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Old 01-03-2012, 10:03 AM
whc.03grady whc.03grady is offline
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Schrodinger's Cat

Please tell me where I've gone wrong.

So the cat is in the box with the particle that may or may not have decayed after ten minutes, setting off a charge that would kill the cat. The physicist says the cat is in a superposition, viz., is both alive and dead.

Why does the physicist get to invent a property (the superposition) that is, in principle, unobservable, and then assign it to the cat? Why doesn't the physicist instead say, "I don't know if the cat's alive or dead", or "I can't know if the cat's alive or dead"? Isn't science about what's observable, not making up stuff about what isn't or cannot be observed?

Last edited by whc.03grady; 01-03-2012 at 10:04 AM. Reason: omitted something
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Old 01-03-2012, 11:10 AM
Candyman74 Candyman74 is offline
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It's just a thought experiment which illustrates the issues Schrodinger had with quantum theory. He began the description with the phrase: "One can even set up quite ridiculous cases." It's a piece of rhetoric, not an actual experiment.

It illustrates the question [v much paraphrased; v much more complex than this] - when does quantum uncertainty become real? The point being that he was posing a question, not making a declaration. He was taking the Copenhagen interpretation of quantum mechanics to its conclusion which, in his view, was a paradox.

Last edited by Candyman74; 01-03-2012 at 11:12 AM.
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Old 01-03-2012, 11:11 AM
Reno Nevada Reno Nevada is offline
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The best answer that I have ever read to this question was of course Cecil's: http://www.straightdope.com/columns/...t-an-epic-poem

The long answer is very complex, but the short answer is that with quantum effects we can demonstrate that in fact a particle is NOT "in one or the other of two states, but we don't know which"; it IS true that "the particle is somehow in both states simultaneously".

The Schrodinger's Cat paradox scales that observation up to macroscopic objects, and there is probably some effect that destroys the paradox during the scaling, but at the particle level there is no doubt of what is going on.
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Old 01-03-2012, 11:23 AM
whc.03grady whc.03grady is offline
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I read the column long ago, and FWIW it seems in fact to bolster my point of view (that physicists should just say, "I don't know", not "It's in a superposition") (emphases added):

"The cylinder's sealed. The hour's passed away. Is
Our pussy still purring — or pushing up daisies?
Now, you'd say the cat either lives or it don't
But quantum mechanics is stubborn and won't.
Statistically speaking, the cat (goes the joke),
Is half a cat breathing and half a cat croaked.
To some this may seem a ridiculous split,
But quantum mechanics must answer, "Tough shit.
We may not know much, but one thing's fo' sho':
There's things in the cosmos that we cannot know.
"

I can accept that statistically the cat is alivedead, because statistics is just a measure of ignorance. But other treatments of quantum physics I've seen want to go beyond that. They don't seem to say, "it's even odds the cat's dead". They seem to say, "There exists a state of being that in principle cannot be observed, and the cat [or decaying atom, or whatever], when unobserved, is in that state."
And THAT. Goes beyond good science. Or so it seems to me.
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Old 01-05-2012, 03:03 PM
Apathetic Coma Apathetic Coma is offline
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Originally Posted by Reno Nevada View Post
The best answer that I have ever read to this question was of course Cecil's: http://www.straightdope.com/columns/...t-an-epic-poem
Dude, I was just browsing...but that link made me sign up.

Don't worry, I'm good.

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Old 01-03-2012, 11:15 AM
Bear_Nenno Bear_Nenno is offline
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That was his whole point to begin with. He came up with the idea to demonstrate his problems with modern quantum theories. It is both a paradox and a parody. He wasn't trying to "invent a property". He was demonstrating the absurdity of the theories.
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Old 01-03-2012, 11:29 AM
whc.03grady whc.03grady is offline
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Originally Posted by Bear_Nenno View Post
That was his whole point to begin with. He came up with the idea to demonstrate his problems with modern quantum theories. It is both a paradox and a parody. He wasn't trying to "invent a property". He was demonstrating the absurdity of the theories.
I realize that the example was invented to demonstrate the absurdity of certain interpretations of quantum physics. But from what I've gathered, mainstream physics has since determined that the absurdity is merely alleged; they bite the bullet and allow that the cat is alivedead. The property they've invented (or discovered, depending on one's predilictions) is that of being in a superposition.

