Shadowing Practice: Has quantum mechanics proved that reality does not exist? - Learn English Speaking with Video
Creating lesson...
1
Physicists have shown that objective reality doesn't exist.
2
This is allegedly an insight derived from quantum mechanics.
3
And not only this, it's been experimentally confirmed.
4
Really?
5
How do you prove that reality doesn't exist?
6
Has it really been done?
7
And do we have to stop saying really now?
8
That's what we'll talk about today.
9
Many of you have asked me to comment on those headlines claiming that reality doesn't exist.
10
It's a case in which physicists have outdone themselves in the attempt to make linear algebra sound mysterious.
11
The outcome is patently absurd.
12
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,
13
does it make a sound?
14
Perhaps not, some say.
15
So, what are those people talking about?
16
The story begins in 1961 with the Hungarian physicist Eugène Wigner.
17
Wigner was part of the second generation of quantum physicists.
18
At his time, the mathematical basis of quantum mechanics had been settled and was experimentally confirmed.
19
Now, physicists moved on to quantum field theory, which would eventually give rise to the standard model.
20
But they still couldn't make sense of what it means to make a measurement in quantum mechanics.
21
The way that quantum mechanics works is that everything is described by a wave function, usually denoted psi.
22
The change of the wave function in time is given by the Schrödinger equation.
23
But the wave function itself isn't measurable.
24
Instead, from the wave function you just calculate probabilities for measurement outcomes.
25
Quantum mechanics might for example predict that a particle hits the left side
26
or the right side of a screen with 50 % probability each.
27
Before the particle hits the screen, it is in a superposition of those two states, which means it's neither here nor there.
28
Instead, it's in some sense both here and there.
29
But once you have measured the particle, you know where it is with 100 % probability.
30
This means after a measurement you have to update the wave function.
31
This update is also called the reduction or collapse of the wave function.
32
What is a measurement?
33
Quantum mechanics doesn't tell you.
34
And that's the problem.
35
Wigner illustrated this problem with a thought experiment now known as Wigner's friend.
36
Suppose Wigner's friend Alice is in a laboratory and does an experiment like the one we just talked about.
37
Wigner waits outside the door.
38
Inside the lab, the particle hits the screen with 50 % probability left or right.
39
When Alice measures the particle, the wave function collapses, and it's either left or right.
40
She then opens the door and tells Wigner what she's measured.
41
But how would Wigner describe the experiment?
42
He only finds out whether the particle went left or right when his friend tells him.
43
So, according to quantum mechanics, Wigner has to assume that before he knows what's happened, Alice is in a superposition of two states.
44
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.
45
The problem is now that according to Alice, the outcome of measurement never was in a superposition, whereas for Wigner it was.
46
So they don't agree on what happened.
47
Reality seems to be subjective.
48
Now, it's rather obvious what's going on, namely that one needs to specify what physical process constitutes a measurement,
49
otherwise the prediction is of course ambiguous.
50
Once you have specified what you mean by measurement, Alice will either do a measurement in her laboratory or not, but not both.
51
And in a real experiment, rather than a thought experiment, the measurement happens when the particle hits the screen.
52
And that's that.
53
Alice is, of course, never in a superposition, and she and Wigner agree on what's objectively real.
54
If that's so obvious, then why did Wigner worry about it?
55
Because in the standard interpretation of quantum mechanics, the update of the wave function isn't a physical process.
56
It's just a mathematical update of your knowledge, which you do after you've learned something new about the system.
57
It doesn't come with any physical change.
58
And if Alice didn't physically change anything, then, according to Wigner, she must indeed herself have been in a superposition.
59
Okay, so that was Wigner's friend in the 1960s.
60
You can't experimentally test this,
61
But in 2016, Daniela Frauchinger and Renato Renner proposed another thought experiment that moved physicists closer to experimental tests.
62
This has been dubbed the extended Wigner's friend scenario.
63
Before we talk more about Wigner and his friends, I want to thank our sponsors on Patreon, especially our tier 4 supporters.
64
Your help is so important to keep this channel going.
65
And you too can help us.
66
Go check out our Patreon page or click on the join button right below this video.
67
Now, what's with the extended weakness friends?
68
In this thought experiment you have two wigners, each of whom has a friend.
69
We'll call these the wigners and the ellises.
70
The ellises each measure one of a pair of entangled particles.
71
As a quick reminder, entangled particles share some property, but you don't know which particle has which share.
72
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,
73
or the other way around.
74
So the ellises each measure an entangled particle.
75
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.
76
Either the left one thinks the spin was up and the right one thinks it's down, or the other way around.
77
And then there's the two weakness, each of which goes to ask their friends something about their measurement.
78
Formally, this asking just means they do another measurement.
79
Frauchinger and Renner then show that there are combinations of measurements in
80
which the two allices cannot agree with the two weakness on what the measurement outcomes were.
