# Problem with Schrodinger's Cat

Discussion in 'Physics & Math' started by Journey0820, Jul 7, 2007.

1. ### Journey0820Registered Member

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I woke up this morning realizing that the famous Schrodinger's Cat experiment is deeply, deeply flawed and does not work.

If you don't know what this thought-experiment entails, a brief description won't help, but here is some history anyway:

It was actually Einstein's idea (not many people are aware of this). Einstein had deep problems with Quantum Mechanics, even though he helped start the field with his non-relativity papers. Quantum Mechanics was championed by Heisenberg, who is famous for his Uncertainty Principle. Heisenberg realized that the more precisely you determined a subatomic particle's Position, the less able you were to determine its momentum.

This isn't just a limitation of our experimental apparatus, this is really how the subatomic world behaves. Bell's theorem cinched this in the 50's when he found that particles which were separated by a great distance somehow "communicated" to one another. If you entangled these particles (so that they have similar properties like spin), measuring one particles would INSTANTANEOUSLY limit what you could measure from the other particle. This is 100% real. Lab-tested and guaranteed.

Einstein had big problems with this. After all, he was the guy that set up the speed limit signs all over the universe. Nothing could travel faster than the speed of light, not even information. (we now know he was wrong) So he was always coming up with thought-experiments to challenge Quantum Mechanics, and Bohr and Heisenberg were always debunking them. Schrodinger's Cat is one of those thought-experiments that Bohr and Heisenberg never debunked because they AGREED with the results.

A little more Quantum Mechanics simplified:

Until you measure a particle's position, it isn't defined. The particle is not "here" or "there", it has a probability of being everywhere all at once. Only, the probability of it being in the next galaxy is very, very slim and the probability of it being in the general neighborhood of where it was last is very, very likely. It isn't until you measure the particle's position that these probabilities "collapse" and it has definite location. And here is where we get the popular maxims that the "observer affects what is observed".

So Einstein wrote Schrodinger, another critic of QM, and said that he could build a bomb that was set off by radioactive decay, and the bomb would both go off and not go off. Schrodinger toyed with this idea and came up with his famous experiment:

In a box you have a Geiger-Counter which is reading the decay of some radioactive material. When the Geiger-Counter hits a certain reading, a hammer smashes a vial which releases a poison which kills a cat.

According to this experiment, until you open the box, the cat is both dead and alive. The probability function spreads out over both of these possibilities, and it isn't until you open the box that you find the cat in one or another of these states.

Now, if you don't really know what Quantum Mechanics is all about, you will reject this out-of-hand. But this experiment has really troubled physicists for 70 years because this seems to be how nature works. Bohr and Heisenberg agreed with this conclusion.

And they were all wrong.

The problem with the thought experiment is quite simple, Schrodinger (and Einstein) were confusing "observing" and "measuring". It is not when humans observe a measurement that the wave function collapses, it is when we take the measurement. By putting the Geiger-Counter in the box, they included a measuring device Even worse, Schrodinger included an observer, the cat. But even Einstein's bomb would either go off or not, as soon as the Geinger-Counter made its measurement!

And this happens every day. Scientists set up experiments, complete with the recording devices which scratch out results on reams of paper (or nowadays records results as ones and zeros in a computer). It might be hours or even days before any human looks at the results of these experiments, and nobody thinks that THIS IS THE MOMENT when the results are solidified. They were determined when they were measured, not when the measurement was observed.

Problem solved. I'm sure Bohr would have found this flaw, except he didn't want to. It conformed to his prejudices so he never examined it.

3. ### OliHeute der Enteteich...Registered Senior Member

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Except that Schrödinger made up his experiment to point out the daftness of the idea.
The cat is an example of irony or sarcasm...

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7. ### OliHeute der Enteteich...Registered Senior Member

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Fairly sure: a number of books I read stated explicitly that Schroedinger's thought experiment was made to point out the (in his opinion) ridiculousness of it.

8. ### GhostofMaxwell.BannedBanned

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A dead cat and a live cat at the same time.

I see nothing ridiculous in his explanation. Quantum physics is all about how collapse resolves uncertainty.

9. ### OliHeute der Enteteich...Registered Senior Member

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Da, and it's about how and when it collapses...
Cats don't resolve it?

10. ### GhostofMaxwell.BannedBanned

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The cats are an analogy to two states of uncertainty. Opening the box resolves it!

