Which interpretation is your favourite?

[Schrodinger's Dog]

 

[Dmitry67]

MWI of course

 

[Schrodinger's Dog]

Of course but why?

 

[Dmitry67]

1. It is minimalistic interpretation, it does not require additional assumptions (except may be a weak form of born rule)
2. It is deterministic
3. It is realistic
4. It allows our Universe to start from very simple or null initial conditions at t=0
5. It is compatible with Max Tegmarks MUH
6. It's weirdness is beautiful

 

[Dmitry67]

BTW I don't think superstring and LQG stuff has anything to do with the Interpretations wars. While these theories will unify the gravity with other interactions, I don't expect TOE to resolve any interpretation issues.

I believe in MWI, so QM is *already* complete, and all these collapse things is just invention of the tortles.

 

[Bob_for_short]

1. It is minimalistic interpretation, it does not require additional assumptions (except may be a weak form of born rule)
2. It is deterministic
3. It is realistic
4. It allows our Universe to start from very simple or null initial conditions at t=0
5. It is compatible with Max Tegmarks MUH
6. It's weirdness is beautiful

Shut-up-and-calculate is even simpler.

 

[Dmitry67]

Yes, but it is not an interpretation. Those who claim that they use only 'Shut up and calculate' are not fair enough - they are using the interpretational things (Born rule for example) to map the number they get into what they observe. When they get 0.5498585 as a result they can say only 'I get 0.549885 after my calculations'. When they say 'I get 0.549885 and hence I expect blah blah blah they DO use interpretation, they just don't admit it.

 

[Schrodinger's Dog]

Yes, but it is not an interpretation. Those who claim that they use only 'Shut up and calculate' are not fair enough - they are using the interpretational things (Born rule for example) to map the number they get into what they observe. When they get 0.5498585 as a result they can say only 'I get 0.549885 after my calculations'. When they say 'I get 0.549885 and hence I expect blah blah blah they DO use interpretation, they just don't admit it.

Would you argue with Dirac or Feynman?

 

[Dmitry67]

Many physicists have subscribed to the instrumentalist interpretation of quantum mechanics, a position often equated with eschewing all interpretation. It is summarized by the sentence "Shut up and calculate!". While this slogan is sometimes attributed to Paul Dirac[17] or Richard Feynman, it is in fact due to David Mermin.[18]

http://en.wikipedia.org/wiki/Copenhagen_interpretation

"Shut up and calculate" is just a slogan. It really means 'When we do experiments we can forget about these weird things'. Like Big Bang, which is not a Bang at all...

 

[RUTA]

Relational Blockworld

 

[humanino]

There are many interpretations on the market. They all are interesting and have their own good features. The reason I chose "shut up and calculate" is not that I do not care about interpretations. It is because I consider most important first to be able to calculate on its own, 6 and a half days a week, while not closing one's eye on alternative interpretations on the basis of philosophical prejudice, but only do it on spare time. The vast majority of working physicists is not working on foundations, and they mostly "shut up and calculate". As far as I can tell, I have seen too often, on this very forum, people arguing about such interpretation while not being able to calculate, and I think it is vain.

 

[Bob_for_short]

There are many interpretations on the market.

Is there somewhere a detailed description of each interpretation to learn "officially" or at least sufficiently professionally?

 

[Demystifier]

I usually do not use the word "stupid" on this forum, but this time I cannot resist. What other word to use for a poll in which string theory, M-theory and LQG are proclaimed - interpretations of QM?

 

[tom.stoer]

I usually do not use the word "stupid" on this forum, but this time I cannot resist. What other word to use for a poll in which string theory, M-theory and LQG are proclaimed - interpretations of QM?

I tend to agree.

String / M and LQG are not interpretations of QM. In addition the list of interpretations is both incomplete and not detailed enough. If you read papers and books carefully you will learn that the experts are familiar with QM and philosophy; as such two people preferring the "same" interpretation will mostly differ in the details. Even Feynman was a realist in his normal course of life. He surely believed in the continuous existence of his bedroom during his labor time in the office. But of course Feynman would have never agreed to a realistic interpretation of QM. You will find many more examples ...

