Poll: Interpretations of Quantum Mechanics

[JamesOrland]

I was wondering who/how many people in the forum subscribe to which interpretation, so I decided to make a poll :)

Also anyone is welcome to post content about each interpretation to illuminate people who may not know the difference and/or definition of an interpretation.

 

[JamesOrland]

By the way, to anyone who might not know or might have misconceptions about Many-Worlds, I recommend Max Tegmark's paper and this FAQ.

 

[K^2]

I like Many-Worlds due to its elegance, but it is important to note that all interpretations are equivalent. Id est, actual predictions are exactly the same, and by definition, no experiment can be devised to distinguish between them. So if one interpretation is more convenient than another for a particular problem, there is no reason not to use it. A lot of basic measurement experiments are a lot easier to picture in Copenhagen, while anything to do with entanglement is usually much easier in Many-Worlds.

 

[JamesOrland]

I like Many-Worlds due to its elegance, but it is important to note that all interpretations are equivalent. Id est, actual predictions are exactly the same, and by definition, no experiment can be devised to distinguish between them. So if one interpretation is more convenient than another for a particular problem, there is no reason not to use it. A lot of basic measurement experiments are a lot easier to picture in Copenhagen, while anything to do with entanglement is usually much easier in Many-Worlds.

No, not by definition. I do believe both Hawking and Tegmark have suggested ways to distinguish between the different interpretations, and the fact that no tests have been made is no evidence that they never will (as I mentioned in another thread, one is reminded of Lord Kelvin's statement that the movement of muscles was infinitely beyond science).

That being said, the objective of the poll is to measure who agrees with what inside their heads, regardless of their calculations :)

--EDIT:

Actually, the FAQ that I posted above does mention a possible way to distinguish between Many-Worlds and Copenhagen, in Q37. It is a very interesting theory, I see promise in it.

 

[K^2]

By definition, interpretations are part of the same theory. If there is distinction, they are distinct theories.

Under axioms of Quantum Mechanics, Copenhagen and Many-Worlds are interpretations. Id est, indistinguishable. While experiment could exist that would point towards one or another, it would simultaneously disprove Quantum Mechanics, as violation of one of the axioms is prerequisite for a distinction.

 

[JamesOrland]

By definition, interpretations are part of the same theory. If there is distinction, they are distinct theories.

Under axioms of Quantum Mechanics, Copenhagen and Many-Worlds are interpretations. Id est, indistinguishable. While experiment could exist that would point towards one or another, it would simultaneously disprove Quantum Mechanics, as violation of one of the axioms is prerequisite for a distinction.

Do elaborate on that. Let's take, for instance, the example discussed in Q37 of the FAQ I mentioned, the one about AI. How would it disprove Q.M. at the same time it disproved the Copenhagen interpretation?

 

[Mark M]

By the way, to anyone who might not know or might have misconceptions about Many-Worlds, I recommend Max Tegmark's paper and this FAQ.

I thought I'd also add Hugh Everett's dissertation that introduced MWI:

http://www.pbs.org/wgbh/nova/manyworlds/pdf/dissertation.pdf

It's funny that Quantum Mechanics is taught in terms of CI, but when it comes down to picking a side, you don't see too many people standing by it.

BTW, I went MWI. Also, great poll, thanks for posting this.

 

[K^2]

Do elaborate on that. Let's take, for instance, the example discussed in Q37 of the FAQ I mentioned, the one about AI. How would it disprove Q.M. at the same time it disproved the Copenhagen interpretation?

Look up Quantum Eraser which performs an experiment similar to the one described.

 

[JamesOrland]

Look up Quantum Eraser which performs an experiment similar to the one described.

That's beautiful. And... it does look to me like evidence against collapse postulates, in one way or another.

 

[K^2]

Not exactly. It basically just says that collapse is relevant with respect to some "external observer". Same thing happens in Schrodinger's Cat experiment, after all. Cat's observations are considered irrelevant. This is still self-consistent so long as you consider only one observer. And there are actually some advantages of doing it this way. Decoherence, for example, can play a major role, and then it's actually convenient to distinguish between "true" observer, who read the measurements once decoherence took place, and intermediate observer, such as a measurement device that remained entangled to the measured state.

