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  #1  
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.
  #3  
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, 11:15 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, 11:23 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.
  #6  
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.
  #8  
Old 01-03-2012, 11:40 AM
Kinthalis Kinthalis is online now
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Quote:
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.
  #9  
Old 01-03-2012, 11:41 AM
whc.03grady whc.03grady is offline
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Originally Posted by Candyman74 View Post
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.
  #11  
Old 01-03-2012, 12:15 PM
leahcim leahcim is offline
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The sequence of events is:

(1) Hey look, electrons are doing weird things in weird situations (like double-slit experiments) that classical physics can not explain.
(2) Well Jeez, let's invent quantum mechanics to deal with that, and look, quantum mechanics explains all of those features of electrons, and a fuck-ton of other particles, too.
(3) But what if we applied the rules of quantum mechanics to cats? Then you have cats doing weird things that they clearly don't do while we're watching!
(4) Well, actually, for certain values of "watching" the electrons don't do silly things while we're watching either, so I think this is all right, just weird.

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Originally Posted by Candyman74 View Post
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.
And oddly, a good chunk of the internet message board community (albeit not this one, because this one is lousy with physicists) jumped all over the superluminal neutrinos with claims that all of physics is shattered and those mean scientist-priests are being dogmatic assholes by criticizing the results. Teh Intarwebs seem very split upon whether or not physicists should get a free pass or not.
  #12  
Old 01-03-2012, 12:24 PM
whc.03grady whc.03grady is offline
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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).
I didn't take it as rude.

I think I see what you're saying. So if the mathematician shows that 1+1=3, and that result is confirmed over and over again, then we're supposed to accept the absurd (or "absurd") result and maybe give her a prize. I suppose I should've said, "Why does physics (meaning the original experimenter and all those who verified the result) get a pass?"

But.

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. Maybe something like that is going on in the two-slit experiment--the result is weird, but not absurd. (Also, there may be some confusion because I'm using "absurd" in the strict sense of "entailing a contradiction".)

The assertion of the existence of a state wherein a cat is simultaneously alive and not-alive (viz., in a superposition) would by definition entail a contradiction and is therefore (it seems to me) an assertion we're entitled to ignore. The laws of logic/math are more basic than the laws of physics, after all.

If a physicist tells me they've found a particle that weighs a pound at time t and also doesn't weigh a pound at time t, and if that result is replicated over and over, then I think it's safer to say there's something systematically wrong with how everyone's going about it, than it is to say a contradiction obtains. (Those who are inclined to quote Whitman here can save their keystrokes. )

Last edited by whc.03grady; 01-03-2012 at 12:29 PM. Reason: Phrase out of place
  #13  
Old 01-03-2012, 12:29 PM
aruvqan aruvqan is offline
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I am not a physicist, but I can state that either way, he will have a box full of seriously pissed off cat.
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Old 01-03-2012, 12:35 PM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
I suppose I should've said, "Why does physics (meaning the original experimenter and all those who verified the result) get a pass?"
I don't really understand where you're going with this. I mean, you're not supposed to believe anything; it's not a crime not to. The experimenter believes it, and the hundreds of scientists who verify it believe it, and the tens of thousands of scientists who subsequently verify it over the decades believe it. I honestly don't know where this "get a pass" thing is coming from. Get a pass from whom? You?


I guess you're welcome to not believe established scientific principles. I don't think the scientific community minds all that much. It's not going to stop them using the principles they've discovered.


Relativity sounds absurd. But your GPS works, so it's clearly not. Quantum computers work, so it can't all be nonsense. But, like I said, anyone's welcome to believe whatever they want to. The scientists aren't asking you for a pass; they're just getting on with their work and if you're interested they're happy to tell you about it.
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Old 01-03-2012, 12:39 PM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
The assertion of the existence of a state wherein a cat is simultaneously alive and not-alive (viz., in a superposition) would by definition entail a contradiction and is therefore (it seems to me) an assertion we're entitled to ignore.
Or - the shorter version of my above post:

Sure, you're entitled to ignore whatever you want.