So I would suggest to read a book on the subject. e.g.
- Bernard d'Espagnat: On Physics and Philosophy
- Jeffrey Bub: Interpreting the Quantum World

 

[ikkyu]

I Like Transactional Interpretation.
- It explains the whole process of "wave function collapse". Wave function does not magically disappeared after it is collapsed. It canceled out as the transaction is completed.
- Wave function is physically "real" wave.
- It's time symmetric.
- Observer has no special role in collapse of wavefunction. Emitter and Absorber(Observer) of wave function are the same

http://faculty.washington.edu/jcramer/PowerPoint/AAAS_20060621.ppt

 

[Demystifier]

I Like Transactional Interpretation.
- It explains the whole process of "wave function collapse". Wave function does not magically disappeared after it is collapsed. It canceled out as the transaction is completed.
- Wave function is physically "real" wave.
- It's time symmetric.
- Observer has no special role in collapse of wavefunction. Emitter and Absorber(Observer) of wave function are the same

What are emitters and absorbers? Does this interpretation say that there are objects not defined by wave functions? Is Schrodinger equation violated at the places where emitters and absorbers are present?

 

[ikkyu]

What are emitters and absorbers? Does this interpretation say that there are objects not defined by wave functions? Is Schrodinger equation violated at the places where emitters and absorbers are present?

Emitter and Absober are exactly the charged particle that radiate the wave. E.g., electron emits/absorbs a photon during transition to another energy state.

See http://en.wikipedia.org/wiki/Wheeler–Feynman_absorber_theory" . The idea of Transactional Interpretation came from this theory.

 

[Dmitry67]

That theory has the same problem as CI.
Observer, or emitter, or absorber are not well defined and magic

 

[Demystifier]

Emitter and Absober are exactly the charged particle that radiate the wave. E.g., electron emits/absorbs a photon during transition to another energy state.

Can you write down equations that govern the behavior of this particle? Is it the classical equation of motion? Also the question that I have already asked but you didn't answer: Is Schrodinger equation violated at the positions of charged particles? Finally, what about particles without charge?

 

[Demystifier]

That theory has the same problem as CI.
Observer, or emitter, or absorber are not well defined and magic

Good point, but I'm afraid that the problem with the transactional interpretation could be even much worse than the problem with CI.

 

[Dmitry67]

Yes, it is not clear how it works for color charges, for example.

In any case, TI is a collapse interpretation, which saves the realism at cost of assuming actions backward in time.

Regarding the collapse it has the same problems as CI. For example, a mirror or a lense is not considered to be an 'absorber' even photon iteracts with atoms of the glass, while our retina is considered to be an absorber.

 

[PTM19]

To me ensemble interpretation is the way to go as it is the minimal interpretation consistent with all experiments. QM is incomplete and cannot describe individual events only their statistics.

MWI on the other hand is an abomination - the most extreme violation of Ockham's Razor one can imagine and I can't see how it solves anything as there still has to be some kind of a "collapse." Something has to determine which possibility happens to each observer since there is at least one special observer - the one in which my conscious resides - and this special observer is only experiencing one possibility and not the other so there has to be a "collapse" to determine which one it is.

 

[Dmitry67]

1
MWI on the other hand is an abomination - the most extreme violation of Ockham's Razor one can imagine and

2
I can't see how it solves anything as there still has to be some kind of a "collapse."

3
Something has to determine which possibility happens to each observer since there is at least one special observer - the one in which my conscious resides - and this special observer is only experiencing one possibility and not the other so there has to be a "collapse" to determine which one it is.

1 No, it is minimalistic. It had been discussed many times. MWI does not introduce additional postulated hence it is minimalistic

2 Quantum Decoherence

3 How do you know that your consiousness resides in only one branch?

 

[PTM19]

1 No, it is minimalistic. It had been discussed many times. MWI does not introduce additional postulated hence it is minimalistic

2 Quantum Decoherence

3 How do you know that your consiousness resides in only one branch?

1. It postulates existence of immense/infinite number of additional unobservable universes whose number is constantly growing and which are being created out of nothing.

3. Experience, there is always only one possible outcome available to my consciousness.

 

[Astepintime]

There are many interpretations on the market. They all are interesting and have their own good features. The reason I chose "shut up and calculate" is not that I do not care about interpretations. It is because I consider most important first to be able to calculate on its own, 6 and a half days a week, while not closing one's eye on alternative interpretations on the basis of philosophical prejudice, but only do it on spare time. The vast majority of working physicists is not working on foundations, and they mostly "shut up and calculate". As far as I can tell, I have seen too often, on this very forum, people arguing about such interpretation while not being able to calculate, and I think it is vain.

Agree 100%. I am also a fan of "Shut up and Calculate" and if you cannot Calculate then you should Shut Up. In the past I thought that it was quite fun and harmless to debate interpretations but now with so much quantum babble going around I am not so sure any more.

