シャドーイング練習: Brian Cox: Why even Einstein doubted the existence of black holes - 動画で英語スピーキングを学ぶ
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242 文
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1
Could black holes be the key to a quantum theory of gravity, a deeper theory of how reality, of how space and time works?
ブラックホールこそが、現実や空間、時間がどのように機能するのかを説明するより深い理論、量子重力理論の鍵となるのでしょうか？
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Well, I think so.
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What are black holes hiding?
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It's interesting, these objects which have been known, I would say, for 40 or 50 years,
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but theoretically for the best part of a century, have always been fascinating.
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They're odd things.
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The simplest way to describe a black hole would be a region of space from which even light can't escape.
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Predictions
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that such objects existed go all the way back to the beginnings of relativity back at the turn of the 20th century.
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But actually really, I would say into the 1960s, perhaps even into the 1980s,
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many physicists felt that because of the intellectual challenges that these predicted objects pose,
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many physicists felt that maybe nature would not create them.
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I even saw the great physicist Steven Weinberg say
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that he in some sense hopes that these things would not exist because they're so confusing.
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But we now know that they do exist and so we have to face the challenges that they pose.
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Black holes are interesting because going back to the work of Stephen Hawking in the 1970s,
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It turns out that they demand that we think about both quantum theory and general relativity together.
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And the quest to unify those two great pillars of 20th
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and 21st century physics into what's often referred to as a
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quantum theory of gravity is in some sense a holy grail for theoretical physicists.
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But the problem has always been,
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well, is there anywhere in nature that we can look to observe something that requires us to merge those two theories together?
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And black holes really are the unique place, as far as we can tell,
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in nature, where we can see a thing sitting there in the sky
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that demands that we consider those two theories working together to hopefully reveal a deeper theory.
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The idea of black holes goes back a long way, actually, back into the 1780s and 1790s.
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There were two physicists, mathematicians, natural philosophers, whatever you want to call them, working at the time that had the same idea,
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apparently independently of each other.
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One was a clergyman, an English clergyman called Mitchell, and the other was the great French mathematician Laplace.
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And they were both thinking in terms of an idea called escape velocity.
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So the The escape velocity is the speed you have to travel to completely escape the gravitational pull of something, a planet or a star.
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For the Earth, for example, the escape velocity from the surface of the Earth is around 8 miles a second, 11 kilometers a second.
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If you go bigger, you make a bigger, more massive thing, let's go up to a star, for example, like the sun,
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then the escape velocity increases because the gravitational pull at the surface increases.
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And actually for the sun, it's somewhere in the region of 400 miles a second.
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It's really fast.
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What Michelin and Laplace thought, and I think it's a very beautiful idea, is they imagined in their mind's eye, well, can you go bigger?
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Can you imagine more and more massive stars,
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giant stars, such that the gravitational pull is so large at the surface that the escape velocity exceeds the speed of light?
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And then you wouldn't be able to see them.
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There's a wonderful quote actually in Naples's paper where he says
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that the largest objects in the universe may go unseen by reason of their magnitude.
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And this is back in the 1780s or 1790s.
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So he's imagining stars where the gravitational pull is so vast that even light can't escape and you couldn't see it.
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Dark stars, I think he referred to them as.
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Now we know that such objects do not exist in the universe in that sense, in the sense that Mitchell and Plath meant.
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But actually, they missed something, which is not surprising, because it sounds almost paradoxical.
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But you can also increase the escape velocity, the surface of an object, by squashing it.
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And it turns out that if you take the Earth
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and you squash it down and squash it down and squash it down until it's about that big, the radius just less than a centimetre,
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then the gravitational pull at the surface would be so great that light couldn't escape.
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And that is essentially the modern concept of a black hole.
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Now, Mitchell and Laplace's calculations or imaginings were based on Newtonian physics, so pre-Einstein.
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We come forward to 1915, Einstein published his General Theory of Relativity, which is a different model, a better theory of gravity.
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And it turns out that black holes also exist in general relativity.
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Now, if we come forward to 1915, Newton's theory of gravity is replaced by a better model, a better theory, which is Einstein's general theory of relativity.
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But the idea that there can be objects that can be compressed such
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that they trap light is also present in Einstein's theory.