That's the whole point of what I'm getting at, that that's a heck of a bullet to bite (viz., rejecting the law of the excluded middle).
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Old 01-03-2012, 11:36 AM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
I realize that the example was invented to demonstrate the absurdity of certain interpretations of quantum physics. But from what I've gathered, mainstream physics has since determined that the absurdity is merely alleged; they bite the bullet and allow that the cat is alivedead. The property they've invented (or discovered, depending on one's predilictions) is that of being in a superposition.

That's the whole point of what I'm getting at, that that's a heck of a bullet to bite (viz., rejecting the law of the excluded middle).
Not that I'm trying to argue for or against the Copenhagen interpretation, but I think we should point out that it "seems absurd" is an even weaker scientific argument than any one might be trying to refute. One should read up on a the actual theories before proclaiming them absurd; but that's a big, big job and beyond me.

Seemingly absurd things happen in physics all the time - especially particle physics. Try firing a stream of electrons one at a time at two slits and you'll see something that seems absurd. But it happens.

Last edited by Candyman74; 01-03-2012 at 11:38 AM.
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Old 01-03-2012, 11:41 AM
whc.03grady whc.03grady is offline
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Not that I'm trying to argue for or against the Copenhagen interpretation, but I think we should point out that it "seems absurd" is an even weaker scientific argument than any one might be trying to refute.
Well, I don't know. If a scientist performs an experiment and the result shows that my car is simultaneously blue all over and red all over, I'd say the absurdity of that result should give one pause.
We don't take absurd results in mathematics (or philosophy) in stride; a mathematician who showed that 1+1=3 would have a lot of 'splaining to do. Why does the physicist get a pass?
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Old 01-03-2012, 11:54 AM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
Well, I don't know. If a scientist performs an experiment and the result shows that my car is simultaneously blue all over and red all over, I'd say the absurdity of that result should give one pause.
We don't take absurd results in mathematics (or philosophy) in stride; a mathematician who showed that 1+1=3 would have a lot of 'splaining to do. Why does the physicist get a pass?
He doesn't. What makes you think he does? He gets extensively peer reviewed and scritinized. His papers and his experiments and his observations and his calculations are examined in minute detail by hundreds of very clever scientists. Years of further testing and observation prove the hypothesis to be true. Maybe a couple of decades later, they get a Nobel Prize for it. And then some guy on a messageboard proclaims it absurd.

Look at the subliminal neutrino debate going on right now. Did scientists say "oh, right, well we believe you - neutrinos move faster than light now"? Nope. The scientific community descended upon it in droves and are scrutinizing it in far more detail than we can even imagine.

The idea that you think physicists just "get a pass" is, however, somewhat absurd. (Sorry, that came across as rude, but it seemed a mildly witty turn of phrase and I couldn't resist using it).

Last edited by Candyman74; 01-03-2012 at 11:54 AM.
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Old 01-03-2012, 11:40 AM
Kinthalis Kinthalis is offline
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Originally Posted by whc.03grady View Post
I realize that the example was invented to demonstrate the absurdity of certain interpretations of quantum physics. But from what I've gathered, mainstream physics has since determined that the absurdity is merely alleged; they bite the bullet and allow that the cat is alivedead. The property they've invented (or discovered, depending on one's predilictions) is that of being in a superposition.

That's the whole point of what I'm getting at, that that's a heck of a bullet to bite (viz., rejecting the law of the excluded middle).
I'm pretty sure that is not the physicist's position. The cat is either a live or dead, the question is not is there a superposition of the quantum particle involevd - There IS. Period. The question is, at what point does that superposition resolve itself? What is the observer and at what point does it observe.
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Old 01-03-2012, 12:40 PM
DrDeth DrDeth is offline
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And of course, the thought experiment *IS* ridiculous, as the cat is a observer.
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Old 01-03-2012, 05:06 PM
Giraffe Giraffe is offline
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And of course, the thought experiment *IS* ridiculous, as the cat is a observer.
The cat is not the observer, in the wavefunction-collapsing sense. The cyanide capsule is the observer, as it couples to the radioactive decay in a way that distinguishes between the decayed and non-decayed states. The cat is merely an unfortunate bystander.