 

[Dmitry67]

1. It postulates existence of immense/infinite number of additional unobservable universes whose number is constantly growing and which are being created out of nothing.

3. Experience, there is always only one possible outcome available to my consciousness.

1. It does not postulate the existence of such universes! This is a very common misconception.

2. So, how does it deny the MWI view? As branches loses an ability to communicate after very short period of time, both "you" in 2 branches are claiming that "there is always only one possible outcome available to my consciousness"

 

[PTM19]

1. It does not postulate the existence of such universes! This is a very common misconception.

2. So, how does it deny the MWI view? As branches loses an ability to communicate after very short period of time, both "you" in 2 branches are claiming that "there is always only one possible outcome available to my consciousness"

1. How does it not postulate them? Maybe not explicitly but that doesn't matter. Compare for example ensemble or Copenhagen interpretation and MWI, observable physics is exactly the same yet one has an immense number of unobservable parallel universes which are constantly being created and the others do not, where does the difference come from if not from postulates of the MWI interpretation?

2. It does not deny it, it shows that it suffers from a certain indeterminism somewhat similar to standard measurement problem. To understand my point you have to realize that there is at least one special conscious observer - in your case it is yourself, in my case it is myself. My consciousness is confined to one branch only making this branch special to me. Even if I assume there are "copies" of me in parallel universes right now (and new ones constantly branch off) those copies are not really me since I can never control them or experience what they do, what's more their history differs from mine. So now the problem is when a measurement occurs what determines which outcome happens in my branch? From my perspective the outcome is indeterministic.

 

[Dmitry67]

1. No, it DOES matter. MWI has *less* axioms then CI because it does not have collapse. Youre right, it creates more "stuff", but exactly the same argument you can use against GR in comparison with a sphere of fixed stars, because GR "postulates"

It postulates existence of immense/infinite number of additional unobservable universes whose number is constantly growing and which are being created out of nothing (c) PMT19

This is exactly what GR predicts (if universe is open) - an infinite number of unobservable Hubble voulmes, and more and more expension!

This is a pure psycological thing: it is very easy to accept the SPACIAL infinity (the existence of infinite number of worlds far away from our) but difficult to accept the same infinity of worlds which are in the same place spacialy but which do not communicate.

2. This is circular. You assume the collapse saying "My consciousness is confined to one branch only making this branch special to me". I don't assume it.

So, there are 2 branches. MWI predicts that both copies are equally conscious, share the same memory and are not aware of each other because of the decoherence. So each copy will say: "Only MY branch is real! But the choice of a branch was RANDOM" This is exactly what MWI predicts and this is exactly what happens. There is no indetermminism at all.

 

[Fredrik]

The difference between ensemble/copenhagen* and the MWI is that the former assumes that QM doesn't tell us what actually happens, while the MWI assumes that QM does tell us what actually happens. That makes it the minimal realist interpretation, because it doesn't contain additional axioms which serve no other purpose than to get rid of the many worlds (like the version of Copenhagen that asserts that there's a mysterious physical process called "wavefunction collapse" that replaces a superposition with an eigenstate).

(I recently questioned the assertion that the MWI requires no additional axioms here, but due to too many distractions I haven't really thought it through yet, so I'm still not sure about this).

Decoherence isn't a problem for the MWI. Quite the opposite. It just singles out the worlds in which a system's environment can contain stable records of the state of the system. A memory about a result of a measurement in a physicist's brain is such a stable record, so only the worlds that are singled out by decoherence theory can contain conscious observers.

*) See this thread for a discussion about those terms.

By the way, I also think the claim that the number of worlds is growing is incorrect. The claim that they're being "created out of nothing" is definitely incorrect.

 

[PTM19]

1. No, it DOES matter. MWI has *less* axioms then CI because it does not have collapse. Youre right, it creates more "stuff", but exactly the same argument you can use against GR in comparison with a sphere of fixed stars, because GR "postulates"

It postulates existence of immense/infinite number of additional unobservable universes whose number is constantly growing and which are being created out of nothing (c) PMT19

This is exactly what GR predicts (if universe is open) - an infinite number of unobservable Hubble voulmes, and more and more expension!

This is a pure psycological thing: it is very easy to accept the SPACIAL infinity (the existence of infinite number of worlds far away from our) but difficult to accept the same infinity of worlds which are in the same place spacialy but which do not communicate.