Point is, yes, it does get messy, and it is a big part of why I prefer MWI, but there is no actual contradiction that breaks Copenhagen. Just a lot of ugliness, which means that any time you rely on Copenhagen, you have to be extra careful with interpretation of results.

 

[Hurkyl]

I did vote for MWI, but I wanted to add two significant caveats:

• The ideas of CI are still useful, but as inspiration for mathematical techniques. Interpreting CI within MWI (rather than as referring to reality directly) does a good job of patching up CI's flaws.
• I expect deBB to turn out to be roughly equivalent to MWI, in a sense similar to how Lorentz Ether Theory is equivalent to Special Relativity.

 

[JamesOrland]

Not exactly. It basically just says that collapse is relevant with respect to some "external observer". Same thing happens in Schrodinger's Cat experiment, after all. Cat's observations are considered irrelevant. This is still self-consistent so long as you consider only one observer. And there are actually some advantages of doing it this way. Decoherence, for example, can play a major role, and then it's actually convenient to distinguish between "true" observer, who read the measurements once decoherence took place, and intermediate observer, such as a measurement device that remained entangled to the measured state.

Point is, yes, it does get messy, and it is a big part of why I prefer MWI, but there is no actual contradiction that breaks Copenhagen. Just a lot of ugliness, which means that any time you rely on Copenhagen, you have to be extra careful with interpretation of results.

I see. But this isn't exactly like the example I mentioned, because in the example I mentioned there is actual reversibility and not just the same irreversible process (release of pairs of entangled photons) repeated under different but related conditions. I am not sure that would make any difference, but intuitively to me it seems it might. Of course, as I myself mention a bit, human intuition isn't a reliable thing, so I talk to people who know more about the subject than I do and who can explain about it.

Whichever use we make, it is my belief that even if all interpretations are truly unprovable and/or indistinguishable, we should try to find the correct one, because matching my inner map with the territory is a terminal value to me (i.e. something I find to be desirable regardless of its practical utility). So even if there are no practical utilities, I strive to make my models of the world as accurate as possible within my limited framework and incomplete knowledge.

 

[Delta Kilo]

Actually, the FAQ that I posted above does mention a possible way to distinguish between Many-Worlds and Copenhagen, in Q37. It is a very interesting theory, I see promise in it.

With all due respect, the answer to Q37 is a collection of epic fails. It will prove nothing.
* Consciousness is not required for collapse in orthodox CI, only the act of measurement.
* Critics will just say AI is not a 'true consciousness' anyway.
* Reducing heat dissipation by itself will not make computations reversible.
* 'Reversible measurement' is oxymoron by definition.
* If the system is in contact with environment, it will not be able to reverse the measurement,
* if the system is isolated, it will not cause world split, just a local entanglement.
etc. etc.

A much better way to go would be to have a good comprehensive model of measurement process that would render collapse postulate totally superfluous. Decoherence certainly goes some way towards this goal.

 

[JamesOrland]

With all due respect, the answer to Q37 is a collection of epic fails. It will prove nothing.
* Consciousness is not required for collapse in orthodox CI, only the act of measurement.
* Critics will just say AI is not a 'true consciousness' anyway.
* Reducing heat dissipation by itself will not make computations reversible.
* 'Reversible measurement' is oxymoron by definition.
* If the system is in contact with environment, it will not be able to reverse the measurement,
* if the system is isolated, it will not cause world split, just a local entanglement.
etc. etc.

A much better way to go would be to have a good comprehensive model of measurement process that would render collapse postulate totally superfluous. Decoherence certainly goes some way towards this goal.

Oh, I don't think the argument was based on the consciousness fact per se, just a reversible machine.

