Does the environment cause wave function collapse

[audioloop]

In this framework, we divide the universe into two parts. A classical world which we are part of, and a quantum world which we are studying.In this framework, quantum mechanics does not describe the whole universe, because it does not describe the classical apparatus.

Decoherence is common to all frameworks.

without the division, how can decohere.


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[atyy]

Now this is an interesting question. What actually constitutes a complex environment? Is there a specific scientific definition for it? If not, I could venture a really off-the-cuff guess, that a complex system is one in which the relationship between the components of the system are such, that it imposes restrictions upon the possible states of the individual components of the system, or a subset of those components.

There is no strict distinction between a simple and a complex experiment. In the experiments, as they introduced one random photon to more random photons, the degree to which the interference was lost increased.

But this definition raises a problem, because the density of the medium within the double slit experiment should then have no effect upon the rate of decoherence. It wouldn't matter how many interactions the particle had between the slits and the screen, if none of those interactions could provide a restriction as to which slit the particle came through. But the experiments cited by Len M and atyy seem to indicate that there is indeed a correlation between the density of the medium, and the rate of decoherence. (Although as I stated in a previous post, I'm not sure that that effect wasn't due to some other factor) But this would seem to indicate that my definition of what constitutes a complex system is inadequate, incomplete, or incorrect.

It's not the density of the medium. It is the ability of the random scattering to provide which path information.

This assumes that there is a classical environment consisting of ball-like particles but so far there is no evidence for the existence of such particles. We have to introduce them for the hypothesis to work, right?

Decoherence assumes everything is quantum, including the environment.

without the division, how can decohere.

Decoherence has no split into classical and quantum. Everything is quantum in decoherence.

Decoherence does not explain why we get classical outcomes, it only explains why we get classical possibilities - ie. why when when a measurement is made, we get a dead cat or an alive cat, but never a dead and alive cat. A measurement is still needed to collapse the wave function, so that we transition from a dead cat or an alive cat to a particular outcome. It is the measurement and collapse to a particular outcome, not decoherence, which requires that we divide the universe into classical and quantum. (Or you can use Many-Worlds or Bohmian mechanics.)

 

[atyy]

David Kokorowski's thesis http://www.atomwave.org/otherarticles/mit/Kokorowski%202001.pdf gives details of an atom interferometer. It looks like the main region (p22) is in a vacuum of 10^-7 Torr.

 

[audioloop]

Decoherence assumes everything is quantum, including the environment.

Everything is quantum in decoherence.

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if everythig is quantum, why the division ?

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[atyy]

if everythig is quantum, why the division ?

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In interpretations with collapse, not everything is quantum. (Yes, this doesn't seem to make sense, but it works - so it is called shut-up-and-calculate. Because of this division, in the view of shut-up-and-calculate, quantum mrchanics is not a complete theory. If you want something that makes more sense try Many-Worlds, in which quantum theory is complete; or de Broglie - Bohm, which completes quantum mechanics with hidden variables.)

 

[audioloop]

In interpretations with collapse, not everything is quantum. (Yes, this doesn't seem to make sense, but it works - so it is called shut-up-and-calculate. Because of this division, in the view of shut-up-and-calculate, quantum mrchanics is not a complete theory. If you want something that makes more sense try Many-Worlds, in which quantum theory is complete; or de Broglie - Bohm, which completes quantum mechanics with hidden variables.)

right, everything is not quantum.


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[Maui]

Decoherence assumes everything is quantum, including the environment.

In the usual interpretation, the interaction between a quantum system and its environment is what causes decoherence. This is of course an oversimplification, as seen above, and only works FAPP but is not right in and of itself. At a more complete level it's the information about the which path that brings decoherence as you seem to agree in post 32.

right, everything is not quantum..

Like what?

 

[StevieTNZ]

As far as my understanding takes me, everything is quantum mechanical in nature. At least in principle. We await the experiment to show us a 40kg mirror is placed in a superposition of positions, for example.

 

[atyy]

In the usual interpretation, the interaction between a quantum system and its environment is what causes decoherence. This is of course an oversimplification, as seen above, and only works FAPP but is not right in and of itself. At a more complete level it's the information about the which path that brings decoherence as you seem to agree in post 32.