Last edited by Candyman74; 01-03-2012 at 12:39 PM.
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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, 12:46 PM
The Hamster King The Hamster King is offline
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Quote:
Originally Posted by whc.03grady View Post
The assertion of the existence of a state wherein a cat is simultaneously alive and not-alive (viz., in a superposition) would by definition entail a contradiction and is therefore (it seems to me) an assertion we're entitled to ignore.
But it's been experimentally proven that individual particles can exist in a state of superposition. There have even been experiments that show superposition large collections of particles. You can call it a logical contradiction if you want, but its true.
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Old 01-03-2012, 12:52 PM
whc.03grady whc.03grady is offline
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Originally Posted by Candyman74 View Post
Or - the shorter version of my above post:

Sure, you're entitled to ignore whatever you want.
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.

Last edited by whc.03grady; 01-03-2012 at 12:53 PM.
  #19  
Old 01-03-2012, 01:03 PM
Omphaloskeptic Omphaloskeptic is offline
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Quote:
Originally Posted by whc.03grady View Post
The assertion of the existence of a state wherein a cat is simultaneously alive and not-alive (viz., in a superposition) would by definition entail a contradiction and is therefore (it seems to me) an assertion we're entitled to ignore. The laws of logic/math are more basic than the laws of physics, after all.
I think there are some misunderstandings in both of these sentences. It is tempting to view logic and mathematics as basic, with physical laws somehow building on these. But physics is fundamentally an empirical science, not a logical one; if empirical physical results contradict logical derivations then it's the logic that's broken, not the physics.

Of course what's more likely than an inconsistency in logic is that there's been an error in the attempt to translate from physical measurements to physical laws to logical statements; and this is what I think is wrong with your first statement. (This is especially easy to do if you're reading popular accounts, which may not be terribly precise in their use of language.) You say that a cat must be either alive or not-alive (excluded middle), and implicitly count this as two distinct well-defined states exhausting all possibilities. At least one of these two properties is empirically shown to fail in quantum mechanics, however. The usual informal way in which physicists talk about this is to label two particular states of the cat system as "alive" and "dead" and then understand that quantum mechanics allows superpositions of these two states. Now you see that there's not actually a logical contradiction. There are more than two possibilities, so excluded middle does not apply, and "not-alive" is not the same as "dead".

So more formally what quantum mechanics predicts--and as already mentioned this has been experimentally verified, though not for actual cats--is that there is a continuum of possible states, each of which has some probabilities of having particular values when actual measurements such as "is the cat alive?" are made. The difference between this prediction and the statistical incomplete-knowledge prediction is that for a superposition there are some measurements that always give the same value.

These measurements are somewhat difficult to describe for cats, but they are pretty easy to describe for an electron, say. If we call |up> and |down> the states in which an electron's z-component of spin (i.e., measured along a chosen z axis) is +1/2 and -1/2 respectively, then measuring the z-component of spin for the state |up>+|down> will give +1/2 half the time and -1/2 half the time. However, measurement of the component of spin along a particular axis orthogonal to the z axis will give +1/2 *all the time*. This is distinct from the statistical case in which you have no information about the electron's spin; in this case measurement along any axis will statistically give +1/2 half the time and -1/2 half the time.
  #20  
Old 01-03-2012, 01:04 PM
Candyman74 Candyman74 is offline
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Quote:
Originally Posted by whc.03grady View Post
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, 01:10 PM
Animastryfe Animastryfe is offline
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Originally Posted by whc.03grady View Post
I didn't take it as rude.

I think I see what you're saying. So if the mathematician shows that 1+1=3, and that result is confirmed over and over again, then we're supposed to accept the absurd (or "absurd") result and maybe give her a prize. I suppose I should've said, "Why does physics (meaning the original experimenter and all those who verified the result) get a pass?"
I don't think you should use this as an example. Mathematics uses deduction based on certain axioms and rules of logic. I do not think there is any a priori reason that, for a certain set of axioms, one cannot make a proof that 1+1=3.

