Double slit experiment and Interaction

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The discussion centers on the interpretation of the double-slit experiment and the necessity of interaction for the existence of physical reality. It argues against the idea that human observation is required for reality to manifest, asserting that the physical world exists independently of observation. The double-slit experiment demonstrates that interactions can alter quantum states, but these interactions do not necessitate human consciousness. The conversation also touches on the Copenhagen interpretation of quantum mechanics and the concept of decoherence, emphasizing that the universe does not rely on human observation for its existence. Ultimately, the thread concludes that the physical world is objective and does not depend on consciousness for its reality.
  • #31
Strilanc said:
I harp on the lack of predictive difference, because that's what I think people like the starter of this thread are asking about. They want to know if there's a physical effect in QM that compels belief in consciousness.

Now you are starting to get a better idea about this interpretation stuff. It's more to do with foundational beliefs you have than actual fact. Those that go on about this conciousness stuff often are influenced by gutter trash like What The Bleep Do We Know Anyway:


Its junk of the first order trying to justify new age stiff like The Secret.

Trouble is the lay person doesn't have the background to realize what it really is and get sucked in. I even heard it was required viewing in an English class with the teacher actually saying it was the view of science - oh dear. Maybe one reason I hated English at high school and failed it. The reason was I didn't do any work because it seems totally vacuous to me. Got an honour at University though for both Professional Communication 1 and 2 which I saw some value in. Interestingly while I had to do those subjects now its simply an elective - something I don't agree with. But when I did it all the math students complained about it - most disliked English as much as I did. If it was taught better perhaps that could be reversed - just a by the by observation

That said, we with a bit deeper understanding, have to give the facts - that it may be true - but is a very very weird view that isn't required - much more common-sense views of QM are possible and it is one of those most physicists ascribe to.

Thanks
Bill
 
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  • #32
bhobba said:
Ok - without agreeing that those interpretations have issues - I think that is highly debatable but just for arguments sake let's assume they do - what about GRW? I haven't seen anyone arguing that has issues - but you may be able to dig up some. Perhaps it might just be that just about any interpretation has people that take exception to it so maybe we have to go with the consensus? And that includes even your favoured Copenhagen and my Ignorant Ensemble.

I am not sure about the status of real collapse models, but I think they don't extend to the standard model either. But unlike Bohmian Mechanics, I don't know how far along it is. With Bohmian Mechanics, one can probably get QED, but the chiral fermions are still at the stage where there are proposals whose correctness and flaws are still not widely understood. http://backreaction.blogspot.com/2013/06/testing-spontaneous-localization-models.html comments on collapse models are in line with my understanding of their current limitatins "Sarcasm aside, my main problem with this, and with most interpretations and modifications of quantum mechanics, is that we already know that quantum mechanics is not fundamentally the correct description of nature. That’s why we teach 2nd quantization to students. To make matters worse, most of such modifications of quantum mechanics deal with the non-relativistic limit only. I thus have a hard time getting excited about collapse models." However, an interesting thing about real collapse models is that it seems they can be Lorentz covariant: http://arxiv.org/abs/1111.1425.

As far as I know, the issues I mentioned are all technical issues, so they are not matters of taste. One of the reasons I like Copenhagen is that it states its issues clearly by placing a classical/quantum cut. So my main point really is that I think the issues should be stressed, and not swept under the rug. That's what makes quantum foundations exciting, as exciting as quantum gravity.
 
  • #33
atyy said:
As far as I know, the issues I mentioned are all technical issues, so they are not matters of taste.

I never said they were matters of taste. What I am saying is they have been discussed in many threads on this forum with no definite conclusion reached. They are matters of debate. It is not the general consensus of the physics community that BM for example is inherently flawed. If you believe otherwise start a thread about it and see what experts in BM like Dymystifyer have to say. But I doubt it will reach any different conclusion than what it has in the past.

Thanks
Bill
 
  • #34
bhobba said:
I never said they were matters of taste. What I am saying is they have been discussed in many threads on this forum with no definite conclusion reached. They are matters of debate. It is not the general consensus of the physics community that BM for example is inherently flawed. If you believe otherwise start a thread about it and see what experts in BM like Dymystifyer have to say. But I doubt it will reach any different conclusion than what it has in the past.

I believe it is the consensus of the physics community that there is, at present, no Bohmian standard model, in particular, because of the chiral fermions interacting with non-Abelian gauge fields.