2. This is circular. You assume the collapse saying "My consciousness is confined to one branch only making this branch special to me". I don't assume it.

So, there are 2 branches. MWI predicts that both copies are equally conscious, share the same memory and are not aware of each other because of the decoherence. So each copy will say: "Only MY branch is real! But the choice of a branch was RANDOM" This is exactly what MWI predicts and this is exactly what happens. There is no indetermminism at all.

1. Your comparison is not valid since GR is the best description of experimental results while MWI doesn't offer any additional predictive power over other interpretations. If some alternative theory existed which gave exactly the same experimental predictions as GR but didn't require singularities or event horizons it would of course be preferable.

2. It is not circular, and I do not assume collapse, if you agree with "I think therefore I am." then it follows from there - you are special due to your consciousness and that there is at least only one such observer.

Or to put in a different way - one can explain anything one wants by postulating parallel universes in which other possibilities take place making distributions normal or explaining otherwise unexplainable phenomena but this is not physics since it has no predictive power and is not falsifiable.

For example why matter dominates? It doesn't! We are just in a universe where it happens to be more abundant but there are other parallel universes where antimatter is more abundant and on average they are equally likely to dominate.

Does it solve the problem? Is such a solution satisfactory to you?

To me it doesn't solve anything since we want to know what made it dominate in *our* universe, we don't care about parallel unobservable universes. The fact that matter dominates here means that there was some process in our universe which lead to it and the problem will only be solved when we understand that process.

Or another example why do particles decay when they do? They decay when a particle in a parallel universe comes through exactly the same location they occupy in our universe! So particle decay is deterministic after all, and there is nothing to worry about.

A similar explanation can be invented for anything you want, is this physics?

 

[PTM19]

1. The difference between ensemble/copenhagen* and the MWI is that the former assumes that QM doesn't tell us what actually happens, while the MWI assumes that QM does tell us what actually happens. That makes it the minimal realist interpretation, because it doesn't contain additional axioms which serve no other purpose than to get rid of the many worlds (like the version of Copenhagen that asserts that there's a mysterious physical process called "wavefunction collapse" that replaces a superposition with an eigenstate).

1. You say "it [is] the minimal realist interpretation, because it doesn't contain additional axioms which serve no other purpose than to get rid of the many worlds" but this is completely backwards, there is no such thing as "many worlds" beyond MWI interpretation. There is no such thing in the rest of physics, it is precisely MWI that postulates "many worlds."

It's as if I developed an interpretation invoking ghost of ancestors and then claimed that all other interpretations require axioms to get rid of ghost of ancestors while mine doesn't so it is clearly minimal.

Ensemble is minimal since it doesn't require one to believe in anything beyond what can be experimentally verified. Instead one has to accept our ignorance - we don't know what exactly happens with single events. But even Copenhagen interpretation with it's mysterious wavefunction collapse is much better then the mysterious multiverse for which there is no justification whatsoever. I'd rather have one mysterious process then the whole mysterious multiverse.

To me MWI looks like nothing more then an elaborate rationalization invented in order to save QM from it's problems. MWI interpretation requires one to take existence of immense number of unobservable parallel universes on nothing but belief, how is that scientific or minimal? Especially when the second interpretation requires no such thing and gives exactly the same predictions? MWI flies in the face of both scientific skepticism and Ockham razor.

2. (I recently questioned the assertion that the MWI requires no additional axioms here, but due to too many distractions I haven't really thought it through yet, so I'm still not sure about this).

3. Decoherence isn't a problem for the MWI. Quite the opposite. It just singles out the worlds in which a system's environment can contain stable records of the state of the system. A memory about a result of a measurement in a physicist's brain is such a stable record, so only the worlds that are singled out by decoherence theory can contain conscious observers.

*) See this thread for a discussion about those terms.

4. By the way, I also think the claim that the number of worlds is growing is incorrect.

5. The claim that they're being "created out of nothing" is definitely incorrect.

2. Thanks for the links I'll have a look at them.

3. Yes, but I'm not sure how it ties to what I said.

4. How can it not grow? Do some universes get erased or merge?

5. We have one universe before measurement and 2 after if it's not created out of nothing then where did the energy and matter come from for one extra universe?

 

[Dmitry67]

PTM19, before I reply, do you accept the Quantum Decoherence or not?
If you do, do you see it as answer to the Measurement problem or not?
(My answer depends on your position)

 

[Dmitry67]

5. We have one universe before measurement and 2 after if it's not created out of nothing then where did the energy and matter come from for one extra universe?