The difference between mathematics and physics in this context is that mathematics is not a 'science', in the sense that one does not do experiments to check its results. A mathematician cannot find a proof that 1+1=3 for the mathematics that most people are familiar with, or else we're in some kind of Lovecraftian universe and any talk of logic or 'that makes sense' is moot.

To help us answer your questions about physics, it would be helpful to know your background knowledge of physics. Have you read any textbook on quantum mechanics? I have not read any popular science books on physics for a few years now, but I cannot think of any popular science example of an author explaining quantum mechanics with enough details so that a layman will really understand superposition of quantum states, entanglement and whatnot.

Edit: Well, Omphaloskeptic just wrote what I wanted to write, but with more detail. Darn.

Last edited by Animastryfe; 01-03-2012 at 01:11 PM.
  #22  
Old 01-03-2012, 01:26 PM
Wheelz Wheelz is online now
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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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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, 01:32 PM
whc.03grady whc.03grady is offline
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Originally Posted by Omphaloskeptic View Post
It is tempting to view logic and mathematics as basic, with physical laws somehow building on these. But physics is fundamentally an empirical science, not a logical one; if empirical physical results contradict logical derivations then it's the logic that's broken, not the physics.
I appreciate the fact that physics isn't built atop logic in the sense that you describe (though I have other, unexpressed feelings about this that aren't germane to the topic at hand), and I likely slid into that way of thinking in an earlier post. But it still seems to me that if we're dealing with something like a miracle here.
I'm thinking of Hume's treatment of miracles, which in short says (taking his example), which is more believable? That someone rose from the dead after three days, or that everyone's evidence supporting that occurrence is mistaken? Which does reason compel you to bet on?

The same kind of reasoning seems to apply here: if you had to bet, would you bet that (a) there are cases where contradictions obtain; or (b) the descriptions/interpretations of those cases are in error? Now, it's clear where I place my money, but I'm curious as to why others might bet differently?

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Originally Posted by Omphaloskeptic View Post
You say that a cat must be either alive or not-alive (excluded middle), and implicitly count this as two distinct well-defined states exhausting all possibilities. At least one of these two properties is empirically shown to fail in quantum mechanics, however. The usual informal way in which physicists talk about this is to label two particular states of the cat system as "alive" and "dead" and then understand that quantum mechanics allows superpositions of these two states. Now you see that there's not actually a logical contradiction. There are more than two possibilities, so excluded middle does not apply, and "not-alive" is not the same as "dead".
I wonder if you could elucidate on this a bit. First, I don't see how changing "not-alive" to "dead" makes a difference with respect to there not actually being a logical contradiction. Second, I don't get how the physicist "understand[s] that quantum mechanics allows superpositions of these two states." (If I could get a handle on this (and if it's true, of course!), it might be resolved for me and render the rest of what I'm saying irrelevant.)

What's more, I don't see how empirical results can trump principles of logic or reasoning. The whole process of science is built upon certain more or less formal principles of reasoning: "If a theory is confirmed so-and-so many times, we can regard it as true" would be an example. I wholeheartedly agree with this principle, but hopefully we all can see that no experiment has ever, will ever, or could ever be performed to show that it's a good principle. The scientific process relies quite heavily on the principles of mathematics for instance, principles which themselves are in no way proven by science.

What I'm trying to say in this post is there are certain meta-scientific principles by which science operates that are not themselves provable within science, yet are accepted (NB: I do not take this to mean scientific reasoning is in any way deficient). But why is it that when some results seem to run contrary to a certain principle (non-contradiction), that the impulse in this case is to pitch the principle, not the results?

