Consequently, as cs increases to c, the absolute speeds v_e and v_a of the emitter and absorber relative to the fixed medium merge into a single relative speed u between the emitter and absorber, independent of any reference to a fixed medium, and we arrive at the relativistic Doppler formula for waves propagating at c for an emitter and absorber with a relative velocity of u:
— 2.4 Doppler Shift for Sound and Light
— Reflections on Relativity
— mathpages
2010.12.21 Tuesday ACHK
If you want to “finish” a thing, you are not living in now-here.
Instead, you should enjoy the process. The journey is the destination.
— Me@2010.10.17
如果你只能享受「完成事情」的樂趣，你就不是活在當下，享受現在。
— Me@2010.10.17
2010.12.20 Monday (c) All rights reserved by ACHK
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We must plan for freedom, and not only for security, if for no other reason than only freedom can make security more secure.
— Karl Popper
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2010.12.20 Monday ACHK
IELTS Speaking Principles
1. Regard your examiner as a noble friend.
2. Say something interesting and useful to your friend.
— Me@2009.11.09
2010.12.20 Monday (c) All rights reserved by ACHK
Lisp looks strange not so much because it has a strange syntax as because it has no syntax; you express programs directly in the parse trees that get built behind the scenes when other languages are parsed, and these trees are made of lists, which are Lisp data structures.
— Paul Graham
2010.12.20 Monday ACHK
擅長入世，但不追求入世
擅長出世，但不追求出世
超世
— Me@2010.10.20
2010.12.19 Sunday (c) All rights reserved by ACHK
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The trouble with being punctual is that nobody’s there to appreciate it.
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2010.12.19 Sunday ACHK
如果你有系統地失敗，你的「失敗」，就是邁向「成功」的必須階梯。
「有系統地失敗」的意思是：
1. 事先你要知道，每次失敗的後果，是你能夠承受的；
2. 每次失敗的方法，相對於全人類來說，都要是全新的。凡是自己或別人犯過的錯誤，都不可以再犯；
3. 失敗的次數要超級多；
4. 失敗的速度要神奇高。
自己犯過的錯誤，相當於自己走過的梯級，不應再走。同理，別人犯過的錯誤，就是自己可以引以為鑑的經驗，相當於現成可用的升降機。不用的話，你就錯失高速省略大量梯級的機會。
— Me@2010.12.19
2010.12.19 Sunday (c) All rights reserved by ACHK
If you 100 percent follow the OCD rules, your thought stays in the OCD eigenstate.
To make it decay to a non-OCD state, you have to perturb it.
That is, do not follow 100 percent of the OCD rules.
— Me@2009.10.16
2010.12.19 Sunday (c) All rights reserved by ACHK
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Act as if each day is the first I have ever seen, and the last I am going to see.
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2010.12.18 Saturday ACHK
這段改篇自 2010 年 4 月 12 日的對話。
提升自己的最快方法是，先做自己最驚恐的事情。例如，做 past paper（歷屆試題）時，如果你只做原本已經擅長的題目的話，短期來說，你會比較開心，但是長遠來說，你的成績不會有明顯增長。
— Me@2010.12.18
It was a high counsel that I once heard given to a young person, — “Always do what you are afraid to do.”
* Heroism
— Ralph Waldo Emerson
2010.12.18 Saturday (c) All rights reserved by ACHK
If you look at these languages in order, Java, Perl, Python, you notice an interesting pattern. At least, you notice this pattern if you are a Lisp hacker. Each one is progressively more like Lisp.
— Paul Graham
We were after the C++ programmers. We managed to drag a lot of them about halfway to Lisp.
— Guy Steele, co-author of the Java spec
2010.12.17 Friday ACHK
Writing is a way of self-discovery.
Writing is a way of bringing your inner-self out.
Teaching is another.
— Me@2010.01.19
2010.12.17 Friday (c) All rights reserved by ACHK
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The key to being a good hacker may be to work on what you like. When I think about the great hackers I know, one thing they have in common is the extreme difficulty of making them work on anything they don’t want to. I don’t know if this is cause or effect; it may be both.
