In physics, the AdS/CFT correspondence (anti-de-Sitter space/conformal field theory correspondence), sometimes called the Maldacena duality, is the conjectured equivalence between a string theory defined on one space, and a quantum field theory without gravity defined on the conformal boundary of this space, whose dimension is lower by one or more.
— Wikipedia on AdS/CFT correspondence
2010.05.04 Tuesday ACHK
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Colleges are a bit like exclusive clubs in this respect. There is only one real advantage to being a member of most exclusive clubs: you know you wouldn’t be missing much if you weren’t. When you’re excluded, you can only imagine the advantages of being an insider. But invariably they’re larger in your imagination than in real life.
— Paul Graham
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2010.05.04 Tuesday
Physicists learned rather unexpectedly, beginning in the early 1970s, that the problem of quantum gravity could be overcome by introducing a new sort of fuzziness. One replaces “point particles” by “strings”. Of course, the point particles and strings must both be treated quantum mechanically. Quantum effects are proportional to Planck’s constant 
— Edward Witten
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2010.05.03 Monday ACHK
魔法文章
專家博士（製作特輯）2
對於系列中的任何一篇文章來說，開始寫時我只有題目。寫完該篇之前，我也不知道我會寫什麼。每次寫，都會有突如奇來的新意念出來。而那些「新意念」，往往是對我自己有很大的幫助，為我解決了（寫該篇文章之前）原本還未解決的問題。
那就好像在「自己教自己」一樣。但是，這個講法很奇怪，因為如果你可以「自己教自己」的話，你就毋須「自己教自己」。如果你「自己教自己」某樣東西的話，即是你原本就懂那樣東西。既然原本就懂那樣東西，為何要再「教自己」呢？
但是，我又好明顯地透過寫文章，而學到新的想法。那如何解釋這個現象呢？
（安：是不是那些資料原本就在你的腦海中，只是很凌亂 …）
再簡單一點的講法是，那些積木原本就在我的腦海中，只是還未砌成我所要的東西。
例如，我把那些積木砌成一隻機械人。我很開心，因為我原本沒有那隻機械人。那隻機械人對我來說，是新的東西。但是，構成那些機械人的積木，原本就在我心中。
我原本沒有那隻機械人，但我原本有那些積木。透過寫作，我可以把那些積木砌成千奇百怪的機械人。而且，那些機械人，還可以合體成為一隻保衛地球的大機械人。
— Me@2010.05.01
2010.05.02 Sunday (c) All rights reserved by ACHK
The real numbers are the dependable breadwinner of the family, the complete ordered field we all rely on. The complex numbers are a slightly flashier but still respectable younger brother: not ordered, but algebraically complete. The quaternions, being noncommutative, are the eccentric cousin who is shunned at important family gatherings. But the octonions are the crazy old uncle nobody lets out of the attic: they are nonassociative.
— John Baez
2010.05.02 Sunday ACHK
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You don’t have to learn everything in order to know everything.
— Me@2010.04
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2010.05.02 Sunday
Golden ratio
The number 5 is quirky and intriguing, thanks in large part to its relation with the golden ratio, the “most irrational” of irrational numbers.
— John Baez
2010.05.01 Saturday ACHK
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The significant problems we have cannot be solved
at the same level of thinking with which we created them.
— Albert Einstein
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2010.05.01 Saturday
Physics Town 