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The first physicist to predict such a thing, or at least derive the mathematics that describes such a thing as a black hole,
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although he didn't know that they existed, was a man called Carl Schwarzschild.
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What Schwarzschild did was provide an exact solution to Einstein's equations that describes space and time,
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the distortion of space and time in the region of a star, or at least an idealized star,
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which is a perfectly spherical, non-spinning ball of matter.
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It's a model, a simple model of a star.
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Now, Schwarzschild described or discovered the solutions to Einstein's equations that describes what happens to space-time outside such a thing way back,
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actually 1916, just after the theory was published.
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What Schwarzschild's solution also describes though, although he didn't think in these terms at the time,
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was what that space looks like if you completely remove the star
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but leave its imprint in the fabric of the universe behind.
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And that is essentially the theoretical description or the model of a modern a relativistic black hole.
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Now, while Schwarzschild's solution, and by solution I mean we're to picture a distortion in space and time,
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a distortion in the fabric of the universe, while Schwarzschild's solution does indeed describe the simplest possible black hole that we can model in the universe,
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people didn't really think in those terms at all until later.
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You see in the 1930s, Einstein and a colleague of his,
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Rosen, for example, exploring that space-time and building models of what that space-time might look like.
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But I think it's true to say that really, certainly until the late 1930s and actually arguably post-war until the 1960s,
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most physicists thought that such things would not exist in nature.
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So they were theoretically interesting, perhaps not practically interesting.
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The reason is that you have to create such a thing.
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So it's one thing to have a model of space
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and time that describes this object called a black hole from which not even light can escape.
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But it's another thing for nature to actually make it.
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So if you go through the 1930s, there's a lot of papers, actually Robert Oppenheimer and a student of his Snyder, a very famous paper just before the war,
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which explored whether a real star in the universe
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at the end of its life could collapse and collapse without limit to form this geometry, this thing that we call a black hole.
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Just before the war, Oppenheimer and Snyder showed that under certain assumptions, a star could behave in such a way.
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But it wasn't really until the work of people like Roger Penrose and Stephen Hawking and several others in the 1960s,
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that it really began to look as if nature would build these things.
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There's this great quote I remember, with some fondness actually, Arthur Eddington, a colleague of Einstein's, he was very English,
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very proper physicist, and he said, nature will prevent such absurdities from existing.
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just that's it nature will prevent it well it turns out nature doesn't prevent it we now know
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and we've observed them that stars do collapse to form black holes
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and then theoretical physics moves on so people accept
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that these things should exist although it's true to say
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that we haven't actually imaged one until the 21st century but in any case people accepted these things should exist
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more and more evidence mounted that they do exist at the centres of galaxies and at the sites of collapsed stars.
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But then we have to face the consequences.
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What does it mean for our understanding of the universe
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if there are these objects where space and time behave in a very strange way,
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where light is trapped, and where it would seem that anything
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that falls in is at the very least locked away from the universe forever.
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So to understand the conceptual problems that are faced if these things exist,
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then it might be worth just describing very briefly the Einsteinian description, the pure description in general relativity.
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A black hole, what do you see from the outside?
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Well, there's an event horizon surrounding the black hole.
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In some sense, it defines the boundary between the external universe and the interior of the black hole.
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The event horizon is very simply and a bit hand-wavingly, but it's a reasonable description.
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It's just, if you can imagine a sphere in space, and if you go across the boundary into the interior of this sphere,
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then even if you can travel as fast as the speed of light, you can't escape.
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So the event horizon separates the interior of the black hole from the external universe.
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We'll see a bit later why that's a bit of a hand wavy description.
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But another description of the event horizon which confused people all the way through the history of black hole research actually,
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certainly to the early papers in the 1930s and perhaps even post-war, was the idea that the event horizon, when viewed from the outside,
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is a place in space where time stops.
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And that's a direct prediction of Einstein's theory of relativity from the external perspective.
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If you watched, for example, an astronaut falling in towards a black hole, then from your external perspective,
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you'd see their time pass more slowly, slower and slower and slower,
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as the astronaut approached the black hole until on the horizon, you would see their time stop.
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That suggested to many people in the early days that a star couldn't collapse to form a black hole confused them.
