Quantum Physics

mcbethcg · Sep 7, 2005

This question deals with observer phenomina- you know, when an observer causes a wave function to collapse. What constitutes an observer? I have asked seemingly knowledgable people about this, and generally, the idea was if something was affected anywhere, then the wave function would collapse. Even a single atom. But what about Schrodingers Cat? According to this example, the wave function does not collapse until the observation occurs outside the box.

dragon04 · Sep 7, 2005

Until you determine the cat's state (by opening the box and looking) the wave function hasn't collapsed. Looking at the closed box itself only tells you the state of the box. Not the cat. I'd guess an observer would be defined as anything that directly interacts with a particle to determine its state. <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

centsworth_II · Sep 7, 2005

"I'd guess an observer would be defined as anything that directly interacts with a particle to determine its state." So why can't this "anything" be in the box with the cat (in fact it would have to be to interact). The interaction that takes place and collapses the wave function takes place in the box without an outside observer needing to open the box. There are billions of interactions and wave function collapses taking place inside your body every second. These are the chemical reaction of your metabolism, protein building, nerve signal transmition, et cetera. Who is the observer for all these? <div class="Discussion_UserSignature"> </div>

Saiph · Sep 7, 2005

I asked the question once of my proffessor (who does work in quantum mechanics...) and he said that was a very, very good question. One way to look at it, is everything is an observer. However, the wavestate is always in question for any individual observer, until that specific observer looks at it. So the box and the cat know the outcome of Schroedingers morbid little experiment...but we don't, the wavestate isn't collapsed for us yet. And as such, it's just as valid to determine the answer as a series of possibilities working upon eachother, as it is to do a deterministic approach (that we use after observation). <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

yevaud · Sep 7, 2005

I got a very odd reaction once, in school, in reference to this. A professor was describing this dichotomy, and finished up with describing how the observation determines the outcome, and how the cat was in an indeterminate state until observed. To which I replied, "assuming, of course, the cat had no opinion in the matter." He harrumphed, "yes, well..." <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

dragon04 · Sep 7, 2005

His question addressed the wave function collapsing from observation "outside" the box. Not from within. The premise of the thought experiment is that the cat exists in more than one state UNTIL we open the box and observe it. Finally, How do I KNOW there are wave function collapses going on without observing them? Unless of course I go and have a CAT scan done? <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "2012.. Year of the Dragon!! Get on the Dragon Wagon!". </div>

Saiph · Sep 7, 2005

My professors reactions are often the same. That professor I asked, basically left it at "very good question" as class ended. Rarely is the teacher saved by the bell. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

alkalin · Sep 7, 2005

As I understand it, the wave equation is some math artifice or notion in quantum physics that applies to particles, does it not? So why are people trying to apply it to gross matter that behaves differently, or am I dense or something? What if I am the cat in the box that thinks? Of course what follows is silly. If science is caught in such logic conundrum, it better start examining its math logic more carefully, else we might be here a looooong time trying to figure out which universe we are in.

yevaud · Sep 7, 2005

Simply put, it's all about probabilities. There is a finite, albeit small, possibility that you will suddenly discover that you're not sitting in your chair, but flotaing in orbit. But as I said, it's all probability, and the odds of that occuring are tiny indeed. Possibly one event over the entire lifetime of the universe, if not longer. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

Saiph · Sep 7, 2005

Ahh, but what you observe of yourself in the box doesn't necessarily change what I may, or may not observe outside. take a standard game: Three doors, behind which is a prize. You're the host, you know which door has the prize. That doesn't mean I know, and the probabilities don't shift for me just because you know. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

alkalin · Sep 7, 2005

I believe the probability involved with particles is a different probability than that of the behavior of gross matter. None of the wave function of quantum physics is ever found in gross matter that I know of, yet this is our real world that is readily observed. I feel there is need to further clarify the definition in QPee. Yet events can happen (one in Godzillions, perhaps) for us that can make almost anything possible. The difference is particles have many influences that make changes to them almost immediately, do they not?

yevaud · Sep 7, 2005

Well, recollect that all gross matter is really merely an assemblage of fundamental particles - each which has it's own probability function. So something extraordinarily unusual can happen to gross matter, but it'd require each and every atom in your body to "decide" to tunnel to another location or state. That's what I meant by the odds being infinitesimal. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

alkalin · Sep 7, 2005

Who needs apples and oranges anyway with this logic? Pure probability is a math concept of gross matter. Particles behave differently, and are influenced differently than that of gross matter. Find me a particle cat hiding in a particle box surrounded with particle people somewhere? Oh wait, probability says it is possible!!!!!

Saiph · Sep 7, 2005

if you want to boil it down to realms where it can actually matter, fine: An electron in a box, is it spin up, or spin down? And yes, we can measure a single electron. But you do address a very specific and important question. How exactly do we transition from the realm of particles, where probability is the best you can do, to the realm of classical, deterministic mechanics? Part of it is our existence as macroscopic objects is dictated by the total probabilities of all our particles. As such, we're very, very, very stable since that's trillions of particles. As such, there is no real (defined as within several million universal lifetimes) of us behaving quantum mechanically. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

cuddlyrocket · Sep 7, 2005

The reason no-one gives you a good answer to these questions is that they are very deep questions as to the nature of the quantum mechanical world that physicists have, as yet, failed to completely grasp. This is why this thought experiment is so famous! There could be a flaw in our understanding, or a flaw in quantum mechanics - take your pick! And yes, macroscopic objects have an associated wave function. In fact, the entire Universe has a wave function (don't ask me to write it down!).

yevaud · Sep 7, 2005

Steven Hawking Lectures <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

nova_explored · Sep 8, 2005

it simply means that an observer changes the initial state of said object and thus there is no true way to know its behaviour (uninterrupted or undisturbed by outside influence). and its specifically geared towards observances that require our complete removal. i.e. the state of an atom and its place. on the other end though- would we affect the changes on large scale- say, galaxy formation and movement? no, and so we can observe its place and its path without interference. <div class="Discussion_UserSignature"> </div>

blairf · Sep 8, 2005

The short answer.. google "quantum information theory" the even shorter answer "we don't know" the slightly longer answer information (knowing) and physical reality (being) are disturbingly close to each other. I don't want to get into a Tao of Physics turtle dreaming style ramble but when you closely examine things it becomes clear that entropy quantum mechanics information theory are all three sides of the same coin. Go figure Maxwells Demon as well

tomnackid · Sep 9, 2005

The problem is that the "Schrodingers Cat" experiment is purely a "though experiment" since it assumes a box that COMPLETELY cuts off its contents from the rest of the universe. No energy or mass transfer whatsoever. Obviously this is impossible in the real world--if it were the contents of the box would be effectively in a separate universe all its own. That is why whenever Schrodingers Cat is brought up in classrooms some wise guy invariably says something like "Why not just shake the box?". The person explaining the experiment often doesn't state, or maybe doesn't realize that "opening the box" is just a metaphor for interacting with the box's contents.

Quantum Physics

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