# 財政自由 1.3.3

PhD, 3.8.3

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（問：你即是話，財政充裕前，讀研究院時，即使智力再高，往往沒有自由去，研究自己喜歡的課題。但是，要等到財政自由時，才研究學術的話，又未必仍然有足夠的智力。）

（問：協同互生？如何執行？可否舉一個例？）

（問：你的生活悲慘？）

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（問：你真的完全不知道嗎？）

（問：只作參考，無傷大雅吧？）

（問：即是有工餘時間。）

（問：用空閒時間，做自己喜歡的事情？

（當然，你亦同時要，做好版權的保護，避免別人盜取你的作品後，反過來指控你抄襲了他。）

— Me@2019-12-30 09:56:25 PM

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# Simcity, 2

I bought this SimCity 2000 box in 1995. It was the first time I went to a big computer centre (mall).

At the first glance, I thought that it was sold at the price 800 HKD, which I could not afford. Luckily, the price label was actually NT800, which meant 800 New Taiwan Dollars.

So I could buy it at 200 Hong Kong Dollars.

— Me@2019-12-29 03:42:26 PM

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# scmutils, 2

The original method of setting up Emacs for scmutils does not work anymore if you uses the newest (August 2019) version of scmutils, because its installation directories are not the same as those in the previous version.

Either use an older version of scmutils in order to follow the previous instructions for setting up Emacs for scmutils, or give up using Emacs for scmutils for the time being.

Using command line is the best way to go, so far.

Do not use the Edwin editor, since you cannot easily run, edit, or copy existing lines of code, unless you are familiar with it. I do not like it anyway, because after all, it does not provide syntax highlighting.

— Me@2019-12-28 07:50:32 PM

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# Physics PageRank

PageRank 7

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Physics has a high PageRank among fields of knowledge.

— Me@2011.07.28

— Me@2011.08.12

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# Principal details

Teaching hint:

Try to integrate all the details into one big principle.

— Me@ < 2008-06-20

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# Ken Chan 時光機 3.2

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— Me@2019-12-26 06:59:01 PM

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# Quick Calculation 13.1

A First Course in String Theory

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Verify that

$\displaystyle{\left[ \bar L_m^\perp, x_0^I \right] = - i \sqrt{\frac{\alpha'}{2}} \bar \alpha^I_m}$,