As long as one takes it that decoherence does not solve all problems, and only solves the "pointer basis problem" then it works completely, not only FAPP. In decoherence, the system, apparatus and environment are in the quantum world.

If decoherence is taken to solve the measurement problem, then it does not work, not even FAPP.

 

[Fiziqs]

It's not the density of the medium. It is the ability of the random scattering to provide which path information.

As I mentioned in an earlier post I have a bit of a problem trying to see how the random scattering in denser mediums can provide "which path" information. How do you gain "which path" information from random scattering?

But because I lack an understanding of the intricacies of the experiments, I may well be missing something. If we set up a double slit experiment and we introduce progressively denser mediums, we would expect the interference pattern to gradually disappear, but this could be accounted for simply by random scattering, and not be due to increased decoherence caused by an increase in "which path" information. Random scattering would cause the interference pattern to disappear regardless of any effects on decoherence.

However, I also assume that the designers of the experiments were aware of this, and accounted for it somehow. I'm just wondering how. I really would like to be sure, whether or not denser mediums cause an increase in decoherence, because this would provide an important clue into the nature of the process of decoherence. So I'm actually hoping that you can clear this up for me. (Not that I'm trying to use you as my own personal assistant, sorry)

 

[Maui]

As I mentioned in an earlier post I have a bit of a problem trying to see how the random scattering in denser mediums can provide "which path" information. How do you gain "which path" information from random scattering?

But because I lack an understanding of the intricacies of the experiments, I may well be missing something. If we set up a double slit experiment and we introduce progressively denser mediums, we would expect the interference pattern to gradually disappear, but this could be accounted for simply by random scattering, and not be due to increased decoherence caused by an increase in "which path" information. Random scattering would cause the interference pattern to disappear regardless of any effects on decoherence.

However, I also assume that the designers of the experiments were aware of this, and accounted for it somehow. I'm just wondering how. I really would like to be sure, whether or not denser mediums cause an increase in decoherence, because this would provide an important clue into the nature of the process of decoherence. So I'm actually hoping that you can clear this up for me. (Not that I'm trying to use you as my own personal assistant, sorry)

See the following excerpt(Nature, Vol.401):

"In quantum interference experiments, coherent superposition
only arises if no information whatsoever can be obtained, even in
principle, about which path the interfering particle took. Interaction
with the environment could therefore lead to decoherence.We
now analyse why decoherence has not occurred in our experiment
and how modifications of our experiment could allow studies of
decoherence using the rich internal structure of fullerenes.
In an experiment of the kind reported here, ‘which-path’ information
could be given by the molecules in scattering or emission
processes, resulting in entanglement with the environment and a
loss of interference. Among all possible processes, the following are
the most relevant: decay of vibrational excitations via emission of
infrared radiation, emission or absorption of thermal blackbody
radiation over a continuous spectrum, Rayleigh scattering, and
collisions.
When considering these effects, one should keep in mind that
only those scattering processes which allow us to determine the path
of a C60 molecule will completely destroy in a single event the
interference between paths through neighbouring slits. This
requires lpd; that is, the wavelength l of the incident or emitted
radiation has to be smaller than the distance d between neighbouring
slits, which amounts to 100nm in our experiment. When this
condition is not fulfilled decoherence is however also possible via
multi-photon scattering7,8,17.
At T < 900 K, as in our experiment, each C60 molecule has on
average a total vibrational energy of Ev < 7 eV (ref. 18) stored in 174
vibrational modes, four of which may emit infrared radiation at
lvib < 7–19mm (ref. 10) each with an Einstein coefficient of
Ak < 100 s21 (ref. 18). During its time of flight from the grating
towards the detector (t < 6 ms) a C60 molecule may thus emit on
average 2–3 such photons.
In addition, hot C60 has been observed19 to emit continuous
blackbody radiation, in agreement with Planck’s law, with a measured
integrated emissivity of e < 4:5 ð 6 2:0Þ 3 1025 (ref. 18). For
a typical value of T < 900 K, the average energy emitted during the
time of flight can then be estimated as only Ebb < 0:1 eV. This
corresponds to the emission of (for example) a single photon at
l < 10mm. Absorption of blackbody radiation has an even smaller
influence as the environment is at a lower temperature than the
molecule. Finally, since the mean free path for neutral C60 exceeds
100min our experiment, collisions with background molecules can
be neglected.
As shown above, the wavelengths involved are too large for single
photon decoherence. Also, the scattering rates are far too small to
induce sufficient phase diffusion. This explains the decoupling of
internal and external degrees of freedom, and the persistence of
interference in our present experiment."

