Schrodinger's cat - I just don't get it....

inogen said:
I think a good way to understand the slit experiment is to think of a lightbulb in a room with two windows. It's trivial to understand that the bulb can be seen by two people each of their windows at the same time. The effect of the bulb being observed is caused by the photons hitting the retinas of the people.

Now imagine instead of a blub, it's a single photon. They can both observe the photon from two different positions. The same photon is hitting both people's retinas at the same time. It is the observation itself that is being observed.

(ignore the fact that our eyes ignore single photons, so we wouldn't see anything) but we COULD technically, it's just that our brains and eyes have evolved to filter out single photons as white noise. And that photons don't stand relatively still like light bulbs and travel at the speed of light.
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Um.. (I'm going to skip a lot of details but try to describe the idea)

So you will have a photon and you can use a single photon detector in each room. However you would only get ONE detector going off. Now if you entangle two photons and then sent a photon to each window with it's detector then both detectors would go off.

If there two photon's (property) state are entangled. One such property for photons is polarisation (like your sunglasses). If two are entangled you can send one into one window with a picture and the other one to a camera in a different room with another window (as you have suggested). The camera sensor will then show the image of the picture without having the light reflected from the picture to the camera.. spooky.

Have a look at parametric down conversation (https://en.wikipedia.org/wiki/Spontaneous_parametric_down-conversion).
 
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sigma said:
Also, isn't the quote often taken out of context? He was actually trying to show the opposite of what most people think he was?
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IIRC, Schrödinger thought that the claims coming out of quantum mechanics were stupid and the thought experiment was supposed to demonstrate it.
 
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Everything that's said about Schrodinger's cat is simultaneously true and not, depending on your POV. And that of the cat.

Anyone who knows anything knows that's pretty true about anything. Quantum mechanics is somewhat comforting in that way.

Everything simple depends on how you look at it. Everything else relies on complexity.
 
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Baldbloke said:
A quick first google on this says:

In simple terms, Schrödinger stated that if you place a cat and something that could kill the cat (a radioactive atom) in a box and sealed it, you would not know if the cat was dead or alive until you opened the box, so that until the box was opened, the cat was (in a sense) both "dead and alive"."

Nope. Call me dense but I think all you could truly say was "The cat is dead OR alive". Not both.

Always niggled me this "both" bit. And wth does "in a sense" mean?
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The story has become a bit garbled as it passed through non-science media and through time.

Schrodinger was arguing against a particular idea in quantum physics (called the Copenhagen interpretation IIRC). He never actually said that the cat in the thought experiment would be dead and alive at the same time. The point was pretty much the opposite - that a cat can't be alive and dead at the same time. It was a means of expressing the fact that the interpretation he was arguing against does not match up correctly with observable reality. They intended it to be memorable and thus to promote thought and debate amongst scientists. Unfortunately they did too good a job of making it memorable and it spread outside of science and a somewhat garbled recounting of it has become the main thing they're known for.

As far as I know, Schrodinger was wrong and the idea he was arguing against seems to be true (though completely weird). Stuff apparently does exist in multiple mutually exclusive states simultaneously unless someone/something observes it. But it doesn't apply to cats. Or trees in the forest that do and don't fall and do and don't make a noise. Or anything else on a scale larger than subatomic particles. Which leads to the question of why not? If that's how reality really works, why does it work completely differently on any larger scale? Maybe someone knows the answer. I don't and I doubt if I'd understand the answer if I read it.




Heisenberg, Schrodinger and Ohm are in a car. Heisenberg is driving.
A police officer pulls them over for allegedly speeding.
The officer asks Heisenberg the traditional question "Do you know how fast you were going?", to which Heisenberg replies "No, but I knew exactly where I was".

The copper's suspicions are raised. Something is a bit off with the situation. They end up looking in the boot of the car, where they find a dead cat.
When the copper questions the people in the car about there being a dead cat in the boot, Schrodinger tells them it wasn't dead until they looked at it.

This is all too weird and the copper arrests them all. Heisenberg and Schrodinger go quietly but Ohm resists.
 
Great post @Angilion. Minor point: AFAIK the Copenhagen Interpretation hasn't been (can't be?) proven true but I believe it's the most widely accepted among Physicists among competing interpretations.
 
Mr Jack said:
Great post @Angilion. Minor point: AFAIK the Copenhagen Interpretation hasn't been (can't be?) proven true but I believe it's the most widely accepted among Physicists among competing interpretations.
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Essentially, no theorem can be proven true, only disproven and so far no-one has disproven the Copenhagen interpretation. Which is the defining feature of a theory, the inability to disprove it. Once a hypothesis is elevated to a theory, then it tends to only get modified slightly around some edge cases or is a sub-set of a more comprehensive theory
 
