Pratique du Shadowing: Has quantum mechanics proved that reality does not exist? - Apprendre l'anglais à l'oral avec la vidéo
Création de la leçon...
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Physicists have shown that objective reality doesn't exist.
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This is allegedly an insight derived from quantum mechanics.
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And not only this, it's been experimentally confirmed.
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Really?
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How do you prove that reality doesn't exist?
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Has it really been done?
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And do we have to stop saying really now?
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That's what we'll talk about today.
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Many of you have asked me to comment on those headlines claiming that reality doesn't exist.
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It's a case in which physicists have outdone themselves in the attempt to make linear algebra sound mysterious.
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The outcome is patently absurd.
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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,
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does it make a sound?
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Perhaps not, some say.
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So, what are those people talking about?
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The story begins in 1961 with the Hungarian physicist Eugène Wigner.
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Wigner was part of the second generation of quantum physicists.
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At his time, the mathematical basis of quantum mechanics had been settled and was experimentally confirmed.
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Now, physicists moved on to quantum field theory, which would eventually give rise to the standard model.
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But they still couldn't make sense of what it means to make a measurement in quantum mechanics.
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The way that quantum mechanics works is that everything is described by a wave function, usually denoted psi.
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The change of the wave function in time is given by the Schrödinger equation.
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But the wave function itself isn't measurable.
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Instead, from the wave function you just calculate probabilities for measurement outcomes.
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Quantum mechanics might for example predict that a particle hits the left side
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or the right side of a screen with 50 % probability each.
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Before the particle hits the screen, it is in a superposition of those two states, which means it's neither here nor there.
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Instead, it's in some sense both here and there.
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But once you have measured the particle, you know where it is with 100 % probability.
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This means after a measurement you have to update the wave function.
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This update is also called the reduction or collapse of the wave function.
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What is a measurement?
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Quantum mechanics doesn't tell you.
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And that's the problem.
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Wigner illustrated this problem with a thought experiment now known as Wigner's friend.
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Suppose Wigner's friend Alice is in a laboratory and does an experiment like the one we just talked about.
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Wigner waits outside the door.
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Inside the lab, the particle hits the screen with 50 % probability left or right.
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When Alice measures the particle, the wave function collapses, and it's either left or right.
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She then opens the door and tells Wigner what she's measured.
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But how would Wigner describe the experiment?
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He only finds out whether the particle went left or right when his friend tells him.
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So, according to quantum mechanics, Wigner has to assume that before he knows what's happened, Alice is in a superposition of two states.
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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.
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The problem is now that according to Alice, the outcome of measurement never was in a superposition, whereas for Wigner it was.
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So they don't agree on what happened.
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Reality seems to be subjective.
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Now, it's rather obvious what's going on, namely that one needs to specify what physical process constitutes a measurement,
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otherwise the prediction is of course ambiguous.
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Once you have specified what you mean by measurement, Alice will either do a measurement in her laboratory or not, but not both.
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And in a real experiment, rather than a thought experiment, the measurement happens when the particle hits the screen.
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And that's that.
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Alice is, of course, never in a superposition, and she and Wigner agree on what's objectively real.
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If that's so obvious, then why did Wigner worry about it?
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Because in the standard interpretation of quantum mechanics, the update of the wave function isn't a physical process.
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It's just a mathematical update of your knowledge, which you do after you've learned something new about the system.
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It doesn't come with any physical change.
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And if Alice didn't physically change anything, then, according to Wigner, she must indeed herself have been in a superposition.
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Okay, so that was Wigner's friend in the 1960s.
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You can't experimentally test this,
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But in 2016, Daniela Frauchinger and Renato Renner proposed another thought experiment that moved physicists closer to experimental tests.
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This has been dubbed the extended Wigner's friend scenario.
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Before we talk more about Wigner and his friends, I want to thank our sponsors on Patreon, especially our tier 4 supporters.
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Your help is so important to keep this channel going.
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And you too can help us.
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Go check out our Patreon page or click on the join button right below this video.
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Now, what's with the extended weakness friends?
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In this thought experiment you have two wigners, each of whom has a friend.
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We'll call these the wigners and the ellises.
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The ellises each measure one of a pair of entangled particles.
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As a quick reminder, entangled particles share some property, but you don't know which particle has which share.
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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,
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or the other way around.
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So the ellises each measure an entangled particle.
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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.
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Either the left one thinks the spin was up and the right one thinks it's down, or the other way around.
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And then there's the two weakness, each of which goes to ask their friends something about their measurement.
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Formally, this asking just means they do another measurement.
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Frauchinger and Renner then show that there are combinations of measurements in
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which the two allices cannot agree with the two weakness on what the measurement outcomes were.
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Again, the obvious answer to what happens is that the allices either measured the particles and collapse the wave function, or they didn't.
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If they did, then their measurement result settles what happens.
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If they didn't do it, then it's the Wigner's results which settle the case.
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Or some combination thereof, depending on who measures what.
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Again, this is only problematic if you think that the measurement is not a physical process.
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Which is insanity of course, but that's indeed what the most widely held interpretation of quantum mechanics says.
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And so, Frauringer and Renner conclude in their paper that quantum mechanics cannot consistently describe the use of itself.
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Because you run into trouble if you're one of the weakness
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and try to apply quantum mechanics to understand how the Ellis' used quantum mechanics.
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You may find this a rather academic argument, but don't get fooled.
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This innocent -sounding statement is a super important result.
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Historically, internal inconsistencies have been the major cause of theory -led breakthroughs in the foundations of physics.
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So we're onto something here.
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But the Frauchinger -Renner paper is somewhat philosophical
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because they go on a lot about what knowledge you can have about other people's knowledge.
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But in 2018, Csáclav Bruckner looked at the problem from a somewhat different perspective and derived a no -go theorem for observer -independent facts.
