5 ms·

Feynman's Public Lectures on Quantum Electrodynamics

108 points by evanb 11y ago

morenoh149 11y ago
are they available elsewhere? the video players don't load on my browser
- m1el 11y ago
  https://www.youtube.com/watch?v=yvl6TBGEoO0 https://www.youtube.com/watch?v=yvl6TBGEoO0 https://www.youtube.com/watch?v=xjdbbnWsdis https://www.youtube.com/watch?v=xjdbbnWsdis https://www.youtube.com/watch?v=FF25Lwt73fg https://www.youtube.com/watch?v=FF25Lwt73fg https://www.youtube.com/watch?v=BtK6FdTg9HU https://www.youtube.com/watch?v=BtK6FdTg9HU A long time ago, I've downloaded and upscaled those videos. Enjoy.
  - andrepd 11y ago
    Thank you, those look very nice.
bsaul 11y ago
Just saw the first video, but i found his analogy with mayan priests calculating Venus trajectory correctly, having no clue of the "why" quite disturbing. There is a HUGE difference between knowing "why" and not knowing it. Mayans priests couldn't guess the real "why", because they had no notion of gravity or a correct description of the solar system, but now we do and we know. The fact that quantum effects aren't grasped right now (at least by me :), means a very different thing whether we believe there will be such an explanation one day, with a more complete description of nature, or if such an explanation is inexistant. Which makes me wonder : i've read that there was a proof that the "hidden variable hypothesis" is wrong. Does anyone know of someone explaining that proof in a comprehensible way ? Has this proof been contested by some parts of the scientist working on the field ?
- db48x 11y ago
  It's called Bell's theorem. Try wikipedia.
- yagyu 11y ago
  The 'proof' you refer to is likely Bell's theorem and friends: "Bell's Theorem states that the predictions of quantum mechanics cannot be reproduced by any local hidden variable theory.": https://en.wikipedia.org/wiki/Bell_test_experiments https://en.wikipedia.org/wiki/Bell_test_experiments https://en.wikipedia.org/wiki/Bell's_theorem https://en.wikipedia.org/wiki/Bell's_theorem edit: the theorem has been fairly thoroughly experimentally tested and still holds.
- m1el 11y ago
  > Has this proof been contested by some parts of the scientist working on the field? Here's a story I find interesting. Einstein got his nobel prize for discovering the law of photoelectric effect [1]. This discovery influenced the development of quantum mechanics quite a lot. I'd say that this discovery alone is enough for the theory of QM to emerge. However, Einstein did not like the "probabilistic" nature of QM, "God doesn't play dice with the world."[2], and he argued against it. Albert Einstein along with Boris Podolsky and Nathan Rosen have formulated a paradox[3] which was resolved many years later by Bell's Theorem and corresponding experiments[4]. So yes, there were scientists arguing against the probabilistic nature of QM. > Does anyone know of someone explaining that proof in a comprehensible way? "Comprehensible" explanation in this case mostly depends on the reader. The wiki[4] gives a pretty good explanation of the Bell's Theorem and experiments. [1]: http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/ http://www.nobelprize.org/nobel_prizes/physics/laureates/192... [2]: https://books.google.com.vn/books?id=QXCyjj6T5ZUC https://books.google.com.vn/books?id=QXCyjj6T5ZUC [3]: https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox [4]: https://en.wikipedia.org/wiki/Bell%27s_theorem#Practical_experiments_testing_Bell.27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem#Practical_exp...
  - bsaul 11y ago
    Thanks for taking the time. I've read the wikipedia article and think i got the argument better : from what i got, you can't have a "classical" effect underlying QM, because it would mean faster than light transmission of information. And yet, experimentally, Bell's experiment has been done, and it is working the way it is predicted by QM (the famous "spooky action at a distance"). Would that be correct ?

108 points by evanb 11y ago

morenoh149 11y ago

are they available elsewhere? the video players don't load on my browser

m1el 11y ago
https://www.youtube.com/watch?v=yvl6TBGEoO0 https://www.youtube.com/watch?v=yvl6TBGEoO0 https://www.youtube.com/watch?v=xjdbbnWsdis https://www.youtube.com/watch?v=xjdbbnWsdis https://www.youtube.com/watch?v=FF25Lwt73fg https://www.youtube.com/watch?v=FF25Lwt73fg https://www.youtube.com/watch?v=BtK6FdTg9HU https://www.youtube.com/watch?v=BtK6FdTg9HU A long time ago, I've downloaded and upscaled those videos. Enjoy.
- andrepd 11y ago
  Thank you, those look very nice.

bsaul 11y ago

Just saw the first video, but i found his analogy with mayan priests calculating Venus trajectory correctly, having no clue of the "why" quite disturbing. There is a HUGE difference between knowing "why" and not knowing it. Mayans priests couldn't guess the real "why", because they had no notion of gravity or a correct description of the solar system, but now we do and we know. The fact that quantum effects aren't grasped right now (at least by me :), means a very different thing whether we believe there will be such an explanation one day, with a more complete description of nature, or if such an explanation is inexistant. Which makes me wonder : i've read that there was a proof that the "hidden variable hypothesis" is wrong. Does anyone know of someone explaining that proof in a comprehensible way ? Has this proof been contested by some parts of the scientist working on the field ?

db48x 11y ago
It's called Bell's theorem. Try wikipedia.
yagyu 11y ago
The 'proof' you refer to is likely Bell's theorem and friends: "Bell's Theorem states that the predictions of quantum mechanics cannot be reproduced by any local hidden variable theory.": https://en.wikipedia.org/wiki/Bell_test_experiments https://en.wikipedia.org/wiki/Bell_test_experiments https://en.wikipedia.org/wiki/Bell's_theorem https://en.wikipedia.org/wiki/Bell's_theorem edit: the theorem has been fairly thoroughly experimentally tested and still holds.
m1el 11y ago
> Has this proof been contested by some parts of the scientist working on the field? Here's a story I find interesting. Einstein got his nobel prize for discovering the law of photoelectric effect [1]. This discovery influenced the development of quantum mechanics quite a lot. I'd say that this discovery alone is enough for the theory of QM to emerge. However, Einstein did not like the "probabilistic" nature of QM, "God doesn't play dice with the world."[2], and he argued against it. Albert Einstein along with Boris Podolsky and Nathan Rosen have formulated a paradox[3] which was resolved many years later by Bell's Theorem and corresponding experiments[4]. So yes, there were scientists arguing against the probabilistic nature of QM. > Does anyone know of someone explaining that proof in a comprehensible way? "Comprehensible" explanation in this case mostly depends on the reader. The wiki[4] gives a pretty good explanation of the Bell's Theorem and experiments. [1]: http://www.nobelprize.org/nobel_prizes/physics/laureates/1921/ http://www.nobelprize.org/nobel_prizes/physics/laureates/192... [2]: https://books.google.com.vn/books?id=QXCyjj6T5ZUC https://books.google.com.vn/books?id=QXCyjj6T5ZUC [3]: https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox [4]: https://en.wikipedia.org/wiki/Bell%27s_theorem#Practical_experiments_testing_Bell.27s_theorem https://en.wikipedia.org/wiki/Bell%27s_theorem#Practical_exp...
- bsaul 11y ago
  Thanks for taking the time. I've read the wikipedia article and think i got the argument better : from what i got, you can't have a "classical" effect underlying QM, because it would mean faster than light transmission of information. And yet, experimentally, Bell's experiment has been done, and it is working the way it is predicted by QM (the famous "spooky action at a distance"). Would that be correct ?