From what I understood, the experiment measures the data with a machine that simply holds it in a single bit, and then erases that bit regardless of what it was, effectively destroying any information of the measurement having been made, after it was made. According to a collapse postulate that doesn't need a conscious observer, once the measurement had been made the wavefunction should've been collapsed, regardless of anything else, just because there was a bit in a classical machine that changed from 0 to 1 because of the measurement.

Unless I misunderstood the experiment or the mathematics or I'm just being a victim of Confirmation Bias :P

 

[Delta Kilo]

Oh, I don't think the argument was based on the consciousness fact per se, just a reversible machine.

Well, why then do they talk about AI and a computer comparable in complexity to human brain? Ah, never mind.

From what I understood, the experiment measures the data with a machine that simply holds it in a single bit, and then erases that bit regardless of what it was, effectively destroying any information of the measurement having been made, after it was made.

Well, they say:

The machine now reverses the entire x-axis measurement - which must be possible, since physics is effectively reversible, if we can describe the measuring process physically - including reversibly erasing its memory of the second measurement.

Well, that's just not going to work. In CI it is simply not possible period. In MWI it depends on how far the interactions are allowed to spread. If the interaction is confined to a small part of the system (eg. a single bit), it might be possible to reverse it but it wouldn't be a measurement, just an entanglement (the bit in memory will be in superposition). If the decoherence spreads to the whole system but not to its environment (system is isolated), then the system will not be able to undo the measurement and it might detect that the collapse has in fact happened. However, from the point of view of outside observer there will be two copies of the system in superposition. Now, depending on how this outside observer interacts with the system, with lots of of luck it might be able to detect this.
And finally, if the decoherence is allowed to escape into the environment, that's it, there will be two copies of the observer, each one seeing the apparent collapse happening.

 

[moogull]

I like Many-Worlds, and this goes back to when I was in sixth grade I held this belief. After seeing the movie the Time Machine, I had a little theory that there were actually different realities all happening at the same time that we couldn't see, only our own. I also thought that these realities were not at the same time, which was different from Many-Worlds, but it allowed for time travel by jumping between these alternate realities at different times.

 

[JamesOrland]

Well, that's just not going to work. In CI it is simply not possible period. In MWI it depends on how far the interactions are allowed to spread. If the interaction is confined to a small part of the system (eg. a single bit), it might be possible to reverse it but it wouldn't be a measurement, just an entanglement (the bit in memory will be in superposition). If the decoherence spreads to the whole system but not to its environment (system is isolated), then the system will not be able to undo the measurement and it might detect that the collapse has in fact happened. However, from the point of view of outside observer there will be two copies of the system in superposition. Now, depending on how this outside observer interacts with the system, with lots of of luck it might be able to detect this.
And finally, if the decoherence is allowed to escape into the environment, that's it, there will be two copies of the observer, each one seeing the apparent collapse happening.

That actually makes a lot of sense. Thanks for explaining it to me :)

I like Many-Worlds, and this goes back to when I was in sixth grade I held this belief. After seeing the movie the Time Machine, I had a little theory that there were actually different realities all happening at the same time that we couldn't see, only our own. I also thought that these realities were not at the same time, which was different from Many-Worlds, but it allowed for time travel by jumping between these alternate realities at different times.

I recommend you read this. Do it with a grain of salt, of course, as you should with everything you read (don't believe everything you're told, that is).

---

On another topic, I was wondering to which interpretation the people who voted for 'Other' subscribe :P

 

[moogull]

I recommend you read this. Do it with a grain of salt, of course, as you should with everything you read (don't believe everything you're told, that is).

Thanks!

 

[billschnieder]

Statistical Interpretation (Ballentine): http://www.kevinaylward.co.uk/qm/ballentine_ensemble_interpretation_1970.pdf

 

[DrChinese]

Don't forget the time symmetric group of interpretations, which I think are very important:

New Insights on Time-Symmetry in Quantum Mechanics
Yakir Aharonov, Jeff Tollaksen
http://arxiv.org/abs/0706.1232

Relational Blockworld: A Path Integral Based Interpretation of Quantum Field Theory
W.M. Stuckey, Michael Silberstein, Timothy McDevitt
http://arxiv.org/abs/0908.4348

Generalized absorber theory and the Einstein-Podolsky-Rosen paradox
John G. Cramer
http://www.npl.washington.edu/npl/int_rep/gat_80/

Interestingly, these are all local; of course they are also contextual and do not claim realism in any meaningful sense.

