Double slit experiment and Interaction

In summary: No, a system is classical when it is able to be described by classical physics. This means that the system is subject to the laws of classical physics, which means that it can be described by things like waveforms and probabilities.
  • #1
Rajkovic
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"An interaction is required to manifest physical reality because it creates distinctions."
my friend referring to the double-slit experiment, is it true?
He said that the physical world, in order to exist, we need to interact (with our senses) lol
 
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  • #2
Rajkovic said:
"An interaction is required to manifest physical reality because it creates distinctions."
my friend referring to the double-slit experiment, is it true?
He said that the physical world, in order to exist, we need to interact (with our senses) lol
No this is not true. It is a misinterpretation of the Copenhagen Interpretation of Quantum Mechanics and it is basically just silly. Put another way, the moon is there whether anyone is looking at it or not.

The double-slit experiment DOES require an interaction (but not a human) to destroy the wave pattern but that has nothing to do with reality existing.
 
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  • #3
Rajkovic said:
"An interaction is required to manifest physical reality because it creates distinctions."

All this is tied up with interpretations of QM. But I don't know if anyone would express it that way - in fact I can't really say I understand it.

Rajkovic said:
my friend referring to the double-slit experiment, is it true?

No.

Rajkovic said:
He said that the physical world, in order to exist, we need to interact (with our senses) lol

That's tied up with an old idea (conciousness causes collapse) that is a very fringe idea these days. It was introduced for reasons that further research showed wasn't really the issue it was thought. Nowadays there is no reason at all to believe there is not an objective world out there independent of if its being observed or not.

Thanks
Bill
 
  • #4
Rajkovic said:
"An interaction is required to manifest physical reality because it creates distinctions."
my friend referring to the double-slit experiment, is it true?
He said that the physical world, in order to exist, we need to interact (with our senses) lol

The double split experiment gives the same result whether or not there's someone in the room watching.

Decoherence is explained with math, not consciousness. Even in the Copenhagen interpretation, where decoherence and measurement are simplified into just collapse, collapse happens when a quantum system interacts with any classical system. If collapse only occurred when systems were observed by brains, we would be able to tell. The timing of collapse has measurable effects on how things interfere. The double-slit experiment would play out differently based on whether someone was in the room or not.

Does that answer your question?
 
  • #5
Rajkovic said:
He said that the physical world, in order to exist, we need to interact (with our senses) lol
Another way to respond to this kind of inanity is with simple logic: If the existence of the universe were dependent on human consciousness, or ANY consciousness, then it could not exist because for consciousness to form the universe has to be there first.
 
  • #6
Thanks for the answers! Last question, about Quantum Erasers..
there are people that claims that it almost proves that "human knowledge" is required for the experiment .. they say that the electron paths were manipulated in such a way that it removes doubt that human "knowledge/observation" has a role".. Human Knowledge? wtfff
(sorry my ignorance, I just hate mumbo-jumbo)
 
  • #7
Rajkovic said:
there are people that claims that it almost proves that "human knowledge" is required for the experiment .. they say that the electron paths were manipulated in such a way that it removes doubt that human "knowledge/observation" has a role".

Even more wrong than the rest of the mumbo-jumbo. The best execution of a delayed choice erase experiment so far has no human awareness of the paths taken by any of the particles.
 
  • #8
THANKS! It's good to read from REAL physicists.
 
  • #9
Rajkovic said:
THANKS! It's good to read from REAL physicists.

Note that posters may not be physicists. I am not a physicist. I just took a course in university, and read some books.

(It's unfortunate that posters aren't tagged with their expertise like they are in the askscience / askphysics sub-reddits, instead of relying on the physicists to call out errors by the likes of me.)
 
  • #10
Strilanc said:
The double split experiment gives the same result whether or not there's someone in the room watching.

Decoherence is explained with math, not consciousness. Even in the Copenhagen interpretation, where decoherence and measurement are simplified into just collapse, collapse happens when a quantum system interacts with any classical system. If collapse only occurred when systems were observed by brains, we would be able to tell. The timing of collapse has measurable effects on how things interfere. The double-slit experiment would play out differently based on whether someone was in the room or not.

Does that answer your question?
I'm sure there are people in the room while such experiments are done, so I don't quite follow your conclusion... interference results.

What makes a system classical? Isn't in principle all systems quantum?
 
  • #11
StevieTNZ said:
What makes a system classical? Isn't in principle all systems quantum?

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. Even a few stray photons from the CMBR is enough to decohere a dust particle so you can say it has a definite position (yes Stevie I know we have apparent instead of actual collapse issue - which is why I used the word say):
http://www.fisica.ufmg.br/~dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf

Einstein had many debates with Bohr and it's generally believed Bohr won them. The interesting thing is from our vantage they were both wrong - but Bohr's error was quite minor:
http://motls.blogspot.com.au/2011/05/copenhagen-interpretation-of-quantum.html

Also it needs to be said Einstein eventually accepted QM as correct - but in his view incomplete.

