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Austrian physicist Erwin Schrödinger is one of the founders of quantum mechanics,
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but he's most famous for something he never actually did:
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a thought experiment involving a cat.
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He imagined taking a cat and placing it in a sealed box
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with a device that had a 50% chance of killing the cat in the next hour.
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At the end of that hour, he asked, "What is the state of the cat?"
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Common sense suggests that the cat is either alive or dead,
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but Schrödinger pointed out that according to quantum physics,
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at the instant before the box is opened, the cat is equal parts alive and dead,
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at the same time.
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It's only when the box is opened that we see a single definite state.
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Until then, the cat is a blur of probability,
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half one thing and half the other.
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This seems absurd, which was Schrödinger's point.
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He found quantum physics so philosophically disturbing,
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that he abandoned the theory he had helped make
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and turned to writing about biology.
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As absurd as it may seem, though, Schrödinger's cat is very real.
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In fact, it's essential.
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If it weren't possible for quantum objects to be in two states at once,
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the computer you're using to watch this couldn't exist.
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The quantum phenomenon of superposition
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is a consequence of the dual particle and wave nature of everything.
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In order for an object to have a wavelength,
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it must extend over some region of space,
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which means it occupies many positions at the same time.
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The wavelength of an object limited to a small region of space
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can't be perfectly defined, though.
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So it exists in many different wavelengths at the same time.
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We don't see these wave properties for everyday objects
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because the wavelength decreases as the momentum increases.
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And a cat is relatively big and heavy.
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If we took a single atom and blew it up to the size of the Solar System,
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the wavelength of a cat running from a physicist
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would be as small as an atom within that Solar System.
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That's far too small to detect, so we'll never see wave behavior from a cat.
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A tiny particle, like an electron, though,
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can show dramatic evidence of its dual nature.
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If we shoot electrons one at a time at a set of two narrow slits cut in a barrier,
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each electron on the far side is detected at a single place at a specific instant,
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like a particle.
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But if you repeat this experiment many times,
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keeping track of all the individual detections,
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you'll see them trace out a pattern that's characteristic of wave behavior:
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a set of stripes - regions with many electrons
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separated by regions where there are none at all.
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Block one of the slits and the stripes go away.
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This shows that the pattern is a result of each electron going through both slits
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at the same time.
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A single electron isn't choosing to go left or right
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but left and right simultaneously.
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This superposition of states also leads to modern technology.
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An electron near the nucleus of an atom exists in a spread out, wave-like orbit.
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Bring two atoms close together,
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and the electrons don't need to choose just one atom
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but are shared between them.
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This is how some chemical bonds form.
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An electron in a molecule isn't on just atom A or atom B, but A+ B.
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As you add more atoms, the electrons spread out more,
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shared between vast numbers of atoms at the same time.
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The electrons in a solid aren't bound to a particular atom
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but shared among all of them, extending over a large range of space.
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This gigantic superposition of states
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determines the ways electrons move through the material,
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whether it's a conductor or an insulator or a semiconductor.
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Understanding how electrons are shared among atoms
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allows us to precisely control the properties of semiconductor materials,
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like silicon.
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Combining different semiconductors in the right way
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allows us to make transistors on a tiny scale,
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millions on a single computer chip.
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Those chips and their spread out electrons
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power the computer you're using to watch this video.
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An old joke says that the Internet exists to allow the sharing of cat videos.
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At a very deep level, though, the Internet owes its existance
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to an Austrian physicist and his imaginary cat.