Lecture 19: Identical Particles

MIT 8.04 Quantum Physics I, Spring 2013
Instructor: Allan Adams

In this lecture, Prof. Adams wraps up the discussion on hydrogen atoms explaining the origin of their magnetic moment. He then moves on to the quantum mechanics of systems where there are multiple identical particles.

License: Creative Commons BY-NC-SA

[santiagoarce]

It's good that he always tries to rephrase or at least re state the questions because most of the time, i can't hear them being asked.

[FermatWiles]

Beautiful lecture, fantastic professor.

[АлександрБагмутов]

There's an intimidating moment here.. imagine the following: Allan Adams gets surrounded by some bully gang and hears "Whatcha doin?Who d'you think youre?", so he uses his stand or smth to just destroy them in one punch, and then 1:04:20

[viniciomonge]

Oh god, I love these lectures. Keep it up, MIT.

[LydellAaron]

17:39 how can there be a current if nothing is moving? 18:01 student offers an interesting geometrical interpretation--charge is a ring or going in a ring.

[ariadne]

1:19:20 ... and now that Prof. Adams told this story, I too have the little picture of Fermi = Fermion stuck in My head! :)

[Almost_Savvy]

These lectures are great! They always put my baby right to sleep and I learned a lot!

[CHistrue]

I tried to advertise that I have a definite magnetic moment but the dating site told me I was all spin without much charge.

[kilianklaiber]

First he talks about the possible different phases of the wave function, which do not change the probability distribution. Then he identifies these phases with the possible Eigenvalues of the swap operator. That's not very clear. Yes, the square of the eigenvalue must be equal to one, since swapping twice gives you the same result. If the Eigenvalues are rear, assuming that P is a hermitesch operator, then there are only two answers 1 and -1.

[hafidbensmail]

now im in the first year of studying physics i hope i will get my doctorat in quantum physics ..

[wilsonbarrosjunior]

@ 45 min it is mentioned that commutation relations are between operators and independent of the states. That's certainly true for [x, p]  but what about angular momentum  [Lx, Ly] ? In this case one gets Lz that will have expected value results depending on which state the system is.

[岡安一壽-gy]

Hello, sir ! The anti-symmetric wave function is not the eigenfunction and does not lead us the total energy. For example, please suppose the case Electron A is in a hydrogen atom and Electron B is in a helium ion He+. And the atom and the ion are far enough. The anti-symmetric wave function of the two electrons is not the eigenfunction of the system. Please calculate it. It is very easy.

[WayneL-ghhd]

51:10 I try to expand the operator of center mass kinetic energy and relative kinetic energy but there is a discrepancy of m1*m2/(m1+m2) to the total energy. How to expand to prove the equal sign?

[brabantstad]

I only watch this for relaxation, I have no clue what he (best teacher ever) is talking about xD

[TheWyrdSmythe]

This, and the other MIT OCW courses, are wonderful and quite a treasure. I’ve enjoyed this series immensely. So it feels ungracious to complain about the camera work, ... but damn MIT. Can you really not find camera people who know how to film a lecture? It’s _really_ distracting, this constant zooming and loss of focus. I’ve had to rewind several times due to being so distracted. There’s one rule here: Keep It Simple!

In particular, I do not _ever_ under _any_ circumstances need an extreme closeup of the teacher’s face or hands writing.

[sebastiancardozo]

who is operating this camera? 😅 Great lecture regardless

[ignaciomartinalliati]

Fermion "that's my spot" Cooper

[TheSecondInitiate]

This whole "collapse of the wave function" nonsense arises from a misunderstanding of the observer effect. The fact that you cannot measure or "observe" something without affecting it means there are no isolated systems in the Universe. Matter and energy persistently exist, as per conservation law, they dont become a quantum mystery when no one is looking at them.

If some particles need to be "aware" of what another set of particles are doing in order for them to exist, which is what observation fundamentally is, then the wave function remains "collapsed" for all particles in the Universe due to the Pauli exclusion principle and again, the fact that no Universe in the system is isolated, which is why why reaching absolute zero is technically impossible. This universal "awareness", where every particle is observing every other particle, is even further reinforced by the fact that range of the electromagnetic and gravitational forces are infinity. Every particle is always "observing" every other particle.

I believe it is the pinnacle of modern arrogance to treat Newtonian physics like theyre somehow primitive or less valid due to his lack of all the intermediate 20th century instruments that we thought proved him wrong at the quantum level but now are seeing more and more with extremely high-tech instruments that maybe everything is actually Newtonian all the way down. Entanglement, plasma wakefields, gravitation, the Casimir effect and even particles seemingly popping in and out of existence in a vacuum all obey Newton.

PS So does the "strong force" when you calculate the protons holographic mass, by the way. In my opinion, the fact that Haramein wasnt given the Nobel prize for nailing the proton radius using the holographic mass, while the Standard Model was 4% off, is criminal.

[creepcreepier]

Cant help but wonder why he didnt erase the board, instead draws a straight line across it, it's a new topic anyway

[shibaneethakur]

Sir do you have lectures on condensed matter and material physics