What is the context of observation in this video?

[ode_to_joy]

What does "to observe" mean?

I am pretty sure that you will recognise this video :
about at 3:50, they claim that, when we observe an electron passing through a double slit, acts as a particle, as opposed to its wave property. Does that mean, if we place a 8 mega pixel digital camera in between the slit and the light source, will electrons behave as particles? I hardly think so. SO my question is, what is the context of observation in this video?

 

[Naty1]

See here:

http://en.wikipedia.org/wiki/Double-slit_experiment

An electron is a particle AND a wave, but both are not simultaneously observable.

It's a reflection of complementarity...or wave-particle duality.

What you observe depends on how you measure!

If you think any of the is wierd, you are correct...as compared with classical large scale observations... check out "quantum erasure" and "delayed choice" for even stranger
observer/system relationships.

 

[kutraj]

An observation interferes with the current state of the electron. If the electron is in some (initially superimposed) state, then performing a measurement will "throw" it into one of the constituent Eigenstates. This is what "destroys" or changes the behaviour of the electron as it passes through the slit.

If you think about it, an electron just going through the slit is not the same as the electron being detected and then going through the slit, because the latter involves an interaction process in between (with the measuring apparatus).

 

[faen]

Observation means that one of the eigenstates become entangled with the measurement instrument, which then become the observed value. It does not require a humean being observing the result to collapse a wavefunction. That is just a stupid philosophy. Quantum states are not particles, they just decohere into smaller waves.

 

[ATOMS13]

We see an electron as a wave before we observe it because, at the quantum scale, you can argue that an electron is here and there so the concept of an electron being a wave is philosophical. When we observe the electron we exert energy on it and it appears that the electron "realizes" it is being observed and acts up. So to observe is simply to exert energy on something.

 

[faen]

so the concept of an electron being a wave is philosophical.

I'd say it's more than just philosophical since the electron shows interference patterns which charecterizes a wave.

 

[2sin54]

We see an electron as a wave before we observe it because, at the quantum scale, you can argue that an electron is here and there so the concept of an electron being a wave is philosophical. When we observe the electron we exert energy on it and it appears that the electron "realizes" it is being observed and acts up. So to observe is simply to exert energy on something.

How exactly do we exert energy on an electron by looking at it?

 

[faen]

How exactly do we exert energy on an electron by looking at it?

We're not "looking" at it, it is reacting with the measurement instrument. Probably with a force. Allthough I have to admit I'm not aware of exactly how such a measurement is performed or with what kind of measurement instrument.

 

[nonequilibrium]

Hello,

The classical reasoning is as follows: what does it mean to see something? You don't just see things by default, it's rather a process that ends with your eyes taking in photons, photons that scattered of the thing you "see". Without the photons scattering of the object, you wouldn't be able to see it, so you see a measurement really entails some kind of physical interaction with the system (and you also see it's not necessary for you to actually register the photons to do a measurement[*]).

Now that's a classical idea, however, since QM doesn't talk about particles being hit by photons or what have you. QM is a bit more abstract, and to describe the measurement of seeing a particle (passing a certain slit) you have to do some math, which in the end suggests that the measurement process has unnegligibly altered your system.

But what "actually" happens is still up for discussion:
http://en.wikipedia.org/wiki/Measurement_problem

I hope this helps somewhat.

[*] This sentence has to be taken with care, it depends on what interpretation of QM you're using... The truth value of my statement is a big part of the so-called "measurement problem".

 

[StevieTNZ]

What counts as an observation, there is no agreed upon definition.

By putting a camera by each slit, the camera either (a) collapses the wave function of the particle to a definite state or (b) the camera and the particle become entangled and no collapse occurs. The apparent loss of interference is because two interference fringes add up to create a scatter pattern (see Quantum Erasure experiment).

 

[nonequilibrium]

By putting a camera by each slit, the camera either [...]

This is a very misleading comment, it gives the camera a powerful status: the camera is just there to register photons. The collapse will only occur / has occurred (depends on your interpretation...) if there are photons for the camera to see. The camera is just one element in a long chain of interactions that constitute "measurement", not a key element as your quote suggests (and while you might understand what you meant, I don't want the OP to get confused).

