シャドーイング練習: String Theory - 動画で英語スピーキングを学ぶ
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Welcome back to Science Click.
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Today, String Theory.
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Our universe contains matter, which when we look closer is made up of particles.
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There are different types of particles, electrons, quarks or neutrinos.
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Particles move in the universe and can interact by exchanging other particles.
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The electromagnetic force, for example, is mediated by the exchange of photons.
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All these different particles are accounted for in what we call the Standard Model.
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It is currently our most precise mathematical description of the quantum world.
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It contains two main categories of particles, fermions which mostly constitute matter, and bosons which mostly describe interactions.
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At first glance, one might think that this is the ultimate theory, that the standard model describes everything.
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But unfortunately, there is another interaction that this model doesn't account for, gravity.
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On a large scale, we know that gravity is described by general relativity.
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Objects curve spacetime, thus attracting other objects.
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As with other types of interactions, we expect that the curvature of spacetime is made up of small particles at the quantum scale.
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Quanta of spacetime curvature, called gravitons.
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But when we try to include the graviton in the standard model, the calculations give absurd results with infinite values that cannot be removed.
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We cannot describe gravity on the quantum scale.
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It is to solve this problem that physicists have been looking for new theories for more than half a century.
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In this video, we are going to build together one of the most promising approaches, string theory.
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The basic idea is quite simple.
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In the standard model, particles are described as small dimensionless points.
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We admit that these points do not all have the same properties to account for the fact
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that there are different types of particles.
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In string theory, we will assume that this is only an approximation, and that if we zoom in on the particles, they are all made up of a small string,
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sometimes open and sometimes closed.
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These little strings have tension like tiny rubber bands and they can vibrate.
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A guitar string can vibrate in different modes, harmonics.
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Likewise, our little strings can in different ways.
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One ripple, two ripples, three ripples and so on.
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And the different vibrating modes behave on our scale like particles of different types.
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When we perform the calculations we discover in particular that some strings behave like photons and better still,
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some like gravitons.
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Starting from the sole principle that particles are tiny strings with tension, we already explain why there are different types of particles.
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We naturally predict the existence of the graviton, thus describing gravity at the quantum scale.
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We now want to understand how these strings evolve through the universe.
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For that, we will use the same principles as our current models.
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Imagine that we throw an electron at a target.
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The electron propagates like a wave, and when it reaches the target, we can't know for sure where it will materialise.
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At the quantum scale, the same experiment can give different results.
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We can only predict the probability of observing such or such result,
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and the goal of physics at this scale is to determine these probabilities.
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The mathematical approach to determine the probability of observing a particular result
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is to consider all possible scenarios that lead to it at the same time.
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We sum all trajectories, but also all possible interactions.
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For example, an electron can emit a photon, then reabsorb it, or two photons, or even three.
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In all the scenarios that we consider, we manually decide to allow such or such types of interactions to reproduce what we observe in reality.
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And by summing all these scenarios, we obtain the desired probability.
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In string theory, the approach is the same, however the particles are no longer points.
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A point traces a trajectory over time, but a string traces a surface.
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And to describe the evolution of a string in a probabilistic way as in quantum physics, you will consider all possible geometries that the string can trace over time.
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It can follow a specific trajectory, vibrate in a certain way,
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but also duplicate itself which amounts to emitting a particle,
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or recombine which amounts to reabsorbing the particle, forming a geometry with a whole.
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By summing up all possible geometries, string theory automatically includes interactions.
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There is no need to add them manually.
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Incidentally, interactions in the standard model were local.
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The emission of a photon was instantaneous, for example.
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In string theory, interactions are now continuous.
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are no longer emitted instantaneously, but gradually.
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This gets rid of the infinities that we obtained when we tried to include the graviton in the standard model.
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In this way, string theory not only predicts the existence of the graviton, but it also allows us to calculate how it interacts with other particles,
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and therefore to describe quantum gravity.
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So far the theory looks very promising.
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It explains why there are different types of particles, it predicts that they can interact,
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and it includes a quantum description of gravity.
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Unfortunately at this stage the model exhibits three problems.
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First problem, all the strings behave like bosons, such as photons or gravitons.
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In our world, there is another category of particles, fermions, such as electrons.
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But so far our model does not predict such particles.
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Second problem, one of the particles predicted by the theory is what we call a tachyon.
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Its mass appears to be an imaginary number, the square root of a negative number.
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It is a mathematical problem that we must get rid of.
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Finally, the third problem.
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Our space-time has four dimensions, three dimensions of space and one of time.
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But this theory only seems to work in a universe with 26 dimensions.
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At this stage, string theory seems very far from describing our universe.
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To solve these problems, we'll have to push the theory a little further.
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To include fermions in our model, the idea is to add spinners on the strings.
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They are the mathematical ingredient that already described fermions in the standard model.
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By simply adding spinners to the strings we solve two problems.
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The model now predicts the existence of fermions and it no longer predicts the tachyon, the particle that was problematic.
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This more complete theory is called super string theory.
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In fact, now that we added spinners, our theory exhibits a fundamental symmetry between fermions and bosons.