To the OP exactly how the classical world emerges is a deep subject books have been written about and is an area of active research:
https://www.amazon.com/dp/3540357734/?tag=pfamazon01-20

I have a copy, and its my bible on such matters. It is highly technical but the bottom line is this. Virtually all the issues have been answered - a couple remain but they are thought to be of the crossing t's and dotting i's variety. But they thought the same thing at the turn of last century and look what happened, So one never really knows.

If you would like to pursue it further at the lay level here is a good book:
https://www.amazon.com/Understanding-Quantum-Mechanics-Roland-Omnès/dp/0691004358

He explains it all as well as touching on some of those dotting i's and crossing t's issues such as the lack of certain key theorems.

Thanks
Bill
 
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  • #12
StevieTNZ,
I've read one of the comments from a guy who did the experiment without being in the room.

"just do the double slit experiment without taking the reading.
first do the regular one without the detectors.
then put detectors that interact like normal detectors, but do not show you anything, do not be inside the room or in any way observe what's inside.
you still get the same results.
Woo disproven!"
 
  • #13
Strilanc said:
Note that posters may not be physicists. I am not a physicist. I just took a course in university, and read some books.

Same here - but I am qualified in applied math so my background is such getting to grips with highly technical texts is made easier - I already know the math - well often anyway.

Thanks
Bill
 
  • #14
Rajkovic said:
I've read one of the comments from a guy who did the experiment without being in the room.

The double slit is often done with photographic plates. You preach quite an absurd position if you believe collapse occurs when the plate is developed, maybe even decades later. It gets even worse if you imagine it recorded to computer memory, millions of copies taken, and one of those copies read centuries later.

Just as an aside collapse isn't really part of QM - but that requires another thread.

Thanks
Bill
 
  • #16
Sorry mate - don't know about that approach.

We do however have quite a few highly knowledgeable physicists that post on this forum so if you do a separate post about it you may get more information.

It does speak about coarse graining which is part of a very modern approach to QM called consistent histories:
http://quantum.phys.cmu.edu/CHS/histories.html

Its interesting because it doesn't even have observations - for them QM is the stochastic theory of histories which are always coarse grained.

Thanks
Bill
 
  • #17
Rajkovic said:
StevieTNZ,
I've read one of the comments from a guy who did the experiment without being in the room.

"just do the double slit experiment without taking the reading.
first do the regular one without the detectors.
then put detectors that interact like normal detectors, but do not show you anything, do not be inside the room or in any way observe what's inside.
you still get the same results.
Woo disproven!"
So here you will see no interference, if I understand correctly. Strictly speaking, all that happens is the system interacts and becomes entangled with the detector, and if you erase the 'which-way' info, you see two interference patterns emerge by doing correlations (much like what happens with the quantum eraser experiment proposed by Scully et al.).
 
  • #18
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. Even a few stray photons from the CMBR is enough to decohere a dust particle so you can say it has a definite position (yes Stevie I know we have apparent instead of actual collapse issue - which is why I used the word say):
http://www.fisica.ufmg.br/~dsoares/cosmos/10/weinberg-einsteinsmistakes.pdf
Glad you have put apparent collapse.

bhobba said:
If you would like to pursue it further at the lay level here is a good book:
https://www.amazon.com/Understanding-Quantum-Mechanics-Roland-Omnès/dp/0691004358
Have Omnes 'Quantum Philosophy' book, which I suspect is similar in material to 'Understanding Quantum Mechanics'.
 
  • #19
Rajkovic said:
Bill,
And what about this "violation of the Garg-Leggett inequality demonstrated by a pair of Anton Zeilinger's students back in 2011: http://adsabs.harvard.edu/abs/2007APS..MARB33005B
The Leggett-Garg inequality rules out certain non-local realistic interpretations of Quantum Mechanics. I don't think, from what I've read, it is suitable for ruling out Bohmian Mechanics.
 
