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Schrödinger’s cat: A thought experiment in quantum mechanics – Chad Orzel

Schrödinger’s cat: A thought experiment in quantum mechanics – Chad Orzel


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.

100 thoughts on “Schrödinger’s cat: A thought experiment in quantum mechanics – Chad Orzel

  1. What if the person opens the box and sees a dead cat, then closes the box, then another person comes in who knows nothing about what the first person did, would the cat be 50/50 dead or alive to the 2nd person?

  2. I spilled water on my laptop. It’s laying upside down on my pillow and I’m praying it’s okay.
    I looked at it and it reminded me of the Schrödinger’s cat. Just like the cat could be dead or alive, my laptop could be damaged or fine. The cat, just like the laptop, is in both states of being either dead or alive until you check.
    My question is, would it be possible to alter states however you wish?

  3. Anybody from 12th sci here?? I understood 90% of the video coz i aldready knew it……
    In fact the reason i clicked was bcoz we study schrodingers wave eq…..right??

  4. This is why I believe whenever we dream, we are actually in an alternate reality and when we are about to die in our dreams we actually wake up to another reality where we are alive. What if those people who die are actually dead in this universe but alive in other alternate reality. 😊

  5. Okay, but jokes aside, I have a serious question. The cat is still a metaphor, right? Nobody in their right mind could be arguing that my knowledge states could affect any aspect of the external world? I mean, there are many things I don't know about, but those are not all two or more things at the same time? The world would be absolute chaos if that was the case?!

  6. The cat is not equal parts alive or dead. The cat may also die from an unrelated issue while in the box. Congenital heart defect, lack of oxygen, etc. The cat is exactly either alive or dead.

  7. Just a thought but, what Schrodinger meant by the cat is dead and alive at the same time maybe he meant like, since there was a radioactive in there, maybe the radioactive was eating away at the cats body, meaning that the cats body is dead, but its brain is still alive. But that just a theory, a cat theory! And cut!

  8. Fact: The Schrödinger's cat paradox outlines a situation in which a cat in a box must be considered, for all intents and purposes, simultaneously alive and dead. Schrödinger created this paradox as a justification for killing cats.

    Like if u got the reference

  9. Just put a cam with a heat sensor inside the box and boom you don't have to open the damn box to check if the cat is dead and give js a headach

  10. Hey guys, I wrote a small article on quantum mechanics for ppl with not much background in the subject (I am myself no expert). Do give it a read to learn more.
    stratagear.com/science/physics/2017/04/the-dead-and-alive-cat-from-pandoras-box-a-short-summary-of-quantum-mechanics/

  11. So something on that small of a scale only becomes reality once it's observed? Did Schrödinger believe we were in a simulation? Is that why he abandoned the theory?

  12. I kind of understand this but at the same time i don't. Never knew i was this interested in this type of stuff

  13. In case some of you are thinking, "Schrödinger's Cat isn't illogical!", try this:

    Suppose there's a box with a lever that protrudes out of it. You can't see inside the box, but flipping that lever will roll a 12-sided die hidden inside it. Suppose you do.
    According to quantum mechanics, the die is in a superposition of 12 states, each equally likely, and each corresponding to the number you could roll on it. Only after you reveal the die does it "decide" which number is rolled, right?
    No, of course not; that's ridiculous. The roll is determined by the starting position of the die and the physics of the roll itself, not ANOTHER die roll. The result didn't suddenly become a 7 when you lifted the box, it was that way BEFORE you lifted the box.

    Same way with the Cat.

    TL;DR: Schrödinger's Cat makes no sense. Dice don't work that way, so the Cat doesn't either, right?

  14. How similar is this to "if a tree falls in the woods and no ones around to hear it, does it make a sound?" Like would the universe really exist if no one was around to see it? So if the box is closed and nobody can physically see if the cat survived it's both alive and dead simultaneously?

  15. Man : I Only Understand Half Of This Video!
    Girl : Well, I Only Understand 25% Of This Video!
    Me : You Guys Understand This Video?

  16. I was really hoping how they would go on to specify that Schrödinger would go on to dispose of that as well as much of the scientific community then and now for its lack of coherence with what it is actually trying to explain.

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