And Schrodinger's Cat pisses me off. Because it's well known, way too many people believe it's true. It's not. As others have pointed out, it's just a complicated way of looking at randomness. Replace the cat and cyanide with a pair of dice: are dice in a superposition of all possible rolls before you open the box? No. Quantum observation is not about knowledge, it's about interaction: if you interact significantly enough with a quantum system in a superposition, that forces a collapse into a single state. It doesn't matter if a person or a cat or a cow learns the result of the interaction, any more than trees falling in the woods fail to make sound if people aren't around. And it doesn't scale up.
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Old 01-03-2012, 01:04 PM
Candyman74 Candyman74 is offline
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I mean "entitled to ignore" in the same sense that we're entitled to ignore someone who claims to have squared the circle. Rationality allows us to ignore propositions that are, well, irrational. If one assumes a contradiction, anything can be shown. So, we're allowed to dismiss contradictions; we can ignore them.

It looks like, in positing a situation wherein something is simultaneously P and not-P, the physicist has made a statement that entails a contradiction, and therefore anything whatsoever follows from it. The physicist's statement can, in principle, prove anything: that Caesar and my banker are the same person; that the moon is made of green cheese; that all equilateral triangles are equiangular triangles; that five is twenty more than 138; that a carrot is an alarm clock; that dogs bark. Anything. As such, AFAICT the physicist's statement is worthless and subject to be ignored.

That's what I meant.
Sure. OK. Go right ahead and ignore it. There's no disagreement here.
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Old 01-03-2012, 01:26 PM
Wheelz Wheelz is offline
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One of my favorite explanations of Schrodinger's Cat was posted right here on the SDMB, so credit where credit's due:

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Originally Posted by Cayuga View Post
Schroedinger made up the story of the cat to say, "If what you're saying about quantum mechanics is true, then the cat is both dead and alive. That's obviously ridiculous, so what you're saying about quantum mechanics must not be true."

And the quantum greasemonkeys (what do you call comeone who works with quantum mechanics, anyway?) replied. "You're right. In the large-scale, everyday world it would be ridiculous. But it's a fact of life in the sub-atomic quantum world. Which is why quantum mechanics is such a bear to understand."
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Old 01-03-2012, 01:27 PM
WarmNPrickly WarmNPrickly is offline
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The physicist says the cat is in a superposition, viz., is both alive and dead.
Physicists don't say that. That is the entire point of the thought experiment. To say that the cat is simultaneously dead and alive is pretty ludicrous. I am not aware of any interpretation that does this. Until we open the box, the mathematics treat it as a 50% chance of either.

Quote:
For one thing, note that, if shown true, neutrions moving faster than light wouldn't entail an absurdity. It would show that a fundamental proposition about physics was false, yes, but there's nothing logically impossible about a neutrino, or a '67 Buick Skylark, going faster than light; there's no absurdity there.
More than likely, if it does turn out that these neutrinos are traveling faster than light, the current understanding of relativity will be slightly modified rather than tossed out as false. In fact, superluminal travel does create something that is logically impossible, but then so did the initial measurements of C. Nevertheless, Newtonian physics largely dominates engineering and designs of modern equipment. Physics adjusts to new information, but it doesn't toss out the old information as false.
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Old 01-03-2012, 01:53 PM
Animastryfe Animastryfe is offline
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In fact, superluminal travel does create something that is logically impossible, but then so did the initial measurements of C.
Please expand on this. What was thought to be logically impossible about C? I assume that by C you mean the speed of light in a vacuum.
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Old 01-03-2012, 03:59 PM
WarmNPrickly WarmNPrickly is offline
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Please expand on this. What was thought to be logically impossible about C? I assume that by C you mean the speed of light in a vacuum.
Probably a physicist can fill in the gaps here, but when they first measured the speed of light, it was quite astounding that no matter how you measured it, you got the same number. That is not something that fit into any classical physics scheme.
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Old 01-03-2012, 08:04 PM
Animastryfe Animastryfe is offline
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Probably a physicist can fill in the gaps here, but when they first measured the speed of light, it was quite astounding that no matter how you measured it, you got the same number. That is not something that fit into any classical physics scheme.
Ah, I understand now. I was thinking that you were referring to the numerical value of c.
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Old 01-03-2012, 05:37 PM
Mgalindo13 Mgalindo13 is offline
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The assertions of quantum physics don't just sound weird. That's the understatement of the year. To be told that a thing can both be something and not be something, at the same time, well, that's a lot (a LOT) weirder than being told the Earth goes around the Sun and not vice versa.
Weirdness is all relative. You may not think the Earth going around the sun is weird, but not too long ago it was an absurd idea that humans weren't the center of the universe. Similarly, pilgrims would find it ludicrous to suggest that one day man would walk on the moon. And now you find it weird that a particle can be in two states at once, despite a mountain of evidence to support that it is true.