 

[StevieTNZ]

The Copenhagen Interpretation is in conflict with QM. Anyone who reads Ghirardi's thought experiment will realize this.

 

[Hurkyl]

The Copenhagen Interpretation is in conflict with QM. Anyone who reads Ghirardi's thought experiment will realize this.

The only reference I can find is your own thread on the topic, which isn't especially clear. Are you just talking about something like a delayed choice quantum eraser?

 

[lugita15]

I expect deBB to turn out to be roughly equivalent to MWI, in a sense similar to how Lorentz Ether Theory is equivalent to Special Relativity.

Yes, I think Demystifier said that Bohmian mechanics is just MWI with an extra variables, describing which world is the "actual" world.

 

[JamesOrland]

On the topic about Many Worlds, Demystifier posted this, and I think it's a very interesting read indeed. It explains Many Worlds (or, at least, why collapse is unnecessary - and IMHO why Occam's Razor rules it out), and also points out its greatest flaw, which I personally think is a necessary sobering up point for us to avoid Confirmation Bias and to try to think a little bit about the subject without just buying into it.

 

[Hurkyl]

points out its greatest flaw,

You mean the argument that starts with

(i.e., weighting each distinct observer equally)​

Honestly, I think that's a serious mistake of analysis, not a flaw of MWI.

But going along with it for the sake of argument... if that's the greatest flaw, then that already puts MWI on better footing in regards to probability than any other interpretation of any physical theory I'm aware of, so it's sort of misleading to call it a flaw of MWI.

 

[JamesOrland]

You mean the argument that starts with

(i.e., weighting each distinct observer equally)​

Honestly, I think that's a serious mistake of analysis, not a flaw of MWI.

But going along with it for the sake of argument... if that's the greatest flaw, then that already puts MWI on better footing in regards to probability than any other interpretation of any physical theory I'm aware of, so it's sort of misleading to call it a flaw of MWI.

I am actually talking about the fact that the Born rule has to be derived from the formulae, since we decided to remove anything ad hoc from Q.M. in order to build that interpretation.

However, since most interpretations have to deal with the exact same problem (except for C.I. which seems to not care about using ad hoc tools), I guess it's not really exclusive to MWI.

 

[euquila]

I really dislike the many worlds interpretation. Edit: but if I had to choose one it would say that the wavefunctions mathematically/"indirectly" represents something real, not deterministic, no observer role, non local.

Personally I think the most relevant philosophical question is whether or not nature is deterministic. My hunch is that it is fundamentally not as there is always an imbalance in symmetry breaking (ex: matter vs antimatter). However, why this would be so I cannot say and call it "God"/spirituality.

 

[czelaya]

This recently came up while I was lecturing in class.

A student began asking about the double slit experiment, and it didn't take long before all these interpretations came up. Within a few minutes the discussion started migrating to the many worlds interpretation, and this is when I started observing some students rolling their eyes.

Overall the class was enjoying the discussion but, of course, we needed to finish the lecture. I ended up telling the students that no one mentioned the "shut up and calculate" interpretation.

 

[Dale]

actual predictions are exactly the same, and by definition, no experiment can be devised to distinguish between them. So if one interpretation is more convenient than another for a particular problem, there is no reason not to use it.

Well said.

 

[JamesOrland]

I really dislike the many worlds interpretation.

Why?

but if I had to choose one it would say that the wavefunctions mathematically/"indirectly" represents something real, not deterministic, no observer role, non local.

That's not really possible, because the wavefunction is deterministic, everything about it is deterministic. And local. Trying to find an interpretation that mentions wavefunctions as not deterministic is like trying to find a set of laws of physics where gravity repels.

Personally I think the most relevant philosophical question is whether or not nature is deterministic. My hunch is that it is fundamentally not as there is always an imbalance in symmetry breaking (ex: matter vs antimatter).

