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Leo32

Entanglement of Schrödinger cats

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Quantum entanglement is quite a challenging subject, and I would like to see if we can make it any easier to think about when using the Schrödinger cat analogy.

 

For this, we can make abstraction of the atom which decays and triggers a poison to kill the cat. Let's just say that the cat itself is in a quantum state of being dead/alive as long as we don't look inside the box. Once we do, the quantum state collapses and we see the cat as being either dead or alive.

For starters, I'll refrain from inserting an analogy to tackle the Heisenberg uncertainty. I'll leave that for another thread.

 

Now, suppose we take 2 boxes with cats and manipulate them in such a way that they become entangled. After this, one of the boxes is taken to the other side of the world.

 

A first thing we can do is open one of the boxes and look. This causes the quantum state of this cat to collapse. Entanglement would mean that we can now 100% sure what state the other cat is in, even without taking a peek.

It might look as if the information which obtained by the state to collapse, the cat is dead, or the cat is alive, can be taken over large distances at a speed greater than light. Remember however that the cat, and thus it's quantum state, had to be taken "hand carried" to the other side of the world, significantly slower than speed of light.

 

A second step might be to influence the quantum state of the cat on one side such that the chances of it being found alive are much higher than they are in the original experiment, after the boxes have been separated.

Some of the texts on entanglement make me think, and I'm not sure about this, that this increased chance of the cat being found alive is "transported" at a speed higher than that of light. In other wordt, the quantum state of the remote cat would be changed immediately together with the manipulated quantum state of the local cat.

 

Checking this might be done by doing the experiment over and over again, while collapsing the quantum state each time to get an idea of probability shifts, but that's a practicality outside the scope of this thread.

 

The big question now is of course, did I remain on the path of quantum mechanics, or, at what point did I leave it ?

 

Greetz,

Leo

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It might look as if the information which obtained by the state to collapse' date=' the cat is dead, or the cat is alive, can be taken over large distances at a speed greater than light. Remember however that the cat, and thus it's quantum state, had to be taken "hand carried" to the other side of the world, significantly slower than speed of light.

[/quote']

 

 

But really, you "hand carried" the cat and a superposision of all quantum states to the other side of the world. Right? Meaning that once the cat is on the other side of the world, it still exists as a supersposition of dead and alive. It has not colapsed to one or the other until you measure it. And carrying the box with the cat to the other side of the world does not constitute measuring the state of the cat.

 

So, you are still left with the fact that you do not know the state of either cat until you measure one. Until that measurement, both cats are dead and alive at the same time. At such a time as you measure one of the cats, the other cats wavefunction will colapse into a single state -- the same state as the cat that you mesured. So it seems that information still is transfered faster than the speed of light, even in your example.

 

But i could be wrong. I am not really a physisist. :)

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If you're talking about what I think you're talking about, the problem here is that the only way you can determine whether information has been transferred is by information transfer, as it were. The collapse of the waveform isn't an information transfer per se.

 

[edit]

 

God that was uninformative.

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If you're talking about what I think you're talking about' date=' the problem here is that the only way you can determine whether information has been transferred is by information transfer, as it were. The collapse of the waveform isn't an information transfer per se.

 

[edit']

 

God that was uninformative.

It's the only thing that's made sense to me today! Should I resume the medication??

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While you were transporting the cat, I suppose you had to feed her half as much food, and clean out her litterbox half as often, as usual? :)

 

Leo32: A second step might be to influence the quantum state of the cat on one side such that the chances of it being found alive are much higher than they are in the original experiment, after the boxes have been separated. Some of the texts on entanglement make me think, and I'm not sure about this, that this increased chance of the cat being found alive is "transported" at a speed higher than that of light. In other words, the quantum state of the remote cat would be changed immediately together with the manipulated quantum state of the local cat.

 

- Evidently that's not possible. Suppose your fellow researchers transported 100 cats as you propose, then you "manipulated" the ones left behind so their probability of living became (let's say) 99%. Then your fellow researchers (who might be very far away, such that light would take a long time to travel there) immediately open the 100 transported boxes and find a huge preponderance of dead ones - they would know, with a very high probability, what you had done. OTOH suppose you manipulated your stationary cats to be 99% dead; when they open the boxes they find 99 live ones, and again they can tell what you did. So we could represent a "1" by lots of deaders, and a "0" by lots of live ones, and thus transfer binary information faster than light (with a high probability). That's not allowed: info can't be communicated faster than light. So we know one of the steps in your proposal is not possible, without even needing to figure out which one.

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Happy to see that my cat story triggers responses which point out the essential questions to understand the entanglement issue.

 

Vending Menace:

Indeed, the question that needs to be asked is which one of both possibilities is the correct interpretation:

1: does the collapse of state of cat 1 initiate an information transport faster than light, which causes the state of cat 2 to collapse

OR 2: is the info on the end result of the colapse of cat 2 already contained within it's quantum state, and as such taken "hand carried".

 

Jakiri:

Indeed, you can only check with another information transfer, but this one does not require to be faster than light, it can be a simple phone call.

 

Greetz,

Leo

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shrodinger pointed out himself the problem with this is that even after he looks int othe box the press outside dont know whether the cat is dead or allive, so therefore it is still in this entangled state, messy huh!

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This is a restatement of the Einstein-Podolsky-Rosin Paradox (you are in eloquent company)

 

Similar experiments have been done, notably by Alain Aspect in 1980, using electrons not cats, though.

He had two electrons sent in opposite directions at close enough to the speed of light that their spins were measured at such a time and displacement that information travelling between them must travel faster than c. The spin on the second electron nevertheless matched up with the spin of the first electron.

The most interesting implication is that, in a relativistic universe, if the first measurement affects the outcome of the second , the second would be seen to affect the first from another moving viewpoint. The information goes backwards in time!

 

See http://www.kheper.net/cosmos/quantum_physics/quantum_physics.htm for a fuller explanation or http://www.mtnmath.com/whatrh/node75.html for lots of equations and detail

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While I find Schrödinger cat fascinating...in short, we can't tell if his cat is dead or alive until we open the bag and observe it, or even if the cat exists at all!

 

Schrodinger years later said he wish he hadn't met the cat....lol.

 

Back back to the twirling world of quantum mechanics.

 

Lets point the finger away from the cat and at ourselves. Could one posit that at the sub atomic level, we are already breaking down...dying. Therefore we are both alive and dead at the same time.

 

Like the cat, who is dying a blurred picture in comparison to a sharp picture, in neither state.

 

Okay so I have entered the area of quantum mysticism....the nature of reality.

 

Zen, St. Thomas Aquanis and followers of Doaism might all find my musing interesting...but what say ye, oh followers of Quantum Mechanics.

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People who tread carefully (like me) into quantum mechanics stay away from the intrcies of the heisenberg uncertancy principle, as well as duel states of both common things and electrons. Electrons are waves, leave the rest to the philosophers.

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QED, QCD, QFD, really only probability is needed for QFD, I dont see why any of the others (at a recreational level) need go into double state prbability.

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Guest DarkEcho

Unfortunetly entanglement of the 2 cats couldn't be used for communication, even at the simplest point of communicating when you open the box and collapsed the experiment, as it would only collapse for you, and not for the person at the other end (who still doesn't know). Also if you somehow modified the probability curve for the unforunate cat on the other side, it would destroy the entanglemont (I think, correct me if I'm wrong here).

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