You really can't base an objection to scientific theory on what might be considered "weird" by some people.

That's not to say that you have to accept it as true, but do some additional research, understand QM a bit more. You'll find a lot of things that will blow your mind, the aforementioned double slit experiment is what really attracted me to the field (if only as a hobby). The overall point that you should take away from this discussion is that logical reasoning and classical physics don't always apply in the QM world.

ETA: Telemark seems to have beaten me to this point...

Last edited by Mgalindo13; 01-03-2012 at 05:39 PM. Reason: ETA: Telemark seems to have beaten me to this point...
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Old 01-03-2012, 05:53 PM
whc.03grady whc.03grady is offline
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Weirdness is all relative. You may not think the Earth going around the sun is weird, but not too long ago it was an absurd idea that humans weren't the center of the universe. Similarly, pilgrims would find it ludicrous to suggest that one day man would walk on the moon. And now you find it weird that a particle can be in two states at once, despite a mountain of evidence to support that it is true.
I hope you can see that there's a huge, huuuuge difference between the weirdness of finding out the Earth isn't the center of the universe (or that humans would some day walk on the moon) on the one hand, and finding out that a particle can be in two mutually-exclusive states at once on the other.

But maybe I'm wrong about the mutually-exclusiveness of the states, as Omphaloskeptic suggests. Then it ain't much weirder than anything else.

Last edited by whc.03grady; 01-03-2012 at 05:56 PM.
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Old 01-03-2012, 05:59 PM
whc.03grady whc.03grady is offline
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I mean, think of it this way.

What if the scientific community told you, "You know, it turns out ducks are actually insects." That's weird. Believable, but weird.

Now what if the scientific community told you, "You know, it turns out in some circumstances an object isn't identical with itself." That's beyond weird. It's something else altogether.

That's the difference I don't think some are appreciating here.

Last edited by whc.03grady; 01-03-2012 at 06:02 PM.
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Old 01-03-2012, 06:05 PM
Mgalindo13 Mgalindo13 is offline
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Originally Posted by whc.03grady View Post
I hope you can see that there's a huge, huuuuge difference between the weirdness of finding out the Earth isn't the center of the universe (or that humans would some day walk on the moon) on the one hand, and finding out that a particle can be in two mutually-exclusive states at once on the other.

Unless I'm wrong about the mutually-exclusiveness of the states, as Omphaloskeptic suggests. Then it ain't much weirder than anything else.
There's not a difference, that's my point. You personally may see a difference, but that's a relative point of view. You grew up knowing that the Earth was round and revolved around the sun, so it's logical to you. For someone many years ago , it would be a completely foreign and absurd concept.

Just because YOU think something is weird doesn't make it a fallacy.
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Old 01-03-2012, 06:25 PM
whc.03grady whc.03grady is offline
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There's not a difference, that's my point. You personally may see a difference, but that's a relative point of view. You grew up knowing that the Earth was round and revolved around the sun, so it's logical to you. For someone many years ago , it would be a completely foreign and absurd concept.