 

[Thenewdeal38]

"Now that's a classical idea, however, since QM doesn't talk about particles being hit by photons or what have you. QM is a bit more abstract, and to describe the measurement of seeing a particle"

That is incorect. Richard Feynamn goes into great detail how electron/photon interactions cause interferance collapse regarless of "seeing" a particle. Yes maths are used to describe the process but it still requires a physical interaction ot collapse a wave function.

 

[nonequilibrium]

@Thenewdeal38: I get what you're saying, but that's just one interpretation of the math, it's not in the math itself. If it were really that easy, then we wouldn't have a "measurement problem".

 

[Thenewdeal38]

There isn't a measurment problem between real physicists. Only between real scientists and sudo quack new agers who misenterpreted bohr's original use of the word "observe". He even stated that type of language would obviously be misenterpreted by the layman and that QM has nothing to do with cousciesness.

 

[nonequilibrium]

I think you misunderstand the idea of the measurement problem, it has nothing to do with a consciousness.
Granted, one suggested solution to the measurement problem uses the concept of consciousness (advocated by nobel laureate Wigner[*]).

If you denote "experimental physicists" with "real physicists", then I'd agree, but if you also include "theoretical physicists", then I disagree.

To get a better view I'd suggest reading the entertaining and insightful article "Six possible worlds of quantum mechanics" by John Stewart Bell, a great physicist.

[*] not that it has to be true because it comes from a nobel laureate, but just as an indication that he isn't a "quack"

 

[2sin54]

How can measurement device somehow affect the result just by watching? Photons bounce of the object to the measurement device and that's it.
A bounce of a ball isn't influenced by a person who catches the ball 3 seconds after.

 

[IRobot]

I would say an observation is an interaction between the system (observed) and an external apparatus causing the wave function to collapse. I know it's pretty vague but I think that the real question concerning quantum measurement is who/what can observe? Is it only human beings, conscious beings, animals, environment? :s

 

[Ken G]

How can measurement device somehow affect the result just by watching? Photons bounce of the object to the measurement device and that's it.

That isn't really quite it, though-- it's more tricky than that. Take for example this experiment. You have a particle in a 1D box, in its ground state. You shine a super bright light on one-half of the box, and get no detection-- no light bounces off the particle in the box, the particle is not found to be on that side of the box. What is the expectation value of the particle energy now, is it still in its ground state?

No, it is not. The new information we have about the particle wavefunction is that the particle wavefunction is zero on one-half the box. The rest of the box must hold the full wave function, but with the same shape it had in its ground state-- we just scale up the normalization. Now a truncated ground state wavefunction is not a ground state wavefunction any more-- the energy of the particle has increased (in expectation value). Where did that additional energy come from? Information is important in quantum mechanics, not just interactions.

 

[Thenewdeal38]

who/what can observe? Is it only human beings, conscious beings, animals, environment? :s

None of the above. The observer is an uncounsciess meausuring device. And to observe is to physiclly interact with something where mathematical deductions based on "the bounce back" of the interacting subatoms reveal location and or position. It does not mean to look at and examine. OVERSIMPLIFICATIONS OF THE OBSERVER EFFECT ARGHHHHHHHH!

Also define in precise terms of QM: Information?

 

[Ken G]

The observer is an uncounsciess meausuring device. And to observe is to physiclly interact with something where mathematical deductions based on "the bounce back" of the interacting subatoms reveal location and or position. It does not mean to look at and examine.

Even this is an oversimplification. If we could really get away with such a simple meaning, we would not need any interpretations of quantum mechanics at all (some people feel this is in fact the case, but in practice, some interpretation is always needed). The problem with the above is it is not consistent with quantum mechanics to simply define observation as interaction. This is for two reasons:
1) as I mentioned just above, some types of information updates involve no interactions with a measuring device at all, and the absence of interaction then becomes a type of interaction, so it's a bit more subtle, but worse:
2) according to quantum mechanics, interactions only produce entanglements. So we could think of observations as entanglements with measuring devices, but that only produces mixed states, again according to quantum mechanics. The "measurement problem" actually comes next-- what does the mixed state mean? The "problem" here is that we never actually perceive mixed outcomes, we perceive definite outcomes. So entanglements with measuring devices really doesn't cut it-- we have to go beyond the entanglement into the definite outcome.