  • #20
Hmmm, I'm not sure I agree exactly with the common sense point of view above, so I would like to give a reference that Rajkovic can read to see why quantum mechanics is sometimes presented in this bizarre way. The Copenhagen interpretation is consistent with common sense - but it is like no other theory of physics before it - and requires an external observer. If we believe the external observer is also governed by laws of physics, then we are challenged to include the observer in the laws of physics, which in the case of quantum mechanics seems to either require presently unobserved hidden variables or many worlds. So there is a measurement problem, which is sometimes presented in a bizarre way to highlight it. An example is given in Zurek's http://arxiv.org/abs/quant-ph/0306072, where the picture on p22 shows Wheeler's evocative depiction of the measurement problem, as the universe observing itself. Zurek is of course perfectly aware of all that decoherence can do, yet in a recent essay http://arxiv.org/abs/1412.5206 he writes, "Quantum Darwinism shows why only such redundantly recorded pointer states are accessible to observers - it can account for perception of 'quantum jumps'. However, full account of collapse involves 'consciousness', and may have go beyond just mathematics or physics." Witten also has very interesting comments on the strange relation between consciousness and quantum mechanics: http://www.preposterousuniverse.com/blog/2015/03/05/the-big-questions/.
 
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  • #21
atyy said:
So there is a measurement problem, which is sometimes presented in a bizarre way to highlight it.

Yes there is a measurement problem - but with our modern knowledge of decoherence it has morphed. Its now, colloquially, why do we get any outcomes at all, or, technically, how does an improper mixture become a proper one (to the OP don't worry about the technical argon - ignore it).

The thing is we have interpretations like Bohmian Mechanics and Many worlds where its trivial and others where its a big mystery and others where its totally bypassed.

I always say the issue with QM is not all this stuff like what causes collapse etc etc. The issue is it doesn't matter what issue worries you we have an interpretation (usually more than one) where its a non-issue. What we don't have is a way to experimentally decide between them. IMHO that's its rock bottom problem that maybe future research will resolve - or maybe not.

Thanks
Bill
 
  • #22
You left me in doubt, for the Universe to exist, it must be interacting with something then? An object must be interacting with "something", and if is not interacting, it ceases to exist?
How do you know that? What is the evidence that the wave really collapses? Some people say that there is no collapse. look: https://www.metabunk.org/threads/debunked-interaction-causes-wave-collapse-in-quantum-mechanics.4479/
 
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  • #23
Daramantus said:
You left me in doubt, for the Universe to exist, it must be interacting with something then?

The universe contains stuff that's constantly interacting - whether it interacts or not with something is irrelevant.

Daramantus said:
An object must be interacting with "something", and if is not interacting, it ceases to exist?

Nope - it's how a classical world emerges. When that interaction is removed strange effects emerge - but ceasing to exist is - well silly.

Daramantus said:
How do you know that? What is the evidence that the wave really collapses? Some people say that there is no collapse. look: https://www.metabunk.org/threads/debunked-interaction-causes-wave-collapse-in-quantum-mechanics.4479/

I think you need to read what was written more carefully and think a bit harder. I already said, for example, collapse isn't really part of QM.

Thanks
Bill
 
  • #24
what type of "strange effects" , can you make it more clear for me?
 
  • #25
Daramantus said:
what type of "strange effects" , can you make it more clear for me?

Liquid Helium close to absolute zero - just one example. From QM its in its lowest energy state and since it can't go lower you get all sorts of funny things eg no friction which would require energy dissipation

Thanks
Bill
 
  • #26
bhobba said:
Yes there is a measurement problem - but with our modern knowledge of decoherence it has morphed. Its now, colloquially, why do we get any outcomes at all, or, technically, how does an improper mixture become a proper one (to the OP don't worry about the technical argon - ignore it).

The thing is we have interpretations like Bohmian Mechanics and Many worlds where its trivial and others where its a big mystery and others where its totally bypassed.

I always say the issue with QM is not all this stuff like what causes collapse etc etc. The issue is it doesn't matter what issue worries you we have an interpretation (usually more than one) where its a non-issue. What we don't have is a way to experimentally decide between them. IMHO that's its rock bottom problem that maybe future research will resolve - or maybe not.

Well, let's say we want to try Bohmian Mechanics or Many Worlds. There is still no Bohmian Mechanics version of the standard model of particle physics, and it is unclear whether Many-Worlds really works, as even proponents like Deustch http://arxiv.org/abs/0712.0149 and Carroll http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/ agree. So I don't think it is true that we have at least one interpretation that solves the definite outcomes problem. That leaves us with Copenhagen which does have the problem, and the only way to solve it is to assert it is not a problem, which I think the consciousness ones do quite nicely :p

Also, Bohmian Mechanics is in principle testable, just as string theory is. Many-Worlds, if in fact the theory of everything, will not be falsified. But if it isn't, then it can be falsified. So the problem with BM or MWI for solving the definite outcomes problem is not experimentally deciding between them.
 
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  • #27
atyy said:
So I don't think it is true that we have at least one interpretation that solves the definite outcomes problem.

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.

Thanks
Bill
 
  • #28
StevieTNZ said:
I'm sure there are people in the room while such experiments are done, so I don't quite follow your conclusion... interference results.

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.