Just because YOU think something is weird doesn't make it a fallacy.
If someone can't see that every thing is identical with itself is true now, was true at the time of the dinosaurs, is true at the center of Mars, and is true regardless of how one is brought up, then I can't help that person. To believe otherwise is to abandon rationality, to reject the fruits of scientific inquiry.
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Old 01-03-2012, 06:42 PM
Exapno Mapcase Exapno Mapcase is offline
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Originally Posted by Mgalindo13 View Post
There's not a difference, that's my point. You personally may see a difference, but that's a relative point of view. You grew up knowing that the Earth was round and revolved around the sun, so it's logical to you. For someone many years ago , it would be a completely foreign and absurd concept.

Just because YOU think something is weird doesn't make it a fallacy.
Quote:
Originally Posted by whc.03grady View Post
If someone can't see that every thing is identical with itself is true now, was true at the time of the dinosaurs, is true at the center of Mars, and is true regardless of how one is brought up, then I can't help that person. To believe otherwise is to abandon rationality, to reject the fruits of scientific inquiry.
Mgalindo is completely correct. There is no conceivable reason why the underlying workings of the very tiniest and very largest scales should have any connection at all to our understanding, our "common sense" interpretation of what happens in the middle scales we live in. You only find QM weird because you haven't studied it, you don't understand it, and it contradicts some simplistic and limited view of matter that is a ridiculously minor fraction of the universe.

The only thing that's weird is that we've been able to develop mathematics that in any way describes how the real universe works. That this mathematics doesn't have an easy and glib translation into common English and that it doesn't correspond to mundane reality is the most totally expected thing I can think of.

It really is you who's at issue here. Or rather, it really is that you are merely human that's at issue. Humans never see the quantum world. It is what it is, without regard to any aspect of humanness. The universe is math, not culture. If you find math weird that unfortunately says more about you than it does about math.
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Old 01-03-2012, 06:46 PM
Mgalindo13 Mgalindo13 is offline
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Originally Posted by whc.03grady View Post
If someone can't see that every thing is identical with itself is true now, was true at the time of the dinosaurs, is true at the center of Mars, and is true regardless of how one is brought up, then I can't help that person. To believe otherwise is to abandon rationality, to reject the fruits of scientific inquiry.
No one asked for your help, you started this thread asking "please tell me where I've gone wrong."

You're not grasping the underlying concepts of quantum mechanics and it's not something that any number posts on an Internet message board can correct.

If you're really committed to understanding the topic there's a bounty of information available online and if you're the self-learning type you can even try OpenCourseWare from MIT that has some great courses/materials on quantum theory.
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Old 01-03-2012, 07:47 PM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
If someone can't see that every thing is identical with itself is true now, was true at the time of the dinosaurs, is true at the center of Mars, and is true regardless of how one is brought up, then I can't help that person. To believe otherwise is to abandon rationality, to reject the fruits of scientific inquiry.
I think the problem here is that people have tried to explain it to you, but you just reject their attempts to explain it out of hand. All that's left is to advise you to go read up on quantum theory, because our superficial attempts aren't doing the trick - and we can't teach a course in it here (well, I couldn't anyway - I understand the concepts, not the mathematics). It's not that you're after help in where you've gone wrong; you're after an opportunity to tell us where we're wrong.

It's kinda like the My Problems With Relativity thread, where someone thinks he's proved Einstein wrong. He hasn't, but he won't accept that.


In order to refute a theory, you need to understand it first. Otherwise how do you even know what it is you're refuting? I mean, you know you're refuting a 3-sentence description of what quantum mechanics is to you, but quantum mechanics is not a 3-sentence description; it's a million equations, experiments, observations, and fulfilled predictions. Those are what you have to refute, not a soundbyte description you heard; and to refute them, you have to understand them very well indeed. You have to intimately know the equations, what they mean, how they were derived, how they are used. Then you can point out what's wrong with them.

Last edited by Candyman74; 01-03-2012 at 07:48 PM.
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Old 01-03-2012, 06:07 PM
dracoi dracoi is offline
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I doubt a simple analogy will help resolve an issue this difficult, but I've heard superposition described by comparing it to spinning a coin. Heads and Tails are mutually exclusive states, but if you spin the coin on a table, it's in a state of heads-tails superposition. You cannot simply say "the coin is either heads or tails, but we don't know which" because that only makes sense when describing the observed outcome.