Last edited by whc.03grady; 01-03-2012 at 01:34 PM.
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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.
  #26  
Old 01-03-2012, 01:54 PM
The Hamster King The Hamster King is offline
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What's more, I don't see how empirical results can trump principles of logic or reasoning.
You have it exactly backwards. It's the success of logic in explaining empirical results that justifies its use.

Depending on the axioms you pick as your starting point, you can construct a wide range of different mathematical systems. You can create a system where 1+1=3 or where TRUE & TRUE = FALSE, if you want.

Now, some of these systems happen to be useful in modelling the behavior of the universe. Systems where 1+1=2 and TRUE & TRUE = TRUE fall into this category.

The reason we trust these systems is because they do a good job of explaining what we observe. However, if we observe things that violate the predictions, then the systems must change.
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Old 01-03-2012, 02:00 PM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
What I'm trying to say in this post is there are certain meta-scientific principles by which science operates that are not themselves provable within science, yet are accepted (NB: I do not take this to mean scientific reasoning is in any way deficient). But why is it that when some results seem to run contrary to a certain principle (non-contradiction), that the impulse in this case is to pitch the principle, not the results?
OK, let's try to narrow it down.


Which scientific principle, specifically, are you referring to? (Schrodinger's Cat isn't a scientific principle).


If you could identify which scientific principle it is that you disagree with, at least we're all on the same page. And perhaps we can discuss the evidence for that principle, or illustrate how it is successfully used in technology, or how it is used to successfully make predictions.
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Old 01-03-2012, 02:02 PM
Candyman74 Candyman74 is offline
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What's more, I don't see how empirical results can trump principles of logic or reasoning.
Of course they can. They must. They have to. Otherwise we'd still believe that the sun revolved around the earth. It was our observations - empirical results - which told us otherwise and contradicted the logic and reasoning of centuries of great thinkers.

If your observations are at odds with your reasoning, the flaw is much more likely to be in your reasoning than in your observation. But you test and retest and retest the obvservation over and over and over again to be sure.

Last edited by Candyman74; 01-03-2012 at 02:04 PM.
  #29  
Old 01-03-2012, 02:30 PM
Omphaloskeptic Omphaloskeptic is offline
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I appreciate the fact that physics isn't built atop logic in the sense that you describe (though I have other, unexpressed feelings about this that aren't germane to the topic at hand), and I likely slid into that way of thinking in an earlier post. But it still seems to me that if we're dealing with something like a miracle here.
I'm thinking of Hume's treatment of miracles, which in short says (taking his example), which is more believable? That someone rose from the dead after three days, or that everyone's evidence supporting that occurrence is mistaken? Which does reason compel you to bet on?

The same kind of reasoning seems to apply here: if you had to bet, would you bet that (a) there are cases where contradictions obtain; or (b) the descriptions/interpretations of those cases are in error? Now, it's clear where I place my money, but I'm curious as to why others might bet differently?
Well, I'm arguing that there is no logical contradiction, and that your interpretations are in error, so I guess that makes (b), but I think it's a different (b) than yours since I think you think it's somebody else's interpretations that are in error.

There's a big difference between quantum mechanics and miracles, which is repeatability. Miracles, at least of the sort you're talking about, are one-time events. This makes them very difficult to consider using the scientific method. With quantum mechanics, you can measure as many electrons as you want; when you always get the answers that quantum mechanics predicts, you may start to think there's something to it after all, weird or not.

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I wonder if you could elucidate on this a bit. First, I don't see how changing "not-alive" to "dead" makes a difference with respect to there not actually being a logical contradiction. Second, I don't get how the physicist "understand[s] that quantum mechanics allows superpositions of these two states." (If I could get a handle on this (and if it's true, of course!), it might be resolved for me and render the rest of what I'm saying irrelevant.)
I gave a little description of the treatment of superpositions later in my post, when I described measurements of an electron's spin. I should note that it is pretty easy to make measurements like this; this description is actually the description of (part of) a classic result called the Stern-Gerlach experiment. It's experiments like this that convince physicists of the need for superpositions.