That last step, that many people simply don't recognize, is also where interpretations come in-- to some, no "collapse" ever occurs, and all we have is an entanglement, not a definite outcome-- but that's MWI. To others, a collapse does occur because it is seen to occur, and that has to be tacked onto QM separately-- that's CI. To others, the collapse was always there, in the initial conditions, we just have no way to see it until the experiment is over-- that's deBB. To still others, QM was never intended to provide a complete description, only a statistical one, so there is simply no need for QM to account for collapse-- that's the "ensemble interpretation." Some might even be fine with all 4 interpretations, and others, they simply see them as different angles from which to view QM and not to be taken very seriously (that's my own personal stance).

But one thing is clear-- the only reason that final step ever comes up at all is because we are conscious beings that think and do science. This is simply an undeniable fact-- if we were not conscious thinkers (I don't attempt to parse the differences in thinking and being conscious), neither an interpretation of QM, nor even QM itself, would ever be necessary or ever exist.

 

[Thenewdeal38]

Youre confusing philosophy with science. Also don't wave functions collapse naturally in the universe even when people arnt performing double slit experiments. Also we are made of uncouncious matter, which made a councious observer which made a uncouncious measuring device that collapsed the wave function, so the whole counscous observer thing really is a huge stretch of the philosophical imagination. Is there a "special" property about counsciesness that trancends both classical physics and QM physics because that's the only explination for what youre arguing and I don't think the transfer of nueral information from one part of the brain to the other where counsieness forms a biological collage of information is so special as destroy the foundations of physics.

Also what do you mean exactly by
"some types of information updates involve no interactions with a measuring device at all, and the absence of interaction then becomes a type of interaction" I know people like QM to be mysterious but that needs to be explained clearly.

If you affect a sub atom its reacts, if you don't then its follows its natural course.

 

[Ken G]

Youre confusing philosophy with science.

No, I am noticing their roles and separating them.

Also don't wave functions collapse naturally in the universe even when people arnt performing double slit experiments.

That question requires an interpretation to answer. What doesn't require an interpretation is that the situation you describe will result in decoherence, and a mixed state treatment of the entanglements. But collapse is something quite different that must be addressed next.

Also we are made of uncouncious matter, which made a councious observer which made a uncouncious measuring device that collapsed the wave function, so the whole counscous observer thing really is a huge stretch of the philosophical imagination.

The scientific fact is that we have no idea what active role our intelligence/consciousness plays in the act of doing science, and the results we obtain from that act. Thus, what actually requires philosophy is making a claim that there is not such an active role. Call it a scientific hypothesis if you will, but it is certainly one that has never been tested-- that's just a fact. It is quite ironic that many people seem to think the claim that requires taking a philosophical stance is that our intelligence/consciousness might leave its fingerprints on the way we do science and the outcomes we achieve, but that is simply the null hypothesis.

Is there a "special" property about counsciesness that trancends both classical physics and QM physics because that's the only explination for what youre arguing and I don't think the transfer of nueral information from one part of the brain to the other where counsieness forms a biological collage of information is so special as destroy the foundations of physics.

If there is a special property about consciousness, you can be sure that the "foundations of physics" rely on it. To claim that the foundations of physics would be destroyed by any such special property, despite the fact that they quite demonstrably invoke it, is to make a philosophical claim that there is something about physics that transcends the process whereby we come upon it. Thus, it is you who are making the claim of transcendance, not I.

Also what do you mean exactly by
"some types of information updates involve no interactions with a measuring device at all, and the absence of interaction then becomes a type of interaction" I know people like QM to be mysterious but that needs to be explained clearly.

See my post to Gytax, it gives an example.