There are experimental findings that back this up. Despite the affront to "common sense," particles really are in a temporary superposition, and not just in a temporary statistical unknown.
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Old 01-03-2012, 06:04 PM
Leo Bloom Leo Bloom is offline
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Didn't one of the founding fathers of QM say something like "if you don't realize the extraordinary weirdness of QM you don't understand QM"?

I'm almost sure somebody said that.
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Old 01-03-2012, 08:19 PM
Leo Bloom Leo Bloom is offline
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This is an excerpt from an English translation of S's paper The Present Situation in Quantum Mechanics--which can be read in its entirety on line--where the cat first appears. It helps to get to primary sources.

The intro graf helps get things going:
That it is in fact not impossible to express the degree and kind of blurring of all variables in one perfectly clear concept follows at once from the fact that Q.M. as a matter of fact has and uses such an instrument, the so-called wave function or psi-function, also called system vector. Much more is to be said about it further on. That it is an abstract, unintuitive mathematical construct is a scruple that almost always surfaces against new aids to thought and that carries no great message. At all events it is an imagined entity that images the blurring of all variables at every moment just as clearly and faithfully as does the classical model its sharp numerical values. Its equation of motion too, the law of its time variation, so long as the system is left undisturbed, lags not one iota, in clarity and determinacy, behind the equations of motion of the classical model.the .... Inside the nucleus, blurring doesn't bother us.

One can even set up quite ridiculous cases. A cat is penned up in a steel chamber, along with the following device (which must be secured against direct interference by the cat): in a Geiger counter there is a tiny bit of radioactive substance, so small, that perhaps in the course of the hour one of the atoms decays, but also, with equal probability, perhaps none; if it happens, the counter tube discharges and through a relay releases a hammer which shatters a small flask of hydrocyanic acid. If one has left this entire system to itself for an hour, one would say that the cat still lives if meanwhile no atom has decayed. The psi-function of the entire system would express this by having in it the living and dead cat (pardon the expression) mixed or smeared out in equal parts.
[ital mine]


That the lack of the excluded middle is justifiable is discuused in almost identical language by Heisenberg on page 124 of Physics and Philosophy
(entire book online in PDF).
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Old 01-03-2012, 08:31 PM
Leo Bloom Leo Bloom is offline
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That the lack of the excluded middle is justifiable and necessary in the real world (in these contexts)--as posted above by a number of people--is discuused in almost identical language by Heisenberg on page 124 of his book Physics and Philosophy
(the entire book is online in PDF).
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Old 01-03-2012, 08:39 PM
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I don't think anyone in the thread has argued that excluded middle is violated by quantum phenomena, including superposition.

And it's not.
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Old 01-04-2012, 09:18 AM
Frylock Frylock is offline
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Put yet another way (sorry): The fact that subtraction isn't commutative doesn't mean that the physical phenomena we model through subtraction "violate commutativity." It doesn't mean that somehow the commutative properties of addition and multiplication are false or invalid.

Similarly, the fact that quantum logic isn't distributive doesn't mean that the phenomena modeled by quantum logic "violate distributivity." It doesn't mean that somehow the distributive properties of the "and" and "or" of propositional logic are false or invalid.
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Old 01-05-2012, 07:51 PM
Candyman74 Candyman74 is offline
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Is if just me, or are the usernames whc.03grady and tomh.4040 reminiscent in style of each other?

One being "I've figured out what's wrong with quantum theory" and the other being "I've figured out that Einstein was wrong about relativity"?
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Old 01-06-2012, 01:49 AM
Half Man Half Wit Half Man Half Wit is offline
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Originally Posted by Candyman74 View Post
Is if just me, or are the usernames whc.03grady and tomh.4040 reminiscent in style of each other?
I don't think so. To me, it seems that whc.03grady has shown himself both more knowledgeable and corrigible on his topic, plus we haven't yet seen any inane thought experiments intended to expose errors in the thinking of some of the smartest people in the world for nearly the past 100 years that can ultimately be reduced to trivial misunderstandings based on biased readings of pop-sci arguments...
  #36  
Old 01-06-2012, 06:58 AM
canterburyales canterburyales is offline
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Many posters have recommended researching the topic to get a better understanding of the strangeness of quantum phenomenon that is being illustrated by the story of Schrodinger's Cat. That is the best approach.
I think the heart of the matter is the difficulty in accepting the quantum view that the world seems to be inherently probabilistic. As a non-physicist I have gotten a lot out of the various Feynman lectures available online.

