雅思阅读 148: The Science of Disappearing（消失的科学）

改编自 National Geographic（Maddie Stone, 2026年1月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.nationalgeographic.com/science/article/invisibility-science-fiction-reality-technology

Reading Passage

A. For as long as stories have been told, people have imagined beings that move unseen — spirits that vanish, magical cloaks, and, more recently, the devices of science fiction. The fantasy is so persistent that it seems bound to remain fantasy. Yet over the last two decades a small community of physicists has shown that invisibility is, at least in principle, a solvable engineering problem. The trick is not to make an object transparent in the ordinary sense, but to guide the waves that reveal it — whether light, sound or even the tremors of an earthquake — smoothly around it, so that they emerge on the far side as if nothing had been there. The illusion is one of empty space: no shadow, no reflection, no telltale scatter to give the game away. Researchers have extended the same idea well beyond hiding people, to shielding buildings from seismic waves and hiding rooms from unwanted noise. Invisibility, on this broader view, has stopped being purely a literary ambition and become a branch of wave control. Once the principle is stated — guide a wave faithfully around an obstacle — it can be aimed at anything that travels in waves, not just the light that human eyes happen to catch.

B. The enabling materials are called metamaterials — substances whose useful properties come not from their chemistry but from tiny, deliberately engineered structures built into them. By arranging holes or rings smaller than the wavelength of the wave they must bend, designers can give a material behaviours no natural substance possesses. The idea moved from speculation to theory in 2006, when two teams — one led by Ulf Leonhardt, the other by researchers at Duke University and Imperial College London — published parallel papers describing mathematically how a cloak could steer light around an enclosed region. Months later the same group built the first working version. It was modest by Hollywood standards: a two-dimensional cloak of ten concentric rings cut from circuit-board material, less than five inches across, hiding a small copper cylinder from microwaves. The waves flowed around the ring and reassembled on the other side so faithfully that, to a microwave detector, both cylinder and cloak seemed absent. It was the first proof that an invisibility device could actually exist.

C. The demonstration exposed the catch immediately. To bend a given wavelength, the structures inside the metamaterial must be far smaller than that wavelength — roughly a tenth of it. Microwaves are long, so a copper-ring cloak is easy to build. Visible light waves, measured in billionths of a metre, demand features on the impossible-to-engineer nanoscale, and the cost would be astronomical. Worse, a cloak tuned for one colour does not hide an object from another: a device that guides red light lets blue light scatter and reveal the shape within. There is a subtler physical reason for this limit. Routing light the long way around an object means the wave must travel further than it would in a straight line, yet it must arrive at exactly the same moment — effectively a demand to exceed the speed of light, a trick that nature permits at only one frequency at a time. Even if all this were solved, a wearer would be in trouble: with no light reaching the inside of the cloak, the person wrapped in it could see nothing of the world outside. The same property that hides them from others would also blind them, a reminder that perfect invisibility and being a functioning observer of the scene may not, in physics, be the same thing.

D. Physicists have therefore explored routes that sidestep the metamaterial cloak entirely. One is cloaking at a distance: place a device some way from the object, and arrange that light scattered between the two cancels itself out, leaving the whole arrangement invisible — while, crucially, light can still reach the hidden object, so it can "see" out. The catch is that such designs are complex and currently practical only for long, low-frequency waves such as radio. A second approach, active exterior cloaking, does not bend waves around an object at all; it surrounds it with sources that emit waves engineered to cancel out the incoming ones. In 2021, researchers showed that wrapping an object in heat pumps could make it invisible to a thermal camera — and even give it a fake heat signature, disguising one object as another. Because the cancelling is controlled electrically rather than built into fixed material, the device can be retuned from one frequency to another, a kind of software control over invisibility.

E. It is when the waves become large that the science turns practical rather than dreamlike. Seismic waves from an earthquake, and the waves of the ocean, are measured in metres, not nanometres, so shielding structures against them needs nothing more exotic than ordinary drilling. By boring a ring of carefully spaced holes into the ground around a building, engineers can redirect earthquake tremors away from it; by planting rods on the seabed, they can protect offshore platforms. Researchers have even noted that a well-spaced forest may act as a natural version of the same idea. In 2024, a team proposed a new kind of acoustic cloak built from "tunnels" that guide sound around an obstacle across a wide band of frequencies, sidestepping the single-colour limit — a proof of principle they hope to extend to light. None of this is Harry Potter's cloak, and the wearable fantasy remains distant. But the impulse that began as a daydream about vanishing has already produced tools for protecting cities from earthquakes, and on the way has rewritten what a material is allowed to do. A natural material, after all, can only bend light the ways its atoms permit; a metamaterial is one whose behaviour we write ourselves, and the invisible object is merely the first, most arresting consequence of that freedom.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The first theory and the first simple demonstration ii. Why a real light cloak is so hard iii. Alternative ways to make things disappear iv. Where the idea of invisibility came from in myth v. The surprisingly practical side — large waves vi. How to sell an invisibility cloak vii. Why natural materials are always better

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. What is the key feature of metamaterials? A. They are made only of pure glass. B. Their properties come from engineered structures smaller than the wavelength. C. They occur naturally in deep caves. D. They cannot bend microwaves.

6. What did the 2006 Duke/Imperial demonstration achieve? A. It hid a person from visible light. B. It shielded a copper cylinder from microwaves in two dimensions. C. It built a cloak from biological tissue. D. It proved invisibility impossible.

7. Why can't a single metamaterial cloak hide all colours at once? A. It quickly melts under bright light. B. Routing light around an object works at only one frequency at a time. C. Paint fades over time. D. The cloak is too heavy to move.

8. What advantage does active exterior cloaking offer? A. It needs no power at all. B. It can be electronically retuned to different frequencies. C. It works only for microwaves. D. It is cheaper than a mirror.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Metamaterials derive their unusual properties from engineered microscopic structures.
10. The first working cloak hid an object from visible light in three dimensions.
11. A person wrapped in a perfect light cloak could see out normally.
12. Seismic cloaking needs nanoscale engineering because earthquake waves are very small.
13. The inventors plan to sell a consumer invisibility cloak within five years.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

Because visible light waves are so short, bending them requires structures built on the (14) _____________ scale. Even if achieved, a wearer inside such a cloak would be (15) _____________, since no light would reach their eyes.

答案与解析

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