 

[faen]

That question requires an interpretation to answer. What doesn't require an interpretation is that the situation you describe will result in decoherence, and a mixed state treatment of the entanglements. But collapse is something quite different that must be addressed next.
The scientific fact is that we have no idea what active role our intelligence/consciousness plays in the act of doing science, and the results we obtain from that act. Thus, what actually requires philosophy is making a claim that there is not such an active role. Call it a scientific hypothesis if you will, but it is certainly one that has never been tested-- that's just a fact. It is quite ironic that many people seem to think the claim that requires taking a philosophical stance is that our intelligence/consciousness might leave its fingerprints on the way we do science and the outcomes we achieve, but that is simply the null hypothesis.
If there is a special property about consciousness, you can be sure that the "foundations of physics" rely on it. To claim that the foundations of physics would be destroyed by any such special property, despite the fact that they quite demonstrably invoke it, is to make a philosophical claim that there is something about physics that transcends the process whereby we come upon it. Thus, it is you who are making the claim of transcendance, not I.

See my post to Gytax, it gives an example.

What you write is interresting, but I don't believe in that the human counciousness directly determines the quantum states.. I kinda believe the issue of time disproves it. Think about this example. You are performing the double slit experiment. You turn on the instruments, fire the electrons etc. So far you have no idea about the results.. Then 1 year later you check the result. Isn't it a little bit late for the human councious to have any effect on which quantum state the electrons ended up in? Wouldn't that require some kind of macroscopic quantum mechanical effect for a human counciousness to determine the state this late?

Or think about this: How could the universe evolve into anything e.g. something as complex as human beings, before human beings are there to create entanglements? I'd say it's quite the contradiction..

You say it's neutral to be open to that the human counciousness determines the mixed states.. Well i think it is not neutral. Neither do i think it is neutral to believe that Santa Clause is dancing behind my back whenever I'm not looking. I believe it is more likely that Santa is not dancing behind my back, isn't that resonable? Well I apply the same principle to believe that it is relatively unreasonable to believe that quantum mechanics is dependent on human counciousness. It is too far fetched, and more likely that the environment determines it.

 

[StevieTNZ]

This is a very misleading comment, it gives the camera a powerful status: the camera is just there to register photons. The collapse will only occur / has occurred (depends on your interpretation...) if there are photons for the camera to see. The camera is just one element in a long chain of interactions that constitute "measurement", not a key element as your quote suggests (and while you might understand what you meant, I don't want the OP to get confused).

I don't quite understand what you're going on about. I gave two options, either/or occurs. A collapse occurs (standard QM interpretation) [camera being the measuring device] or it doesn't.

 

[StevieTNZ]

What you write is interresting, but I don't believe in that the human counciousness directly determines the quantum states.. I kinda believe the issue of time disproves it. Think about this example. You are performing the double slit experiment. You turn on the instruments, fire the electrons etc. So far you have no idea about the results.. Then 1 year later you check the result. Isn't it a little bit late for the human councious to have any effect on which quantum state the electrons ended up in? Wouldn't that require some kind of macroscopic quantum mechanical effect for a human counciousness to determine the state this late?.

I would say your statement does not invalidate the consciousness collapse interpretation, the reason being the experiment done in reference to Wheeler's delayed-choice proposal.

My personal conviction is consciousness does cause wave function collapse.

 

[StevieTNZ]

Youre confusing philosophy with science. Also don't wave functions collapse naturally in the universe even when people arnt performing double slit experiments. Also we are made of uncouncious matter, which made a councious observer which made a uncouncious measuring device that collapsed the wave function, so the whole counscous observer thing really is a huge stretch of the philosophical imagination. Is there a "special" property about counsciesness that trancends both classical physics and QM physics because that's the only explination for what youre arguing and I don't think the transfer of nueral information from one part of the brain to the other where counsieness forms a biological collage of information is so special as destroy the foundations of physics.

Also what do you mean exactly by
"some types of information updates involve no interactions with a measuring device at all, and the absence of interaction then becomes a type of interaction" I know people like QM to be mysterious but that needs to be explained clearly.

If you affect a sub atom its reacts, if you don't then its follows its natural course.

