Logical arrow of time, 6.4.3

Logical arrow of time, 6.1.3

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The source of the macroscopic time asymmetry, aka the second law of thermodynamics, is the difference between prediction and retrodiction.

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In a prediction, the deduction direction is the same as the physical/observer time direction.

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In a retrodiction, the deduction direction is opposite to the physical/observer time direction.

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In other words:

In a prediction, the meta-time direction is the same as the object-time direction.

In a retrodiction, the meta-time direction is opposite to the object-time direction.

— Me@2022-02-18 06:52:27 AM

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— guess —

If a retrodiction is done by a time-opposite observer, he will see the entropy increasing. For him, he is really making a prediction.

— guess

— Me@2013-10-25 3:33 AM

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How to create a time-inverted observer?

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Just invert the retrodiction direction.

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Retrodiction to a backward-time observer is just equivalent to retrodiction-for-backward-time to a forward-time observer.

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However, retrodiction-for-backward-time is just prediction.

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In other words, retrodiction to a backward-time observer is equivalent to a prediction for a normal time direction observer.

That’s why

— guess —

If a retrodiction is done by a time-opposite observer, he will see the entropy increasing. For him, he is really making a prediction.

— guess

— Me@2013-10-25 3:33 AM

— Me@2022-02-18 06:37:59 AM

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2022.02.18 Friday (c) All rights reserved by ACHK

EPR paradox, 11.8

physical definition

~ define the microscopic events in terms of observable physical phenomena such as the change of readings of the measuring device

~ define unobservable events in terms of observable events

— Me@2022-01-31 08:33:01 AM

The second clue:

If in your experimental design, you have planned to activate a detector when each particle is still on its path, then this activation action itself is already part of your experimental design.

The detector and the planned action of activating it have already formed a “physical definition” that makes your experiment design to have the system being in a mixed state, instead of superposition state, since the beginning of the experiment.

Put it more accurately, since a wave function is a mathematical function, not a physical field, it does not exist in physical spacetime.

Superposition is a property for some wave functions (quantum states). So superposition is not a physical phenomenon. Instead, it is a mathematical property of some physical variables of your experimental-setup design.

In a sense, instead of existing at the time level of the experiment and the observer, a wave function exists at the meta-time level, the time level of the experiment-setup designer.

So it is meaningless to say “the experimental setup is in a superposition state (or not) in the beginning of the experiment”.

Instead, whether a system is in superposition or not (with respect to a particular variable) is an intrinsic property of your experimental setup design, which includes not just objects and devices, but also operations.

“Wave function collapse” is not a physical event that happens during the operation of the experiment. Instead, it “happens” when you replace one experiment design with another.

— Me@2022-02-16 10:45:01 AM

If the experimenter does not follow the original experiment design, such as not turning on the detector at the pre-defined time, then he is actually doing another experiment, which will have a completely different probability distribution (for any particular variable).

— Me@2022-02-14 10:35:27 AM

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An experiment-setup design is composed of not only objects and devices, but also operations. A different experiment-setup design will give a different probability distribution for any particular physical variable.

Also, a different observer will see a different probability distribution for any particular physical variable. The same observer at different times actually should be regarded as different observers.

In other words, “where and when an observer should do what during the experiment” is actually part of your experimental-setup design, defining what probability distribution (for any particular variable) you (the observer) will get.

— Me@2022-02-18 07:40:14 AM

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2022.02.18 Friday (c) All rights reserved by ACHK

EPR paradox, 11.7

Even in this stranger case, all experimental results are still consistent with special relativity (aka causality), because wave functions are not physical quantities. Instead, they are mathematical quantities for calculating probabilities, which themselves are also mathematical quantities, for predicting experimental results.

physical definition

~ define the microscopic events in terms of observable physical phenomena such as the change of readings of the measuring device

~ define unobservable events in terms of observable events

— Me@2022-01-31 08:33:01 AM

(Me@2022-02-17 03:34:27 PM: I think I have the answer now. I plan to publish it soon. But I keep the following as a record of thoughts.)

A further strangeness is that

~ How come the results are always consistent when the EPR pair has no definite states before measurement the activation of at least one detector?

~ How does the universe to do such bookkeeping for a system exists across several light-years when the physical variables are still in superposition when the pair is emitted from the source?

~ … when the difference of possible values (such as the difference of spin-up and spin-down) still have no physical definition yet?

~ … when the difference of possible values have not yet defined by the difference of possible readings of a detector (before any detector is allowed to be installed-and-activated)

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However, this kind of strangeness also happens in classical physics, for example:

1. How come energy is always conserved? How is energy conservation “executed”?

2. How does probability work? How does the universe work to fulfill the predicted probability patterns?

— Me@2022-02-11 12:47:14 AM

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A clue (but not yet the whole final solution) is that probability is with respect to observers.