What experiments have been telling us since the dawn of Science is that Nature is deterministic. The only exception to that ever observed was the wavefunction collapse, which more and more people agree is simply unphysical. Other than that, everything else ever observed was deterministic. That is tremendous evidence for the possibility that Nature is, in fact, deterministic, and most TOE-candidates do have that property. So you would need a lot of evidence to even start considering that possibility.

As for symmetry breaking, I cannot explain it to you, because physics cannot explain it yet, to the best of my knowledge. Maybe the quantum theory of gravity will magically explain that as well :P

However, why this would be so I cannot say and call it "God"/spirituality.

Yeah... let's not go there :P

--EDIT:

I wish all those people who voted for 'Other' explained which one it was :P

 

[euquila]

Why?

Because I means that in some worlds I'm gouging my own eyes out or committing heinous acts because the brain is based on quantum decisions and this whole concept seems absurd.

That's not really possible, because the wavefunction is deterministic, everything about it is deterministic. And local. Trying to find an interpretation that mentions wavefunctions as not deterministic is like trying to find a set of laws of physics where gravity repels.

What about entanglement? This is not local, but I believe a wavefunction encompasses the two objects and the collapse affects the object that was not first subjected to decoherence. I say it is real because I believe that the wavefunction is a mathematical description of some underlying spacetime "trick" (ie: hidden variables). I say not deterministic because I believe that the observer could not possibly gather enough information to know the exact outcome (which I suppose makes it deterministic in the sense that if you *could* trace back Nature to the beginning and gather all the information about all the broken symmetries but alas I believe nature regresses infinitely/no beginning). Perhaps I got my semantics wrong but this is how I understand determinism.

What experiments have been telling us since the dawn of Science is that Nature is deterministic.

This does not seem to be the case with human thought or how nature decided matter of antimatter. Again, asymmetry (I believe) traces back infinitely and this inherent chaos is diffuse in all matter/energy in our universe.

Maybe the quantum theory of gravity will magically explain that as well :P

Yea I don't believe quantum gravity is the correct approach. Our lack of understanding of spacetime and mass is the bane of our enlightenment of gravity. We do not even know why particles have the masses they do. A better mathematical description (ie string theory or alike) is required to get the crux of gravity. Personally, I think gravity will make sense when we better understand matter/mass.

Yeah... let's not go there :P

But science without religion is lame haha

 

[JamesOrland]

Because I means that in some worlds I'm gouging my own eyes out or committing heinous acts because the brain is based on quantum decisions and this whole concept seems absurd.

So... no scientific objections, just human feelings?

What about entanglement? This is not local, but I believe a wavefunction encompasses the two objects and the collapse affects the object that was not first subjected to decoherence. I say it is real because I believe that the wavefunction is a mathematical description of some underlying spacetime "trick" (ie: hidden variables). I say not deterministic because I believe that the observer could not possibly gather enough information to know the exact outcome (which I suppose makes it deterministic in the sense that if you *could* trace back Nature to the beginning and gather all the information about all the broken symmetries but alas I believe nature regresses infinitely/no beginning). Perhaps I got my semantics wrong but this is how I understand determinism.

Determinism means strict causality, that is, everything has a cause. There is nothing random, physics determines all the possible outcomes of actions. In Einstein's words, god does not play dice.

Enganglement is local, it just lacks counterfactual definiteness, according to most non-collapse interpretations.

Bell proved that no local hidden variables theory can explain all the results of Q.M. through his inequalities. And most physicists agree that anything non-local is unphysical, because that would violate causality in some inertial systems, which directly breaks Special Relativity, that has been thoroughly proved.

Also, there is a huge amount of evidence against time having existed forever, at least in this Universe.

So, the basic question of a rationalist: what do you think you know and how do you think you know it? Or put differently, why do you believe what you believe?