http://atomfizika.elte.hu/akos/orak/atfsz/dualitas/fulleren.pdf

 

[zonde]

For objects other than photons - yes - for photons its probably related to they travel so quickly and there is so many of them, since their decoherence time is so long, very few interact with objects on the way through enough to decohere them - although it may decohere other objects. Of course those that are decohered and given an actual position will not participate in the interference effect.

This position is falsified by simple quantum eraser experiment (the do-it-yourself type - http://www.scientificamerican.com/slideshow.cfm?id=a-do-it-yourself-quantum-eraser)
Photons definitely interact with polarizers and yet interference is seen after "erasure" of which way polarization information.

 

[Jilang]

As I mentioned in an earlier post I have a bit of a problem trying to see how the random scattering in denser mediums can provide "which path" information. How do you gain "which path" information from random scattering?

But because I lack an understanding of the intricacies of the experiments, I may well be missing something. If we set up a double slit experiment and we introduce progressively denser mediums, we would expect the interference pattern to gradually disappear, but this could be accounted for simply by random scattering, and not be due to increased decoherence caused by an increase in "which path" information. Random scattering would cause the interference pattern to disappear regardless of any effects on decoherence.

However, I also assume that the designers of the experiments were aware of this, and accounted for it somehow. I'm just wondering how. I really would like to be sure, whether or not denser mediums cause an increase in decoherence, because this would provide an important clue into the nature of the process of decoherence. So I'm actually hoping that you can clear this up for me. (Not that I'm trying to use you as my own personal assistant, sorry)

Fiz, there can be no interference if there is random scattering. That's why experiments with particles must be performed in a vacuum. Experiments with photons can be performed in an atmosphere as they are affected much less.

 

[atyy]

As I mentioned in an earlier post I have a bit of a problem trying to see how the random scattering in denser mediums can provide "which path" information. How do you gain "which path" information from random scattering?

But because I lack an understanding of the intricacies of the experiments, I may well be missing something. If we set up a double slit experiment and we introduce progressively denser mediums, we would expect the interference pattern to gradually disappear, but this could be accounted for simply by random scattering, and not be due to increased decoherence caused by an increase in "which path" information. Random scattering would cause the interference pattern to disappear regardless of any effects on decoherence.

However, I also assume that the designers of the experiments were aware of this, and accounted for it somehow. I'm just wondering how. I really would like to be sure, whether or not denser mediums cause an increase in decoherence, because this would provide an important clue into the nature of the process of decoherence. So I'm actually hoping that you can clear this up for me. (Not that I'm trying to use you as my own personal assistant, sorry)

Random means the environment is too complex for us to really know its quantum state. Since the environment is not really random, it encodes the which way information. When we say the information about the path is in the environment, we don't mean that a path has already been chosen. In decoherence, the path is not chosen yet, the information is encoded in different correlations between the environment and each possible path. So in simple cases like the one photon case, if we are able to know enough about the environment, we can make the coherence come back. Here's an experiment which used information in the environment to regain coherence http://www.physics.arizona.edu/~cronin/Research/Publications/photon_scattering.pdf .

Kokorowski's thesis http://www.atomwave.org/otherarticles/mit/Kokorowski%202001.pdf , however, does say in section 3.6.1, "Despite decades of work and hundreds of papers published on the subject, there currently exists no single, well-accepted definition of decoherence. In some sense, no such definition is necessary. What is more important is that the physical model describing how a given system's density matrix evolves appropriately includes any influence of its environment." He also has a very interesting discussion in section 3.6.5 on distinguishing between decoherence and classical dephasing.

