Category Archives: physics

Transcender time

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This essay is adapted from an dialogue on 2010.04.09.

I have transcended past-present-future in my mind. The future may be as fixed as the past. 

(Kinon: Determinism?)

I have transcended Free-Will/Determinism. Like “finite” and “boundless”, they are not necessarily mutually exclusive. Our universe is finite and boundless, just like the surface of the Earth. The surface of the Earth is both finite and boundless.

(Kinon: I agree that Free-Will and Determinism are not necessarily mutually exclusive. They may be the same thing.)
 
NO! It should be “They may be two aspects of the same thing.”
 
— Me@2010.04.09

2010.12.09 Thursday (c) All rights reserved by ACHK

Physicist

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You should be self-employed.

1. If some experience cannot be learned through self-employing work, work for others for several years first. (I had worked as a teacher for 3 years.)

2. For being a physicist, you have to join a university first, as a postgraduate student or a researcher. I did it by being a master student. And I have applied for UU.

The main point is your teacher and your boss have to be much more intelligent and experienced than you. Otherwise, you cannot learn much. 

Start a small business.

— Me@2010.01.01

2010.12.02 Thursday (c) All rights reserved by ACHK

Problem solving (physics)

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There are currently some problems that hinder a unified comprehension of Physics. Lee Smolin (in The Trouble with Physics, 2006) has listed 5 major problems:

   1. Combine general relativity and quantum theory into a single theory.
   2. Resolve the problems in the foundations of quantum mechanics.
   3. Determine whether or not the various particles and forces can be unified in a theory that explains them all as manifestations of a single, fundamental entity.
   4. Explain how the values of the free constants in the standard model of particle physics are chosen in nature.
   5. Explain dark matter and dark energy.

— Wikipedia

2010.11.30 Tuesday ACHK

Box

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In quantum mechanics, a particle in a box has discrete energy levels, while a particle in infinite space has a continuum of energy levels. The discreteness comes from the “compactness” of the box. Can we use this idea to explain why spin is quantized? Yes! The “box” in this case, however, is the group SU(2)!

Geometrically, SU(2) is the same as what we mathematicians call S^3, or the 3-sphere – which is the unit sphere in R^4.

— Spin and the Harmonic Oscillator, John Baez

2010.11.29 Monday ACHK

The Prestige

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死亡魔法

Copyrighted by respective owner.
Do not use this image commercially.

The Prestige 令我心緒不寧. 一套戲, 竟然可以有百幾條伏線.

初中時, 我有學過少少魔術, 可惜沒有開花結果.

或者, 科學就是真正的魔術.

— Me@2009.02.27

2010.11.27 Saturday (c) All rights reserved by ACHK

Particles and Fields

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To reveal it in advance, quantum field theory finally unified particles and fields. All particles became just quanta of fields. Some fields such as the Dirac field used to be known just as particles – electrons – while others were originally known as fields and not particles – such as photons that were appreciated later.

— Lubos Motl

2010.11.18 Thursday ACHK

The Sixth Sense

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.

Cole: I see dead people.
Malcolm: In your dreams? (Cole shakes his head no)
Malcolm: While you’re awake? (Cole nods)
Malcolm: Dead people like, in graves? In coffins?
Cole: Walking around like regular people. They don’t see each other. They only see what they want to see. They don’t know they’re dead.
Malcolm: How often do you see them?
Cole: ALL THE TIME.

— The Sixth Sense

.

Cole: I see dumb people.
Malcolm: In your dreams? (Cole shakes his head no)
Malcolm: While you’re awake? (Cole nods)
Malcolm: Dumb people like, in graves? In coffins?
Cole: Walking around like regular people. They don’t see each other. They only see what they want to see. They don’t know they’re dumb.
Malcolm: How often do you see them?
Cole: ALL THE TIME.

— Me@2010.09.15

.

.

.

2010.09.16 Thursday ACHK

Superstring theory 4

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String theory is the most conservative among all the extensions of quantum field theories that go beyond the standard framework of QFT.

— Lubos Motl

2010.09.03 Friday ACHK

Bayesian probability

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Bayesian probability is one of the most popular interpretations of the concept of probability. The Bayesian interpretation of probability can be seen as an extension of logic that enables reasoning with uncertain statements. To evaluate the probability of a hypothesis, the Bayesian probabilist specifies some prior probability, which is then updated in the light of new relevant data. The Bayesian interpretation provides a standard set of procedures and formulae to perform this calculation. Bayesian probability interprets the concept of probability as “a measure of a state of knowledge”, in contrast to interpreting it as a frequency or a physical property of a system.

— Wikipedia on Bayesian probability

2010.09.02 Thursday ACHK

Binomial distribution

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Limits

    * As n approaches and p approaches 0 while np remains fixed at or at least np approaches , then the Binomial(n, p) distribution approaches the Poisson distribution with expected value .

    * As n approaches while p remains fixed, the distribution of

   
       
    approaches the normal distribution with expected value 0 and variance 1 (this is just a specific case of the Central Limit Theorem).
      
— Wikipedia on Binomial distribution

2010.09.01 Wednesday ACHK

Black Holes and Time Warps

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Black Holes and Time Warps: Einstein’s Outrageous Legacy (1994)

by Kip Thorne

It is my all-time favorite among the popular-science physics books. It presents a serious discussion on how to build a time machine, without misleading the readers.

— Me@2010.08.31

2010.08.31 Tuesday (c) All rights reserved by ACHK

Central limit theorem

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In probability theory, the central limit theorem (CLT) states conditions under which the mean of a sufficiently large number of independent random variables, each with finite mean and variance, will be approximately normally distributed (Rice 1995). The central limit theorem also requires the random variables to be identically distributed, unless certain conditions are met. Since real-world quantities are often the balanced sum of many unobserved random events, this theorem provides a partial explanation for the prevalence of the normal probability distribution. The CLT also justifies the approximation of large-sample statistics to the normal distribution in controlled experiments.

— Wikipedia on Central limit theorem

2010.08.27 Friday ACHK

A First Course in String Theory

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Rather than speculate on the ideas that might have developed in the absence of string theory, we can celebrate the remarkable insights that have emerged from it. It has explained, for example, why black holes have entropy and temperature. It has also demonstrated a surprising fact: theories of strong nuclear forces are equivalent to theories of gravity. Over the last two months, several new papers use string theory to describe the motion of quarks in the plasma created by the Relativistic Heavy Ion Collider at Brookhaven! Not bad for a theory whose critics say is pie in the sky.

— Barton Zwiebach: a letter to the editor

2010.08.25 Wednesday ACHK