It seems an experiment that provides which-way information is enough to wash out interference effects. However, by that which-way info being available, it is hard to say whether collapse has occurred or not. I say that in light of which-way info being available in the Scully et al. delayed-choice quantum eraser thoguth experiment, but Paul Kwiat saying prior to 'erasure' no collapse has occurred (despite which-way info being available).

 

[TGlad]

"My personal conviction is consciousness does cause wave function collapse"
So what level of consciousness? A drunk person? A sleepy person? A person with no short term memory? A foetus? A monkey? A fly? An amoeba?
What if you observe something consciously then forget the result? What if you miss-read the result? What if 10 people observe at the same time, is it a stronger effect?

Doesn't really make a good scientific theory to rely on consciousness does it.

 

[StevieTNZ]

"My personal conviction is consciousness does cause wave function collapse"
So what level of consciousness? A drunk person? A sleepy person? A person with no short term memory? A foetus? A monkey? A fly? An amoeba?
What if you observe something consciously then forget the result? What if you miss-read the result? What if 10 people observe at the same time, is it a stronger effect?

Doesn't really make a good scientific theory to rely on consciousness does it.

All the matters is whether my consciousness can collapse it.
I don't see any significance of forgetting a result. The wf still collapsed when I first observed it.

Whether the ten people observing have consciousness or not is not the sort of question I can verify. Well, in principle, I think it is a question I can answer. I don't see any importance of whether more than one person is conscious of the outcome or not.

Whether a fly or a monkey can collapse a wavefunction - all good questions. Let's see if they do collapse a wf. They may just well be able to have that ability.

 

[Ken G]

You are performing the double slit experiment. You turn on the instruments, fire the electrons etc. So far you have no idea about the results.. Then 1 year later you check the result. Isn't it a little bit late for the human councious to have any effect on which quantum state the electrons ended up in? Wouldn't that require some kind of macroscopic quantum mechanical effect for a human counciousness to determine the state this late?

It requires a pretty die-hard idealist stance to claim that the mixed state remains mixed until some consciousness comes into contact with it. I tend to prefer a "softer" role of consciousness-- the concept of a hypothetical consciousness suffices. That handles the "tree falling in the woods" issue. The point is, most scientists are too realist to want to imagine that a consciousness is actually required to collapse a wave function, but one does need to introduce a hypothetical consciousness into the problem to collapse the mixed state. The way that looks is, we say the mixed state is "actually" one result or the other, because we can imagine introducing a hypothetical consciousness/intelligence/analyzing agent into the situation without disrupting the system (because it is already highly macroscopic) to adjudicate which outcome occured. It doesn't matter if the consciousness is there, what matters is that our consciousness can imagine that one.

The collapse then occurs via a kind of "mini me" mindset, much like the way "which way" information collapses a two-slit experiment whether or not any consciousness is actually there to interpret that information. Note that in this brand of interpretation, the consciousness is still required to give meaning to the experiment, it is just not required to be on hand in the actual apparatus. This approach allows for realism, which most scientists view as a convenient philosophical stance whenever possible.

Or think about this: How could the universe evolve into anything e.g. something as complex as human beings, before human beings are there to create entanglements? I'd say it's quite the contradiction..

This doesn't present any problem. The idealist simply holds that the universe is in a kind of unactualized state until the consciousnesses come along to collapse it into a definite state. But the realist finds that too radical, yet can still easily find a role for consciousness in the same "mini me" fashion I mentioned above-- we simply say that because we can imagine a consciousness being present without altering the reality, it doesn't matter if the consciousness was really there or not. Note this is what you cannot do inside an atom, say-- there is no way to imagine a consciousness present inside an atom without changing the atom, the atom has not been rendered into a macroscopic mixed state that the (hypothetical) consciousness could collapse.

Now I know what some might say-- they'll say that a hypothetical entity cannot actually "do" anything in a physical situation. But that is because they have already adopted a fairly radical philosophical stance that reality can actually be parsed into "doers" that cause things to happen, and "onlookers" that have no effect. That approach has worked for us for so long that we forgot to notice how radical a stance it it, but it is in quantum mechanics that this stance falls all apart. Instead, in quantum mechanics we find that even the onlooker is responsible for the information they are using in their physics-- their fingerprints are all over the way they are choosing to think about any situation, the coherences they are choosing to track and those they are choosing to average over and ignore. Quantum mechanics is simply not possible without making choices like that.

