SICM, 4.2

This was a virtual machine running the installation of MS-DOS 6.22 in the program VMware Player.

VMware Player was able to run virtual machines, but not to create one. Luckily, there was a website that helped me create virtual machine files. A virtual machine file is just a VMware-formatted text file. It defines the specifications of that virtual machine.

Running MS-DOS 6.22 was just for nostalgia. The real reason for learning virtual machines was to use the mechanics software library of the textbook “Structure and Interpretation of Classical Mechanics”. That library was available only for Linux.

— Me@2021-12-31 01:29:46 PM

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Ex 1.22. Driven pendulum

Structure and Interpretation of Classical Mechanics

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Show that the Lagrangian (1.89) can be used to describe the driven pendulum, where the position of the pivot is a specified function of time: Derive the equations of motion using the Newtonian constraint force prescription, …

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[guess]

\displaystyle{ \begin{aligned} m \ddot{y} &= F \cos \theta - mg \\ m \ddot{x} &= - F \sin \theta \\ \end{aligned}}

\displaystyle{ \begin{aligned} m \ddot{y} &= F \frac{y_s - y}{l} - mg \\ m \ddot{x} &= - F \frac{x - x_s}{l} \\ \sqrt{(x_s - x)^2 + (y_s - y)^2} &= l \\ \end{aligned}}

[guess]

— Me@2021-12-30 09:25:17 AM

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pjmorris 4 hours ago [-]

Seems to me like PM’s would think in the most positive terms about the same issue, e.g. what is the maximum amount of ad space that we can use before users lose interest?

No one would directly attempt to be evil, it’d just turn out that way.

“The truly terrible thing is that everybody has their reasons.” ― Jean Renoir

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rytis 1 hour ago [-]

Socrates agrees: “no one ever knowingly does wrong”. :)

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— Hacker News

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2021.12.29 Wednesday ACHK

無拍之拖

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— Me@2009.04.05

— Me@2012.01.01

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（CPK: 廿五歲的我，才認識 28 歲的他？會不會太遲？）

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— Me@2021-12-28 04:30:02 PM

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2.10 A spacetime orbifold in two dimensions, 5

A First Course in String Theory

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(c) Use the expression

$\displaystyle{-ds^2 = -2dx^+ dx^-}$

for the interval to show that any curve in (3) is spacelike.

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\displaystyle{ \begin{aligned} x^+ x^- &= a^2 \\ x^- &= a^2 \frac{1}{x^+} \\ d x^- &= a^2 \frac{-1}{(x^+)^2} d x^+ \\ \end{aligned}}

\displaystyle{ \begin{aligned} -ds^2 &= -2dx^+ dx^- \\ &= \frac{2 a^2}{(x^+)^2} (d x^+)^2 \\ ds^2 &< 0 \\ \end{aligned}}

— Me@2021-12-27 12:24:09 PM

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Book Underlining Principle

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When you are reading, you would underline key words. At one extreme, you underline nothing. So you wouldn’t know which parts are important. At the opposite extreme, you underline everything. Then you also wouldn’t know which parts are important. So the effect of underlining nothing is exactly the same as underlining everything.

This is an example of the principle that

The extreme of Yin is Yang

The extreme of Yang is Yin

That is why I call the principle the Book Underlining Principle.

The source of this principle is that when you push something to one extreme at the object level, that action may also push it to the opposite extreme at the meta level.

For example, when you underlining all the words, at the object level, it means that everything is important. However, at the meta level, “being important” must be relative to something else. You need to distinguish the important words from the unimportant ones. When you underlining all the words, there is no such distinction. So “being important” has become meaningless.

— Me@2021-12-13 11:08 AM

— Me@2021-12-26 03:39 PM

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相聚零刻 1.2

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2021.12.26 Sunday ACHK

因果鏈捷徑

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（安：我從來未試過，從這個角度思考。那可以解釋到，為何物理學可先進到，有相對論和量子力學，但經濟學暫時不能。

— Me@2021-12-25 11:34:13 AM

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Ex 1.21 The dumbbell, 3.4.2

Structure and Interpretation of Classical Mechanics

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e. Make a Lagrangian ($\displaystyle{= T - V}$) for the system described with the irredundant generalized coordinates $\displaystyle{x_{cm}}$, $\displaystyle{y_{cm}}$, $\displaystyle{\theta}$ and compute the Lagrange equations from this Lagrangian. They should be the same equations as you derived for the same coordinates in part d.