Now the problem is, because strongly-quantum-mechanical effects primarily occur far outside of the range of everyday experience, human language is not very well-equipped to describe states like |alive>+|dead>. This I think is where your real problem is. You are trying to describe this state as "both alive and not-alive" and claiming a logical contradiction. But that description is intended to be very loose; it's not intended as a formal description of the state that you can directly translate into logic in the way you're trying to do. If you want you can tighten the language to make it clear that there's no immediate logical contradiction. One way to do this is to eliminate the definitions not-alive<=>dead and not-dead<=>alive, and say that "alive" describes precisely the quantum state |alive>, and "dead" describes precisely the quantum state |dead>. You could then describe the state as "not-alive" (i.e., not the state |alive>) and "not-dead" (i.e., not |dead>) without a logical contradiction. I don't find this particularly interesting, but I'm more in the shut-up-and-calculate school myself.

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What's more, I don't see how empirical results can trump principles of logic or reasoning. The whole process of science is built upon certain more or less formal principles of reasoning: "If a theory is confirmed so-and-so many times, we can regard it as true" would be an example. I wholeheartedly agree with this principle, but hopefully we all can see that no experiment has ever, will ever, or could ever be performed to show that it's a good principle. The scientific process relies quite heavily on the principles of mathematics for instance, principles which themselves are in no way proven by science.

What I'm trying to say in this post is there are certain meta-scientific principles by which science operates that are not themselves provable within science, yet are accepted (NB: I do not take this to mean scientific reasoning is in any way deficient). But why is it that when some results seem to run contrary to a certain principle (non-contradiction), that the impulse in this case is to pitch the principle, not the results?
A full response to these paragraphs would probably be an entire essay on the philosophy of the scientific method; that at least is what my fingers keep trying to type here.

- Why pitch the principle instead of the results? Because that's the scientific method, as I said earlier. If logic and empirical results disagree, it's the logic that eventually has to give. Obviously it's more complicated than this. What usually happens in the most exciting experiments is that a new result appears to contradict an existing *physical theory* (not "logic"--you still seem to be glossing over the necessary but fallible steps in translation between physical theories and logical statements, which is why you seem to be confused); this is usually because the new experiment takes place outside the parameter regime explored by the previous experiments which were used to "derive" (in an inductive sense, not the logical-proof sense) and confirm that theory. If the new experiment is repeatedly confirmed with enough confidence (something that can't be done with one-time miracles), then these experiments are used to derive a new theory, and the old theory is now discarded (or considered a special case usable only in restricted circumstances).

- The relation of mathematics and science is much more complicated than you seem to be describing. The Hamster King already did a good job discussing this, so I will stop here for now.
  #30  
Old 01-03-2012, 02:56 PM
whc.03grady whc.03grady is offline
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Which scientific principle, specifically, are you referring to? (Schrodinger's Cat isn't a scientific principle).


If you could identify which scientific principle it is that you disagree with, at least we're all on the same page. And perhaps we can discuss the evidence for that principle, or illustrate how it is successfully used in technology, or how it is used to successfully make predictions.
None. I didn't say I was disagreeing with any scientific principle. And I realize Schrodinger's Cat isn't a scientific principle, it's a thought experiment.

I'm pointing out what I think may be an instance of a particular branch of science (quantum physics) overstepping the bounds of what science is allowed to make statements about. Science makes statements about the observable (empirical) world. The unobserved particle is, by definition, unobserved. What I'm asking is, on what basis does the quantum physicist get to make the claim that, during the time when it's unobserved, the particle has such-and-such property? The particle was unobserved! Science is only supposed to tell us about what IS observed. How can the physicist (who is a scientist, an empiricist) make a claim about a property a particle has during a time when she didn’t look at it?