— Me@2022-02-11 10:13:36 AM

A probability is partially objective and partially subjective. So a wave function, which is used for calculating probabilities, is also partially objective and partially subjective.

A major fault of the many-worlds interpretation of quantum mechanics is that it uses an unnecessarily complicated language to state an almost common sense fact that any probability value is partially subjective and thus must be with respect to an observer.

— Me@2022-02-14 10:36:52 AM

— Me@2022-02-14 10:35:27 AM

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2022.02.17 Thursday (c) All rights reserved by ACHK

Job: Security, 2

Ask HN: What was the best decision you made in your career?

DerekQ on Sept 26, 2018 | next [–]

Moving from permanent to contractor.

I made the jump 5 years ago and have worked for a number of companies since, on 6-12 month contracts. The money has jumped each time, such that I’m on what I consider to be silly money now for the job I do — Ireland, not US.

The work is always interesting for at least 6 months and I learn a ton of new stuff with every contract, much of which I use when building my own products (Downtime between contracts).

Every aspect of contracting is better than being permanent: the ability to jump ship quickly without affecting my hireability, the exposure to so many different technologies and different ways of doing things, the constant freshness of new things and new people, the ideas that come with seeing how different teams create and build different software, the ease with which you can step into new contracts (often one 30 minute interview as opposed to multipel interviews tests and take home projects for perm roles), and of course the money.

In terms of learning, each contract is like spending 3 years in a permie job, and I’ve had 7 in the past 5 years.

— Hacker News

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2022.02.17 Thursday ACHK

量子力學 3.1

這段改編自 2021 年 12 月 5 日的對話。

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量子力學這門學問,「奇怪」的地方,不在於它奇怪。

「學習新領域時,學到新東西,遇到前所未見,意想不到的事物,而感到奇怪震驚」本身是,正常不過的事情。

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量子力學的真正「奇怪」的地方是,在一連串的誤會之下,人們以為量子力學遺反了,最基本的邏輯定律。那又稱為「亞里士多德定律」,主旨是:

對於任何命題「甲」,「甲」或「非甲」的其一必為真,但兩句一定不會同時為真。

(證明很簡單,因為根本毋須證明;那只是「非」這個字的定義。)

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「量子遺反邏輯」這錯覺,來自教學上的失誤,例如:

在電子雙狹縫實驗中,如果沒有安裝任何偵測器,去觀察電子的路徑軌跡的話,每一粒電子都會,同時通過左狹縫和右狹縫,去到板的另一邊。

由於隔板上,只有左右兩個狹縫,所以,「右」就即是「非左」。那就即是話:「每一粒電子都會同時,通過左狹縫和不通過左狹縫。

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如果認清和防範,這類嘩眾取寵式,而導致錯誤的表述的話,你最終會知道,量子力學不單遵守邏輯,而且還甚至,「主動」守護了因果律。

— Me@2022-02-17 10:31:59 AM

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2022.02.17 Thursday (c) All rights reserved by ACHK

EPR paradox, 11.6

What is more difficult to understand is the non-classical part:

What if, instead of turning on a detector before the time of emitting, we turn it on after the pair is emitted but before either of them has reached its destination?

In the common (but inaccurate) language, the action of activating a detector has collapsed the wave function of the system.

Would the pair of (such as) spin values be correlated?

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(Me@2022-02-16 12:07:25 AM: I think I have the answer now. I plan to publish it soon. But I keep the following as a record of thoughts.)

There are 2 possibilities.

(I do not know which of them is true, because I have not yet found an actual experiment that has tested against them.)

[guess]

1.

They are correlated only in the statistical sense.

2.

Every pair is correlated.

This is stranger than the first case, because if the two detectors are several light-years apart, the whole system exists across those light-years. The strangeness is the fact that even for a system-across-light-years, operations at one end can influence the probability of an event at the other end.

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For the time being, I guess that the second case is the true one.

Even if the first case is the true one, it is still strange because it implies that an action at one part of the system influences the statistical properties of another part, which may be several light-years away.

[guess]

Even in this stranger case, all experimental results are still consistent with special relativity (aka causality), because wave functions are not physical quantities. Instead, they are mathematical quantities for calculating probabilities, which themselves are also mathematical quantities, for predicting experimental results.

— Me@2022-02-11 12:47:14 AM

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Bug fixes:

1.1  It is not the particle’s state that is in a superposition or not, but the system’s state.

2.1  We need to specify which observer that the wave function is with respect to.

A wave function is for an observer to calculate the probabilities of different possible results in an experiment.

