跟讀練習: Has quantum mechanics proved that reality does not exist? - 通過影片學習英語口語

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Physicists have shown that objective reality doesn't exist.

This is allegedly an insight derived from quantum mechanics.

And not only this, it's been experimentally confirmed.

Really?

How do you prove that reality doesn't exist?

Has it really been done?

And do we have to stop saying really now?

That's what we'll talk about today.

Many of you have asked me to comment on those headlines claiming that reality doesn't exist.

It's a case in which physicists have outdone themselves in the attempt to make linear algebra sound mysterious.

The outcome is patently absurd.

In one article, Erik Kalvakanti, a physicist who works on the foundations of quantum mechanics, writes, If a tree falls in a forest and no one is there to hear it,

does it make a sound?

Perhaps not, some say.

So, what are those people talking about?

The story begins in 1961 with the Hungarian physicist Eugène Wigner.

Wigner was part of the second generation of quantum physicists.

At his time, the mathematical basis of quantum mechanics had been settled and was experimentally confirmed.

Now, physicists moved on to quantum field theory, which would eventually give rise to the standard model.

But they still couldn't make sense of what it means to make a measurement in quantum mechanics.

The way that quantum mechanics works is that everything is described by a wave function, usually denoted psi.

The change of the wave function in time is given by the Schrödinger equation.

But the wave function itself isn't measurable.

Instead, from the wave function you just calculate probabilities for measurement outcomes.

Quantum mechanics might for example predict that a particle hits the left side

or the right side of a screen with 50 % probability each.

Before the particle hits the screen, it is in a superposition of those two states, which means it's neither here nor there.

Instead, it's in some sense both here and there.

But once you have measured the particle, you know where it is with 100 % probability.

This means after a measurement you have to update the wave function.

This update is also called the reduction or collapse of the wave function.

What is a measurement?

Quantum mechanics doesn't tell you.

And that's the problem.

Wigner illustrated this problem with a thought experiment now known as Wigner's friend.

Suppose Wigner's friend Alice is in a laboratory and does an experiment like the one we just talked about.

Wigner waits outside the door.

Inside the lab, the particle hits the screen with 50 % probability left or right.

When Alice measures the particle, the wave function collapses, and it's either left or right.

She then opens the door and tells Wigner what she's measured.

But how would Wigner describe the experiment?

He only finds out whether the particle went left or right when his friend tells him.

So, according to quantum mechanics, Wigner has to assume that before he knows what's happened, Alice is in a superposition of two states.

One in which the particle went left and she knows it went left, and one in which it went right and she knows it went right.

The problem is now that according to Alice, the outcome of measurement never was in a superposition, whereas for Wigner it was.

So they don't agree on what happened.

Reality seems to be subjective.

Now, it's rather obvious what's going on, namely that one needs to specify what physical process constitutes a measurement,

otherwise the prediction is of course ambiguous.

Once you have specified what you mean by measurement, Alice will either do a measurement in her laboratory or not, but not both.

And in a real experiment, rather than a thought experiment, the measurement happens when the particle hits the screen.

And that's that.

Alice is, of course, never in a superposition, and she and Wigner agree on what's objectively real.

If that's so obvious, then why did Wigner worry about it?

Because in the standard interpretation of quantum mechanics, the update of the wave function isn't a physical process.

It's just a mathematical update of your knowledge, which you do after you've learned something new about the system.

It doesn't come with any physical change.

And if Alice didn't physically change anything, then, according to Wigner, she must indeed herself have been in a superposition.

Okay, so that was Wigner's friend in the 1960s.

You can't experimentally test this,

But in 2016, Daniela Frauchinger and Renato Renner proposed another thought experiment that moved physicists closer to experimental tests.

This has been dubbed the extended Wigner's friend scenario.

Before we talk more about Wigner and his friends, I want to thank our sponsors on Patreon, especially our tier 4 supporters.

Your help is so important to keep this channel going.

And you too can help us.

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Now, what's with the extended weakness friends?

In this thought experiment you have two wigners, each of whom has a friend.

We'll call these the wigners and the ellises.

The ellises each measure one of a pair of entangled particles.

As a quick reminder, entangled particles share some property, but you don't know which particle has which share.

You may know, for example, that the particle spins more set up to zero, zero, but you don't know whether the left particle has been plus one and the right particle has been minus one,

or the other way around.

So the ellises each measure an entangled particle.

Now the thing with entangled particles is that if the ellises measurements don't collapse the wave function, then now the two ellises are entangled.

Either the left one thinks the spin was up and the right one thinks it's down, or the other way around.

And then there's the two weakness, each of which goes to ask their friends something about their measurement.

Formally, this asking just means they do another measurement.