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They thought, well, if the star's collapsing, then does it not freeze forever in some sense on the horizon?
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So all sorts of initial early conceptual problems, which ultimately were solved.
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The thing about relativity, just the one sentence thing to understand, is that time can stop from one perspective,
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but time can pass at the usual rate from another perspective.
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And indeed, from the perspective of an astronaut falling into a black hole, then for a sufficiently large black hole,
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like the ones that we find at the centres of galaxies,
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the astronaut would notice nothing at all as they fell across the horizon into the interior of the black hole.
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So time passes at one second per second on the watch of an astronaut falling in, but from the external perspective, time freezes on the horizon.
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So black holes are full of these apparent conceptual challenges, which are actually not conceptual challenges at all.
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They're just a central part of Einstein's general theory of relativity.
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So that confusion was eventually dealt with and solved and people understood,
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certainly by the 1960s, what these things are and how general relativity models them.
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There is a central problem though, which is still not solved, which is, you put it this way, what lies at the centre, and I'll be careful with my language,
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what lies at the centre of a black hole?
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Now in pure, just in Einstein's general theory of relativity.
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Actually, it's not right to talk about the centre of a black hole, really.
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So what are we picturing?
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It's this thing called the singularity.
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You might think of it as an infinitely dense point to which this massive star collapses.
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It's kind of the natural way to think of it.
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But actually, just even in pure general relativity, when you look at a nice map of a black hole, the so-called Penrose diagram named after Roger Penrose,
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you see is that the singularity is not really a place in space at all.
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It's a moment in time.
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And actually, it's the end of time.
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So one way of picturing what's happened
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when a star collapses to form a black hole is that space and time are so distorted that, in a sense, their roles swap.
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And so what we thought of as an infinitely dense point, a place in space, at the centre, at the centre of the collapse of the star,
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if you like, actually becomes a moment in time and the end of time, the singularity.
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But the nature of that thing was not and is still not understood.
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So that's a great mystery.
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And it's been long accepted that we will need a so-called quantum theory of gravity, a deeper theory of gravity, in order to explain the singularity.
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And for many, many years actually until quite recently then people thought well there
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we are we have a problem with the singularity we don't
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really have any access to it we don't have the conceptual tools to explore it
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so it may remain a mystery for a century to come
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it's not clear what to do the great revolution in black hole research was to notice
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and it began with stephen hawking's work in the mid-1970s,
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was to notice that actually there are conceptual problems at the event horizon of the black hole, not in this extreme place,
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not only in this extreme place, the singularity, whatever that might be, but at the horizon.
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Now, that was a real challenge and extremely interesting because we think,
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we strongly expect the laws of nature that we understand now,
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laws of nature that we have full mathematical and conceptual control of, to apply at the event horizon.
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And so that's why black holes have become so interesting.
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It's because we have a place where we think, we assume, and indeed we're right to assume, it seems, that we have full control of the physics.
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We understand what's happening, but there is a fundamental clash of principle between our two basic theories of nature,
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general relativity and quantum mechanics.
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And that is ultimately why the event horizon of a black hole
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and black holes themselves have become so fascinating and so important.
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The modern revolution in our thought, which is still ongoing, by the way,
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in understanding black holes and quantum gravity, really does begin with work that Stephen Hawking did in the mid-1970s.
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Stephen Hawking, in his own words, showed that black holes ain't so black.
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So we've described them as prisons, in a sense.
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We're picturing them as a region of space from which nothing can escape.
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What Stephen Hawking showed in a landmark couple of papers, a tour de force of calculation actually,
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is that if you consider quantum theory, quantum mechanics in the vicinity of the horizon of a black hole,
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then you find that they glow, they produce particles, they have a temperature.
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This thing that we've pictured in Einstein's theory as pure geometry,
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as just distorted space and time, actually emits particles.
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It's called Hawking radiation.
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And one way to picture that, and Stephen in his 1974 paper gives this, He says it's a hand wavy description.
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So it's not a full description.
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You need the mathematics for that.
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But he gives this hand wavy description, which is kind of a nice way to picture what's happening.
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The idea is to imagine, to zoom in on space in the vicinity of the event horizon of a black hole.