 

[audioloop]

Kokorowski's thesis http://www.atomwave.org/otherarticles/mit/Kokorowski%202001.pdf[/URL] , however, does say in section 3.6.1, "Despite decades of work and hundreds of papers published on the subject,
[B]there currently exists no single, well-accepted definition of decoherence[/B]"[/QUOTE]

because, we don't know, what causes it, just we describe what we see.
no explanation at all.[quote="StevieTNZ, post: 4588369"]the experiment to show us mirror is placed in a superposition of positions, for example.[/QUOTE]

indeed.
with big solid objects.

[B]Observation of a kilogram-scale oscillator near its quantum ground state[/B]
[url]http://iopscience.iop.org/1367-2630/11/7/073032/[/url]

"cooling technique capable of approaching the quantum ground state of a kilogram-scale system...
...to probe the validity of quantum mechanics on an enormous mass scale"

[url]http://prd.aps.org/abstract/PRD/v65/i2/e022002[/url]
[url]http://cds.cern.ch/record/451662/files/0008026.pdf[/url][url]http://prd.aps.org/abstract/PRD/v64/i4/e042006[/url]
[url]http://arxiv.org/abs/gr-qc/0102012[/url]

[URL]http://www.nature.com/nature/journal/v444/n7115/full/nature05273.html[/URL]
[url]http://arxiv.org/abs/quant-ph/0607068[/url]
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[bohm2]

If we set up a double slit experiment and we introduce progressively denser mediums, we would expect the interference pattern to gradually disappear, but this could be accounted for simply by random scattering, and not be due to increased decoherence caused by an increase in "which path" information. Random scattering would cause the interference pattern to disappear regardless of any effects on decoherence.

There are other ways of getting rid of the interference pattern:

In one experiment, Kim et al. controlled the exact interval between independent signal photons emitted in pairs [12]. As the time delay between photons was increased, first-order interference gradually vanished.

Interpreting Negative Probabilities in the Context of Double-Slit Interferometry
http://arxiv.org/pdf/physics/0611043v1.pdf

How would you interpret such results?

 

[bhobba]

if everythig is quantum, why the division ?

With decoherence there is no division, because everything is quantum.

Thanks
Bill

 

[bhobba]

As long as one takes it that decoherence does not solve all problems, and only solves the "pointer basis problem" then it works completely, not only FAPP. In decoherence, the system, apparatus and environment are in the quantum world.

Precisely :thumbs::thumbs::thumbs:

Decoherence likely solves the pointer basis problem, but a bit more work needs to be done to say 100% for sure. That being the case the world no longer needs to be divided between classical and quantum - in analysing the measurement problem everything is now quantum.

What it doesn't solve, and the exact way its 'solved' varies between interpretations, is the problems of outcomes - ie why we get any outcomes at all - and exactly what determines what those outcomes are eg MW solves it by the world you happen to be in.

Thanks
Bill

 

[bhobba]

This position is falsified by simple quantum eraser experiment (the do-it-yourself type - http://www.scientificamerican.com/slideshow.cfm?id=a-do-it-yourself-quantum-eraser)Photons definitely interact with polarizers and yet interference is seen after "erasure" of which way polarization information.

And exactly how that invalidates my claim that in your usual double slit experiment, the reason you get an interference pattern is because photons interact weakly with the air, dust particles etc that is usually what lies between it and the screen, and in that situation have long decoherence times, as well as there are a huge number of them so those that do is negligible, is beyond me. Of course they interact STRONGLY with polarizes, that the randomly polarized photons that go through such are in effect observed, and only those of a certain polarization in effect get through.

In other words, in the Scientific American article you linked to, it was done in the air with dust particles and whatever else there is, and you still got the interference pattern. I contend the reason that is possible is the long decoherence times of photons because they are true quantum particles of zero mass, the fact we have a huge number of them, and they have such a fast transit time.

I want to add, and in such discussions it is hardly ever mentioned, but to be 'exact' it should, describing photons traveling through a medium like air the way I have is very very wrong:
https://www.physicsforums.com/showthread.php?t=511177

But things like this are done in physics all the time to get an intuitive idea of what's going on.

Thanks
Bill.

 

[bhobba]

How do you gain "which path" information from random scattering?

