How does one observer win out over another?

[galadriel]

Ok, I am an absolute beginner. I've just seen the basic experiment of shooting a particle(unobserved) through 2 slits and seeing on the wall behind that it has landed in all of the possible places it could go simultaneously.. and of course when it is observed at slit level it behaves differently and only goes along ONE of its possible paths. My question is: if there are two or more observers(humans) present and observing, what is the science of how the particle decides to behave ? Whos perception does it abide by and why? I am eager to find out wether (from a purely hippy/spiritual point of view!) one persons energy or belief can win out over anothers in terms of making particles behave differently by being more finely tuned/stronger. Please help!

 

[etamorphmagus]

HUMANS HAVE NOTHING TO DO WITH IT. The hell with that Dr. Quantum video.

Observation is when the particle does any physical interaction that causes it to lose coherence (hence, decoherence), meaning it is pushed, changed its phase, any kind of interaction that is strong enough to destroy the interfernce.

Now, measurement, of a location (which slit), is an interaction by itself, that if it is strong enough to give you the information of what path the "particle" took (it has to be or it is a lousy measurement), it destroys the interference pattern.

I wanted to give you this background to help you understand that humans and spirits and mojo have nothing to do with it.
Back to the question, the first interaction is the one that kills the interference, of course.

 

[Doc Al]

My question is: if there are two or more observers(humans) present and observing, what is the science of how the particle decides to behave ? Whos perception does it abide by and why?

The presence of an actual human observer plays no fundamental role at all when we talk about observing the path of the particle. Think in terms of the experimental setup and whether a record of the position or path could be made.

I am eager to find out wether (from a purely hippy/spiritual point of view!) one persons energy or belief can win out over anothers in terms of making particles behave differently by being more finely tuned/stronger.

Nah. Despite claims made in popular presentations, there's no reason to think that you can affect the behavior of the particles except in the trivial sense that you can change the experimental setup.

 

[Upisoft]

HUMANS HAVE NOTHING TO DO WITH IT.

How can you possibly know that for sure? I don't see how you can gain knowledge by not observing. Basically you claim that the world behaves the same way in both cases (observed by humans and not observed). You have empirical evidence that the world behaves in some way when it is observed, but you will never have any empirical evidence for the second case. Therefore you cannot make any scientifically valid claim about it.

 

[snackster17]

Wait up a min. That Dr quantum vid is really misleading then because i was under the impression that a human viewing or "measuring it" changes the outcome. So your saying that its simply the disturbance we are causing to the particle by bouncing photons off of it?
Why would it go through only one slit then all of the time?

 

[Upisoft]

There is no way to tell if Dr. quantum video is misleading or not. The best we can do is to assume it is misleading and that is what etamorphmagus is doing. In his mind this assumption is a postulate and therefore he concludes that humans have nothing to do with the outcome.

 

[mrspeedybob]

HUMANS HAVE NOTHING TO DO WITH IT. The hell with that Dr. Quantum video.

Observation is when the particle does any physical interaction that causes it to lose coherence (hence, decoherence), meaning it is pushed, changed its phase, any kind of interaction that is strong enough to destroy the interfernce.

Now, measurement, of a location (which slit), is an interaction by itself, that if it is strong enough to give you the information of what path the "particle" took (it has to be or it is a lousy measurement), it destroys the interference pattern.

I wanted to give you this background to help you understand that humans and spirits and mojo have nothing to do with it.
Back to the question, the first interaction is the one that kills the interference, of course.

OK suppose we determine which path the photon took by timing it from source to screen. For all pathes except ones ending equi-distant from both slits there will be a difference in travel time. If the experimental setup is made large enough it will be very obvious which path the photon took. If each photon or particle is emited on command and its arival time at the screen recorded you can know which slit it went through with absolutely no interaction whatsoever.

 

[etamorphmagus]

By "humans don't matter" I meant that some people like saying "but what if a dog watches? or a bee?" this it ridiculous, because we refer to measurement, and it's not like your eyes send "interacting photons". YOU aren't doing the watching, the detecting device does, like a light source that can show you an electron's path.

And about the question "how do you know if humans matter or not?", it might. maybe our existence changes everything, but this is a Physics forum, and in Physics everything arises from some assumptions you make and continue with it, if you wish to question the "reality" of the assumption that without humans everything would still be the same, and the tree would still fall in an empty forest, you may - but that is pure philosophy... we must assume something. Or else this thread should reopen in a philosophy forum, but then I agree with you, you can't know.

OK suppose we determine which path the photon took by timing it from source to screen. For all pathes except ones ending equi-distant from both slits there will be a difference in travel time. If the experimental setup is made large enough it will be very obvious which path the photon took. If each photon or particle is emited on command and its arival time at the screen recorded you can know which slit it went through with absolutely no interaction whatsoever.

No, that doesn't work. You think no-one thought of that simple trick before? You can't get which-path information like that.

 

[Upisoft]

By "humans don't matter" I meant that some people like saying "but what if a dog watches? or a bee?" this it ridiculous, because we refer to measurement, and it's not like your eyes send "interacting photons". YOU aren't doing the watching, the detecting device does, like a light source that can show you an electron's path.