StevieTNZ said:
What makes a system classical? Isn't in principle all systems quantum?

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.
 
  • #29
Strilanc said:
I'm asserting that, if it was the case that only consciousness caused collapse, then the experiments would play out differently

I think this conciousness stuff is a very very big crock of the proverbial, but it must be said a fully coherent interpretation can be built from it - just a very very weird one. We even have people that believe in solipsism despite the fact it leads to just as weird a view. Most people, correctly IMHO, reject such - but it can't be proven incorrect.

Thanks
Bill
 
  • #30
bhobba said:
I think this conciousness stuff is a very very big crock of the proverbial, but it must be said a fully coherent interpretation can be built from it - just a very very weird one. We even have people that believe in solipsism despite the fact it leads to just as weird a view. Most people, correctly IMHO, reject such - but it can't be proven incorrect.

Thanks
Bill

I agree.

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.
 
  • #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
 
<h2>1. What is the double slit experiment?</h2><p>The double slit experiment is a classic experiment in quantum physics that demonstrates the wave-like nature of particles. It involves passing a beam of particles, such as electrons or photons, through two parallel slits and observing the resulting interference pattern on a screen. This experiment has been used to study the behavior of particles at the subatomic level and has led to significant discoveries in the field of quantum mechanics.</p><h2>2. How does the double slit experiment demonstrate wave-particle duality?</h2><p>The double slit experiment shows that particles can exhibit both wave-like and particle-like behaviors. When the particles are sent through the slits, they behave like waves, creating an interference pattern on the screen. However, when observed, they behave like particles, hitting the screen at specific points. This duality is a fundamental concept in quantum mechanics and has been confirmed by numerous experiments.</p><h2>3. What is the role of the observer in the double slit experiment?</h2><p>The role of the observer in the double slit experiment is crucial in determining the behavior of particles. When the particles are not observed, they behave like waves and create an interference pattern. However, when the observer tries to determine which slit the particles pass through, the interference pattern disappears, and the particles behave like particles. This suggests that the act of observation affects the behavior of particles at the quantum level.</p><h2>4. Can the double slit experiment be performed with macroscopic objects?</h2><p>No, the double slit experiment has only been successfully performed with microscopic particles such as electrons and photons. The wave-like behavior of particles becomes more apparent at the quantum level, and macroscopic objects are too large to exhibit this behavior. However, there have been attempts to conduct similar experiments with larger molecules, but the results have been inconclusive.</p><h2>5. How does the double slit experiment relate to the concept of superposition?</h2><p>The double slit experiment is closely related to the concept of superposition, which states that particles can exist in multiple states or positions at the same time. In the experiment, the particles pass through both slits simultaneously, creating an interference pattern. This illustrates the idea that particles can exist in multiple states until observed, at which point they collapse into a single state. Superposition is a fundamental principle in quantum mechanics and is essential for understanding the behavior of particles at the subatomic level.</p>

1. What is the double slit experiment?

The double slit experiment is a classic experiment in quantum physics that demonstrates the wave-like nature of particles. It involves passing a beam of particles, such as electrons or photons, through two parallel slits and observing the resulting interference pattern on a screen. This experiment has been used to study the behavior of particles at the subatomic level and has led to significant discoveries in the field of quantum mechanics.

2. How does the double slit experiment demonstrate wave-particle duality?

The double slit experiment shows that particles can exhibit both wave-like and particle-like behaviors. When the particles are sent through the slits, they behave like waves, creating an interference pattern on the screen. However, when observed, they behave like particles, hitting the screen at specific points. This duality is a fundamental concept in quantum mechanics and has been confirmed by numerous experiments.

3. What is the role of the observer in the double slit experiment?

The role of the observer in the double slit experiment is crucial in determining the behavior of particles. When the particles are not observed, they behave like waves and create an interference pattern. However, when the observer tries to determine which slit the particles pass through, the interference pattern disappears, and the particles behave like particles. This suggests that the act of observation affects the behavior of particles at the quantum level.

4. Can the double slit experiment be performed with macroscopic objects?

No, the double slit experiment has only been successfully performed with microscopic particles such as electrons and photons. The wave-like behavior of particles becomes more apparent at the quantum level, and macroscopic objects are too large to exhibit this behavior. However, there have been attempts to conduct similar experiments with larger molecules, but the results have been inconclusive.

5. How does the double slit experiment relate to the concept of superposition?

The double slit experiment is closely related to the concept of superposition, which states that particles can exist in multiple states or positions at the same time. In the experiment, the particles pass through both slits simultaneously, creating an interference pattern. This illustrates the idea that particles can exist in multiple states until observed, at which point they collapse into a single state. Superposition is a fundamental principle in quantum mechanics and is essential for understanding the behavior of particles at the subatomic level.

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