So that is what hell is. I would never have believed it. You remember: the fire and brimstone, the torture. Ah! the farce. There is no need for torture: Hell is other people.
— Garcin, Act 1, sc. 5
— No Exit (1944)
— Jean-Paul Sartre
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Heaven is also other people.
— Me@2012-09-05 10:30:44 AM
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2012.09.05 Wednesday (c) All rights reserved by ACHK
Electric Field and Electric Potential, 2.2 | 物理語言 2.2
這段改編自 2010 年 6 月 9 日的對話。
空間上，每一點有一個數字，就為之有一個「field」。例如，這兒的空間有溫度。這一點是 26 度、那一點是 27 度、另一點是 26.5 度 等等。你發覺在這兒空間上的每一點，都可以標籤一個數字，用來代表溫度。所以我們說，這裡有一個 temperature field（溫度場）。
溫度是 scalar（純量）還是 vector（向量）？
溫度是 scalar。溫度只是用數字來代表，沒有所謂方向。所以，我們亦可以說，這裡有一個 temperature scalar field。
如果我們放一粒 electric charge（電荷）在這兒，為什麼我們會說，它的周圍會形成一個 electric field（電場）呢？
假設原本的 electric charge 叫做「甲」。如果我們放另一粒 electric charge（電荷乙）在甲附近的任何一點，乙都會感受到一個 force（力）。（至於是吸力或斥力，則要視乎甲乙是同性還是異性。）在這一點，乙會感受到 26N 的力；在那一點，則感受到 27N；另一點是 26.5N 等等。你發覺在甲附近空間上的每一點，都可以標籤一個數字，用來代表力的強度。所以我們說，這裡有一個 force field（力場）。
由於這個 force field 是由 electric charge 引起的，所以這個 field 又稱為 electric force field（電力場）。另外，要表示 force（力），單單用數字是不足夠的，因為力除了有大小外，還有方向。所以，「force field」的意思，不單是指空間上的每一點有一個數字，而且指每一點有一支箭。箭的長度，代表乙所感受到的力的大小；箭的方向，代表力的方向。換句話說，力是 vector（向量）。所以我們說，電荷甲的周圍，有一個 electric force vector field（電力向量場），簡稱 electric field（電場）。
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| This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication. |
— Me@2012.09.04
2012.09.04 Tuesday (c) All rights reserved by ACHK
Entailment [logical implication] vs material implication
The difference between material implication and entailment is that they apply in different contexts. The first is a statement of logic, the second of metalogic. If p and q are two sentences then the difference between “p implies q” and “p is a proof of q” is that the first is a statement within formal logic, the second is a statement about it. Entailment is a concept of proof theory, whereas material implication is the mechanics of a proof.
— Wikipedia on Entailment
2012.09.03 Monday ACHK
Turn what is against you, for you.
— Me@2012-09-01 10:59:30 AM
2012.09.03 Monday (c) All rights reserved by ACHK
這段改編自 2010 年 3 月 27 日的對話。
作家 John T. Reed 出過一本書，叫做《How To Write, Publish, and Sell Your Own How-To Book》（如何靠編寫和出版工具書為生）。書中的其中一個要點是，要出版書籍的話，就應該自己出版，而不應透過出版社。靠出版社出書的最大問題是，你心血結晶作品的版權，將會屬於出版社。
John T. Reed 說，他有一個朋友（甲），寫了一本工具書《甲書》，透過出版社（乙）出版。後來甲想為《甲書》更新，編寫第二版（《甲書二》）。不幸，因為甲和出版社意見不合，出版社不肯出版《甲書二》。於是，甲想找另一間出版社，又或者自資出版。
但是，因為《甲書》版權歸乙所有，甲沒有權力出版《甲書二》。甲唯有放棄修訂和更新《甲書》的大計。結果，《甲書》既會絕版，因為它的內容會過時；又會絕後，因為它不會有新版。
（安：香港都有類似的事件。早前「博益出版」結業，初時沒有把書籍版權，歸還給作者們，導致那些書籍，幾乎從此絕版絕後，在這個宇宙中，永恆地消失。幸好事件最終圓滿解決。）
— Me@2012.09.02
2012.09.02 Sunday (c) All rights reserved by ACHK
Originally proposed in 1899 by German physicist Max Planck, these units are also known as natural units because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one system of natural units among other systems, but are considered unique in that these units are not based on properties of any prototype object, or particle (that would be arbitrarily chosen) but are based only on properties of free space.
— Wikipedia on Planck units
2012.09.01 Saturday ACHK
Being able to do more push-ups doesn’t mean that you can endure more pain. Instead, it means you have stronger muscles so that you can feel less pain for the original number of push-ups.
— Me@2011.09.05
2012.09.01 Saturday (c) All rights reserved by ACHK
Electric Field and Electric Potential, 2.1
這段改編自 2010 年 6 月 9 日的對話。
「Field」（場）貌似是一個抽象的概念。實質可以很簡單容易。究竟什麼是「field」（場）呢？
空間上，每一點有一個數字，就為之有一個「field」。例如，這兒的空間有溫度。這一點是 26 度、那一點是 27 度、另一點是 26.5 度 等等。你發覺在這兒空間上的每一點，都可以標籤一個數字，用來代表溫度。所以我們說，這裡有一個 temperature field（溫度場）。
— Me@2012.09.01
2012.09.01 Saturday (c) All rights reserved by ACHK
Thus, the holographic correspondence is not just a wild new possibility for a quantum theory of gravity. Rather, in a fundamental way, it connects string theory, the most studied approach to quantum gravity, with theories of quarks and gluons, which are the cornerstone of particle physics.
