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  • Austrian physicist Erwin Schrödinger is one of the founders of quantum mechanics,

  • but he's most famous for something he never actually did:

  • a thought experiment involving a cat.

  • He imagined taking a cat and placing it in a sealed box

  • with a device that had a 50% chance of killing the cat in the next hour.

  • At the end of that hour, he asked, "What is the state of the cat?"

  • Common sense suggests that the cat is either alive or dead,

  • but Schrödinger pointed out that according to quantum physics,

  • at the instant before the box is opened, the cat is equal parts alive and dead,

  • at the same time.

  • It's only when the box is opened that we see a single definite state.

  • Until then, the cat is a blur of probability,

  • half one thing and half the other.

  • This seems absurd, which was Schrödinger's point.

  • He found quantum physics so philosophically disturbing,

  • that he abandoned the theory he had helped make

  • and turned to writing about biology.

  • As absurd as it may seem, though, Schrödinger's cat is very real.

  • In fact, it's essential.

  • If it weren't possible for quantum objects to be in two states at once,

  • the computer you're using to watch this couldn't exist.

  • The quantum phenomenon of superposition

  • is a consequence of the dual particle and wave nature of everything.

  • In order for an object to have a wavelength,

  • it must extend over some region of space,

  • which means it occupies many positions at the same time.

  • The wavelength of an object limited to a small region of space

  • can't be perfectly defined, though.

  • So it exists in many different wavelengths at the same time.

  • We don't see these wave properties for everyday objects

  • because the wavelength decreases as the momentum increases.

  • And a cat is relatively big and heavy.

  • If we took a single atom and blew it up to the size of the Solar System,

  • the wavelength of a cat running from a physicist

  • would be as small as an atom within that Solar System.

  • That's far too small to detect, so we'll never see wave behavior from a cat.

  • A tiny particle, like an electron, though,

  • can show dramatic evidence of its dual nature.

  • If we shoot electrons one at a time at a set of two narrow slits cut in a barrier,

  • each electron on the far side is detected at a single place at a specific instant,

  • like a particle.

  • But if you repeat this experiment many times,

  • keeping track of all the individual detections,

  • you'll see them trace out a pattern that's characteristic of wave behavior:

  • a set of stripes - regions with many electrons

  • separated by regions where there are none at all.

  • Block one of the slits and the stripes go away.

  • This shows that the pattern is a result of each electron going through both slits

  • at the same time.

  • A single electron isn't choosing to go left or right

  • but left and right simultaneously.

  • This superposition of states also leads to modern technology.

  • An electron near the nucleus of an atom exists in a spread out, wave-like orbit.

  • Bring two atoms close together,

  • and the electrons don't need to choose just one atom

  • but are shared between them.

  • This is how some chemical bonds form.

  • An electron in a molecule isn't on just atom A or atom B, but A+ B.

  • As you add more atoms, the electrons spread out more,

  • shared between vast numbers of atoms at the same time.

  • The electrons in a solid aren't bound to a particular atom

  • but shared among all of them, extending over a large range of space.

  • This gigantic superposition of states

  • determines the ways electrons move through the material,

  • whether it's a conductor or an insulator or a semiconductor.

  • Understanding how electrons are shared among atoms

  • allows us to precisely control the properties of semiconductor materials,

  • like silicon.

  • Combining different semiconductors in the right way

  • allows us to make transistors on a tiny scale,

  • millions on a single computer chip.

  • Those chips and their spread out electrons

  • power the computer you're using to watch this video.

  • An old joke says that the Internet exists to allow the sharing of cat videos.

  • At a very deep level, though, the Internet owes its existance

  • to an Austrian physicist and his imaginary cat.

Austrian physicist Erwin Schrödinger is one of the founders of quantum mechanics,

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TED-ED】シュレーディンガーの猫。量子力学の思考実験 - チャド・オーゼル (【TED-Ed】Schrödinger's cat: A thought experiment in quantum mechanics - Chad Orzel)

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    稲葉白兎 に公開 2021 年 01 月 14 日
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