Check the MWI FAQ
Common objections and misconceptions http://en.wikipedia.org/wiki/Many-worlds_interpretation#Common_objections_and_misconceptions

for example:
Conservation of energy is grossly violated if at every instant near-infinite amounts of new matter are generated to create the new universes.
MWI response: Conservation of energy is not violated since the energy of each branch has to be weighted by its probability, according to the standard formula for the conservation of energy in quantum theory. This results in the total energy of the multiverse being conserved.

 

[PTM19]

PTM19, before I reply, do you accept the Quantum Decoherence or not?
If you do, do you see it as answer to the Measurement problem or not?
(My answer depends on your position)

Personally as I said I accept ensemble interpretation and that we don't know what happens in the case of individual events - we can only make predictions about an ensemble.

But I don't see how decoherence can solve the problems of MWI I mentioned if that answers your questions.

 

[PTM19]

Check the MWI FAQ
Common objections and misconceptions http://en.wikipedia.org/wiki/Many-worlds_interpretation#Common_objections_and_misconceptions

for example:
Conservation of energy is grossly violated if at every instant near-infinite amounts of new matter are generated to create the new universes.
MWI response: Conservation of energy is not violated since the energy of each branch has to be weighted by its probability, according to the standard formula for the conservation of energy in quantum theory. This results in the total energy of the multiverse being conserved.

But this is a complete redefinition of conservation of energy - we are dealing with macroscopic world and in macroscopic world there is no weighting of energy by probability.

Besides it doesn't even make sense since before measurement there exist n universes (with probability equal to 1) and after measurement there are n+1 universes (with probability equal to 1) so what probability is that supposed to be that we use to weigh energy with?
If MWI is deterministic as it claims how can there be a probability of a branch?

Finally as I said before one can explain anything that way - you can make any quantity you want conserved if you place the right amount in parallel universes - this is not science.

 

[Fredrik]

Ensemble is minimal since it doesn't require one to believe in anything beyond what can be experimentally verified. Instead one has to accept our ignorance - we don't know what exactly happens with single events.

Agreed. Ensemble is at least as simple, but it's an anti-realist interpretation. What I said is that the MWI is the minimal realist interpretation.

1. You say "it [is] the minimal realist interpretation, because it doesn't contain additional axioms which serve no other purpose than to get rid of the many worlds" but this is completely backwards, there is no such thing as "many worlds" beyond MWI interpretation. There is no such thing in the rest of physics, it is precisely MWI that postulates "many worlds."

The MWI is just the assumption that QM, without modifications, tells us what actually happens, and what does QM tell us? It says that a measurement of an observable A changes a pure state \rho=|\psi\rangle\langle\psi| into a mixed state:

\rho\rightarrow \sum_i P_i\rho P_i

If this is a description of what actually happens, we would need an additional axiom in order to give one of the terms a different meaning than the others. (If you want to argue against that claim, please do it in the other thread).

It's as if I developed an interpretation invoking ghost of ancestors and then claimed that all other interpretations require axioms to get rid of ghost of ancestors while mine doesn't so it is clearly minimal.

If you think so, you haven't understood the MWI at all.

But even Copenhagen interpretation with it's mysterious wavefunction collapse is much better then the mysterious multiverse for which there is no justification whatsoever. I'd rather have one mysterious process then the whole mysterious multiverse.

The assumption of realism can't be justified, but once we have made it, we're stuck with many worlds until we introduce another assumption to get rid of them. The worlds don't need justification. Their elimination does.

To me MWI looks like nothing more then an elaborate rationalization invented in order to save QM from it's problems.

The ensemble interpretation doesn't have any problems. To me the MWI looks like what you're more or less forced to accept if you believe that QM tells us what actually happens. I also think that QM looks like the first thing a mathematician would come up with if asked to find out if it's possible to define a theory of physics that assigns non-trivial probabilities to possible results of experiments. It doesn't look like a description of anything, but it might be.

MWI interpretation requires one to take existence of immense number of unobservable parallel universes on nothing but belief, how is that scientific or minimal? Especially when the second interpretation requires no such thing and gives exactly the same predictions? MWI flies in the face of both scientific skepticism and Ockham razor.

QM describes a single physical system. The states of that system are represented by the unit rays of a Hilbert space. The time evolution of that state is represented by a curve in the Hilbert space. That's it. To identify our world in there, you have to decompose the system into subsystems, and then choose bases for the subsystems. How is it more minimal to do that than to not do that?