— The Illusion of Gravity
— Juan Maldacena
2012.08.31 Friday ACHK
Sorrow is Knowledge: they who know the most
Must mourn the deepest o’er the fatal truth,
The Tree of Knowledge is not that of Life.
— LORD BYRON, Manfred
We need both the Tree of Knowledge and the Tree of Life.
Both are crucial.
— Me@2012-08-31 9:51:11 AM
2012.08.31 Friday (c) All rights reserved by ACHK
The accuracy of the measured value of G has increased only modestly since the original Cavendish experiment. G is quite difficult to measure, as gravity is much weaker than other fundamental forces, and an experimental apparatus cannot be separated from the gravitational influence of other bodies. Furthermore, gravity has no established relation to other fundamental forces, so it does not appear possible to calculate it indirectly from other constants that can be measured more accurately, as is done in some other areas of physics.
— Wikipedia on Gravitational constant
2012.08.30 Thursday ACHK
Angels can fly because they take themselves lightly; devils fall because of their [own] gravity.
– G. K. Chesterton
In order to develop yourself and transcend yourself, you have to decentralize yourself.
— Me@2011.11.04
2012.08.30 Thursday (c) All rights reserved by ACHK
Electric Field and Electric Potential
這段改編自 2010 年 6 月 9 日的對話。
千萬不要以為，「electric field」（電場）和「electric potential」（電勢）是兩種不同的東西。實情是，它們只不過是，描述同一類物理現象的兩種不同的語言。換言話說，同一個電學現象，你既可以用「electric field」來解釋，亦可以用「electric potential」來說明。
例如，有一對金屬板，左邊帶正電，右邊帶負電。如果放一粒正電荷於兩者之間，該正電荷會向右走。
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| This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. |
這個現象，一方面，你可以用「electric field」來解釋：因為 electric field lines（電力線）向右指，而正電荷的天性是，跟著電力線的方向走，所以該正電荷會向右走。
另一方面，你亦可以用「electric potential」來解釋：因為左邊的 electric potential 高於右邊，而正電荷的天性是，由高 potential 的地方，流向低 potential，所以該正電荷會向右走。
記住，「electric field」（電場）和「electric potential」（電勢）不是兩種東西，而是同一種東西的兩種語言。就正如「蘋果」和「apple」，它們是同一種東西的兩種語言。至於用哪一種語言，則要視乎情況而定，哪一種比較方便就用哪一個。例如，見到中國人時，就用「蘋果」；見到英國人時，則用「apple」。
— Me@2012.08.30
2012.08.30 Thursday (c) All rights reserved by ACHK
Charge (physics), the susceptibility of a body to one of the fundamental forces
— Wikipedia on Charge
2012.08.29 Wednesday ACHK
Data Statistics Information Studying Knowledge Aging Wisdom Dying Next What is Next?
Data and Information
First, differentiate data and information: Data is raw. Data have no meaning. Information is processed data. Information has meaning. The process to transform data to information is statistics.
Information and Knowledge
Information is higher-level than data. What is higher than information?
Knowledge.
What is the process of transforming information to knowledge?
Studying. (or AI for computers)
If you want a lot of mathematics information, just buy 50 maths books, then you get a lot of information. But if you want a lot of mathematics knowledge, you have a lot of hard work to do.
Knowledge and Wisdom
After knowledge, what is next? Wisdom.
What is the process of transforming knowledge to wisdom?
Aging.
If you want to have a lot of knowledge, buy a lots of books, read them and read them well. But if you want to have a lot of wisdom, you need to live your life for a long time or a long long time.
Wisdom and Next
Is there anything higher than wisdom? If yes, what is the process to go from wisdom to there?
Dying. (This can be trivial. When you age to certain extent, you die.)
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2008.06.11 Wednesday (c) All rights reserved by ACHK
這段改編自 2010 年 3 月 27 日的對話。
我發覺很難和地球人有精神交流。平日和地球人相處，例如朋友聚會，很難可以有有意義的對話。很多時，企圖說稍為有智力的內容，只會令人反感。
教書的好處是，你可以名正言順地，說一些有意義、有智力的內容，不會受人歧視。
— Me@2012.08.29
2012.08.29 Wednesday (c) All rights reserved by ACHK
An important technical difference between decoherence and the collapse of the wave function is that decoherence actually doesn’t decide which result will be measured. It just diagonalizes the density matrix to diag(p1,p2,…,pN) where p_i then play the role of the probabilities that the individual preferred basis vectors will be detected. Because the information about the relative phases is getting quickly lost, the off-diagonal elements rapidly converge to zero. But decoherence never transforms the density matrix with the many p’s to something like (0,0,1,0,…,0). Never, ever. Quantum mechanics remains the only player here and its predictions remain and will always stay probabilistic. One can never and one will never restore determinism and decoherence doesn’t try to do anything of the sort.
— Lubos Motl
2012.08.28 Tuesday ACHK
Imagination is not an empirical or superadded power of consciousness, it is the whole of consciousness as it realizes its freedom.
— Jean-Paul Sartre
2012.08.28 Tuesday ACHK
Such QFTs arise naturally in generalizations of QCD from three colors to a larger number of colors, N.
— Solving quantum field theories via curved spacetimes
— Igor R. Klebanov and Juan M. Maldacena
2012.08.27 Monday ACHK
機 — 先決條件 — 原因
會 — 相交點
所有先決條件 ＝ 充分條件
機會 — 眾多「先決條件」的「會合」 — 因緣和合
— Me@2012.08.19
— Me@2012.08.24
— Me@2012.08.27
2012.08.27 Monday (c) All rights reserved by ACHK
Physics Town 
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