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If you zoom in on any piece of space, the piece of space in front of your nose right now, if you could zoom in and slow time down with a big microscope,
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you can picture what's happening as a series of particles coming in
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and out of existence all the time so-called entangled particles
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so it's a picture of what the vacuum of space looks
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like just to emphasize again it's not a complete picture it's not supposed to be precise
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but it's a reasonable model of what's happening so particles in
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and out of existence all the time and that's happening everywhere in space everywhere
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that you look in the most empty piece of space you
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could imagine that's what's happening in the vicinity of the horizon
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of a black hole you can have the situation where one
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of those particles those pairs of particles is on the inside of the event horizon
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and one is on the outside and then it can happen
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that the one on the outside instead of merging back with its partner again can escape into the universe.
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It's essentially made real by the presence of the black hole.
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So the other partner is interior to the black hole and this particle heads off into the universe,
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removing energy from the black hole as it goes.
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This rain of particles, this glow of particles is called Hawking radiation.
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That has profound implications.
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So it's kind of a simple picture of what's happening.
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But the upshot is, imagine this thing, it's a black hole, it's glowing,
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it's just space-time geometry, but it's emitting particles, losing energy, therefore it's shrinking, which means that one day it will be gone.
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So black holes are not eternal prisons, they have a lifetime.
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One day whatever's in there is returned to the universe.
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The question was, the central question
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that was immediately raised by those calculations is this what happened to all the stuff
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that fell in the way i've described it the way einstein's theory describes it is somehow
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that stuff goes to the singularity whatever
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that thing is the end of time a region of space time that's
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so convoluted and distorted that we don't understand how to describe it at all but then
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One day the whole thing is gone.
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All that's left in the far far future is Hawking radiation, those particles that were produced in the vicinity of the event horizon.
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The question is, is it possible if you could collect all that radiation, all the Hawking radiation through the whole life of the black hole,
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is it somehow possible in principle that the information
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about everything that fell into the black hole throughout its history is imprinted in that radiation in the far future.
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Is that true or is it not true?
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You might say, why did I ask that question?
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Seems like a bit of a random question.
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It's a very important question.
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Let's say that I take anything in here, in this room, a book, a table, the camera, anything at all,
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And I set fire to it.
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I incinerate it.
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I destroy it in any way that I can.
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I could throw it into a furnace.
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I could put it in the heart of a nuclear bomb and explode it, whatever, just completely incinerate it.
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In physics, in basic fundamental physics, then it turns out that if you could collect every
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piece of that thing that i detonated
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or incinerated every quantum of radiation every photon every particle everything in principle
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if i could just collect it all
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and i was clever enough then i could reconstruct the thing
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that i had destroyed information is conserved in the universe as far as we know.
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So every law of nature that we have says that information is conserved.
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The problem was that Stephen Hawking's initial calculation of the way those black holes evaporate away said that information is not conserved,
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said that black holes are erasers of information.
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To put it very bluntly, the calculation said that once that black hole had gone,
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then even in principle there is absolutely no way you could learn anything, reconstruct anything, about the things that fell in,
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including the star that collapsed to form it.
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So information erasers, the only information erasers that we know of in nature.
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That was the initial picture of black holes as Stephen Hawking understood them back in the 1970s and 1980s.
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This became known as the black whole information paradox.