Angilion said:
As far as I know, Schrodinger was wrong and the idea he was arguing against seems to be true (though completely weird). Stuff apparently does exist in multiple mutually exclusive states simultaneously unless someone/something observes it. But it doesn't apply to cats. Or trees in the forest that do and don't fall and do and don't make a noise. Or anything else on a scale larger than subatomic particles. Which leads to the question of why not? If that's how reality really works, why does it work completely differently on any larger scale? Maybe someone knows the answer. I don't and I doubt if I'd understand the answer if I read it.
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Macro scale is the sum of many parts the fact that particles may exist in an indeterminate state only affects on the quantum level because the probability is that enough things will be in a particular state for the macro to appear determinate. The chance of enough particle alignment coinciding to make the macro indeterminate is so astronomically small as to be negligible. So for example for quantum tunnelling to affect a cup of tea for all the particles in your tea to quantum tunnel over to the left so that the tea suddenly moves out of the cup and sploshes all over your desk the chance is so small it'd take longer than the age of the universe for this to become a statistical reality. But the possibility exists however remote.

n.b. if anyone wishes to know more I'd recommend In Search of Schrodinger's Cat by John Gribben he really makes the quantum world accessible and down to earth.
 
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D.P. said:
Essentially, no theorem can be proven true, only disproven and so far no-one has disproven the Copenhagen interpretation.
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I was being loose with language there. My point is that the Interpretation is not a theory, it is an interpretation, the facts of Quantum Mechanics are compatible with multiple interpretations.

Once a hypothesis is elevated to a theory, then it tends to only get modified slightly around some edge cases or is a sub-set of a more comprehensive theory
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I'm of the view that the idea that ideas in Science start as hypothesises and later get elevated to theories is a toy version taught in schools rather than a reflection of fact. Look at String Theory vs. the Out of Africa Hypothesis for example.
 
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Mr Jack said:
I'm of the view that the idea that ideas in Science start as hypothesises and later get elevated to theories is a toy version taught in schools rather than a reflection of fact. Look at String Theory vs. the Out of Africa Hypothesis for example.
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Evolution itself is a fact, as are many other aspects of it suck as gene frequencies and mutations. All together these form the Theory of Evolution.

That mavity exists is also a fact, as are it's effects on the universe. The large bodies bend space-time is also a fact. All together these and many other facts form the Theory of mavity.

The Big Bang happened, space IS expanding, and the Cosmic Microwave Background still exists. These facts form part of the Big Bang Theory (and Kaley Cuoko.)

It's mostly semantics really, and the Wikipedia page for the Out of Africa idea even calls it the Out of Africa Theory. There are scientific usages and colloquial usages, and a lot of the time they can be interchanged and it doesn't make a huge amount of difference - theory, idea and hypothesis all infer the same thing.

It DOES matter when creationists try and use the excuse of 'it's only a theory' to say evolution or the Big Bang aren't proven.
 
Penfold101 said:
It's mostly semantics really, and the Wikipedia page for the Out of Africa idea even calls it the Out of Africa Theory. There are scientific usages and colloquial usages, and a lot of the time they can be interchanged and it doesn't make a huge amount of difference - theory, idea and hypothesis all infer the same thing.
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Believe me, scientists are just as sloppy in their use as the general population. Also, in my experience, most scientists aren't Popperian in outlook.

It DOES matter when creationists try and use the excuse of 'it's only a theory' to say evolution or the Big Bang aren't proven.
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I think we should spend a lot less time caring what nutjobs think, and I don't really think presenting another myth (it starts as a hypothesis and become a theory) really helps.
 
Blackjack Davy said:
Macro scale is the sum of many parts the fact that particles may exist in an indeterminate state only affects on the quantum level because the probability is that enough things will be in a particular state for the macro to appear determinate. The chance of enough particle alignment coinciding to make the macro indeterminate is so astronomically small as to be negligible. So for example for quantum tunnelling to affect a cup of tea for all the particles in your tea to quantum tunnel over to the left so that the tea suddenly moves out of the cup and sploshes all over your desk the chance is so small it'd take longer than the age of the universe for this to become a statistical reality. But the possibility exists however remote.

n.b. if anyone wishes to know more I'd recommend In Search of Schrodinger's Cat by John Gribben he really makes the quantum world accessible and down to earth.
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Schrodinger's thought experiment was devised to ensure that the outcome was determined by a single subatomic particle, so quantum effects would apply. The release of the poison gas was determined by whether or not a single atom underwent radioactive decay and emitted a subatomic particle. Deliberately chosen as an unpredictable event involving a single subatomic particle. So the Copenhagen interpretation would be that the particle was in an indeterminate state, simultaneously part of the atom and emitted from the atom. As far as I can tell, this was a key part of Schrodinger's argument - that situations could occur in which the state of a subatomic particle has a macroscopic effect, therefore quantum effects should (in such situations) have a macroscopic effect. In the famous thought experiment, that the state of the subatomic particle determines whether the cat is alive or dead because it determines whether or not the container of poison gas is opened.

I'm way out of my depth here, but my guess at the counter-counter argument would be that the detector is observing the state of the subatomic particle and that causes the indeterminacy to collapse into one of the two possible states.
 
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Diddums said:
Can someone open the bloody box already :mad:
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One of the funniest cartoons I've seen recently explains why opening the box isn't necessary. It depicts Schrodinger holding a box and explaining that you can't tell if the cat is alive or dead without opening the box. A "Meow" comes from inside the box, invalidating a key part of the argument :)
 
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