# Principle of Least Action

Me 20090909:

Based on K. Young’s notes:

Action S should be defined in a way that

1. It is invariant.

3. It fulfills the experimental results.

Me 20090909:

Hamiltonian (in classical mechanics) may not be the total energy of the system.

The formal definition should be H = pv – L.

Me 20090909:

Principle of least time is the principle of least action for photon via de Broglie’s relation.

2009.11.30 Monday (c) ACHK

# Theory and Practice

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It doesn’t matter how beautiful your theory is,
it doesn’t matter how smart you are.
If it doesn’t agree with experiment, it’s wrong.

— Richard Feynman

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2009.11.30 Monday $ACHK$

# Action

Planck’s constant is the quantum of action.

— Wikipedia on Action (physics)

2009.11.29 Sunday ACHK

# Exception

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Good people are exceptions.

— Me@2009.11.26

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2009.11.29 Sunday $copyright ACHK$

# Vacuum polarization and Self energy

What is the relationship between vacuum polarization and self-energy?

Vacuum polarization is the self energy of photon.

— Me@2009.11.25

2009.11.28 Saturday (c) ACHK

# The third impromptu

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Fourth presentation (The third impromptu), about dreams

1. “Ah” from 14 (in Project one) to zero (the pauses do not count)

2. The evaluator did not understand my speech

3. My overall appearance was too serious (?)

— Me@2009.11.26

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2009.11.28 Saturday $copyright ACHK$

# Wave function

One of the paradoxes of quantum theory is that wave function seems to be more than just information (otherwise interference effects are hard to explain) and often less than real, since the collapse seems to take place faster-than-light and triggered by observers.

— Wikipedia on Wave function collapse

2009.11.26 Thursday ACHK

# Holographic Spacetime

July 10, L T M Meeting

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— Me@2009.07.15

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2009.11.26 Thursday $copyright ACHK$

# Nonlinear optics

In nonlinear optics, the superposition principle no longer holds.

— Wikipedia on Nonlinear optics

2009.11.25 Wednesday ACHK

# 醫者 2

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— Me@2009.11.17

— My brother

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2009.11.25 Wednesday $copyright ACHK$

# Normal distribution

The normal distribution was first introduced by Abraham de Moivre in an article in 1733, which was reprinted in the second edition of his The Doctrine of Chances, 1738 in the context of approximating certain binomial distributions for large n.

— Wikipedia on Normal distribution

2009.11.24 Tuesday ACHK

# The Incredibles

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How much of time, staffing and money does your organization spend on creating incredible experiences (vs. avoiding bad outcomes)?

— Seth Godin

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2009.11.24 Tuesday $ACHK$

# ‘Cold’ electrons

If the electrons are cold, it is possible to show that the charge density oscillates at the plasma frequency \omega_{pe} = \sqrt{\frac{4 \pi n_e e^{2}}{m}} (cgs units) = \sqrt{\frac{n_e e^{2}}{m\varepsilon_0}} (SI units) \left[s^{-1}\right], where n_e is the density of electrons, e is the electric charge, m is the mass of the electron, and ε0 is the permittivity of free space. Note that the above formula is derived under the approximation that the ion mass is infinite. This is generally a good approximation, as the electrons are so much lighter than ions. (One must modify this expression in the case of electron-positron plasmas, often encountered in astrophysics). Since the frequency is independent of the wavelength, these oscillations have an infinite phase velocity and zero group velocity.

— Wikipedia on Plasma oscillation

2009.11.23 Monday ACHK

# David Griffiths

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I have never felt the need to “sell” physics,

and efforts to do so under the banner “physics is fun” seem to me demeaning.

Lay out our wares attractively in the marketplace of ideas and eager buyers will flock to us.

— David Griffiths

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2009.11.23 Monday $ACHK$

# Stationary states

| \psi(t) \rangle = e^{-iEt / \hbar} | \psi(0) \rangle

Thus we see that the eigenstates of the Hamiltonian are stationary states, they only pick up an overall phase factor as they evolve with time.

— Wikipedia on Schrodinger picture

2009.11.22 Sunday ACHK

# IELTS 5

Score

9.0   39 – 40
8.5   37 – 38
8.0   35 – 36
7.5   32 – 34
7.0   29 – 31
6.5   26 – 28
6.0   22 – 25

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7.5   Overall

8.0   Listening
6.5   Writing
8.0   Speaking

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— Me@2009.11.20

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2009.11.21 Saturday $copyright ACHK$

# Tractatus Logico-Philosophicus

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You won’t — I really believe — get too much out of reading it. Because you won’t understand it; the content will seem strange to you. In reality, it isn’t strange to you, for the point is ethical. I once wanted to give a few words in the foreword which now actually are not in it, which, however, I’ll write to you now because they might be a key for you: I wanted to write that my work consists of two parts: of the one which is here, and of everything which I have not written. And precisely this second part is the important one.

* On his Tractatus Logico-Philosophicus, in a letter to Ludwig von Ficker (1919), published in Wittgenstein : Sources and Perspectives (1979) by C. Grant Luckhard

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2009.11.18 Wednesday $ACHK$

# Best 2

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If you pursuit a perfect lesson,
you get the worst one.

If you pursuit the best lesson,

— Me@2005-2008

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2009.11.17 Tuesday $copyright ACHK$

# Impromptu speech

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It usually takes more than three weeks to prepare a good impromptu speech.

— Mark Twain

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2009.11.15 Sunday $ACHK$