2.2  There is no “god’s eye view” in physics.

Every physical event must be described with respect to an observer. Every physical event, even if the event is “to compare observation results”, must be described with respect to an observer. — Me@2017-05-10 07:45:36 AM

2.3  A wave function is mathematical, not physical.

It is a mathematical function for an observer to calculate the probabilities. It is not something existing in physical spacetime. Thus superposition is also not something existing in physical spacetime. So it is meaningless to ask if the system state is in a superposition at a particular time.

Instead, whether a system is in superposition or not (with respect to a particular variable) is an intrinsic property of your experimental setup design, which includes not just objects and devices, but also operations.

“Wave function collapse” is not a physical event that happens during the operation of the experiment. Instead, it “happens” when you replace one experiment design with another.

— Me@2022-02-16 10:45:01 AM

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2022.02.16 Wednesday (c) All rights reserved by ACHK

EPR paradox, 11.5

Black hole information paradox, 2.2.5

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What is more difficult to understand is the non-classical part:

What if, instead of turning on a detector before the time of emitting, we turn it on after the pair is emitted but before either of them has reached its destination?

Since neither of the detectors at the two end destinations is activated in the beginning, the entangle variables are still physically-undefined (i.e. in a superposition) at that moment the pair is emitted.

However, while the particles are still on the way, at the moment one of two detectors is first activated, the entangled variables get their physical definitions. The system state is no longer in a superposition state. Instead, it becomes a mixed state. In other words, the system has become a classical system (with respect to those entangled variables).

In the common (but inaccurate) language, the action of activating a detector has collapsed the wave function of the system.

Would the pair of (such as) spin values be correlated?

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(Me@2022-02-16 12:07:25 AM: I think I have the answer now. I plan to publish it soon. But I keep the following as a record of thoughts.)

There are 2 possibilities.

(I do not know which of them is true, because I have not yet found an actual experiment that has tested against them.)

[guess]

1.

They are correlated only in the statistical sense.

Individual pair of values may be not correlated, but a lot of pairs that have the same superposition (at time of emitting) will form that statistical pattern that is indistinguishable from the one that predicted with the assumption that every pair is correlated.

In analogy, in the double-slit experiment, an individual dot on the final screen cannot tell whether the particle was in a superposition. It is only after a lot of dots forming on the final screen, we can check whether there is an interference pattern. When the interference appears (and we assume that the wave function that governs every particle is the same), we say that every particle is in a superposition state. Or put it more accurately, the system is in the same superposition state before each particle has reached the screen.

2.

Every pair is correlated.

[guess]

— Me@2022-02-11 12:47:14 AM

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2022.02.16 Wednesday (c) All rights reserved by ACHK

靈感天線

Amazing Gags 4.3

這段改編自 2010 年 10 月 14 日的對話。

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其實,根據剛才的討論內容,這個理論本來,可以叫作「種子靈感天線搞 gag 間書太極謀事在人成事在天可遇不可求有心栽花花不香無心插柳柳成蔭踏破鐵鞋無覓處得來全不費功夫原理」。

今年三月時,我和一位朋友,想為這個原理,起一個簡潔的名字,因為沒有的話,每次要提起它時,也十分麻煩。

一個可能可用的名字是「天線原理」。 例如,如果要「搞 gag」(弄笑話)的話,不刻意去弄,就不會有笑話。但是,如果刻意去弄的話,又只會弄到冷笑話。那怎樣辦呢?

那就唯有要,開著「靈感天線」,將自己的心理狀態,調節到適當的天界頻道,企圖去接收,來自未來的訊息。有時接收得到,有時接收不到,不可強求。

你在作其他事情時,就有時會接收到。相反,如果不作他事,專心弄笑話的話,大概可以保證,一定接收不到。

弄巧反拙,寧拙無巧。創意呢家嘢,可遇不可求——沒法勇敢爭取,只能大方接收。

把手緊握 什麼都沒有

把手放開 你得到一切

— 臥虎藏龍

— Me@2022-02-15 01:03:23 PM

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2022.02.15 Tuesday (c) All rights reserved by ACHK

EPR paradox, 11.4

Black hole information paradox, 2.2.4

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physical definition

~ define the microscopic events in terms of observable physical phenomena such as the change of readings of the measuring device

~ define unobservable events in terms of observable events

— Me@2022-01-31 08:33:01 AM

In the EPR experiment, if at least one of the detectors at the two end destinations is already turned on at the time of emitting, then (the system that contains) the pair is NOT in a superposition since the beginning.

