Advanced Quantum Mechanics Lecture 5

(October 21, 2013) Leonard Susskind introduces the spin statistics of Fermions and Bosons, and shows that a single complete rotation of a Fermion is not an identity operation, but rather induces a phase change that is detectable.

Originally presented by the Stanford Continuing Studies Program.

Stanford University:

Continuing Studies Program:

Stanford University Channel on YouTube:

[joabrosenberg]

Fermions and Bosons; Pauli exclusion principle 13:00; Spin 31:30; Rotaion by 2 Pi simmetry 40:00; Proving the basic symmetry of the world is rotation by 4 Pi 51:00; Rotation 2 Pi Plus exchange is Identity 57:00; Experiments on rotation and interference 1:18:00;

[sansha]

Magical Physics, Shown by Magician No.1 Physicist Susskind at 51:51. For me the whole lecture after that till last second was mesmerising and magical Quantum Mechanics.

[KipIngram]

This stuff around 1:00:00 - on belts, solitons, spin-statistics, etc.- this is fascinating, and important, I think.

[erwinmarschall]

0:38:30 if Wikipedia is correct:
"According to Dirac, it was first studied by Fermi, and Dirac called it
Fermi statistics and the corresponding particles Fermions."

[YORGS.ONERIZM]

Are photons considered solitons? Would this imply the 1/2 spin topology for light? How would a wave be integer spin topology instead?

[nemuritai]

Is there an intuitive reason why the spin or helicity of a boson dictates whether it mediates attractive(gravity) or repulsive(like charges) forces?

[dustintracy]

Wouldn't sending any charge, including one as small as an electron, through a solenoid cause a fluctuation of the magnetic field? If so, why wouldn't that be considered an observation?

[petergreen]

❤thank you very much Professor and class

[pwlywzh]

11:00 How about the Majorana fermions? Don't they violate the Pauli's exclusion principle?

[RedLeaderBL]

Here's what I don't understand. He's making a claim about QM symmetry with the 2pi vs 4pi rotation for bosons and fermions, which is ultimately traced back to the magnetic quantum number. But the belt or the Dirac box arguments seem to hold for anything, not just QM. What do I have wrong?

[dailysentinal]

a million years lets see that's a monday right

[jannisalexakis]

Can we make an equivalent demonstration as in 1:03:00 using a Mobius Band ?

[bunklypeppz]

Lmao he referred to Gerard T'Hooft as a circus performer. I wonder if he ever actually was in the circus or if Susskind is just poking fun at him since they're friends. But for those who don't know, Gerard T'Hooft is a nobel prize winning theoretical physicist.

[zphuo]

@26:40, If particle is indistinguishable, then Ψ0(x1) should equal Ψ0(x2). Why did he say that Ψ0(x1)Ψ1(x2) not equal to Ψ0(x2)Ψ1(x1)??
Before @35:00 I think the explanation about boson&fermion in Pauli exclusive state is reluctantly and unclearly!

[PetraAxolotl]

At about 20:00, the professor explains that an exchange of position can lead to a phase change of exp(i * phi).

But what if phi is a function of x1 and x2, e.g. phi = x1 - x2? This will automatically make two consecutive exchanges equal to 1.

[FerdarPleaseSubscribe]

I left autoplay on and this is where it ended up

[mikikaboom]

So basically bosons are well-behaved particles and fermions are bad guys.

[dirklutz]

A great example of swapping en rotating can be seen in this short video: