quantum mechanics!!!

[Guest D. Resurrected]

A few days ago I saw something that was very strang but plosiblePpersonaly I think this is true but Id like more opinions.What is everyone elses thought on the matter?

In the world of quantum mechanics, the laws of physics that are familiar from the everyday world no longer work. Instead, events are governed by probabilities. A radioactive atom, for example, might decay, emitting an electron, or it might not. It is possible to set up an experiment in such a way that there is a precise fifty-fifty chance that one of the atoms in a lump of radioactive material will decay in a certain time and that a detector will register the decay if it does happen. Schrödinger, as upset as Einstein about the implications of quantum theory, tried to show the absurdity of these implications by imagining such an experiment set up in a closed room, or box, which also contains a live cat and a phial of poison, so arranged that if the radioactive decay does occur then the poison container is broken and the cat dies. In the everyday world, there is a fifty-fifty chance that the cat will be killed, and without looking inside the box we can say, quite happily, that the cat inside is either dead or alive. But now we encounter the strangeness of the quantum world. According to the theory, neither of the two possibilities open to the radioactive material, and therefore to the cat, has any reality unless it is observed. The atomic decay has neither happened nor not happened, the cat has neither been killed nor not killed, until we look inside the box. Theorists who accept the pure version of quantum mechanics say that the cat exists in some indeterminate state, neither dead nor alive, until an observer looks into the box to see how things are getting on. Nothing is real unless it is observed.

sound correct right?

[Delta]

[COLOR=#656446][SIZE=1]Ugh... my head...

*recovers*
Ah, so that's what the story about Schrodinger's cat means! I picked up a book about it nearly four years ago and the only thing I understood was that there's a cat in the box. :animeswea

[quote name='D. Resurrected']Nothing is real unless it is observed.[/quote]Umm... ain't this supposed to be [b]"The state of the cat ain't really one (dead) or the other (alive) unless we can ascertain by observation that the cat is of one state and surely not the other (or vice versa)"[/b]? It's not that we can scratch out the existence of the cat; we can only go so far thinking about how the cat is. So, if you construct the thought experiment that way, it's a lot easier to relate to Schrodinger's equations, probability density and consequently Heisenberg's Uncertainty Principle.

...Sorry if that sounded incoherent. I believe I half-slept through the lecture about this exercise in our Physics class. (Yes, that's right! I was in a state of sleep and wakefulness at the same time!)

[b]P.S.[/b] [COLOR=#EAEAEA]Also, if we take it that we have [i]two[/i] observers, the cat and Schrodinger, then the cat's state doesn't really go unobserved. I'm pretty sure if if I were the cat, I'd know if I'm still alive, yeah? :3[/COLOR][/SIZE][/COLOR]

[Petie]

[quote name='Delta][color=#656446][size=1]Umm... ain't this supposed to be [b]"The state of the cat ain't really one (dead) or the other (alive) unless we can ascertain by observation that the cat is of one state and surely not the other (or vice versa)"[/b]? It's not that we can scratch out the existence of the cat; we can only go so far thinking about how the cat is. So, if you construct the thought experiment that way, it's a lot easier to relate to Schrodinger's equations, probability density and consequently Heisenberg's Uncertainty Principle.[/size'][/color][/quote][font=Verdana][color=blue]We talked about this recently in my Physics class actually. If I remember correctly, it wasn't so much that you don't know if the cat is dead or alive but because you can't see it, the cat is both dead [i]and[/i] alive at the same time, from your point of view anyway. The subject is really pretty interesting but some of it doesn't make too much sense at first.[/color][/font]

[Fasteriskhead]

Ah, this is always an interesting topic. I think you've pretty much nailed the cat thing, D.R., except I would correct you a little bit on one part of it.

The infamous "Schrodinger's cat" thought experiment was specifically leveled at the [i]Copenhagen interpretation[/i] of quantum mechanics, and can really only be understood in that context. What makes the Copenhagen interpretation unique in terms of this problem, compared to later theories as to how all this stuff actually works, is that it's [i]non-deterministic[/i]. Determinism basically means that you can accurately predict what something's going to do from a certain starting time to a certain ending time; so, for example, if I throw a ball and I know the initial velocity and all other variables, I can know where that ball's going to be, say, two seconds later. Now, quantum mechanics is more complex because you've got these things called waveforms (I'll let folks look it up), but in certain other interpretations you can still work out all the possibilities for how a system will turn up at the close of the experiment. The Copenhagen interpretation nixes this: it's willing to rack up the [i]statistical results[/i] of a certain experimental setup, but it's [i]unwilling[/i] to say anything at all about objects in a system before the experiment is observed (this is a fairly strict reading of the Heisenberg uncertainty principle). For Bohr and the rest of the Copenhageners, although not for eveyone else, it is incorrect to ascribe [i]any existence or nonexistence at all[/i] to any element in a quantum system before it is measured. Thus the cat problem, which you illustrate nicely when you say, "...neither of the two possibilities open to the radioactive material, and therefore to the cat, has any reality unless it is observed." Obviously this strikes us as silly, which is the intent. But again, this problem only really happens with the Copenhagen interpretation (which you call "the pure version of quantum mechanics" [???]): another theory, e.g. the many worlds interpretation (I'll let folks look it up), would have no problem simply taking up the common sense view that the cat really is either alive or dead, even though we ourselves don't actually learn which way he turned up until we pop the door open. Although, I should note that ALL of these other interpretations have bitten their own kinds of bullets and end up completely weird in their own way.

As a final note (I've talked enough about this, I think), it's worth saying that Schrodinger's cat is also part of a much larger problem which physics has been trying to work out for nearly a century. This is the question of how extremely small-scale events, which can only be treated by quantum theory and its various interpretations (i.e. according to probability), can be reconciled with larger-scale events which operate classically under general relativity (which can always be accurately predicted). Or, more simply: the rules which work so well for a particle start to break down and become useless once you get up to, say, a cat. Attempts to bring together QT and classical physics go anywhere from working out reality as having many more dimensions than we usually assume (string theory) to demonstrating that once a quantum system reaches a sufficiently dense point, it no longer really "works" as a quantum system (decoherence). If you end up a theoretical physicist, this stuff seems to be what everyone is getting headaches over. Anyways, though, that stuff is way over my head, so I leave it for someone more qualified to talk about it.

Good topic, by the way! And to anyone reading this: no fair complaining that I've dropped too much that you don't know about, as you can probably wikipedia through all of this stuff in ten minutes.

[Guest D. Resurrected]

[QUOTE=Fasteriskhead]Ah, this is always an interesting topic. I think you've pretty much nailed the cat thing, D.R., except I would correct you a little bit on one part of it.

The infamous "Schrodinger's cat" thought experiment was specifically leveled at the [i]Copenhagen interpretation[/i] of quantum mechanics, and can really only be understood in that context. What makes the Copenhagen interpretation unique in terms of this problem, compared to later theories as to how all this stuff actually works, is that it's [i]non-deterministic[/i]. Determinism basically means that you can accurately predict what something's going to do from a certain starting time to a certain ending time; so, for example, if I throw a ball and I know the initial velocity and all other variables, I can know where that ball's going to be, say, two seconds later. Now, quantum mechanics is more complex because you've got these things called waveforms (I'll let folks look it up), but in certain other interpretations you can still work out all the possibilities for how a system will turn up at the close of the experiment. The Copenhagen interpretation nixes this: it's willing to rack up the [i]statistical results[/i] of a certain experimental setup, but it's [i]unwilling[/i] to say anything at all about objects in a system before the experiment is observed (this is a fairly strict reading of the Heisenberg uncertainty principle). For Bohr and the rest of the Copenhageners, although not for eveyone else, it is incorrect to ascribe [i]any existence or nonexistence at all[/i] to any element in a quantum system before it is measured. Thus the cat problem, which you illustrate nicely when you say, "...neither of the two possibilities open to the radioactive material, and therefore to the cat, has any reality unless it is observed." Obviously this strikes us as silly, which is the intent. But again, this problem only really happens with the Copenhagen interpretation (which you call "the pure version of quantum mechanics" [???]): another theory, e.g. the many worlds interpretation (I'll let folks look it up), would have no problem simply taking up the common sense view that the cat really is either alive or dead, even though we ourselves don't actually learn which way he turned up until we pop the door open. Although, I should note that ALL of these other interpretations have bitten their own kinds of bullets and end up completely weird in their own way.

As a final note (I've talked enough about this, I think), it's worth saying that Schrodinger's cat is also part of a much larger problem which physics has been trying to work out for nearly a century. This is the question of how extremely small-scale events, which can only be treated by quantum theory and its various interpretations (i.e. according to probability), can be reconciled with larger-scale events which operate classically under general relativity (which can always be accurately predicted). Or, more simply: the rules which work so well for a particle start to break down and become useless once you get up to, say, a cat. Attempts to bring together QT and classical physics go anywhere from working out reality as having many more dimensions than we usually assume (string theory) to demonstrating that once a quantum system reaches a sufficiently dense point, it no longer really "works" as a quantum system (decoherence). If you end up a theoretical physicist, this stuff seems to be what everyone is getting headaches over. Anyways, though, that stuff is way over my head, so I leave it for someone more qualified to talk about it.

Good topic, by the way! And to anyone reading this: no fair complaining that I've dropped too much that you don't know about, as you can probably wikipedia through all of this stuff in ten minutes.[/QUOTE]

hmm very interesting if I do say so myself.Its wierd that "Schrodinger's cat" thoery works on paper but is yet hard to understand in a real world situation.I think you've clean my mind of this problimatic thoery.hmm I didn't know that the string theory could be involved in this.you put it very well good job anyone elts has any thoughts on the mater?
:animesmil

[HarveyDandylion]

I read about quantum mechanics alot but mainly for myself, not as part of an educational thing.
So yeah, you have the wave particul duality thing where if you look for certain properties they are what you find. Also if you look for both properties you find both, and finally if you don't look for any they are all present untill you collapse the wave functions by observing it. So with the Schrodinger's cat thing to me suggest that you look at the cat and it dies or doesnt based on weather or not the electron is in the rights side of the box or not; but only once you look.

Then you have this theory about there needing to be an observer of the entire universe to collapse the many wave functions or else the universe would never stop being in this supersition of states untill the 'god' type thing look at us.

So either the 'god' thing observes us, in which case he would also be looking at the cat and so the experiment could never happen because there would always be an observer, and then there is always and observer of the quantum world even when one of us isnt looking at it. Or else the need for an observer isnt necesary but rather when we obser things there wave function collapses because of the interaction that our observation has with the quanta, electron or whatever other particle is in question. By looking at the results the exchange particles invol;ved in that interaction cause the said partcle to react to it in a certain way.

I don't think it can be as easy has a cat staying in two states untill its observed, maybe it is more to do with the theories (i dont know much about currently) that time isnt moving forward but everything is happening in one moment. Maybe this thought experiment is proof of that. Time being quite tricky to understand. So the cat may always be in these two states because time doesnt move forward but at the same time the cat does die or live before we open the box but that event in itself is in the same time as the cat.

P.s. The many world theory is much easier to digest. i geuss in part because of that famous sci-fi cult program. It does, from my point of view, create many more problems and unnecesary complexities.
I read pysics books for my own pleasure but am more of a philosipher in my way of thinking; i believe/think that the results show a truth on the whole that when you look at these things and do these experiments (mental or not) that you will always find certain results that conform to previously learnt things. It may be that the rules of the quantum world are created by our own imagination and that our perception of how things work is what defines the way these things do work. So the Schrodinger's cat thing is especially interesting to me because it suggests that it is our perceptions that determine the interaction we have.
What if an alien look into the box instead, not knowing what the cat is and weather or not it will die: what would he see?

Its all abit mad really, isnt it.

[DBZgirl88]

[COLOR=#004a6f]I was so confused when I read this theory, and wikipedia made it more complicated.

But this website explained it insimple terms: [url]http://whatis.techtarget.com/definition/0,,sid9_gci341236,00.html[/url]

Anyway, this kind of reminds me of something my chemistry teacher one said: "You can only prove the existence of here".

So as I'm sitting here in typing away in a school computer, I cannot prove that my house exists, Because I can't see it. And if I get up and go home to see that my house does exist, my house no longer becomes a "there" but only a "here". So therefore, you can only prove the existence of "here".[/COLOR]

[Guest D. Resurrected]

Hmm so technically speaking even this thread does not exist until I observe it.

Also another questions were does the non existent thing go is it stored in a state of mind if I may call it that.

If this is true here is a perfect example.

Say there is a button on a peace of cloth knowing it?s their means it exists in your state of mind. But then your friend does not notice it. Through his point of view that mean that the button does not exist until it is seen or seen again. What do you guys think?

[HarveyDandylion]

[QUOTE=D. Resurrected]Hmm so technically speaking even this thread does not exist until I observe it.

Also another questions were does the non existent thing go is it stored in a state of mind if I may call it that.

If this is true here is a perfect example.

Say there is a button on a peace of cloth knowing it?s their means it exists in your state of mind. But then your friend does not notice it. Through his point of view that mean that the button does not exist until it is seen or seen again. What do you guys think?[/QUOTE]

I know what your saying but i geuss that is more of a question of perspective than of wuantum mechanics. I dont think it is ment to be thought of that philosophically. Its not that the button isnt there when its not being observed, its that quanta or other such particles exist in a supersition of states when not being observed. That only means that when you observe it it must choose for example weather it is a particle or a wave.
In terms of things that are big enough to be objects in our world you would have to concider many millions or billions of particles. The cat thing is not about the cat being both dead or alive at the same time, its about the fact the molecules, particles and everything else simply hasnt decided what state its in untill then, its like there are many different worlds with different outcomes and when you look at it it chooses which world/outcome is there for the observer to see. The cat is only dead or alive because of the two possible outcomes of the molecule that triggers the event, not because the cat itself is both. If you think about it from the cats point of view he either dies or stays alive instantly, he wont be dead and alive at the same time from his own perspective.

So i think in terms of the button, it would exist as it is, but if it were to be changed somehow by a quantum effect then it wouldnt change untill someone was there to observe it. Before the observation ocured it would be as it is and how it may change at the same time untill you look at it.

I dont think youd have tom worry about not existing if ytou became lost in a cave would you, though when your own no one is observing you but you still exist. This is of course only my interpretation of the stuff i know, i dont have a degree in the subject.

[The13thMan]

[FONT=Century Gothic] [COLOR=DarkOrange]I was talking with one of my friends earlier today about existence and what is real and what can be considered real. My friend says that just because you can feel and observe something doesn't make it real since your senses can be deceived.

Take this situation for example: Let's say that there's a brain in a vat hooked up to a machine. The machine allows the brain and the consciousness of the person to exist. The machine, which obviously doesn?t exist, creates images for the mind and creates a reality for the brain. It?s a lot like the matrix, if you guys can relate to that better. Anyways, what the brain perceives to be real is NOT real. It does not exist in reality. So what we perceive to be real isn?t necessarily real. Just because we see that the cat is dead or alive (or neither by not observing) doesn?t make it so (or not so). The cat, if it?s real, does exist and is either dead or alive regardless of whether it is observed or not.

That?s what my friend says, and I sort of agree with him, but I sort of don?t. To me, real is a man made word and can only be defined by the sense that man has. So by sensing something to be real it becomes or is real. The keyboard under my fingers is real to me because I feel and see it. But I suppose I?m a little hypocritical in the sense that I also think that something exists whether or not we sense it. Just because we cannot feel something doesn?t mean it?s not real or doesn?t exist. But it?s not so for the other way around. If I do feel it, then it does exist, to me anyways. I guess it exists, but not in an ?absolute? way.

Well, I'm done talking, not necessarily because i have no more to say, simply because i'm tired of talking. ^J^

Later.

PS: I'd love to talk about this to someone, so if anyone wants to IM me on yahoo messenger, my screenname is attimus331. Or if you want to IM me on aim, you'll have to tell me, because i don't use it much anymore.
[/COLOR] [/FONT]

[Fasteriskhead]

The13thMan - go read Descartes' Meditations on First Philosophy. No really, I'm serious, it's actually fairly quick and painless and tackles precisely the questions you seem concerned with. You'd like it!

I should note again, just to keep things honest, that the weirdness about things both "existing" and "not existing" at the same time that y'all seem to be worrying about [i]only happens in non-deterministic interpretations of quantum theory[/i], specifically Bohr's Copenhagen interpretation (which I explained above) and any other interpretations involving measurement (or "conscious observation," one of the variants) causing the collapse of all the possibilities involved in a waveform. Again: other interpretations have NO PROBLEM with this, i.e. for them things really are what they are at any given time (although there may be things like alternate univeses...), so Schrodinger's Cat shouldn't be taken as representative of the entire field of quantum physics. And actually, from what little I've done paying attention to the people who really work on this kind of thing, they spend very little time cogitating about what the universe may be like; mostly it involves doing a lot of math which is, uh, completely beyond me. Metaphysics is a side effect at best.

Okay, side note. The worst charge that's been leveled at the Copenhagen interpretation (which, I say again, is the one where we can say nothing about the existence of a quantum object until it is measured) is this. Assuming quantum mechanics is [i]the[/i] fundamental, underlying physical reality of the universe, then that means that [i]everything that exists[/i] is part of one big quantum system. Now, since for Copenhagen neither the existence nor nonexistence of any element in a quantum system can be determined until measurement, this means that everything that is is unverifiable unless measured. This is a problem when the measurement tools [i]themselves[/i], including everything in our lab and ourselves, are of course also quantum objects. The big question ends up being, what finally constitutes measurement? At what point does the waveform finally break down? The obvious answer is to impart some kind of special quality to the observing subject (i.e. the scientist), but it's a bit tougher to determine what exactly would make such an observer special. I'm willing to throw this one to the audience.

(again, it's worth noting that most scientists, perhaps unjustly, find this kind of question silly; the results work, why worry about it?)