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His formulation allows one to use the measurement of certain correlations in measurement outcomes to demonstrate
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that the observers in the extended weakness front scenario actually had measurement results which disagree with each other.
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If that was so, there would in certain cases be no observer -independent facts.
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This is the origin of all the talk about objective reality not existing and so on.
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And yeah, it's really just linear algebra.
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There aren't even differential equations to be solved.
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I assure you I'm not saying this to be condescending or anything, I just mean to say, this isn't rocket science.
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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.
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Now you may wonder who in Edinburgh played the role of the two ellices and the two weakness.
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How did the ellices feel while they were in a superposition?
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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.
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But of course an interaction with a single photon doesn't constitute a measurement.
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We already know this experimentally.
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A measurement requires an apparatus big enough to cause decoherence.
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If you claim that a single photon is an observer who makes a measurement, that's not just a fanciful interpretation, that's nonsense.
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The alleged mystery of all those arguments
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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.
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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.
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This video was sponsored by Brilliant.
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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.
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If you want to understand quantum mechanics in more depth, Brilliant is a great starting point.
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Brilliant is a website and app that offers courses on a large variety of topics in science and mathematics.
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Whether you want to learn something new or freshen up your knowledge, Brilliant is a simple and fun way to do it.
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All their courses are interactive, so you are challenged with questions and can check your understanding along the way.
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For this video, for example, I recommend their courses on linear algebra and quantum objects.
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To support this channel and learn more about Brilliant, go to brilliant .org slash Sabine and sign up for free.
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The first 200 subscribers using this link will get 20 % off the annual premium subscription.
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Thanks for watching, see you next week.
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale s’appuie sur la vidéo « Has quantum mechanics proved that reality does not exist? ». Les mots qui reviennent le plus souvent : measurement, quantum, particle, mechanics, Wigner. Cette vidéo contient 133 phrases et 1787 mots à répéter en shadowing. La partie parlée dure 11:02. Le locuteur parle à un rythme naturel d’environ 162 mots par minute, proche d’une conversation courante. Seuls 76 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
15 mots de la vidéo à retenir, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| measurement nom | /ˈmɛʒ.ə.mənt/ | mesure |
| quantum nom | /ˈkwɑntəm/ | quantité |
| particle nom | /ˈpɑɹtək(ə)l/ | particule |
| mechanic nom | /mɪˈkænɪk/ | mécanicien, mécanicienne |
| experiment nom | /ɪkˈspɛɹ.ə.mənt/ | expérience |
| weakness nom | /ˈwik.nɪs/ | faiblesse |
| collapse verbe | /kəˈlæps/ | s'effondrer |
| linear adjectif | /ˈlɪn.i.əɹ/ | linéaire |
| probability nom | /ˌpɹɑ.bəˈbɪl.ə.ti/ | probabilité |
| observer nom | /əbˈzɝvɚ/ | observateur |
| algebra nom | /ˈæl.d͡ʒɪ.bɹə/ | algèbre |
| confirm verbe | /kənˈfɝm/ | confirmer |
| settle verbe | /ˈsɛtəl/ | régler |
| extend verbe | /ɛkˈstɛnd/ | étendre |
| interpretation nom | /ɪnˌtɜːpɹəˈteɪʃən/ | interprétation |
Les verbes à particule que vous entendrez
| Mot | Sens |
|---|---|
| check out verbe | mater, regarder |
| find out verbe | découvrir, savoir |
| get off verbe | descendre, faire descendre |
Des phrases à répéter
Des phrases courtes et complètes de la vidéo, à réutiliser dans la conversation de tous les jours :
- 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.
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| Present perfect have/has + participe passé — une action passée qui compte encore maintenant | have shown · have asked · have measured |
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | been done · had been settled · is described |
Prononciation à surveiller
Le locuteur utilise 31 contractions et formes réduites, comme doesn't, don't, isn't. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « th »: mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, breakthrough /ˈbɹeɪk.θɹuː/, mathematics /mæθ(.ə)ˈmæt.ɪks/, thereof /ðɛˈɹʌv/, theorem /ˈθiərəm/
- Les sons « sh » et « zh »: measurement /ˈmɛʒ.ə.mənt/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, equation /ɪˈkweɪ.ʒən/, correlation /ˌkɔɹ.əˈleɪ.ʃən/, reduction /ɹɪˈdʌk.ʃən/
- Mots longs — placez bien l’accent: experiment /ɪkˈspɛɹ.ə.mənt/, probability /ˌpɹɑ.bəˈbɪl.ə.ti/, interpretation /ɪnˌtɜːpɹəˈteɪʃən/, laboratory /ˈlæb(ə)ɹəˌtɔɹi/, experimental /ɪkspɛɹəˈmɛntəl/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: headline /ˈhɛd.laɪn/, whereas /(h)wɛɹˈæz/, historically /hɪˈstɔɹɪkli/, decoherence /diːkəʊˈhɪəɹəns/, incomprehensible /ɪnˌkɑmpɹəˈhɛnsɪb(ə)l/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: algebra /ˈæl.d͡ʒɪ.bɹə/, objective /ɒbˈd͡ʒɛk.tɪv/, allegedly /əˈlɛdʒ.ɪd.li/, subjective /səbˈd͡ʒɛktɪv/, allege /əˈlɛd͡ʒ/
- /r/ anglais — langue recourbée, sans frotter la gorge: particle /ˈpɑɹtək(ə)l/, experiment /ɪkˈspɛɹ.ə.mənt/, linear /ˈlɪn.i.əɹ/, probability /ˌpɹɑ.bəˈbɪl.ə.ti/, algebra /ˈæl.d͡ʒɪ.bɹə/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme measurement, quantum, particle.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.