It is not ridiculous. Let's do a thought experiment. Suppose you have setup your own double slit experiment at home. And suppose you have a dog. You have trained the dog to bring you the result of the experiment when a bell rings. The result is on a photo paper, that for simplicity develops itself (or you may develop it if you wish). After testing it 10 times you get the interference pattern each time and your dog delivers the result to you after the bell rings. So now you decide to stop watching yourself and repeat the experiment. After some time your dog brings the result. What do you think you will see?

And about the question "how do you know if humans matter or not?", it might. maybe our existence changes everything, but this is a Physics forum, and in Physics everything arises from some assumptions you make and continue with it, if you wish to question the "reality" of the assumption that without humans everything would still be the same...

In Physics you make assumption and then test if that corresponds to your empirical data. There is no point to make an assumption that cannot be confirmed nor it has any impact on observed data. So telling us that humans do not matter is philosophy and not Physics. Same, of course, is valid for the opposite statement - that humans matter. The best is to say we don't know and we will possibly never know.

 

[snackster17]

so we pretty much have no idea what happens when were not looking?

 

[mrspeedybob]

No, that doesn't work. You think no-one thought of that simple trick before? You can't get which-path information like that.

Why not? Would you mind backing this statement up with either some sound logic or experimental evidence?

 

[Upisoft]

so we pretty much have no idea what happens when were not looking?

Pretty much. However "looking" can be done beforehand. If you prepare experiment and make sure that nothing disturbs it then you have already done the observation. The result will be delayed, but that does not matter. Of course this is the ideal case. You really can't make it 100% sure. There is always possibility that someone of your colleagues spills coffee making most possible damage...

This is why your kitchen knife will not suddenly start to attack you when you turn your back at it. Then again there is always small chance that there is someone hiding and willing to help that knife to do the job. So, yes, you really don't know what happens when you don't look. You may have pretty good idea what is most probable to happen, though.

 

[etamorphmagus]

Why not? Would you mind backing this statement up with either some sound logic or experimental evidence?

Well you might do that and for every particle then say from which slit it came (by your distance analysis). But looking at the big picture, you'll get an interference pattern, and bam, you're in a paradox. what you see doesn't sit with the particle model.

To resolve this you say that the particle travels like a wave and for every point that you assumed it came from slit X, it actually came as a wave from the both slits, not the nearest slit, but a superposition of both slits. By examining the intensity of said-hypothetical-wave on every spot of the detector, you find this is proportional exactly to the probability or the distribution of the overall particles.

You might say "but as the wave reaches the 2 slits and becomes 2 new waves, one wave will always be faster than the other for a tiny bit, in a region where there is no interference yet, that small part always travels outward, so by the time they reach the detector we should get diffraction rather than interference in the "outer regions", and then we know from which slit it came!"
Actually I'm not 100% sure. We need an expert reply.

 

[snackster17]

so did the term "wave" arise from this uncertainty. When physicists say objects can be particles or waves, they really mean objects can either be particles with their position specified or with unknown locations

 

[Upisoft]

so did the term "wave" arise from this uncertainty. When physicists say objects can be particles or waves, they really mean objects can either be particles with their position specified or with unknown locations

It is not quite easy as that. States of the QM systems are represented by complex vector space. In general the vectors can be complex functions. When you know where is the particle you know its function. But when you substitute that function in the equations that define the probability density of the momentum of the particle you find that for each point the probability density is the same. That means when you know where the particle is it can have any momentum. The same happens if you know the momentum with absolute certainty. Then plugging the function into the equations for position will yield uniform probability that the particle can be anywhere.
We can have mixed measurement, but then the best you can get is to have probability distribution for both position and momentum. It is just not possible to find any function that will give you definite answer for both position and momentum.

 

[snackster17]

i think what I am trying to get at is this. i understand the uncertainty aspect but i would like to know how it effects the outcome of the double slit experiment and more specifically if double slit experiment is dependent on this unspecification in order to exhibit wave particle duality. i doubt we have ever seen individual electrons hit the phosphorous screen.

 

[nouveau_riche]

suppose the intereference experiment is set up again,the light used is of very high frequency(so that it's wavelength could match with that of slits) ,now the distance at which interefence pattern is seen is at max distant from slit(max in sense that pattern can b seen nicely).,now one of the observer set up apparatus to see the intereference pattern while the other one set up an apparutus to measure position of photon(to see from which slit it passes through)
question is-will the interference pattern b lost or both will see their portion of reality ?

 

[HallsofIvy]

The latter. It doesn't matter whether there is one observer or two or a dozen- and it doesn't matter whether the observers are human, animal, vegetable, or mechanical. With no observer you get a diffraction pattern. With one or more observers you get no pattern. "one of the observer set up apparatus to see the intereference pattern while the other one set up an apparutus to measure position of photon(to see from which slit it passes through)" is impossible. For the first observer to "set up apparatus to see the intereference pattern" he would have to remove the second observer. Since you require that there be a second observer, there must be no diffraction pattern.

 

[nouveau_riche]

. For the first observer to "set up apparatus to see the intereference pattern" he would have to remove the second observer. Since you require that there be a second observer, there must be no diffraction pattern.

why?