Mainly, I believe sweeping problems under the rug is not a favour to the Bohmian spirit.
 
  • #35
atyy said:
I believe it is the consensus of the physics community that there is, at present, no Bohmian standard model, in particular, because of the chiral fermions interacting with non-Abelian gauge fields.

I would like that confirmed by someone like Demystifier. BTW the issue isn't if there is such a model - it is if its impossible, utterly impossible to create one. If such was the case then you have disproved BM which would be very big news. It holds a strong fascination for many philosophy types and I think you would hear a loud collective scream if it was the case.

Thanks
Bill
 
  • #36
bhobba said:
I would like that confirmed by someone like Demystifier. BTW the issue isn't if there is such a model - it is if its impossible, utterly impossible to create one. If such was the case then you have disproved BM which would be very big news. It holds a strong fascination for many philosophy types and I think you would hear a loud collective scream if it was the case.

Well, my claim is not that it is impossible, but that it is unknown either way at the moment. vanhees71 is secretly working on this problem :p I'm kidding, of course. The technical problem is that Bohmian mechanics is probably able to deal with lattice gauge theory. However, there is no lattice gauge theory of the standard model, because lattice gauge theory has problems with chiral fermions. The problem can be overcome in special cases, but whether those methods can be extended to the standard model is, I think, unknown. So the problem is not just in Bohmian Mechanics, but for all who would like to consider a lattice formulation as a non-perturbative definition of quantum field theory as a low-energy effective theory.

Without a non-perturbative definition, maybe virtual particles are real :biggrin:
 
  • #37
atyy said:
Well, my claim is not that it is impossible, but that it is unknown either way at the moment.

If its simply unknown right now then I don't get your issue.

I don't like BM, IMHO people who believe in it don't face the quantum world head on - they want the crux of something familiar, along the lines of their intuition developed in the common-sense classical world. It's like a comfort blanket.

Now purely as a side comment on my intellectual background I will mention at one time I was very beguiled by Ayn Rand and her philosophy. Slowly, oh so slowly, I figured her out - she has a problem with novelty. If it doesn't conform to her idea of what's rational - well - you are in error. She never cottoned onto the central lesson of science - all knowledge is provisional - it can be invalidated by observation. She believes all stateism is evil - Soviet Russia where she was raised was evil - but all forms of stateism and collectivism are not evil as simple observation of free countries prove. In fact some forms are simply common sense. IMHO its exactly the same with BM - in fact some Objectiveists I have discussed QM with simply do not get it can't be like how they view the world - not all - but some. It leads to views like the following where many of the very fundamental errors often encountered here are on display - eg a mathematical description can't be reality:
http://ari.convio.net/site/PageServer?pagename=reg_ls_physics

This is not a forum to discus philosophy, and rightly so IMHO. I give it purely as an example of pre conceived ideas not allowing us to face issues squarely which I believe is at the heart of the fascination with BM is certain quarters.

That said its a valid interpretation until proved not and deserves to be treated as such.

Thanks
Bill
 
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  • #38
bhobba said:
That said its a valid interpretation until proved not and deserves to be treated as such.

I don't agree. How can one assert things without proof - this is not even asking for rigourous proof - the problem is open even at the physics level of rigour. Unlike you, I do like the Bohmian spirit very much, which is why I think its problems should be clearly stated.

I should say, in my view, BM is not an "interpretation" of quantum mechanics, any more than string theory is an "interpretation" of quantum gravity. BM and string theory are approaches which have open theoretical problems, and which must also be tested by experiment, if the theoretical problems are solved.
 
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  • #39
bhobba said:
http://ari.convio.net/site/PageServer?pagename=reg_ls_physics

I reacquainted myself with the above. It really is bad. If anyone wants to see fundamental error after error give it a squiz.

Thanks
Bill
 
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  • #40
atyy said:
BM and string theory are approaches which have open theoretical problems, and which must also be tested by experiment, if the theoretical problems are solved.

I agree entirely with the experimental bit - trouble is no one yet has figured out how to do it.

Thanks
Bill
 
  • #41
bhobba said:
IMHO its exactly the same with BM - in fact some Objectiveists I have discussed QM with simply do not get it can't be like how they view the world - not all - but some.