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Of course [empirical results can trump principles of logic or reasoning]. They must. They have to. Otherwise we'd still believe that the sun revolved around the earth. It was our observations - empirical results - which told us otherwise and contradicted the logic and reasoning of centuries of great thinkers.
The Ptolemaic theory doesn't entail a contradiction; there's nothing impossible about it being true. It ISN'T true, yes. But there is a sense in which it could be. Nothing about the discovery that the Earth goes around the Sun (and not the other way 'round) required the revamping or even the serious reconsideration of any principle of reasoning. It did require the revamping and serious reconsideration of certain accepted principles of astronomy (and anthropology, religion, probably others). Big deal. We find out certain of our contingent principles (I should say “principles”) are wrong all the time.

It's a mistake to think that "logic and reasoning" somehow belong to times or persons, as you seem to be thinking. There's just no sense in which "If a=b, and b=c, then a=c" was a caveman principle 20,000 years ago and in which it's a modern human principle now. Mistakes in logic and reasoning may very well belong to times and persons, sure. If a bunch of (or even all) cavemen thought, "If a=b, and b=c, a≠c," that wouldn't mean the principles of cavemen reasoning were different than ours, or that reasoning operated differently 20,000 years ago. It would just show that a bunch of cavemen were wrong about transitivity.

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If your observations are at odds with your reasoning, the flaw is much more likely to be in your reasoning than in your observation.
I have no idea on what basis you could make this assertion.
  #31  
Old 01-03-2012, 03:10 PM
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Originally Posted by whc.03grady View Post
It's a mistake to think that "logic and reasoning" somehow belong to times or persons, as you seem to be thinking.
It's a mistake to think that logic as you know it applies to all situations, such as QM where strange things happen.

It's akin to applying Newtonian logic to a Relativistic situation. How can two objects each traveling towards each other at .9c to a neutral observer appear to approach each other at .99c? It doesn't make logical sense to in Newtonian terms, but it has been demonstrated to be accurate.

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There's just no sense in which "If a=b, and b=c, then a=c" was a caveman principle 20,000 years ago and in which it's a modern human principle now.
Yes there is such a sense. It's called QM, which defies conventional logic.
  #32  
Old 01-03-2012, 03:19 PM
The Hamster King The Hamster King is offline
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Originally Posted by whc.03grady View Post
If a bunch of (or even all) cavemen thought, "If a=b, and b=c, a≠c," that wouldn't mean the principles of cavemen reasoning were different than ours, or that reasoning operated differently 20,000 years ago. It would just show that a bunch of cavemen were wrong about transitivity.
No, it would simply mean they had chosen a mathematics in which the transitive property of equality doesn't hold. Such a mathematics wouldn't be much use if they were trying to use it for counting woolly mammoths, but it wouldn't be "wrong".
  #33  
Old 01-03-2012, 03:45 PM
Cheesesteak Cheesesteak is offline
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It's a mistake to think that logic as you know it applies to all situations, such as QM where strange things happen.
This is seriously the truth. You cannot rely on everyday logic for Quantum matters.

A simple example is the Double Slit Experiment Scroll down to the first variation "interference of individual particles". The experiment makes all kind of sense until you ratchet down the intensity to where you only have individual particles going through the slits at one time. At that point, they continue to show the same interference pattern, even though there isn't any second particle/photon for it to interfere with. It makes absolutely no sense, but the effect has been known for over 100 years.
  #34  
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.
  #35  
Old 01-03-2012, 04:10 PM
Candyman74 Candyman74 is offline
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Originally Posted by whc.03grady View Post
None. I didn't say I was disagreeing with any scientific principle. And I realize Schrodinger's Cat isn't a scientific principle, it's a thought experiment.

I'm pointing out what I think may be an instance of a particular branch of science (quantum physics) overstepping the bounds of what science is allowed to make statements about. Science makes statements about the observable (empirical) world. The unobserved particle is, by definition, unobserved. What I'm asking is, on what basis does the quantum physicist get to make the claim that, during the time when it's unobserved, the particle has such-and-such property? The particle was unobserved! Science is only supposed to tell us about what IS observed. How can the physicist (who is a scientist, an empiricist) make a claim about a property a particle has during a time when she didn’t look at it?
Huh? You can observe the properties of a particle. You just can't accurately determine both its position and velocity at the same time.