The entangled variables (that the detector measures) are already physically defined by the detector’s potential behaviors. The system state is already a mixed state, not a superposition.

superposition

~ lack of the existence of measuring device to provide the physical definitions for the (difference between) microscopic events

— Me@2022-01-31 08:33:01 AM

— Me@2022-02-12 10:22:09 AM

With respect to that pair of entangled variables, the experiment setup is just a classical one, which directly follows Aristotle’s 3 laws of logic.

For any proposition \displaystyle{A}, either \displaystyle{A} is true or \displaystyle{\text{NOT}~A} is true, but not both.

There is nothing non-classical about the correlation between the (such as) spin values of the pair.

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What is more difficult to understand is the non-classical part:

What if, instead of turning on a detector before the time of emitting, we turn it on after the pair is emitted but before either of them has reached its destination?

— Me@2022-02-11 12:47:14 AM

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2022.02.14 Monday (c) All rights reserved by ACHK

EPR paradox, 11.3

Black hole information paradox, 2.2.3

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It shouldn’t be so surprising that unitarity survives completely while causality doesn’t. After all, the basic postulates of quantum mechanics, including unitarity, the probabilistic interpretation of the amplitudes, and the linearity of the operators representing observables, seem to be universally necessary to describe physics of any system that agrees with the basic insights of the quantum revolution.

On the other hand, geometry has been downgraded into an effective, approximate, emergent aspect of reality. The metric tensor is just one among many fields in our effective field theories including gravity.

— Black hole information puzzle

— Lubos Motl

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identical particles

~ some particles are identical, except having different positions

~ some particle trajectories are indistinguishable

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trajectory indistinguishability

~ particle identity is an approximate concept

~ causality is an approximation

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spacetime is defined by causality

~ so spacetime is also an approximation

— Me@2022-02-11 12:47:14 AM

— Me@2022-02-13 03:38:35 PM

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2022.02.13 Sunday (c) All rights reserved by ACHK

Calendar items

The calendar items are action triggers, not action plans, nor procedures.

— Me@2015-11-23 01:39:39 PM

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2022.02.13 Sunday (c) All rights reserved by ACHK

程式員頭腦 15

數學教育 7

這段改編自 2010 年 4 月 24 日的對話。

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But while you don’t literally need math for most kinds of hacking, in the sense of knowing 1001 tricks for differentiating formulas, math is very much worth studying for its own sake. It’s a valuable source of metaphors for almost any kind of work.[3] I wish I’d studied more math in college for that reason.

[3] Eric Raymond says the best metaphors for hackers are in set theory, combinatorics, and graph theory.

— Undergraduation

— March 2005

— Paul Graham

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(安:另外,他提的另一個,有關學習數學的要點是,即使假設你在大學中,學到的數學,在日常生活中沒有用,單單是為獲取,那些嶄新的元素概念本身,就已經能夠令你有超能力;令你有一些,常人沒有的思考工具、比喻語言。)

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那和我之前,叫你學 programming(電腦編程),意思是一樣的。

那本 programming 教科書《SICP》(Structure and Interpretation of Computer Programs),竟然教曉我,時間的定義和數字的定義等。

— Me@2022-02-13 10:46:08 AM

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2022.02.13 Sunday (c) All rights reserved by ACHK

Lego System 6571

搜神記 3 | Extraordinary, 3.2

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Do not ask your children to strive for extraordinary lives. Such striving may seem admirable, but it is the way of foolishness. Help them instead to find the wonder and the marvel of an ordinary life. Show them the joy of tasting tomatoes, apples and pears. Show them how to cry when pets and people die. Show them the infinite pleasure in the touch of a hand. And make the ordinary come alive for them. The extraordinary will take care of itself.

— William Martin

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只要敢遠飛  亦能自創我的煙花紀
神是我自己  若然目光高過聚散分離
奉承你  因往日雙眼無珠不停放大你

想快樂不靠神跡  才懂創世紀

— 搜神記

— 林夕

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2022.02.12 Saturday (c) All rights reserved by ACHK

EPR paradox, 11.2

Black hole information paradox, 2.2.2

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physical definition

~ define the microscopic events in terms of observable physical phenomena such as the change of readings of the measuring device

~ define unobservable events in terms of observable events

— Me@2022-01-31 08:33:01 AM

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superposition

~ lack of the existence of measuring device to provide the physical definitions for the (difference between) microscopic events

— Me@2022-01-31 08:33:01 AM

— Me@2022-02-12 10:22:09 AM

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In the EPR experiment, how come the two always correlate if there are no definite states before the measurements?