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このレッスンの語彙とスピーキングのポイント
このC1レベルのスピーキングレッスンは、動画「Brian Cox: Why even Einstein doubted the existence of black holes」を教材にしています。 繰り返し出てくる語は次のとおりです：hole, space, theory, star, horizon。 この動画には、シャドーイング用の文が242文、単語が3451語あります。 音声の長さは23:02です。 話す速さは1分あたり約150語で、日常会話に近い自然なペースです。 単語の83%は英語の頻出3,000語に含まれます。残りは練習の前に確認しておきましょう。
この動画の重要語彙
動画の中で特に難しい単語15語を、発音と意味つきで紹介します。
| 単語 | 発音 | 意味 |
|---|---|---|
| horizon 名詞 | /həˈɹaɪ.zən/ | 地平線, 水平線 |
| relativity 名詞 | /ɹɛl.əˈtɪv.ɪ.ti/ | 相対性, 相対 |
| particle 名詞 | /ˈpɑɹtək(ə)l/ | 粒子 |
| quantum 名詞 | /ˈkwɑntəm/ | 量 |
| physicist 名詞 | /ˈfɪzɪsɪst/ | 物理学者 |
| singularity 名詞 | /ˌsɪŋɡjəˈlæɹətɪ/ | 単独性, 単一性 |
| conceptual 形容詞 | /kənˈsɛp.tjʊəl/ | 概念的 |
| velocity 名詞 | /vəˈlɑsəti/ | 速度 |
| astronaut 名詞 | /ˈæstɹəˌnɔt/ | 宇宙飛行士, アストロノート |
| calculation 名詞 | /ˌkælkjuˈleɪʃn̩/ | 計算 |
| squash 名詞 | /skwɔʃ/ | 南瓜 |
| vicinity 名詞 | /vəˈsɪnəti/ | 近傍, 付近 |
| conserve 動詞 | /kənˈsɜː(ɹ)v/ | 節約する |
| distort 動詞 | /dɪsˈtɔːt/ | 歪める, 曲げる |
| eraser 名詞 | /ɪˈɹeɪsɚ/ | 消しゴム |
動画に出てくる句動詞
| 単語 | 意味 |
|---|---|
| go back 動詞 | 戻る, 帰る |
この動画の文法
話し手がよく使っている文型を、動画の実際の表現とともに紹介します。
| 文型 | 動画での表現 |
|---|---|
| 現在完了形 have/has + 過去分詞 — 過去の出来事が今も関係している | have been known · has always been · we've observed |
| 受動態 be + 過去分詞 — 誰がするかより、何が起きるかに焦点を当てる | have been known · were based · is replaced |
| 関係詞節 who / which + 節 — 人や物について情報を加える | objects which have · something, which is · Relativity, which is |
注意したい発音
話し手はcan't, couldn't, didn'tなど、短縮形や弱形を30回使っています。聞こえたとおりの短い形で発音しましょう。
- 「th」の音: theoretical /ˌθi.əˈɹɛt.ɪ.kəl/, mathematician /ˌmæθ.(ə.)məˈtɪʃ.ən/, mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/
- 「sh」と「zh」の音: gravitational /ˌɡɹævɪˈteɪʃənəl/, calculation /ˌkælkjuˈleɪʃn̩/, squash /skwɔʃ/, distortion /dɪsˈtɔːʃən/, mathematician /ˌmæθ.(ə.)məˈtɪʃ.ən/
- 長い単語（アクセントの位置に注意）: relativity /ɹɛl.əˈtɪv.ɪ.ti/, singularity /ˌsɪŋɡjəˈlæɹətɪ/, velocity /vəˈlɑsəti/, gravitational /ˌɡɹævɪˈteɪʃənəl/, vicinity /vəˈsɪnəti/
日本語話者が苦手な音：
- /r/ と /l/ の区別 — /l/ は舌先を歯茎につけ、/r/ はどこにもつけない: relativity /ɹɛl.əˈtɪv.ɪ.ti/, particle /ˈpɑɹtək(ə)l/, singularity /ˌsɪŋɡjəˈlæɹətɪ/, gravitational /ˌɡɹævɪˈteɪʃənəl/, theoretical /ˌθi.əˈɹɛt.ɪ.kəl/
- /v/ — /b/ にならないように、上の歯を下唇に当てる: relativity /ɹɛl.əˈtɪv.ɪ.ti/, velocity /vəˈlɑsəti/, gravitational /ˌɡɹævɪˈteɪʃənəl/, vicinity /vəˈsɪnəti/, conserve /kənˈsɜː(ɹ)v/
- /f/ — 「フ」ではなく、上の歯と下唇で出す: physicist /ˈfɪzɪsɪst/, fascinate /ˈfæsɪneɪt/, infinitely /ˈɪnfɪnɪtli/, sphere /sfɪɚ/, fabric /ˈfæb.ɹɪk/
この動画での練習方法
- まず声を出さずに動画を最後まで聞き、知らない単語をメモします。
- まず0.75倍速で一文ずつシャドーイングし、慣れてきたら通常の速度に戻します。
- 自分の声を録音して元の音声と比べます。horizon, relativity, particleなどの単語に特に注意しましょう。
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。