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I have no idea on what basis you could make this assertion.
Clearly.


I'm afraid the whole subject of the scientific method is too much for me to want to get into a long debate about. I'll leave it to others; suffice it to say that you are misunderstanding some fairly fundamental concepts. But it's too much for me to want to engage in because I know how these threads go.

Last edited by Candyman74; 01-03-2012 at 04:10 PM.
  #36  
Old 01-03-2012, 04:38 PM
Leo Bloom Leo Bloom is offline
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Originally Posted by whc.03grady View Post
I don't see how empirical results can trump principles of logic or reasoning. The whole process of science is built upon certain more or less formal principles of reasoning: "If a theory is confirmed so-and-so many times, we can regard it as true" would be an example. I wholeheartedly agree with this principle, but hopefully we all can see that no experiment has ever, will ever, or could ever be performed to show that it's a good principle. The scientific process relies quite heavily on the principles of mathematics for instance, principles which themselves are in no way proven by science.
That mathematics and proof of its correctness needs science for validation is backwards, I believe, but that is an enormous and different field of inquiry.

[Bold mine]
Experiments are what are important. If, for example, after four million times of looking sideways at a Hereford cow, a principle is established that Herefords are spotted. But along comes someone who figures out that 1) there may be another side to the cow, and 2) tries to get a way to confirm this, checking 1) against 2), repeatedly.

Then maybe the former principle begins to totter.

(Isn't there some joke about this example? Or one about the Umpire, the someone, and the someone judging reality?)
  #37  
Old 01-03-2012, 05:00 PM
whc.03grady whc.03grady is offline
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I have no idea on what basis you could make this assertion.
Clearly.


I'm afraid the whole subject of the scientific method is too much for me to want to get into a long debate about. I'll leave it to others; suffice it to say that you are misunderstanding some fairly fundamental concepts. But it's too much for me to want to engage in because I know how these threads go.
I'm sorry if you think I'm trying to drag you (or anyone) into a debate on the pitfalls of the scientific method (if there are any), or anything like that. Myself, I don't know how such threads usually go but if you're worried that I'm looking for some point at which I can say "a-HA! Science is fundamentally flawed, the Bible is the literal truth, evolution sucks", trust me, I'm not going there (it would be pretty weird if I did, as a dyed-in-the-wool atheist). But like I said, I don't know if that's how these threads usually pan out anyway, that's just my guess. If I were to debate someone on the subject of the scientific method, I assure you, I'd keep it on the level (which isn't to say I'd just unquestioningly eat up anything you'd try to feed me).

I also appreciate the responses you and others have given of examples of revolutions in science, but those kinds of shifts in thinking aren't what I see to be happening in the situation being discussed (quantum physics). This situation is different from any other revolution in science I can think of--Copernican, Newtonian, Darwinian, Einsteinian--in that it's not some contingent principle that's being overturned, it's something much deeper.

If anyone who's made it this far doesn't understand just how utterly, completely, mind-blowingly, dauntingly different the claims of quantum physics are from the claims of any of these others (respectively and in short, "The Earth goes around the Sun," "An object at rest tends to stay at rest, etc.," "Human beings, like all biota, are descended and differentiated from antecedent forms by the mechanism of natural selection," "Light is the speed limit of the universe"), then I thank you for your time.

I don't take myself to be smarter than most of you and certainly not smarter than the average quantum physicist. But I have a degree (and some graduate study but no post-graduate degree in) philosophy (analytic philosophy, not the wishy-washy, beret-wearing, coffeehouse kind), so pardon me but I'm not inclined, generally, to take advice to "just trust what the scientists are saying" lightly, at least for these types of results.

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.

