Lecture 7 | Quantum Entanglements, Part 1 (Stanford)

[samurai1999]

The people asking questions should really learn not to ask questions

- they really destroy the flow of what Susskind is trying to explain

[BagarozziBoi]

Re: my comment below - turns out that yes, he's a many-worlds guy, so what he's saying is at least self-consistent.

[BagarozziBoi]

Great lecture. He sweeps the measurement/wavefunction collapse problem under the carpet though, (like most modern physicists) by trying to substitute measurement with entanglement. His explanation is ok, until you get to Schrodinger's cat type situations where the entangled states in the system post-experiment represent vastly different states even on a macroscopic level. (Couple the detector to the trigger of a nuclear bomb to see how dramatically different the entangled states can be).

[BagarozziBoi]

At this stage you have two choices. Either you subscribe to an Everret style many-worlds interpretation where the two macroscopically different states decohere and continue to evolve as parallel universes with minimal interference between them, or you accept that there's an unknown mechanism missing from current models of quantum mechanics whereby one of the macroscopic branches is selected by nature a-la Penrose. If he's going for a many-worlds view fine, but he should state that explicitly.

[grunder20]

Bald professors are always geniuses.

[HomemadeBanjo]

The whole section from 0:45 to 1:05 can be skipped with no loss. I'm amazed at his patience.

[rmgorichanaz]

Yes, please make an editing pass through these and remove the Geraldo Rivera-esque monologing from the peanut gallery

[MrRobotoToo]

Outstanding lecture, despite all the annoying questions.

[san34451]

Does anyone know where to find "Quantum Entanglements, Part 2"? Was it video-recorded? Only Part 1 and Part 3 are available on YouTube. StanfordUniversity did clarify that Part 2 "is unavailable at this time", but that was an year ago.

[jqlewis]

if only the idiots in the audience asking these dumb questions kept quiet we'd have had more time for Dr Susskind to teach the course !

[fermista]

@jqlewis

I agree! God I love it at 59:20, when he says "I'm trying to figure out how to get out of this situation". I lol'd :D

[demondelight]

Some of the questions asked did help because they made the prof. give more info about some stuff, but other questions stopped him from giving the fine point and blew it...cannot really tell when some questions just did not do anything to advance the lecture...its tough for sure...

[garywpearson1955]

This stuff is pure gold!!! Thanx for posting.

[timcabc]

So for the 2 split experiment, if start with an electron with down spin, and put 2 detector at A, the first detector flips the spin the up, and the second detector that is right next to the first flips the spin back to down, will we see the same interference pattern as if there is no measurements at A?

[tfy6600]

@timcabc @timcabc No I believe. Because the interference pattern is destroyed not just by the change in the spin of the electrons, but it is destroyed by a change in spin of a particle at the detector. If you have 2 detectors, although the spin of the electrons is unchanged, but now the two particles used in the detectors has changed their spins. The state at slit A is | A u u >, instead of just | A>. The two ups refer to state of the particles in the detectors.

[denisosu]

students asking questions is ok, but these long monologues (which are wrong!) are very annoying. I wonder could they edit out the stupid and long-winded questions.

[openuniverse2003]

Agreed. Any way we can get supporting reading material(s) for this, or can anyone recommend a good introductory primer for this? What textbook did Susskind's students use?

[landin048]

This is harder without accompanying reading resources, but it's still wonderful to have the access to the information. Thank you for posting.