When you actually know the results of your experiment, it does affect your expectations of the faraway results if there are correlations – and correlations are almost always there iff the two subsystems have interacted or been in contact in the past). — Lubos Motl

Microscopically, there is no time, in the sense that all the (past and future) quantum states have one-one correspondences. All results are deterministic. No causality violation required nor allowed. — Me@2016-10-14 07:55:48 PM

This is called quantum determinism, which may or may not be correct. But quantum determinism, even if true, is not necessary for explaining the EPR experiment, if we understand that:

1. Superposition is mathematical, not physical.

2. “Wave function collapse” is mathematical, not physical. It just means that we have to replace the wave function with another if we replace the system with another.

The system before and after the detectors activated should be regarded as two distinct systems. In other words, when you activate the detectors, you have actually replaced a system-without-detectors with a system-with-detectors.

“Wave function collapse” replaces the pure state wave function with a mixed state wave function. In other words, it replaces the pure state of superposition with a mixed state of eigenstates. In other other words, it replaces quantum probability with classical probability.

Before opening the box, the cat is not in a superposition state. Instead, it is in a mixed state.

The uncertainty is classical probability, which is due to lack of detailed knowledge, not quantum probability, which is due to lack of definition (in terms of physical phenomena difference).

— Me@2022-01-29 10:38:19 PM

— Me@2022-02-12 10:28:57 AM

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2022.02.12 Saturday (c) All rights reserved by ACHK

EPR paradox, 11.1

Black hole information paradox, 2.2.1

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superposition

~ lack of the existence of measuring device in the definition of the experimental setup to define the difference between microscopic events in terms of the difference between observable physical events

— Me@2022-01-31 08:33:01 AM

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Note that superposition is mathematical, not physical. A wave function is not probabilities, nor a physical wave. Superposition applies only to wave functions, not to probabilities, nor to physical realities.

If superposition had been of probabilities or of physical realities, there would have been no interference patterns in the double-slit experiment.

— Me@2022-02-11 03:32:47 PM

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For example, in the double-slit experiment, if no detector is installed, the system is in a quantum superposition state.

It is not that each individual photon is in a superposition, because an individual particle has no 100% objective identity, due to the indistinguishability of identical particles. Instead, it is that the system of the whole experimental setup is in a superposition.

This applies also to other more complicated experimental setups, such the EPR experiment, the delayed-choice experiment, the delayed-choice quantum eraser, etc.

— Me@2021-01-23 12:57 AM

— Me@2022-02-11 03:29 PM

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physical definition

~ define the microscopic events in terms of observable physical phenomena such as the change of readings of the measuring device

~ define unobservable events in terms of observable events

— Me@2022-01-31 08:33:01 AM

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a definite state

~ an eigenstate

~ a state that has given a physical definition

— Me@2022-02-11 01:19:57 PM

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What we do in the present does not change the past, but changes we can see/say about the past. — Wheeler on Delayed choice quantum eraser, paraphrased, Me@2018-02-04 03:40:27 PM

Physics is not about reality, but about what one can say about reality. — Bohr, paraphrased

Physics should deduce what an observer would observe, not what it really is, for that would be impossible. — Me@2018-02-02 12:15:38 AM

It is because, tautologically, any state that cannot be physically defined is logically and physically meaningless.

In other words, any state that has no distinguishing observable effects does not make sense. For example, if in a double-slit experiment, no detector is allowed, then it is no point to label the state either as “go-left” or as “go-right”. Instead, we have to label the state as a superposition state.

Some unobservable (aka microscopic) variables are meaningless. It is not because of any philosophical points of view, but because we have not defined those variables in terms of observables or observable events, aka physical phenomena. In other words, those variables have no physical definitions yet.

— Me@2022-02-11 03:50:59 PM

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Quantum mechanics, and physics in general, gives the rules of storytelling about reality. A story is a post hoc description of a physical event. In other words, quantum mechanics, and physics in general, is about phenomena, not noumena.

phenomenon (plural phenomena)

~ thing appearing to view

~ reality with respect to an observer

noumenon (plural noumena)

~ thing-in-itself

~ reality independent of any observers

— Me@2022-02-11 3:00 PM

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2022.02.11 Friday (c) All rights reserved by ACHK

原來是我

原來是你, 3

這段改編自 2010 年 10 月 14 日的對話。

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你所追求的東西,可能一直在你身邊,只是你沒有留意。

這原理不只適用於,愛情方面。它也會現身於,才能和興趣等。

例如,我小時候,在中三之始,就開始修讀物理科。但是,我要在兩年後,中五前的暑假才發現,物理是我事業中的最愛;自始以其為人生目標。

— Me@2022-02-10 08:08:53 PM

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2022.02.11 Friday (c) All rights reserved by ACHK