This series is a good place to start:

http://vega.org.uk/video/programme/45

He talks about the idea of understanding at 20:15.
  #37  
Old 01-08-2012, 03:33 PM
Leo Bloom Leo Bloom is offline
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Quote:
Originally Posted by canterburyales View Post
Many posters have recommended researching the topic to get a better understanding of the strangeness of quantum phenomenon that is being illustrated by the story of Schrodinger's Cat. That is the best approach.
I think the heart of the matter is the difficulty in accepting the quantum view that the world seems to be inherently probabilistic. As a non-physicist I have gotten a lot out of the various Feynman lectures available online.

This series is a good place to start:

http://vega.org.uk/video/programme/45

He talks about the idea of understanding at 20:15.
Astounding, great great cite.

I can't wait to watch the next three lectures.

Thanks.
  #38  
Old 01-11-2012, 09:34 PM
canterburyales canterburyales is offline
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Quote:
Originally Posted by Leo Bloom View Post
Astounding, great great cite.

I can't wait to watch the next three lectures.

Thanks.
When you are done with those check this out:

http://research.microsoft.com/apps/t...uva/index.html
  #39  
Old 01-06-2012, 06:52 PM
Chronos Chronos is offline
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Fundamentally, Schrödinger's point about the cat was that the Copenhagen interpretation of quantum mechanics led to results which seem intuitively absurd. About that, he's right. But there are many different possible interpretations of quantum mechanics, all of them exactly equivalent in the sense that they predict the same sets of observations, and not all of them lead to that particular absurdity. The tricky part, though, is that all of them lead to their own particular absurdities: Bell's Inequality proves that any model which does not lead to one of a variety of things we consider intuitively absurd, cannot be consistent with the results of the measurements we've actually performed. So somehow or another, there's something about physics that we consider intuitively absurd (which should, of course, be taken as a flaw in our intuitions, not as a flaw in physics), but we can't actually say just what the absurdity is.
  #40  
Old 01-07-2012, 04:28 AM
Senegoid Senegoid is offline
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Quote:
Originally Posted by Chronos View Post
Fundamentally, Schrödinger's point about the cat was that the Copenhagen interpretation of quantum mechanics led to results which seem intuitively absurd. About that, he's right.

<snip>

Bell's Inequality proves that any model which does not lead to one of a variety of things we consider intuitively absurd, cannot be consistent with the results of the measurements we've actually performed. So somehow or another, there's something about physics that we consider intuitively absurd (which should, of course, be taken as a flaw in our intuitions, not as a flaw in physics), but we can't actually say just what the absurdity is.
This is the Quantum Meta-Heisenberg Uncertainty Theorem
  #41  
Old 01-06-2012, 07:07 PM
Leo Bloom Leo Bloom is offline
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Chronos! Where the heck you been, man?
  #42  
Old 01-06-2012, 08:34 PM
Chronos Chronos is offline
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Visiting my mom (who has lousy internet access) for vacation. But I'm back in the land of broadband now.
  #43  
Old 01-07-2012, 03:01 AM
Boyo Jim Boyo Jim is offline
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Why is it so hard to believe that science has proved the existence of zombie cats?
  #44  
Old 04-22-2017, 04:17 AM
Half Man Half Wit Half Man Half Wit is offline
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Quote:
Originally Posted by septimus View Post
Yes, I realize I provide more questions than answers. But I think my intuitionthat admitting retrocausality is the way Occam would be most delighted to cut with his razor — is sound.
While I agree that retrocausality furnishes a possible explanation for Bell inequality violation, I don't really agree that it's a more parsimonious solution. For instance, you incur new explanatory burdens: why, if there is retrocausality, can we not actively influence the past? What additional mechanisms prevent chronology violation, or the sending of information into the past, or even to spacelike separated events?

In contrast, in ordinary quantum mechanics, you merely need to give up the assumption that all measurements should obey a joint probability distribution.