11. ### OliHeute der Enteteich...Registered Senior Member

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Really?
Or does something else?
You actually believe the cat is in both states until the box is opened?

12. ### GhostofMaxwell.BannedBanned

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I believe it is equally both A)dead B)Alive before one opens the box.

13. ### OliHeute der Enteteich...Registered Senior Member

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Hence Schrodinger's "experiment".
That's what I find vaguely silly - a cat in both states.
PS haven't they actually discovered that the collapse level is far lower than cat-sized anyway?

14. ### GhostofMaxwell.BannedBanned

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The cats in the box only represent what is happening at the quantum level.

15. ### PandaemoniValued Senior Member

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How do you know that the geiger counter's ticking is a "measurement" and not the observation of that ticking? In reality there is no formal way to know the difference. If the geiger counter counts as a "measurement" then imagine this: Suppose two electrons are fired at one another. Since the the first electron will necessarily react to the precise charge and proximity of the second (and vice versa), why isn't that a "measurement"? Or take the double slit experiment. Why does a photon's passing through the two slits *not* count as a measurement, but a photon hitting the photographic plate behind the slits does?

The Cat thought experiment was designed to show up the metaphysical implications of the Copenhagen school of interpretation, but there are *many* different schools of thought on that matter, some of which do not require "measurements" to collapse wave functions. (In fact, some of the interpretation, like the de Broglie-Bohm interpretation are entirely deterministic, albeit with "hidden variables" and many more interpretations allow for "objective collapse" of the wavefunction).

Few of even the diehard proponents of the Copenhagen school really believed that the cat was neither dead nor alive. What Bohr himself said was that the question of whether the cat is dead or alive is unscientific because there is no way for us to know. All we have are the probabilities about what things will look like once we crack open the box. (In the same way, he believed that the question of "what an electron is doing when we are not observing it" was also a meaningless question...a question for philosophy rather than physics, since physics requires the observation be made)

Moreover, there is no scientific way to determine which interpretation of QM is "right," as they are all mathematically equivalent. These are, as Bohr suggested, questions of philosophy that are, at present, well beyond any ability to test them. In many of these theories the "cat" is definitely dead or definitely alive, and in others the cat's status is uncertain.

In any event, I prefer the quantum decoherence explanation of the specific problem of what happens to cat-sized objects, and really have no particular favorite amongst the interpretations in cases where decoherence does not occur.

16. ### OliHeute der Enteteich...Registered Senior Member

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They do NOW, but at the time it was postulated that a conscious mind was required to cause the collapse.

17. ### GhostofMaxwell.BannedBanned

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Thats because you have read interpretations instead of hearing it from the horses mouth I suggest.

18. ### OliHeute der Enteteich...Registered Senior Member

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I wasn't there at the time...

19. ### allisone417i'll be in my roomRegistered Senior Member

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the possibility of the cat being dead increases with time, and reaches 1 after a certain amount of time. I never liked it.

20. ### Journey0820Registered Member

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I hope this came across in my original post. You are quite correct. Schrodinger was a critic of QM as Bohr and Heisenberg described it. The original thought-experiment was devised by Einstein, another critic of "God playing dice".

And modern physicists see nothing much wrong with the thought experiment. They write popular books with boxes and cats on the cover. But the experiment is flawed for reasons given above.

Most of Einstein's thought experiments were flawed in similar ways. Bohr spent his life pointing out such flaws. One time Einstein came up with a sealed box that had bouncing photons in it. You threw a switch at a known time to open a shutter that let out a single photon. You can weigh the box before and after, and with his famous e=mc^2 know the mass of the escaped photon, and with the precise time of the open shutter, know its location.

This one came up at one of the Salvoy conferences, and it really stumped Bohr. Einstein and other critics gloated for a day, but Bohr awoke beaming and explained the flaw to Einstein: Einstein had neglected to account for his own theory of relativity! The change in mass of the box would affect time, introducing the precise amount of uncertainty that Heisenberg predicted. It was stunning blow to Einstein, and he spent the rest of his life saying cryptic things about "Gods" and "dice".

21. ### GhostofMaxwell.BannedBanned

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:bugeye: We are talking of Edwin Schrodinger's cat here?

22. ### GhostofMaxwell.BannedBanned

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Chinese whispers! You need to go closer to the source.

Last edited: Jul 7, 2007
23. ### OliHeute der Enteteich...Registered Senior Member

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11,888
Nope. Erwin Schrödinger.