Yea I don't believe quantum gravity is the correct approach. Our lack of understanding of spacetime and mass is the bane of our enlightenment of gravity. We do not even know why particles have the masses they do. A better mathematical description (ie string theory or alike) is required to get the crux of gravity. Personally, I think gravity will make sense when we better understand matter/mass.

Umm... Are you talking about Loop Quantum Gravity? Because String Theory is a quantum description of gravity.

Also, we do quite understand matter and mass. Or at the very least, our models seem to be backed up by a significant amount of evidence; maybe not as much evidence as Special Relativity, but still a lot.

And spacetime is also well understood, most of the time, General Relativity seems to be pretty good. The only problems with spacetime (and with gravity) arise when we get down to those teeny tiny sizes. Which is why I say we need a quantum theory for gravity.

But science without religion is lame haha

As I said, let's not go there :P

 

[euquila]

Determinism means strict causality, that is, everything has a cause.

Hmm, then I think I'm on the fence. I believe that Nature/reality does not "play dice", but I think that *inside* our universe that there are systems whose states cannot ever be exactly known (and this would seem non deterministic unless you where some superbeing that existed outside the universe). I do think there are secrets to consciousness that would transcend the boundaries of the universe... but this is going into territory unsuitable in a science forum :)

Enganglement is local, it just lacks counterfactual definiteness, according to most non-collapse interpretations.

But what I think is that when you prepare a pair of entabled objects, you inadvertently prepared a third "spacetimey"-type object that embodies them and it does supersede the speed of light limit. That's just my own opinion however.

Umm... Are you talking about Loop Quantum Gravity? Because String Theory is a quantum description of gravity.

Your talking to a guy who does not believe in gravitons nor higgs bosons btw. And string theory proposes gravitons but does not necessitate them. Also, when I talk about spacetime, my semantics is about an object that has more than 4 dimensions (ie compact dimensions). My view of spacetime is a very dynamic one and particles are the result of "properties" of a region of this spacetime (like oscillations/energy).

 

[Mark M]

Umm... Are you talking about Loop Quantum Gravity? Because String Theory is a quantum description of gravity.

I just want to correct this - String Theory is not primarily a quantum theory of gravity, but John Schwarz showed that it does predict the graviton, and hence solves the problem of quantum gravity. But, it doesn't have an in depth explanation of QG, like LQG, because string theory is a theory of everything, not a QG theory.

My view of spacetime is a very dynamic one and particles are the result of "properties" of a region of this spacetime (like oscillations/energy).

And your basis is...?

BTW, I wonder what the people who voted 'Other' had in mind, considering it's winning.

 

[JamesOrland]

Hmm, then I think I'm on the fence. I believe that Nature/reality does not "play dice", but I think that *inside* our universe that there are systems whose states cannot ever be exactly known (and this would seem non deterministic unless you where some superbeing that existed outside the universe).

Oh, of course, all quantum systems by definition have properties that cannot be known under certain specific conditions, just take a good look at the HUP. When we say that it is deterministic we do mean in the "bird perspective," which is the "outside view" that a superbeing, as you mentioned, might have.

But what I think is that when you prepare a pair of entabled objects, you inadvertently prepared a third "spacetimey"-type object that embodies them and it does supersede the speed of light limit. That's just my own opinion however.

Your talking to a guy who does not believe in gravitons nor higgs bosons btw. And string theory proposes gravitons but does not necessitate them. Also, when I talk about spacetime, my semantics is about an object that has more than 4 dimensions (ie compact dimensions). My view of spacetime is a very dynamic one and particles are the result of "properties" of a region of this spacetime (like oscillations/energy).

And you do not believe in gravitons based on... what, exactly?

Besides, a quantum theory of gravity does not need gravitons, per se. The meaning of the phrase 'quantum theory of gravity' is a theory that can explain gravity at the scale where quantum effects come into play.

I just want to correct this - String Theory is not primarily a quantum theory of gravity, but John Schwarz showed that it does predict the graviton, and hence solves the problem of quantum gravity. But, it doesn't have an in depth explanation of QG, like LQG, because string theory is a theory of everything, not a QG theory.

Yes, that is right, thank you for correcting me :)