Tuesday, October 17, 2006

Quantum Computing Since Democritus

In the ongoing upgrade process of my brain, I found Scott Aaronson's lecture notes of "PHYS771 Quantum Computing Since Democritus*" very interesting. Only the first four lectures are available as of today, but I eagerly await the rest.

I haven't learned much about quantum computer yet, but I really like the way he reviewed the math/computer science/philosophy ideas (that took me decades to haphazardly absorbed) in four lectures. I especially like his lecture about sets and different types of infinities--I remember having a lot of fun trying to understand them when I was young.

According to some scientists (such as Seth Lloyd and Ed Fredkin), we are already parts of a quantum computer called the Universe, therefore knowing the nature of quantum computation should help to understand Nature better. (No, when we talk about quantum computer and computation, we are not talking about a Matrix-like simulation; we are talking about the way elementary particles interact and change their states to update the Universe's status, following the rules of quantum mechanics. If the Universe is a simulation, the type of simulation is lower-leveled than in the Matrix--the simulation is at the elementary particles and space-time level, not at the level of human neural inputs.)

I have a few favorite questions that are about two decades old now: How can an atom know when to fall to the ground? Why should anything obey the law of Nature? Where is the law of nature stored? How is it accessed by the particles in our space-time**? I suspect that clues to these questions might come from thinking of Nature as information transformation. Unfortunately, I'm too stupid to refine my suspicion into guesses that can be checked for correctness (or incorrectness) by experiments or observations.

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*Democritus, by the way, was the guy who proposed the existence of atoms (and void) around 2,500 years ago.

From Wikipedia: "...According to legend, Democritus was supposed to be mad because he laughed at everything, and so he was sent to Hippocrates to be cured. Hippocrates pointed out that he was not mad, but, instead, had a happy disposition. That is why Democritus is sometimes called the laughing philosopher..."

**Some people think everything is made of space-time, including elementary particles, which are various braids of space-time. These people study loop quantum gravity. Other people think space-time and elementary particles are separate and elementary particles are modes of vibration of something called strings. These people study string theory. If I'm a betting man, I would bet on loop quantum gravity, but I'm quite ignorant in both fields--I'm just biased about the background-independence idea.

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