The difference between the classical and quantum dynamical equations is just hidden in the fact that rho,x,p are operators in quantum theory and they generally don’t commute with each other. But otherwise, the interpretation from classical physics may be pretty much directly extended to the quantum theory!
— Density matrix and its classical counterpart
— Lubos Motl
2011.06.09 Thursday ACHK
維繫感情 4
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情 = 處境 = 上文下理
感情 = 感受情境
有感情 = 感受到相同的情境
— Me@2011.06.04
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2011.06.08 Wednesday (c) All rights reserved by ACHK
One of the most dangerous illusions you get from school is the idea that doing great things requires a lot of discipline. Most subjects are taught in such a boring way that it’s only by discipline that you can flog yourself through them. So I was surprised when, early in college, I read a quote by Wittgenstein saying that he had no self-discipline and had never been able to deny himself anything, not even a cup of coffee.
I’m not saying you can get away with zero self-discipline. You probably need about the amount you need to go running. I’m often reluctant to go running, but once I do, I enjoy it. And if I don’t run for several days, I feel ill. It’s the same with people who do great things. They know they’ll feel bad if they don’t work, and they have enough discipline to get themselves to their desks to start working. But once they get started, interest takes over, and discipline is no longer necessary.
— Paul Graham
2011.06.07 Tuesday ACHK
diff 4
The version history is paired with the use of delta encoding technology. To conserve bandwidth and time, if a file in a user’s Dropbox folder is changed, Dropbox only uploads the pieces of the file that are changed when syncing.
— Wikipedia on Dropbox (service)
2011.06.07 Tuesday ACHK
Instead, the energy is universally defined in such a way that it is conserved as a result of the time-translational symmetry; and the action is defined in such a way that the condition δS=0 (stationarity of the action) is equivalent to the equations of motion. These are the general conditions that define the concepts in general and that make them important; particular formulae for the energy or action are just particular applications of the general rules.
— Lubos Motl
2011.06.06 Monday ACHK
維繫感情 3
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緣 = 相遇
份 = 共同問題
有緣無份 = ？
— Me@2011.06.03
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份 = 共同話題
有緣無份 = dead air
— Me@2022-06-24
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2011.06.05 Sunday (c) All rights reserved by ACHK
（安：對我來說，這個是一個嶄新的想法。）
哪個想法？
（安：你那個「地球人大部分是『瘋子』」的比喻。）
如果你覺得這個只是一個「比喻」的話，即是你未完全領會它的意思。
（安：這個牽涉到語意問題。如果「地球人大部分是『瘋子』」中的「瘋子」不是比喻的話，你就扭曲了「瘋子」這個字眼的意思。）
如果「瘋子」是指「瘋人院內的病人」的話，那當然不是每一個人也是「瘋子」。但是，如果「瘋子」是指「不理性的人」的話，地球人中，「瘋子」佔了大多數。
還有，即使假設，對於「個人」而然，「理性的人」比「不理性的人」多；對於「群體」來說，「瘋狂的機構」遠比「理性的機構」多。
— Me@2011.06.04
2011.06.04 Saturday (c) All rights reserved by ACHK
Fermat’s principle is the main principle of quantum electrodynamics where it states that any particle (e.g. a photon or an electron) propagates over all available (unobstructed) paths and the interference (sum, or superposition) of its wavefunction over all those paths (at the point of observer or detector) gives the correct probability of detection of this particle (at this point). Thus the extremal (shortest, longest or stationary) paths contribute into this interference most as they can not be completely canceled out.
— Wikipedia on Fermat’s principle
2011.06.04 Saturday ACHK
He began making something for himself, but then realized that it could benefit lots of people with the same problem.
— Wikipedia on Dropbox (service)
2011.06.03 Friday ACHK
 |
| Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. |
2011.06.04 Saturday ACHK
How does the particle find the right path?
Does it ‘smell’ the neighboring paths to find out whether or not they have more action?
In the case of light, when we put blocks in the way so that the photons could not test all the paths, we found that they couldn’t figure out which way to go, and we had the phenomenon of diffraction.
— Chapter 19. The principle of least action
— Volume 2. Mainly electromagnetism and matter
— The Feynman Lectures on Physics
2011.06.02 Thursday ACHK
Hacker: Prequel
4.10 Hacker approach
— Me@2011.06.02
2011.06.02 Thursday (c) All rights reserved by ACHK
（安：我同意這個講法。如果我真的要在日常生活過得快樂的話，我一定要改變工作環境，轉換上司。但是，我現在沒有可能做到這一點。那我應該怎麼辦呢？）
即是話，現在不是理論問題，而是「如何在實際環境，恰當執行這個理論」的問題。
（安：無錯。）
第一，最重要的是，你知道最理想的情況是什麼；如果沒有任何形式的限制的話，你想你的世界是怎麼樣。
第二，原則上的目標知道了後，並未足夠，因為現實會有很多技術細節和外在限制，阻礙你走到最終理想。但是，即使你現在的現實和理想相差「十萬八千里」，你總會有方法把它們的距離減至「十萬七千里」。
（安：如果真的是沒有方法呢？）
那就先試試把現實拉近至，和理想只相差「十萬七千九百九十九里」；完成以後，再試試把現實拉近至，和理想至只相差「十萬七千九百九十八里」；如此類推。
一步也走不到的話，就走 0.1 步； 0.1 步都走不到的話，就走 0.01 步；如此類推。
— Me@2011.06.01
2011.06.01 Sunday (c) All rights reserved by ACHK
Curiosity turns work into play. For Einstein, relativity wasn’t a book full of hard stuff he had to learn for an exam. It was a mystery he was trying to solve. So it probably felt like less work to him to invent it than it would seem to someone now to learn it in a class.
–- Paul Graham
2011.06.01 Wednesday ACHK
Physics Town 