To do something well you have to love it. So to the extent you can preserve hacking as something you love, you’re likely to do it well. Try to keep the sense of wonder you had about programming at age 14. If you’re worried that your current job is rotting your brain, it probably is.
— Paul Graham
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Hacker here means a highly skilled programmer, not a computer criminal. — Me
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2010.12.17 Friday ACHK
Always make new mistakes, 2.3
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（安：你可不可以重新解釋，什麼是「對自己的了解」？什麼是「對自然定律的了解」？）
「對自己的了解」的意思是，要準確描述「自己什麼可以做到，什麼不可以」。
對於一件事，「做到」的話，可以做到什麼程度？「做不到」的話，是不是百分百，完全做不到？還是其實可以，做到一點？又或者，是否可以通過訓練，令自己由「做不到」，變成「做到」呢？
「對自然定律的了解」的意思是，要知道「你大部分嘗試的新東西，一定會失敗」。
這句好像自相矛盾，因為同一句有「大部分」，又有「一定」。應該這樣說：「你嘗試的新東西中，大部分會失敗。」但是，只要有一次成功，你就可以把成果循環再用，無限複製。
失敗的次數無論有多少，都是有限數；但是，由失敗過程所吸收的經驗，所帶來的成功，所達致的成果，卻可以使用無限次。
— Me@2010.12.17
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2010.12.17 Friday (c) All rights reserved by ACHK
After all, it’s a main conclusion of quantum gravity that the qualitative distinction between elementary particles and black holes fades away. However, small black holes are “different” elementary particles – especially because they tend to decay “isotropically” to many other particles – those that we call the Hawking quanta if the black holes are large.
— Lubos Motl
2010.12.16 Thursday ACHK
This essay is adapted from a dialogue on 2010.04.09.
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There are at least 3 dimensions of different selves:
1. time-selves
2. at a same time, there are more than one-selves,
e.g. the Left-brain self and the Right-brain self <– at least 2 selves
3. surface-inner selves
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Writing is a way to communicate with yourselves.
— Me@2010.04.09
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2010.12.16 Thursday (c) All rights reserved by ACHK
The Sims:
In addition, the game includes a very advanced architecture system. The game was originally designed as an architecture simulation alone, with the Sims there only to evaluate the houses, but during development it was decided that the Sims were more interesting than originally anticipated and their initially limited role in the game was developed further.
Flickr:
Flickr was developed by Ludicorp, a Vancouver-based company that launched Flickr in February 2004. The service emerged out of tools originally created for Ludicorp’s Game Neverending, a web-based massively multiplayer online game. Flickr proved a more feasible project and ultimately Game Neverending was shelved.
Early versions of Flickr focused on a multiuser chat room called FlickrLive with real-time photo exchange capabilities. There was also an emphasis on collecting images found on the web rather than photographs taken by users. The successive evolutions focused more on the uploading and filing backend for individual users and the chat room was buried in the site map. It was eventually dropped as Flickr’s backend systems evolved away from the Game Neverending’s codebase.
— Wikipedia
— Me@2010.01.18
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2010.12.16 Thursday ACHK
這段改篇自 2010 年 4 月 12 日的對話。
「計時間」做完某一年（例如 2000 年）的 past paper 後，你要為自己立刻批改。那樣，你就可以馬上得到一個分數，從而知道以你現時的實力，可以獲得哪一個成績等級。你的心理會穩定了一點。
另一方面，你會知道自己因為哪一個 topic（課題），導致損失得最多分數。你在下次做 past paper 時，就不應「按年份」做，而應「按 topic」做。例如，你發現自己在力學方面是最弱的話，你就應該狂轟力學部分的 past paper。再下次做 past paper 時，才重新「按年份」，做（例如）2001 年的試卷。
由於你已經修補了損失得最多分數的 topic，才開始做 2001 年的試卷，你一定會有幾分的進步。假設，你每做一對 past paper（一份按年份 + 一份按 topic），都會有 5 分進步的話，做 10 對，就會有 50 分的進步。
按年份做 past paper（要計時間和計分數）–> 按 topic 做 past paper –> 按年份做 past paper –> 按 topic 做 past paper –> …
— Me@2010.12.15
2010.12.15 Wednesday (c) All rights reserved by ACHK
Physics Town 
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