is good. One remark: If the 45° photon goes through the x-polarizer then the exiting photon is x-polarized. In this way the measurement changes the state of the photon.

[DasKrabbe]

@bhigr

... Not really, you could explain that classically.

[bhigr]

@DasKrabbe You can explain single photon polarization classically?

[mechapple]

all hermitian operators are observables? 1:48:14. really?

[bhigr]

@mechapple All observables are hermitian operators.

[FlamingPope]

@mechapple Yes, all hermitian operators are physical observables. Meaning you have the *ability to experimentally measure them. Your only limited to the money and technology used to take measurements and your own ability to reason through what they mean physically.

[QuaternionEM]

I've had some very, very good professors and Susskind is as good as the best of them...............at lecturing...................

When he explains the nature of commonly seen factors (like 1/(2*pi) factor

that occurs as we move from a Kronecker delta to a Dirac delta) it really is an epiphany for me.

Good, good stuff..............I watch these lectures every night now.

[joppadoni]

lenny is a shit teacher. however its all we have outside of any tutionioned state. so i love him. i also love him because like most quality minds when trying to explain anything, be it obvious and easy or otherwise, he struggles sometimes to explain. repeated viewing usually gets it i think. i hope we get more and immmm glad for them. dont hate me coz i can say shit and love in one too long a paragraph.

[luzzie9]

Always amazing how a master teacher can make a complex topic appear easy.  If you cannot learn quantum mechanics from Susskind, you never will.

[cmfluteguy]

Susskind is like most physics professors I have had. He loves his topic, and he thinks about it an awful lot.

Physicists are so devoted to understanding things, that they understand how to make things understood!

Ask an "economist" do describe a financial "derivative" if you want to see the difference!

[akudigobo]

thank you so much !!!