Actually, what is your view here? Copenhagen has a flavour in which naive, common sense realism is privileged, a view completely consistent with BM and MWI. But in another thread, kith brought up that maybe all physical theories need a cut. As I understand it, since a cut means the observer cannot be included in the theory, if we believe that the observer is also governed by laws of physics, then we are challenged to construct a more complete theory. This doesn't mean that we will ever have a final theory, merely a sequence of theories, some of which have a cut and some which do not, with those having a cut showing their incompleteness. I do agree with kith that in some sense there is a cut ultimately somewhere, but I think a cut within the theory itself is always is a challenge to complete it. As an analogy, if we have the intuitive natural numbers (analogue to naive, common sense reality), we can prove that no theory can ever completely capture the intuitive natural numbers (analogue to the presumed incompleteness of physical theory). So this means we have a sequence of theories. Of course it becomes harder and harder to see how the present theory should be extended to capture the natural numbers. Right now we have things like the Paris-Harrington theorem (analogue to string theory and BM), which isn't relevant to the research of most mathematicians (analogue to experimentalists and non-strong theorists).

Anyway, that is what I understand the naive, common sense realism flavour of Copenhagen to be. Is what you are calling the objectivist view the same as naive realism? If that is so, then why don't you like it, and how is your alternative different from the view that the observer in some sense creates reality?
 
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  • #42
Strilanc said:
I'm asserting that, if it was the case that only consciousness caused collapse, then the experiments would play out differently whenever the experimenter looked away or was distracted or just wasn't in the room because the experiment had to be left to run for a week. A very specific example is that I think the lack-of-interference-when-there's-a-detector-in-one-slit would go away when the experimenter wasn't looking, if consciousness-only-collapse was correct.
I answer why this is the case, and that interference is still present (just hidden), in post #17.

Strilanc said:
In many (most?) interpretations, classical systems are indeed just a type of large heavy decohery-ish quantum system. In the Copenhagen interpretation, quantum and classical systems are essentially just defined to be different distinct things that both exist and interact in specified ways. I was not advocating that view point, just explaining it.
Decoherence doesn't produce collapse -- only apparent collapse -- so how can a quantum system then become classical?
 
  • #43
Doesn't consciousness cause collapse in MWI?
 
  • #44
bhobba said:
The deep reason - interaction with the environment.

Einstein once quipped to Bohr do you really believe the moon not there when no one is looking? The answer is - its being looked at all the time by its environment.

But who then is observing the environment? This reminds me of Berkley's Subjective Idealism.
 
  • #45
atyy said:
Is what you are calling the objectivist view the same as naive realism?

I think its pretty similar to it. The issue with Objectiveism is they refuse to consider other alternatives - that's the problem with the philosophy - it has issues with novelty ie alternatives to their view of the world.

atyy said:
If that is so, then why don't you like it, and how is your alternative different from the view that the observer in some sense creates reality?

Its exactly like I said - they have a particular view of the world and want to shoe-horn the world to that view rather than face the facts head on and understand, in the case of QM, there are a number of equally valid interpretations. They favour BM on those grounds. As I have said many times the choice of interpretation is more revealing of your beliefs than facts. And of course its the same with me - I favour ignorance ensemble because it faces the key issue - the measurement problem - head on. Its modern version is how does an improper mixed state become a proper one. I form no hypothesis - others evoke BM, GRW etc etc to explain it.

Thanks
Bill
 
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  • #46
StevieTNZ said:
Decoherence doesn't produce collapse -- only apparent collapse -- so how can a quantum system then become classical?

Stevie - you know the answer as well as I do - why you continue to ask it beats me. It requires an additional interpretative assumption, and a number exist eg my assumption an improper mixture is a proper one - but others exist.

Thanks
Bill
 
  • #47
Ahmad Kishki said:
But who then is observing the environment? This reminds me of Berkley's Subjective Idealism.

It doesn't have to be observed.

Thanks
Bill
 
  • #48
bhobba said:
I think its pretty similar to it. The issue with Objectiveism is they refuse to consider other alternatives - that's the problem with the philosophy - it has issues with novelty ie alternatives to their view of the world.

bhobba said:
Its exactly like I said - they have a particular view of the world and want to shoe-horn the world to that view rather than face the facts head on and understand, in the case of QM, there are a number of equally valid interpretations. They favour BM on those grounds. As I have said many times the choice of interpretation is more revealing of your beliefs than facts. And of course its the same with me - I favour ignorance ensemble because it faces the key issue - the measurement problem - head on. Its modern version is how does an improper mixed state become a proper one. I form no hypothesis - others evoke BM, GRW etc etc to explain it.