Now if it's like Omphaloskeptic says and I'm seeing the claim of a contradiction where there isn't one, then that's something I'd like to know because I like to know when I'm wrong. (I've read and reread your posts, Omphaloskeptic; thank you.) The Hamster King has made some enlightening comments as well (though none I haven't heard before, no offense; it's just that Phil Sci was a few years ago), and perhaps point the way to where I should focus my energy; maybe at base I'm struggling with certain assumptions of the scientific method, and is expressed as a misunderstanding of the results of quantum physics.

Anyway.

Last edited by whc.03grady; 01-03-2012 at 05:03 PM.
  #38  
Old 01-03-2012, 05:06 PM
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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.
  #39  
Old 01-03-2012, 05:06 PM
clairobscur clairobscur is offline
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I didn't take it as rude.

I think I see what you're saying. So if the mathematician shows that 1+1=3, and that result is confirmed over and over again, then we're supposed to accept the absurd (or "absurd") result and maybe give her a prize.
But there are a number of perfectly absurd theories in physics that have been verified by experimentation. The particle going through two slits at the same time that a previous poster mentioned, for instance.

So, it's already a given that our perception of what is absurd or logical just isn't reliable in physics. And, as a result, there's no reason to scrutinize more (or less) a theory because it contradicts common sense.
  #40  
Old 01-03-2012, 05:11 PM
clairobscur clairobscur is offline
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(Isn't there some joke about this example? Or one about the Umpire, the someone, and the someone judging reality?)
I heard it about a liberal art major, an engineer or physicist and a mathematician (respectively saying "sheeps are white", "at least 20 sheeps are white" and "at least 20 sheeps are white on one side", so showing that the mathematician totally ignores common sense)

Last edited by clairobscur; 01-03-2012 at 05:14 PM.
  #41  
Old 01-03-2012, 05:19 PM
whc.03grady whc.03grady is offline
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Relativity sounds absurd. But your GPS works, so it's clearly not. Quantum computers work, so it can't all be nonsense.
And Newton's Laws are all wrong, but I can still use them effectively to lob shells at the bad guys on the other side of the hill. And Ptolemy's theory is wrong, but I can use it to figure out where Jupiter will be next week. So what?
  #42  
Old 01-03-2012, 05:22 PM
Leo Bloom Leo Bloom is offline
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Originally Posted by whc.03grady View Post
....(Those who are inclined to quote Whitman here can save their keystrokes. )
But I am large!!!

This is what the Cat says in the box:

I know I have the best of time and space, and was never measured and
never will be measured.
  #43  
Old 01-03-2012, 05:29 PM
whc.03grady whc.03grady is offline
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Originally Posted by clairobscur View Post
I heard it about a liberal art major, an engineer or physicist and a mathematician (respectively saying "sheeps are white", "at least 20 sheeps are white" and "at least 20 sheeps are white on one side", so showing that the mathematician totally ignores common sense)
Maybe that's where Heinlein got it--remember in Stranger... when the Fair Witness is asked about the color of a house across the way: "It's white on this side."
  #44  
Old 01-03-2012, 05:34 PM
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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.
And yet all evidence points to it being the case. The universe is weird at certain levels, and this is one of them. And it's just as weird as general relativity; there is stuff there that simply doesn't make sense to the everyday world. But experiment after experiment has shown that it is the way the universe works. Deal with it.

It's never going to to make sense on an instinctive level. It just isn't. Lots of scientists had and have trouble with QM because it goes against their common sense. But you can't really argue with experimental data. Well, you can, but either you show the data is wrong or your change your mindset and move on.
  #45  
Old 01-03-2012, 05:37 PM
Mgalindo13 Mgalindo13 is offline
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Originally Posted by whc.03grady View Post

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...
  #46  
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.

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  #47  
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.
  #48  
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.
  #49  
Old 01-03-2012, 06:05 PM
Mgalindo13 Mgalindo13 is offline
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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, 06:07 PM
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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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