81
Again, the obvious answer to what happens is that the allices either measured the particles and collapse the wave function, or they didn't.
82
If they did, then their measurement result settles what happens.
83
If they didn't do it, then it's the Wigner's results which settle the case.
84
Or some combination thereof, depending on who measures what.
85
Again, this is only problematic if you think that the measurement is not a physical process.
86
Which is insanity of course, but that's indeed what the most widely held interpretation of quantum mechanics says.
87
And so, Frauringer and Renner conclude in their paper that quantum mechanics cannot consistently describe the use of itself.
88
Because you run into trouble if you're one of the weakness
89
and try to apply quantum mechanics to understand how the Ellis' used quantum mechanics.
90
You may find this a rather academic argument, but don't get fooled.
91
This innocent -sounding statement is a super important result.
92
Historically, internal inconsistencies have been the major cause of theory -led breakthroughs in the foundations of physics.
93
So we're onto something here.
94
But the Frauchinger -Renner paper is somewhat philosophical
95
because they go on a lot about what knowledge you can have about other people's knowledge.
96
But in 2018, Csáclav Bruckner looked at the problem from a somewhat different perspective and derived a no -go theorem for observer -independent facts.
97
His formulation allows one to use the measurement of certain correlations in measurement outcomes to demonstrate
98
that the observers in the extended weakness front scenario actually had measurement results which disagree with each other.
99
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.
105
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?
109
Well, I'm afraid I have to disappoint you, because the two ellices were single photons, and the two weakness were photodetectors.
110
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.
113
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.
117
But, since quantum mechanics doesn't require you to define just what this process is, You can make contradictory assumptions about it,
118
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.
120
So, to summarize, no one has proved that reality doesn't exist, and no experiment has confirmed this.
121
What these headlines tell you instead is that physicists slowly come to see
122
that quantum mechanics is internally inconsistent and must be replaced with a better theory, one that describes what physically happens in a measurement.
123
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.
📺 Same Channel
C16
Superfluid Dark Matter
IELTS PrepTOEFL PrepUniversity Students
C1The End of Human Mathematics? AI's Recent Breakthrough -- And What's Next
Business EnglishUniversity StudentsWorking Adults
C14
Make AI Believe in God to Keep Humans Safe, Scientist Argues
IELTS PrepTOEFL PrepUniversity Students
C13
FINALLY: A Proof that Particles Take All Paths At Once?
IELTS PrepTOEFL PrepUniversity Students
C1The Uncertainty Principle: What Does It Mean, How Does It Work?
IELTS PrepTOEFL PrepUniversity Students
C1Mathematician Collapses All Functions to One Weird Formula
Business EnglishUniversity StudentsWorking Adults
C13
AI Will End Philosophy, Physicist Claims
IELTS PrepTOEFL PrepUniversity Students
C1We Can Now Simulate a Human Brain, Scientists Show
IELTS PrepTOEFL PrepUniversity Students
C19
Does God exist? Science does not have an answer.
IELTS PrepTOEFL PrepUniversity Students
C15
What is time?
IELTS PrepTOEFL PrepUniversity Students
C1Our Solar System Lost Two Planets!
IELTS PrepTOEFL PrepUniversity Students
C1I was SO wrong about quantum computing.
IELTS PrepBusiness EnglishUniversity Students
✨ Recommend Video
C13
63 sentences
Your brain doesn’t detect reality. It creates it. | Lisa Feldman Barrett
IELTS PrepTOEFL PrepUniversity Students
C163
66 sentences
What science can’t answer, according to physicist Jim Al-Khalili | Big Think
IELTS PrepTOEFL PrepUniversity Students
C14
39 sentences
Why Walls STOP Light Waves But Not Radio Waves?
IELTS PrepTOEFL PrepUniversity Students
C16
104 sentences
How real are the real numbers, really?
IELTS PrepTOEFL PrepUniversity Students
C12
13 sentences
Where Did the Antimatter Go?
IELTS PrepTOEFL PrepUniversity Students
C13
353 sentences
Something Strange Happens When You Look Inside an Atom (Feynman Was Right)
IELTS PrepTOEFL PrepUniversity Students
C12
148 sentences
If You Don't Understand Quantum Physics, Try This!
British AccentIELTS PrepTOEFL PrepUniversity Students
C11
144 sentences
Way of Thinking by Richard Feynman | The Cosmological Reality
IELTS PrepTOEFL PrepUniversity Students
C12
233 sentences
Are we WRONG about most FAMOUS LINGUISTICS experiment??