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In a way, it predicts that there would be as many bosons as there are fermions.
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This is called supersymmetry.
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What about the third problem?
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Before we included supersymmetry, the mathematics required a 26 dimensional universe.
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Now, superstring theory requires a universe with 10 dimensions.
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Unfortunately this third problem is not resolved.
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The theory does not seem to fit our universe, which only has 4 dimensions.
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Yet so far the model was very promising, should we abandon it for all that?
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If they exist, where would these 6 missing dimensions be?
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One possibility is that our universe could just be a three dimensional slice of a larger nine dimensional super universe.
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Another possibility could be that the six dimensions that we do not observe are curled up on themselves.
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To understand, let's imagine an ant walking on a straw.
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The straw has two dimensions.
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The ant can walk back and forth, and left to right, around the circumference of the straw.
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But if we zoom out enough, we only notice one of the two dimensions.
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The second one that curls around the straw is very small and cannot be seen on this scale.
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In string theory we can assume a similar phenomenon.
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Our universe would have 9 dimensions of space, but 6 of them would be very small dimensions curled up on themselves
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so that we do not see them on our scale.
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This hypothesis may seem a little far-fetched.
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Is it reasonable to assume the existence of dimensions that we do not observe?
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But it turns out that the existence of additional dimensions is a very interesting question that suggest phenomena that we might observe.
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For example, we could imagine a massless particle that moves at the speed of light, but partially inside a compact dimension.
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From our point of view, we do not see this dimension, and therefore the particle seems slower to us, we only observe part of its full motion.
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It seems slowed down as if it it had a mass.
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The idea of additional compactified dimensions thus suggests a fairly simple mechanism through which some particles might exhibit a large mass.
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However, it would currently require too much energy for us to create them in our particle accelerators
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and confirm or not their existence.
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The presence of these additional dimensions also allows a much more varied range of vibrational modes,
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and therefore a greater diversity of potential types of particles.
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In addition, there are a multitude of different ways to curl up six dimensions, and each possibility will predict a different universe,
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where the strings can adopt different vibrational modes and therefore behave like different particles.
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By carefully choosing the way in which these six dimensions are compactified,
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we can adjust our description so that it predicts the same particles as those we observe in our world.
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That said, among the myriad of possibilities, it is not yet clear why our universe would contain the particles of the standard model, rather than some other possibility.
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According to some still speculative hypotheses, the geometry of the universe might even have varied over time,
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transitioning from one compactification to another, and the laws of physics could thus have changed during the first instance of our universe.
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To conclude, string theory remains to this day a speculative model,
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very difficult to test experimentally since the strings would be incredibly tiny,
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and which is only one approach among many others in the quest of finding the ultimate theory.
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However, it is still one of the most promising models, whose insights have far exceeded its original goals.
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Strings allow us to describe gravity on the quantum scale, and open doors to the study of black holes.
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They help develop several fields of mathematics, and get a better understanding of the standard model itself.
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String theory even offers hypothetical candidates for particles, such as axions, to potentially explain dark matter.
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That said, there is still a lot of research to do.
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In particular, the aspects of string theory that are best understood rely heavily on supersymmetry,
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which tends to predict the existence of additional particles which we don't seem to observe yet.
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There are some compactifications that would explain that we don't observe supersymmetry, however these are still very rare and not well understood.
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Finally, to venture even further, there actually exist five different versions of superstring theory describing different types of universes.
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We can show mathematically
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that these five theories are in reality approximations of a single more complete model describing a universe with 11 dimensions.
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M-theory.
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科学の世界を語る場面
このビデオでは、粒子物理学や弦理論について説明しています。科学的なトピックを英語で話す場面は、学術的な用語や複雑な概念を伝えるのに役立ち、YouTubeで英語学習する際の良い教材です。特に、「粒子」「相互作用」「重力」などの単語を使って、自然な会話や説明を練習できます。
覚えておきたい便利なフレーズとコロケーション
- be made up of：「～で構成される」。例：Matter is made up of particles.（物質は粒子で構成される）
- account for：「～を説明する」「～を考慮に入れる」。例：The Standard Model accounts for different particles.（標準模型はさまざまな粒子を説明する）
- mediate by：「～によって媒介される」。例：Electromagnetic force is mediated by photons.（電磁相互作用は光子によって媒介される）
- sum all trajectories：「すべての軌道を合計する」。例：We sum all trajectories to predict probabilities.（確率を予測するためにすべての軌道を合計する）
- trace a surface：「表面を描く」。例：A string traces a surface over time.（弦は時間とともに表面を描く）
あなたのシャドーイングチャレンジ
さあ、今すぐ練習しましょう！shadowing siteやshadow speechの技法を使って、ビデオの一部を繰り返し聞き、その直後に同じように話してみてください。特に、「In string theory, the approach is the same, however the particles are no longer points.」という文を選び、イントネーションやリズムを真似てください。shadowspeaksやshadow speakの方法で、10回ほど繰り返すと、自然な発音が身につきます。この練習で、科学的な英語の表現力が向上するだけでなく、聴解力も伸びるはずです。挑戦してみてください！
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。