Photons that have been scattered by for example a dust particle have been decohered - actually both the dust particle and photon are decohered, and in effect both given a position. The reason position is usually what's 'observed' by decoherence is tied up with the inverse square like nature of most interactions and you will need to consult the technical literature, such as the textbook on decoherence mentioned previously, for the detail. Since they now have a definite localized position they have lost 'which path' information as you put it.

The reason you still can get an interference pattern is the massive number of photons that make it to the screen without being decohered.

Also this is a very rough and ready description, photons traveling through a medium like air is a very much more complicated process than this.

Thanks
Bill

 

[bhobba]

What is more important is that the physical model describing how a given system's density matrix evolves appropriately includes any influence of its environment." He also has a very interesting discussion in section 3.6.5 on distinguishing between decoherence and classical dephasing.

Actually that's a VERY important point - thanks for sharing.

Thanks
Bill

 

[bhobba]

because, we don't know, what causes it, just we describe what we see.
no explanation at all.

Just because there is no generally agreed definition on exactly when decoherence has occurred, it does not follow that in many many cases we can't tell it has occurred.

Thanks
Bill

 

[zonde]

And exactly how that invalidates my claim that in your usual double slit experiment, the reason you get an interference pattern is because photons interact weakly with the air, dust particles etc that is usually what lies between it and the screen, and in that situation have long decoherence times, as well as there are a huge number of them so those that do is negligible, is beyond me. Of course they interact STRONGLY with polarizes, that the randomly polarized photons that go through such are in effect observed, and only those of a certain polarization in effect get through.

I take your claim that "the reason you get an interference pattern is because photons interact weakly with the air, dust particles etc" and make a prediction that follows from that statement - when photons interact strongly with the medium on their way interference pattern should disappear.
The first stage of experiment with markers at the slits demonstrates that photons indeed interact strongly with markers and the second stage with additional polarizer at 45° demonstrates that despite strong interaction with makers interference is still observable i.e. prediction falsified.

 

[audioloop]

everything is now quantum.
Bill

just a claim, has to be proved over very wide range of experimental facts.
example; on 10²⁰ atoms.
so, not proved yet.


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[audioloop]

Just because there is no generally agreed definition on exactly when decoherence has occurred, it does not follow that in many many cases we can't tell it has occurred.

Thanks
Bill

when or what are different questions, sir.


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[bhobba]

when or what are different questions, sir.

Which is of relevance exactly how?

My point is simple in the extreme - while there is no generally agreed way to determine if decoherence has occurred, there are many cases where for sure we know it has.

Many of these such as decohereing dust particles by photons are discussed in the reference I gave earlier by Schlosshauer.

Thanks
Bill

 

[bhobba]

just a claim, has to be proved over very wide range of experimental facts. example; on 10²⁰ atoms. so, not proved yet

It's not an experimental issue - its if a pointer basis is determined by decoherence. It is generally thought it is, but some key theorems are lacking, and the definitive answer needs to wait until then.

Thanks
Bill

 

[DennisN]

Regarding "proofs" in science:

I don't intend to nitpick, but I think it's nevertheless important for others who may read this thread that there are no proofs in science, proofs are for mathematics.

In science there are evidence, e.g. strong evidence, weak evidence, no evidence. A hypothesis can be confirmed or ruled out (or not confirmed, if the evidence is irrelevant w.r.t. to the hypothesis).

From Introduction to the Scientific Method (University of Rochester):

As just stated, experimental tests may lead either to the confirmation of the hypothesis, or to the ruling out of the hypothesis. The scientific method requires that an hypothesis be ruled out or modified if its predictions are clearly and repeatedly incompatible with experimental tests.

 

[bhobba]

prediction falsified.

I think you need to explain, very carefully, what you are getting at, and I do mean carefully, because I have zero idea what prediction has been falsified and if it is of any relevance at all.

Thanks
Bill

 

[bhobba]

I don't intend to nitpick, but I think it's nevertheless important for others who may read this thread that there are no proofs in science, proofs are for mathematics.

The context of proofs in science is in the area of the logical consequences of theories eg if QM is true such and such follows.

Here the idea is does QM, as a theory, single out a pointer basis. If so then a very important part of the measurement problem is solved. The theorems at present are not general enough to decide, but it is generally thought it does.

Thanks
Bill