As far as I understand your view is a version of Copenhagen, and the improper to proper mixed state transformation is wave function collapse. But there are, broadly speaking, two flavours of Copenhagen.

In the first flavour, naive realism is privileged, so that we have a real side of the cut, and an FAPP side which is not necessarily real. The cut can be shifted, and everything can be real, because naive realism is privileged by assumption. This view is first and foremost a matter of faith, but in the tradition of science it believes that it is challenged to construction approaches like BM and MWI.

In the second flavour, naive realism is seriously weakened, and I don't see how this is so different from the observer creating reality as in the OP. So if you reject naive realism, then why isn't your view more or less the same as that in the OP? Here is an argument as to why your view is similar to that in the OP. It is based on an argument that decoherence cannot place the cut entirely objectively. Let's say there are quantum experiments in Texas and Singapore. For the experimenter in Texas, the experiment in Singapore is classical, while the experiment in Texas is classical for the experimenter in Singapore. If decoherence places the cut objectively for the experimenter in Texas, then the cut will be wrong for the experimenter in Singapore. So it seems that decoherence cannot place the cut totally objectively. If the observer is still needed to place the cut, and naive reality is rejected, then it would seem that the observer does create reality.
 
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  • #49
bhobba said:
Stevie - you know the answer as well as I do - why you continue to ask it beats me. It requires an additional interpretative assumption, and a number exist eg my assumption an improper mixture is a proper one - but others exist.

Thanks
Bill
I know you know, but I am replying to Strilanc.
 
  • #50
I googled:
"an improper mixture is a proper" mixture
I got 1 result. It is in this forum!
 
  • #51
naima said:
I googled:
"an improper mixture is a proper" mixture
I got 1 result. It is in this forum!

The reduced density matrix obtained after a partial trace over entangled subsystems is what is being referred to as an "improper mixture". So here are some examples of similar discussions, even though they don't use the term "improper mixture".

http://arxiv.org/abs/quant-ph/0312059 p9 "However, note that the formal identification of the reduced density matrix with a mixed-state density matrix is easily misinterpreted as implying that the state of the system can be viewed as mixed too (see also the discussion by d’Espagnat, 1988)."

Similar language is used in the very interesting discussion of http://arxiv.org/abs/quant-ph/9706027 p3 "This argument is often summarized as the statement “the partial trace does not derive state reduction.”

Also discussed in https://www.amazon.com/dp/0198509146/?tag=pfamazon01-20 p82. This one is not free, unfortunately.
 
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  • #52
atyy, do you really believe in MWI? lol .. I Don't even know why you brought that **** metaphysical nonsense here
Bill took all my doubts, all this woo woo is BS, period.

Bill, and about the pilot wave theory ? To me, It's the best theory, and makes sense!
 
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  • #54
Rajkovic said:
atyy, do you really believe in MWI? lol .. I Don't even know why you brought that **** metaphysical nonsense here

Atty believes in Copenhagen which is actually very similar to mine - ignorance ensemble - the difference basically being the view of probability:
http://en.wikipedia.org/wiki/Ensemble_interpretation

You have to understand however mathematically MWI is extremely elegant - when you look at it carefully its not non-sense - but still too weird for me.

Rajkovic said:
Bill took all my doubts, all this woo woo is BS, period.

Glad to be of help.

Rajkovic said:
Bill, and about the pilot wave theory ? To me, It's the best theory, and makes sense!

That's fine - its a valid interpretation. But you may find your view changing as you learn more.

Thanks
Bill
 
  • #55
atyy said:
The reduced density matrix obtained after a partial trace over entangled subsystems is what is being referred to as an "improper mixture". So here are some examples of similar discussions, even though they don't use the term "improper mixture".

I have been reading on this continuously in any available references and figured out that if you don't perform the trace over the other degrees of freedom or over other entangled subsystems you have to measure each subsystem and have many mixed states.. here can one consider many proper mixed states (instead of just one improper mixed state in one subsystem) in different subsystem of the entangled system measured? What is the implication or consequence. What topic does this fall under so I'll just read about the details in the references (so I won't have to ask each detail which I know can piss people). Thank you.

http://arxiv.org/abs/quant-ph/0312059 p9 "However, note that the formal identification of the reduced density matrix with a mixed-state density matrix is easily misinterpreted as implying that the state of the system can be viewed as mixed too (see also the discussion by d’Espagnat, 1988)."

Similar language is used in the very interesting discussion of http://arxiv.org/abs/quant-ph/9706027 p3 "This argument is often summarized as the statement “the partial trace does not derive state reduction.”