Frauchinger and Renner then show that there are combinations of measurements in

which the two allices cannot agree with the two weakness on what the measurement outcomes were.

Again, the obvious answer to what happens is that the allices either measured the particles and collapse the wave function, or they didn't.

If they did, then their measurement result settles what happens.

If they didn't do it, then it's the Wigner's results which settle the case.

Or some combination thereof, depending on who measures what.

Again, this is only problematic if you think that the measurement is not a physical process.

Which is insanity of course, but that's indeed what the most widely held interpretation of quantum mechanics says.

And so, Frauringer and Renner conclude in their paper that quantum mechanics cannot consistently describe the use of itself.

Because you run into trouble if you're one of the weakness

and try to apply quantum mechanics to understand how the Ellis' used quantum mechanics.

You may find this a rather academic argument, but don't get fooled.

This innocent -sounding statement is a super important result.

Historically, internal inconsistencies have been the major cause of theory -led breakthroughs in the foundations of physics.

So we're onto something here.

But the Frauchinger -Renner paper is somewhat philosophical

because they go on a lot about what knowledge you can have about other people's knowledge.

But in 2018, Csáclav Bruckner looked at the problem from a somewhat different perspective and derived a no -go theorem for observer -independent facts.

His formulation allows one to use the measurement of certain correlations in measurement outcomes to demonstrate

that the observers in the extended weakness front scenario actually had measurement results which disagree with each other.

If that was so, there would in certain cases be no observer -independent facts.

100

This is the origin of all the talk about objective reality not existing and so on.

101

And yeah, it's really just linear algebra.

102

There aren't even differential equations to be solved.

103

I assure you I'm not saying this to be condescending or anything, I just mean to say, this isn't rocket science.

104

Finally in 2019 a group from Edinburgh actually measured those correlations which Bruckner calculated.

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That's the experimental test which the headlines are referring to.

106

Now you may wonder who in Edinburgh played the role of the two ellices and the two weakness.

107

How did the ellices feel while they were in a superposition?

108

Did the weakness see any wave functions collapse?

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Well, I'm afraid I have to disappoint you, because the two ellices were single photons, and the two weakness were photodetectors.

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That's okay of course, I mean some of my best friends are photons too.

111

But of course an interaction with a single photon doesn't constitute a measurement.

112

We already know this experimentally.

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A measurement requires an apparatus big enough to cause decoherence.

114

If you claim that a single photon is an observer who makes a measurement, that's not just a fanciful interpretation, that's nonsense.

115

The alleged mystery of all those arguments

116

and experiments disappears once you take into account that a measurement is an actual physical process.

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But, since quantum mechanics doesn't require you to define just what this process is, You can make contradictory assumptions about it,

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and then more contradictions follow from it.

119

It's like you have assumed that zero equals one, and then show that a lot of contradictions follow from it.

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So, to summarize, no one has proved that reality doesn't exist, and no experiment has confirmed this.

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What these headlines tell you instead is that physicists slowly come to see

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that quantum mechanics is internally inconsistent and must be replaced with a better theory, one that describes what physically happens in a measurement.

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And when they find that theory, that will be the breakthrough of the century.

124

This video was sponsored by Brilliant.

125

I wasn't kidding when I said quantum mechanics isn't rocket science, it's really mostly linear algebra and not remotely as incomprehensible as most physicists want you to believe.

126

If you want to understand quantum mechanics in more depth, Brilliant is a great starting point.

127

Brilliant is a website and app that offers courses on a large variety of topics in science and mathematics.

128

Whether you want to learn something new or freshen up your knowledge, Brilliant is a simple and fun way to do it.

129

All their courses are interactive, so you are challenged with questions and can check your understanding along the way.

130

For this video, for example, I recommend their courses on linear algebra and quantum objects.

131

To support this channel and learn more about Brilliant, go to brilliant .org slash Sabine and sign up for free.

132

The first 200 subscribers using this link will get 20 % off the annual premium subscription.

133

Thanks for watching, see you next week.

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本課的詞彙與口語要點

這節口語課以影片“Has quantum mechanics proved that reality does not exist?”為素材。影片中反覆出現的詞有：measurement, quantum, particle, mechanics, Wigner。這段影片共有 133 個句子、1787 個單詞可供跟讀。講話部分時長為 11:02。說話人語速自然，每分鐘約 162 個詞，接近日常對話。只有 76% 的單詞屬於英語最常用的 3,000 詞，詞彙難度較高。

