Lecture 7 | New Revolutions in Particle Physics: Basic Concepts

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[fitnesus]

I Really Like The Video From Your Leonard Susskind discusses the theory and mathematics of angular momentum.

[cenedywong]

Your Video Is Very Useful Sharing Leonard Susskind discusses the theory and mathematics of angular momentum.

[grunder20]

Contemplating the relativity of Physics and Chemistry, I would personally prefer

Physics.

[technopagan724]

If a system of two electrons makes a boson, then how come, even though two individual electrons of the same spin cannot inhabit the same orbital, why couldn't multiple coupled systems of two electrons (a singlet) inhabit the same orbital. Electron singlets would be spin 0 (+1/2 - 1/2). Therefore, should they not be able to behave as bosons and coexist in the same orbital?

[alhobbel]

@technopagan724

Two electrons with opposite spin do not make a boson, but a superposition of two electrons,total spin 0. From a reasonable distance, this can be approximated by a single particle with spin 0, i.e. a boson: the unc. princ.: ΔxΔv = hbar/2m so if the mass is very large, then it's a good approximation (pi meson) if you don't localize the particle so that the speed of its parts takes it far of the localization. Electrons around the atom OTOH do see the separate parts.

[agapitoflores001]

I'd like to meet this prof personally and learn physics from him directly.

[csmcmillion]

0:24:55 - The anus and bnus of a system???

[newtonswig]

He finds the spin commutator relations using 'angular momentum operators' which he builds from classical angular momentum and the operator definitions of position and momentum. Do these operators have eigenstates in the space of 'ordinary' wavefunctions (normalised L^2 integrable maps R(3,1)-> C ? If so, what's with everyone using the vector representation? Surely, then, the use of that representation would be redundant....

[bhigr]

I think he is jumping from angular momentum of a point like particle to the spin of a particle. L is the angular momentum, not the spin. Classically a point like particle doesn't have a spin, in quantum mechanics the spin is a property of the particle like its charge.

[chloeagnew1]

@bhigr

Do you think there is any mathematical difference between spin angular momentum and orbital angular momentum?

They are just some sort of representations of rotation group, I guess.

[technopagan724]

@chloeagnew1 The mathematical difference is that the orbital angular momentum is (classically) the motion of the center of mass of the system with respect to a fixed axis. In classical systems of discrete particles, the spin angular momentum of the system is the vector sum of the angular momenta of the constituent particles (usually with respect to an axis that passes through the object, and specifically one that passes through the moment of inertia)...

[technopagan724]

...for a solid object, it would be the integral of the angular momentum of the individual differential mass elements over the object. Quantum particles, however, have a spin angular momentum due to the "intrinsic spin" of the particle. It's a quantity that has no equivalent conceptualization in classical physics. Whereas the spin angular momentum for a classical system can be described as Iw (moment of inertia times angular velocity), this equation breaks down when talking about point particles.

[bhigr]

The experiment related to the discovery of spin is the Stern-Gerlach-experiment.

[TheBobathon]

The Uncertainty Principle: delta x delta p is greater than or equal to ... whatever ... er.... 29:30

[emailcity]

The downloads haven't been working for more than a week. Is it a YouTube problem?

[piraders]

good teacher

[piraders]

interesting TNX

[Qounoclubpenguin]

My dad loves Stanford lectures. Y'all excellent!

[69erthx1138]

If QM is ultimately the correct description of physical reality, then this idea applied to the so-called holographic principle (which depends deeply on waves, not particles) implies that this universe is a sophisticated digital hologram.

[TristanTheSaint]

ahem... waves are particles and vice-versa: two aspects of the same thing.