Also discussed in https://www.amazon.com/dp/0198509146/?tag=pfamazon01-20 p82. This one is not free, unfortunately.
 
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  • #56
lucas_ said:
I have been reading on this continuously in any available references and figured out that if you don't perform the trace over the other degrees of freedom or over other entangled subsystems you have to measure each subsystem and have many mixed states.. here can one consider many proper mixed states (instead of just one improper mixed state in one subsystem) in different subsystem of the entangled system measured? What is the implication or consequence. What topic does this fall under so I'll just read about the details in the references (so I won't have to ask each detail which I know can piss people). Thank you.

By the way. The following is the exact details of the problems I have. I know already the math of proper mixed state and my most deep impression of it is Bill calling it "sweet in quantum land" (see below). So I figure if you can separately measure each subensemble of entangled system, then you have many separate proper mixed states (because you don't trace out other subsystem bec you measure each too). So would this avoid improper mixed state (where you trace out other subsystem/subensemble) and just treat it as many proper mixed states (by measuring each subsystem) which would make everything also "sweet in quantumland" and there prior to observation. This is my only question and I'd have no further questions for the sake of the OP. Bhobba wrote:

"If you observe a system whose state is already in one those possible outcomes then nothing happens, no collapse - nothing - QM is easy. One way to physically get a mixed state is to randomly present pure states to be observed, the pi representing the probability that state has been selected for observation. Suppose the |bi><bi| are the outcomes of your observation. For such a situation measurement problem solved - the state you observe is what's there prior to observation, nothing collapses or changes, and everything is sweet in quantum land. Such states are called proper mixed states."
 
  • #57
lucas_ said:
By the way. The following is the exact details of the problems I have. I know already the math of proper mixed state and my most deep impression of it is Bill calling it "sweet in quantum land" (see below). So I figure if you can separately measure each subensemble of entangled system, then you have many separate proper mixed states (because you don't trace out other subsystem bec you measure each too). So would this avoid improper mixed state (where you trace out other subsystem/subensemble) and just treat it as many proper mixed states (by measuring each subsystem) which would make everything also "sweet in quantumland" and there prior to observation. This is my only question and I'd have no further questions for the sake of the OP. Bhobba wrote:

"If you observe a system whose state is already in one those possible outcomes then nothing happens, no collapse - nothing - QM is easy. One way to physically get a mixed state is to randomly present pure states to be observed, the pi representing the probability that state has been selected for observation. Suppose the |bi><bi| are the outcomes of your observation. For such a situation measurement problem solved - the state you observe is what's there prior to observation, nothing collapses or changes, and everything is sweet in quantum land. Such states are called proper mixed states."

Is the answer you can't attribute any mixed state to the subsystem independently because it is one entangled system and only a single or isolated subsystem can be measured via the concept of improper mixed state? If yes. Then it answers my question and entangled system is not sweet in quantum land as Bill expressed proper mixture is. Please someone confirm if this is completely true so I can move on. Thank you!
 
  • #58
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  • #59
lucas_ said:
Is the answer you can't attribute any mixed state to the subsystem independently because it is one entangled system and only a single or isolated subsystem can be measured via the concept of improper mixed state? If yes. Then it answers my question and entangled system is not sweet in quantum land as Bill expressed proper mixture is. Please someone confirm if this is completely true so I can move on. Thank you!

After reading 50% of bhobba and atyy old messages. I think I got it. Proper mixed state is classical ignorance. But in the improper (and even proper mixed state if you consider the entire pure state of the system), why is the transition from the entangled pure state to mixed state.. why this outcome. Herein lies the mystery. While you can choose between MWI or bohmians. I think the Tegmark mathematical universe interpretation makes more sense in such we are living inside a system programmed by math. Nuff said. I will finally move on. Thanks bhobba, atyy and others for our weeks of exchanges on the math aspect of it all. Now you can continue focus on the OP questions so he learns more.
 
  • #60
Can someone tell me if this interpretation of MWI is correct?MWI: "Every time you make a choice or imagine anything you create at least two POTENTIAL universes. Once there's outcome all the other POTENTIAL universes cease to exist"

give me a light... in this "theory" , Where are these "universes" (Or hypotheses, whatever) that were created? in Universe's imagination? lol, I can't understand it. MWI would be almost equal to the Multiverse?

I just want to learn it, even tho, I know this isn't correct. at all.
 
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