Quote:
I do not "throw out the notion of causality" nor are there "faster than light actions."
Well, if there is retrocausality, then either there is the possibility of causes influencing their effects, or there must be a mechanism to prevent this; furthermore, you can produce FTL effects by simply sending a signal to the future, and then sending one to a different point in the past. Indeed, nonlocality and superluminal signalling are really two sides of the same coin, and retrocausation leads at least to effective nonlocality.

Quote:
I'll agree there are probably severe constraints on what kind of information can be exchanged, but information is manifestly exchanged in the case of EPR and GHZ paradoxes.
No. In fact, the No Communication-theorem entails that no information can be transmitted using entanglement alone (any more than information can be transmitted using a setup where each of us has an envelope with a colored card in it, such that yours is red if mine is green, and vice versa; opening your envelope, you'll immediately know the color of my card, but no information has been transmitted). In order to send information, you always have to rely on classical communication

Quote:
I certainly admit the possibility of boundary conditions, just as other models do, e.g. Big Bang Hypothesis, or for that matter 19th century physicists like Boltzmann.
Actually, I don't think there's really a well-posed initial value problem anymore in the presence of retrocausality; seems to me that at minimum, you'd have to also fix some far future conditions; which again entails extra explanatory burdens.
  #45  
Old 04-22-2017, 01:07 PM
Kedikat Kedikat is offline
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I feel that a lot of quantum mechanics is still a manufactured framework to enable people to work in that difficult realm. It has not yet fully reflected the reality of what is going on. I liken it to navigating with two dimensional maps before you know the world is a sphere. You can make it work. But you need to invent rules in order to do it. A little creative math to straighten or curve things to plot the best path that works in the reality that you do not yet know. Many places where there be monsters.

That doesn't mean it does not work. We use flat maps all the time and get where we want to go. Quantum mechanics is a developing map. It helps explore that world. The explorers may at some point see it for what it is. Possibly far outside the boundaries of their map.
  #46  
Old 04-22-2017, 01:45 PM
rat avatar rat avatar is offline
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To clarify for other users due to the use of various terms in this thread.

EPR experiment nor any other quantum experiment has demonstrated that faster-than-light signaling is possible. The lack of transfer of usable "faster-than-light signaling" or what is commonly also called information has not been demonstrated.

Because of this lack of useable information the speed of causality is not violated at this date.

While a lack of a unifying theory may make these paradoxes fairly confusing as there is a significant amount of unsettled science the restriction on the speed of causality is related to communication faster than the speed of light and not other aspects of our universe.

In fact in the future even the expansion of the universe is expected to exceed the speed of light. This does not imply that the particles themselves are superluminal, but that the distances between them will be.

As of this date the no-communication theorem is still firmly in place.
  #47  
Old 04-22-2017, 02:22 PM
rat avatar rat avatar is offline
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Alice and Bob each take one of an entangled pair.
Alice reads the Z spin on one of the entangled pair but Bob doesn't have a way to detect that she did.
Alice can't control what the value is that will be read, she reads a "random value.
Alice my read an up or a down. Bob will read a complement of Alice's "random" value, to Bob it appears random as well.

Bob would need a way to know that Alice has actually performed a measurement or if he is the first one to measure a member of the pair.
Bob's statistics for his particle alone look the same either way. If Alice and Bob are not local to each other they cannot tell if something is random or due to entanglement.

It is easy to confuse tests that do have locality and non FTL communication with thought experiments that describe how entanglement interactions are FTL but to reference Kedikats post remember that most of the math is in done in Hilbert space or other Euclidean spaces and thus will not apply to space like intervals.

While our theories are incomplete, any violation of the speed of causality is purely theoretical and there is no experimental proof for "faster-than-light signaling" but only for "faster-than-light interactions".

I do want to address this from the OP:

Quote:
Originally Posted by whc.03grady View Post
Why does the physicist get to invent a property (the superposition) that is, in principle, unobservable
While others have cited tests for this theory I also wanted to point out that it was recently observed on a physical object.

http://physicsworld.com/cws/article/...visible-object

Last edited by rat avatar; 04-22-2017 at 02:24 PM.
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