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[guess]


(define ((L-cm m0 m1 l) local)
(let* ((q (coordinate local))
(v (velocity local))
(x_cm (ref q 0))
(y_cm (ref q 1))
(theta (ref q 2))

(x_cm_dot (ref v 0))
(y_cm_dot (ref v 1))
(theta_dot (ref v 2))

(M (+ m0 m1))
(mu (/ 1 (+ (/ 1 m0) (/ 1 m1)))))

(+ (* (/ 1 2) M (+ (square x_cm_dot) (square y_cm_dot)))
(* (/ 1 2) mu (square l) (square theta_dot)))))



$\displaystyle{ L_{cm} = \frac{1}{2} (m_0 + m_1) (\dot x_{CM}^2 + \dot y_{CM}^2 ) + \frac{1}{2} \mu l^2 \dot \theta^2 }$


(show-expression
(((Lagrange-equations
(L-cm 'm_0 'm_1 'l))

(up (literal-function 'x_cm)
(literal-function 'y_cm)
(literal-function 'theta)))
't))



[guess]

— Me@2021-12-22 01:20:55 PM

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Eternal return, 2

A “perfect copy” is not a “copy”, because if a copy is perfect, it would be logically indistinguishable from the original.

In other words, we would not be able to determine which one is the “copy” and which one is the “original”, even in principle.

There would be no meaningful difference between the meanings of the labels “copy” and “original”.

— Me@2013-08-11 1:38 PM

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To realize is to realize, 1.4

The Buddha attacked all attempts to conceive of a fixed self, while stating that holding the view “I have no self” is also mistaken. This is an example of the middle way charted by the Buddha.

— Wikipedia on Philosophy of self

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The ultimate self-fulfilling prophecies:

1. free will or not

2. god or no god

3. afterlife or not

4. future spouse exists or not

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Why self-fulfilling?

3. afterlife or not

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Whether “afterlife” exists or not depends on your definitions of “self” and “afterlife”.

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At one extreme, the definition of “afterlife exists” is that, after death, the same fixed self will continue to exist; “you” will exist in exactly the same way as before. In this definition, afterlife does not exist.

Note that even before death, during your normal lifetime, there is actually no “same fixed self”, “you” keeps changing every day and every second.

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At the opposite extreme, the definition of “afterlife exists” is that, some aspects of you continue to exist in some way. In this definition, afterlife exists.

For example, if some of your writings still exist after your death, they will preserve some of your mind.

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This question is like, when your old computer is dead and has got replaced, does it still exist?

The old computer hardware does not exist anymore. However, some of the software and the data do. But just some, not all.

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Continue to exist?

All of you?

NO

Some of you?

YES

— Me@2021-12-18 07:24:32 PM

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He attributes his lifelong habit of writing every day to an incident in 1932 when a carnival entertainer, Mr. Electrico, touched him on the nose with an electrified sword, made his hair stand on end, and shouted, “Live forever!” It was from then that Bradbury wanted to live forever and decided his career as an author in order to do what he was told: live forever.

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2.10 A spacetime orbifold in two dimensions, 4

A First Course in String Theory

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(b) … the family of curves

$\displaystyle{x^+ x^- = a^2}$,

where $\displaystyle{a > 0}$

Show that the identification (2) relates points on each separate curve.

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Identification (2):

$\displaystyle{(x^+, x^-) \sim \left( e^{-\lambda} x^+, e^{\lambda} x^- \right)}$, where $\displaystyle{e^\lambda \equiv \sqrt{\frac{1+\beta}{1-\beta}}}$.

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\displaystyle{ \begin{aligned} (x^+)' &= e^{- \lambda} x^+ \\ (x^-)' &= e^{\lambda} x^- \\ \end{aligned} }

\displaystyle{ \begin{aligned} (x^+)' (x^-)' &= e^{- \lambda} x^+ e^{\lambda} x^- \\ &= a^2 \\ \end{aligned} }

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— Me@2021-12-15 04:18:27 PM

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Minority Report

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Minority Report is a 2002 American science fiction action film directed by Steven Spielberg, starring Tom Cruise, and loosely based on the 1956 short story “The Minority Report” by Philip K. Dick. The picture is set in Washington, D.C. and Northern Virginia in the year 2054, where Precrime, a specialized police department, apprehends criminals based on foreknowledge provided by three psychics called “precogs”.

— Wikipedia on Minority Report

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2021.12.14 Tuesday ACHK

Ordinary

The power of a man’s virtue should not be measured by his special efforts, but by his ordinary doing.

— Blaise Pascal

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2021.12.14 Tuesday ACHK

改變因果鏈起點, 1.2

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（安：何謂「接棒接得切」呢？）

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（安：第二種情況，我不太明白。）

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— Me@2021-12-11 07:18:17 PM

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