IELTS PrepTOEFL PrepCambridge Exam Prep
C13
128 sentences
The Most Controversial Problem in Philosophy
IELTS PrepTOEFL PrepUniversity Students
Vocabulary and speaking notes for this lesson
This speaking lesson is built on the video “Has quantum mechanics proved that reality does not exist?”. The speaker keeps coming back to these words: measurement, quantum, particle, mechanics, Wigner. This video has 133 sentences and 1787 words to shadow. The speech runs for 11:02. The speaker talks at a natural 162 words per minute, close to everyday conversation. Only 76% of the words are among the 3,000 most common in English, so the vocabulary is demanding.
Key vocabulary in this video
15 words from the video worth learning, with pronunciation and meaning:
| Word | Pronunciation | Meaning |
|---|---|---|
| measurement noun | /ˈmɛʒ.ə.mənt/ | The act of measuring. |
| quantum noun | /ˈkwɑntəm/ | The total amount of something; quantity. |
| particle noun | /ˈpɑɹtək(ə)l/ | A very small piece of matter, a fragment; especially, the smallest possible part of something. |
| mechanic noun | /mɪˈkænɪk/ | Someone who builds or repairs machinery, a technician; now specifically, someone who works with and repairs the mechanical parts of a motor vehicle, aircraft… |
| experiment noun | /ɪkˈspɛɹ.ə.mənt/ | A test under controlled conditions made to either demonstrate a known truth, examine the validity of a hypothesis, or determine the efficacy or likelihood of… |
| weakness noun | /ˈwik.nɪs/ | The condition of being weak. |
| outcome noun | /ˈaʊtkʌm/ | That which is produced or occurs as a result of an event or process. |
| collapse verb | /kəˈlæps/ | To break apart and fall down suddenly; to cave in. |
| linear adjective | /ˈlɪn.i.əɹ/ | Having the form of a line; straight or roughly straight; following a direct course. |
| probability noun | /ˌpɹɑ.bəˈbɪl.ə.ti/ | The state of being probable. |
| observer noun | /əbˈzɝvɚ/ | One who makes observations, monitors or takes notice. |
| algebra noun | /ˈæl.d͡ʒɪ.bɹə/ | Elementary algebra: A system for representing and manipulating unknown quantities (variables) in equations. |
| confirm verb | /kənˈfɝm/ | To strengthen; to make firm or resolute. |
| settle verb | /ˈsɛtəl/ | To determine (something which was exposed to doubt or question); to resolve conclusively; to set or fix (a time, an order of succession, etc). |
| extend verb | /ɛkˈstɛnd/ | To increase in extent. |
Phrasal verbs you will hear
| Word | Meaning |
|---|---|
| check out verb | To record the departure or withdrawal of someone or something (such as guests, employees, books, etc.). |
| find out verb | To discover, as by asking or investigating. |
| get off verb | To move from being on top of (something) to not being on top of it. |
Sentences worth repeating
Short, complete lines from the video that you can reuse in everyday conversation:
- 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.
Grammar in this video
The structures the speaker uses most, with the exact words from the video:
| Structure | In the video |
|---|---|
| Present perfect have/has + past participle — a past action that still matters now | have shown · have asked · have measured |
| Passive voice be + past participle — the focus is on what happens, not who does it | been done · had been settled · is described |
Pronunciation to watch
The speaker uses 31 contractions and reduced forms, such as doesn't, don't, isn't. Say them the short way, as you hear them.
- The “th” sounds: mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, breakthrough /ˈbɹeɪk.θɹuː/, mathematics /mæθ(.ə)ˈmæt.ɪks/, thereof /ðɛˈɹʌv/, theorem /ˈθiərəm/
- The “sh” and “zh” sounds: measurement /ˈmɛʒ.ə.mənt/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, equation /ɪˈkweɪ.ʒən/, correlation /ˌkɔɹ.əˈleɪ.ʃən/, reduction /ɹɪˈdʌk.ʃən/
- Long words — get the stress right: experiment /ɪkˈspɛɹ.ə.mənt/, probability /ˌpɹɑ.bəˈbɪl.ə.ti/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, laboratory /ˈlæb(ə)ɹəˌtɔɹi/, experimental /ɪkspɛɹəˈmɛntəl/
How to practise with this video
- Listen to the whole video once without speaking and note the words you do not know.
- Start at 0.75× speed, shadow it sentence by sentence, then go back to normal speed once it feels easy.
- Record yourself and compare with the original, paying attention to words like measurement, quantum, particle.
What is the Shadowing Technique?
Shadowing is a science-backed language learning technique originally developed for professional interpreter training and popularized by polyglot Dr. Alexander Arguelles. The method is simple but powerful: you listen to native English audio and immediately repeat it out loud — like a shadow following the speaker with just a 1–2 second delay. Unlike passive listening or grammar drills, shadowing forces your brain and mouth muscles to simultaneously process and reproduce real speech patterns. Research shows it significantly improves pronunciation accuracy, intonation, rhythm, connected speech, listening comprehension, and speaking fluency — making it one of the most effective methods for IELTS Speaking preparation and real-world English communication.