You say it's neutral to be open to that the human counciousness determines the mixed states.. Well i think it is not neutral. Neither do i think it is neutral to believe that Santa Clause is dancing behind my back whenever I'm not looking.

The analogy doesn't hold-- we don't need Santa to do science. We do need consciousnesses/intelligences/analyzing agents (again I make no effort to parse any distinctions there), they are demonstrable and inextricable elements of doing physics. We just didn't need to think about them before quantum mechanics, because we never faced the question, "where does the definite outcome come from?" That is exactly the question that forces us to adopt an interpretation of quantum mechanics where we did not have to adopt an interpretation of classical mechanics, because we never included any indefinite outcomes in our theories before.

 

[StevieTNZ]

The collapse then occurs via a kind of "mini me" mindset, much like the way "which way" information collapses a two-slit experiment whether or not any consciousness is actually there to interpret that information. Note that in this brand of interpretation, the consciousness is still required to give meaning to the experiment, it is just not required to be on hand in the actual apparatus. This approach allows for realism, which most scientists view as a convenient philosophical stance whenever possible.

I'm a bit weary of having which-way info available and allowing the quantum system to be in a definite state. I say that because of Scully's eraser experiment. I think it is natural to say had the particle really gone one way or the other prior to erasure of information, interference wouldn't return.

 

[Thenewdeal38]

Ken G, StevieTNZ are either of you physicists?

Here are some physicists who argue counsciesness has nothing to do with the QM process. Roger Penrose dosent count he's a topologist.

Among them Bohr, Heisenberg, Einstein also only very few prominent physicists, e.g. E. Wigner, have argued for a role of consciousness in the measurement process, but later in his life, however, Wigner changed his views, persuaded by the work of Zeh [5]. But such exceptional cases do not justify ignoring the warning of Bell “that it is not right to tell the public that a central role for consciousness is integrated into modern physics.”Michael Nauenberg http://physics.ucsc.edu/~michael/qefoundations.pdf

Victor Stenger http://www.csicop.org/si/show/quantum_quackery/

 

[Thenewdeal38]

Also http://physicsandcake.wordpress.com/2010/11/23/the-observer-with-a-hammer-effect/

The label "observer effect" is a misnomer as the observation conducted by the conscious agent is only a secondary action, the primary action is that of interaction. In the most famous case, Youngs double slit experiment, the waveform of the electron being measured is collapsed by its interaction with the photon used to detect it. The misunderstanding arises because of the experimenter is essentially interfering with the experiment in the act of measuring the desired phenomenon.

It's a bit like switching a light on to see how dark it is.

 

[TGlad]

"Among them Bohr, Heisenberg, Einstein"
And don't forget Feynman

 

[Low-Q]

I am pretty sure that you will recognise this video :
about at 3:50, they claim that, when we observe an electron passing through a double slit, acts as a particle, as opposed to its wave property. Does that mean, if we place a 8 mega pixel digital camera in between the slit and the light source, will electrons behave as particles? I hardly think so. SO my question is, what is the context of observation in this video?

The problem with observing electrons is that we have to shine a light on it in order to see it. However, if we do, the electron will move to another location when exited by the photons from the light... Maybe that wasn't your point?

Vidar

 

[Ken G]

I'm a bit weary of having which-way info available and allowing the quantum system to be in a definite state. I say that because of Scully's eraser experiment. I think it is natural to say had the particle really gone one way or the other prior to erasure of information, interference wouldn't return.

Yes, it's very important not to give a casual meaning to the word "available." Note that when I imagine a hypothetical consciousness on the scene, I am not affording that consciousness any supernatural powers or "god's eye" views of anything-- it has access only to whatever information a real consciousness could have in the exact same situation. Hence, it has no effect on whether or not information is erased before it is ever made "available"-- one must still have the availability or it just isn't which way information.