影片中的重點詞彙

影片中 15 個值得學習的單詞，附發音和釋義：

單詞	發音	釋義
measurement 名詞	/ˈmɛʒ.ə.mənt/	尺寸
quantum 名詞	/ˈkwɑntəm/	量
particle 名詞	/ˈpɑɹtək(ə)l/	粒子
mechanic 名詞	/mɪˈkænɪk/	技工, 機械工 /機械工
experiment 名詞	/ɪkˈspɛɹ.ə.mənt/	實驗 /實驗
weakness 名詞	/ˈwik.nɪs/	虛弱 /虛弱, 軟弱 /軟弱
collapse 動詞	/kəˈlæps/	倒坍, 崩潰 /崩潰
linear 形容詞	/ˈlɪn.i.əɹ/	線性
probability 名詞	/ˌpɹɑ.bəˈbɪl.ə.ti/	可能性
observer 名詞	/əbˈzɝvɚ/	觀察者 /觀察者
algebra 名詞	/ˈæl.d͡ʒɪ.bɹə/	代數 /代數
confirm 動詞	/kənˈfɝm/	證實 /證實, 確認 /確認
interpretation 名詞	/ɪnˌtɜːpɹəˈteɪʃən/	翻譯 /翻譯
headline 名詞	/ˈhɛd.laɪn/	標題 /標題
spin 動詞	/spɪn/	轉動 /轉動, 自轉 /自轉

影片中出現的短語動詞

單詞	釋義
check out 動詞	退房
find out 動詞	找出, 查明

值得反覆跟讀的句子

影片中簡短而完整的句子，可以直接用在日常對話裡：

How do you prove that reality doesn't exist?
That's what we'll talk about today.
Quantum mechanics doesn't tell you.
We'll call these the wigners and the ellises.

影片中的語法

說話人最常用的結構，並附上影片中的原話：

結構	影片中的用法
現在完成時 have/has + 過去分詞 — 過去發生但與現在仍有關聯的事	have shown · it's been · Has it really been done
被動語態 be + 過去分詞 — 強調發生了什麼，而不是誰做的	been done · had been settled · is described

需要注意的發音

說話人用了 31 次縮略和弱讀形式，例如 doesn't, don't, isn't。請按聽到的簡短形式來說。

“th” 音: mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, breakthrough /ˈbɹeɪk.θɹuː/, mathematics /mæθ(.ə)ˈmæt.ɪks/, thereof /ðɛˈɹʌv/, theorem /ˈθiərəm/
“sh” 和 “zh” 音: measurement /ˈmɛʒ.ə.mənt/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, equation /ɪˈkweɪ.ʒən/, correlation /ˌkɔɹ.əˈleɪ.ʃən/, reduction /ɹɪˈdʌk.ʃən/
長單詞——注意重音位置: experiment /ɪkˈspɛɹ.ə.mənt/, probability /ˌpɹɑ.bəˈbɪl.ə.ti/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, laboratory /ˈlæb(ə)ɹəˌtɔɹi/, experimental /ɪkspɛɹəˈmɛntəl/

中文母語者容易讀錯的音：

/v/ — 不要讀成 /w/，上齒輕觸下唇: observer /əbˈzɝvɚ/, objective /ɒbˈd͡ʒɛk.tɪv/, derive /dɪˈɹaɪv/, solve /sɒlv/, interactive /ˌɪn.tɚˈæk.tɪv/
詞尾子音 — 要讀清楚，後面不要加母音: measurement /ˈmɛʒ.ə.mənt/, mechanic /mɪˈkænɪk/, experiment /ɪkˈspɛɹ.ə.mənt/, weakness /ˈwik.nɪs/, collapse /kəˈlæps/
/r/ 和 /l/ 的區別: particle /ˈpɑɹtək(ə)l/, linear /ˈlɪn.i.əɹ/, probability /ˌpɹɑ.bəˈbɪl.ə.ti/, algebra /ˈæl.d͡ʒɪ.bɹə/, laboratory /ˈlæb(ə)ɹəˌtɔɹi/

如何用這段影片練習

先完整聽一遍影片，不要開口，記下不認識的單詞。
先用 0.75 倍速逐句跟讀，熟練之後再回到正常速度。
錄下自己的聲音並與原聲對比，特別注意 measurement, quantum, particle 這類單詞。

什麼是跟讀法？

跟讀法 (Shadowing) 是一種有科學依據的語言學習技巧，最初開發用於專業口譯員的培訓，並由多語言者Alexander Arguelles博士普及。這個方法簡單而強大：您在聽英語母語原聲的同時立即大聲重複——就像是一個延遲1-2秒緊跟說話者的影子。與被動聽力或語法練習不同，跟讀法強迫您的大腦和口腔肌肉同時處理並模模擬實的講話模式。研究表明它能顯著提高發音準確性，語調，節奏，連讀，聽力理解和口語流利度——使其成為雅思口語備考和真實英語交流最有效的方法之一。

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跟讀練習: Has quantum mechanics proved that reality does not exist? - 通過影片學習英語口語

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