$\displaystyle{\left[ L_m^\perp, x_0^I \right] = - i \sqrt{\frac{\alpha'}{2}} \alpha^I_m}$.

~~~

Equation (13.37):

$\displaystyle{\bar L_m^\perp = \frac{1}{2} \sum_{p \in \mathbf{Z}} \bar \alpha_p^J \bar \alpha_{n-p}^J}$,$\displaystyle{~~~L_m^\perp = \frac{1}{2} \sum_{p \in \mathbf{Z}} \alpha_p^J \alpha_{n-p}^J}$.

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\displaystyle{ \begin{aligned} \left[ \bar L_m^\perp, x_0^I \right] &= \frac{1}{2} \sum_{p \in \mathbb{Z}} \left[ \bar \alpha^J_p \bar \alpha^J_{m-p}, x_0^I \right] \\ &= \frac{1}{2} \sum_{p \in \mathbb{Z}} \bar \alpha^I_p \left[ \bar \alpha^J_{m-p}, x_0^I \right] + \frac{1}{2} \sum_{p \in \mathbb{Z}} \left[ \bar \alpha^J_p, x_0^I \right] \bar \alpha^I_{m-p} \\ &= \frac{1}{2} \bar \alpha^J_m \left[ \bar \alpha^J_{0}, x_0^I \right] + \frac{1}{2} \left[ \bar \alpha^J_0, x_0^I \right] \bar \alpha^J_{m} \\ \end{aligned} }

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By Equation (13.33):

\displaystyle{ \begin{aligned} \left[ \bar L_m^\perp, x_0^I \right] &= - \frac{1}{2} \bar \alpha^J_m \left[ i \sqrt{\frac{\alpha'}{2}} \eta^{IJ} \right] - \frac{1}{2} \left[ i \sqrt{\frac{\alpha'}{2}} \eta^{IJ} \right] \bar \alpha^J_{m} \\ &= - i \sqrt{\frac{\alpha'}{2}} \eta^{IJ} \bar \alpha^I_m \\ \end{aligned} }

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Since $I$ and $J$ are transverse coordinate indices, neither of them can be zero.

\displaystyle{ \begin{aligned} \left[ \bar L_m^\perp, x_0^I \right] &= - i \sqrt{\frac{\alpha'}{2}} \bar \alpha^I_m \\ \end{aligned} }

— Me@2019-12-25 10:56:15 AM

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# Two dimensional time 5.2.3

The first time direction is uncontrollable; the second is controlled by making choices, traveling through different realities. Future is a set of parallel universes.

— Me@2017-12-15 10:59:49 AM

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The first time direction, which is along the timeline, is uncontrollable, because one can only travel from the past to the future, not the opposite.

The second direction, which is across different timelines, is controlled by making choices, forming different realities.

— Me@2019-12-21 11:03:23 PM

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# Two dimensional time 5.2.2

time direction ~ direction of change

multiple time directions ~ multiple directions of change

— Me@2019-12-22 04:38:47 PM

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the first dimension of time ~ direction of change

the second dimension of time ~ direction of change of changes

— Me@2019-12-22 04:46:47 PM

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# Pandemonium, 2

Batman: You sold us out, Clark. You gave them the power that should have been ours. Just like your parents taught you. My parents taught me a different lesson… lying on this street… shaking in deep shock… dying for no reason at all. They showed me that the world only makes sense when you force it to.

— Batman

— The Dark Knight Returns

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2019.12.21 Saturday ACHK

# PhD, 3.8.2

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（問：但是，你又提議最好在，已經有財政自由時，才讀研究院？那樣，豈不是起碼要三、四十歲時，才可以讀研究院？

（問：那即是怎樣？）

（問：你即是話，財政充裕前，讀研究院時，即使智力再高，往往沒有自由去，研究自己喜歡的課題。但是，要等到財政自由時，才研究學術的話，又未必仍然有足夠的智力。）

（問：協同互生？如何執行？可否舉一個例？）

— Me@2019-10-22 09:44:23 PM

— Me@2019-12-17 09:35:51 PM

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# University

In this picture, he was at his 15.

Later on, he studied at another university.

— Me@2019-12-15 03:27:25 PM

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# Varying the action, 2.2

\displaystyle{ \begin{aligned} &= \int_{t_1}^{t_2} (D L \circ \Gamma[q]) \delta_\eta \Gamma[q] \\ \end{aligned}}

\displaystyle{ \begin{aligned} &= \int_{t_1}^{t_2} [\partial_0 L (t, q, v), \partial_1 L (t, q, v), \partial_2 L (t, q, v)] (0, \eta(t), D\eta(t)) \\ \end{aligned}}

There are two kinds of tuples: up tuples and down tuples. We write tuples as ordered lists of their components; a tuple is delimited by parentheses if it is an up tuple and by square brackets if it is a down tuple.

— Structure and Interpretation of Classical Mechanics

So $\displaystyle{\left[\partial_0 L (t, q, v), \partial_1 L (t, q, v), \partial_2 L (t, q, v)\right] (0, \eta(t), D\eta(t))}$ is really a dot product:

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\displaystyle{ \begin{aligned} & \int_{t_1}^{t_2} (D L \circ \Gamma[q]) \delta_\eta \Gamma[q] \\ &= \int_{t_1}^{t_2} [\partial_0 L (t, q, v), \partial_1 L (t, q, v), \partial_2 L (t, q, v)] (0, \eta(t), D\eta(t)) \\ &= \int_{t_1}^{t_2} [\partial_1 L (t, q, v) \eta(t) + \partial_2 L (t, q, v) D\eta(t)] \\ \end{aligned}}

— Me@2019-12-14 06:11:22 PM

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# Classical physics

Quantum Mechanics 6

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As Gene and Sidney Coleman have pointed out, the term “interpretation of quantum mechanics” is a misnomer encouraging its users to generate logical fallacies. Why? It’s because we should always use a theory, or a more accurate, complete, and universal theory, to interpret its special cases, to interpret its approximations, to interpret the limits, and to interpret the phenomena it explains.

However, there’s no language “deeper than quantum mechanics” that could be used to interpret quantum mechanics. Unfortunately, what the “interpretation of quantum mechanics” ends up with is an attempt to find a hypothetical “deeper classical description” underneath the basic wheels and gears of quantum mechanics. But there’s demonstrably none. Instead, what makes sense is an “interpretation of classical physics” in terms of quantum mechanics. And that’s exactly what I am going to focus in this text.

Plan of this blog entry

After a very short summary of the rules of quantum mechanics, I present the widely taught “mathematical limit” based on the smallness of Planck’s constant. However, that doesn’t really fully explain why the world seems classical to us. I will discuss two somewhat different situations which however cover almost every example of a classical logic emerging from the quantum starting point:

1. Classical coherent fields (e.g. light waves) appearing as a state of many particles (photons)

2. Decoherence which makes us interpret absorbed particles as point-like objects and which makes generic superpositions of macroscopic objects unfit for well-defined questions about classical facts

— How classical fields, particles emerge from quantum theory

— Lubos Motl

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There is no interpretation problem for quantum mechanics. Instead, if there is a problem, it should be the interpretation of classical mechanics problem.

— Lubos Motl

— paraphrased

— Me@2011.07.28

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# 點石成金 8

The Metagame, 2

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For an interesting but useless activity, add a meaningful context.

For example, I use video games to train my courage.

— Me@2011.08.24

— Me@2019-12-12

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# Ken Chan 時光機 3.1

— Me@2019-12-08 10:36:20 AM

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