Compare e.g. to the amount of information required to specify a single natural number. It can be arbitrarily large. But to specify all of them, you just need to say "Step 1: Start with 0. Step 2: Add 1 to what you've got so far. Step 3: Go back to step 2." More is sometimes less.

I would say that Occam favors the MWI over all the other realist interpretations, since the other ones seem to require additional axioms.

4. How can it not grow? Do some universes get erased or merge?

5. We have one universe before measurement and 2 after if it's not created out of nothing then where did the energy and matter come from for one extra universe?

It's the same matter. The worlds are just correlations between subsystems. At any point on the curve that represents the time evolution of the state of the universe, there's infinitely many decompositions into subsystems, and infinitely many bases to choose from. A "split" between classical worlds is just the observation that a short segment of the curve can be described as an interaction between subsystems that makes their states correlated. (I disagree with that FAQ answer about conservation of energy).

 

[PTM19]

Agreed. Ensemble is at least as simple, but it's an anti-realist interpretation. What I said is that the MWI is the minimal realist interpretation.

I don't understand what you mean by anti-realist, ensemble doesn't have anything to say about realism, why do you think it does? Realism is the belief that objective reality exists independent of measurements, is this the realism you are talking about?

For example if someone were to develop a local realist contextual hidden variable theory which does away with c as maximum signal propagation limit (setting some higher limit) such a theory would be perfectly compatible with ensemble interpretation so this interpretation doesn't rule out realism.

The MWI is just the assumption that QM, without modifications, tells us what actually happens, and what does QM tell us? It says that a measurement of an observable A changes a pure state \rho=|\psi\rangle\langle\psi| into a mixed state:

\rho\rightarrow \sum_i P_i\rho P_i

If this is a description of what actually happens, we would need an additional axiom in order to give one of the terms a different meaning than the others. (If you want to argue against that claim, please do it in the other thread).

I don't want to argue about additional axiom, I want to argue that what you state doesn't make much sense as a defense of MWI. Here is what one normally should do - one should make a hypothesis, not assumption, that QM without any additional axioms describes what really happens. Then one performs an experiment and sees that the outcome of an observation is not a mixed state therefore the hypothesis is ruled out. End of story.

You on the other hand assume that QM without any additional axioms describes what really happens and then when it doesn't agree with experiments you argue that it is the experiment which is flawed - but for that you have to postulate parallel unobservable universes.

As you yourself stated in another thread the theory is not just mathematics, what is also needed is interpretation which links mathematics with real world. And it is this part that I object to, it's the interpretation of MWI that postulates additional unobservable universes created every second - this is an extreme violation of Ockham's razor since there is absolutely no reason for all those baroque extensions other then to save the assumption which doesn't lead anywhere anyway.

The fact that there is one less axiom is meaningless, the excessive interpretation far outweighs this questionable benefit. Besides you can always reformulate a theory without an axiom if you are willing to expand interpretation, you can probably even create a theory without any axioms at all just a lot of interpretation if you are desperate, that's why the number of axioms is hardly a measure of anything.

One other important thing is that the approach MWI takes to save the above assumption can be used to save any pseudoscience from contradictory experiments, if you can postulate arbitrary unobservable universes any result can be explained.

The assumption of realism can't be justified, but once we have made it, we're stuck with many worlds until we introduce another assumption to get rid of them. The worlds don't need justification. Their elimination does.

Again, what kind of realism are you talking about? It seems to me that by realism you mean the statement that QM math describes real world but why would you call it "realism"? Or why would anyone find this assumption so important that he would rather introduce unobservable parallel universes in order to save it? Why is this assumption so important to you?

1. To me the MWI looks like what you're more or less forced to accept if you believe that QM tells us what actually happens.
2. I also think that QM looks like the first thing a mathematician would come up with if asked to find out if it's possible to define a theory of physics that assigns non-trivial probabilities to possible results of experiments. It doesn't look like a description of anything, but it might be.

QM describes a single physical system. The states of that system are represented by the unit rays of a Hilbert space. The time evolution of that state is represented by a curve in the Hilbert space. That's it. To identify our world in there, you have to decompose the system into subsystems, and then choose bases for the subsystems. How is it more minimal to do that than to not do that?

Compare e.g. to the amount of information required to specify a single natural number. It can be arbitrarily large. But to specify all of them, you just need to say "Step 1: Start with 0. Step 2: Add 1 to what you've got so far. Step 3: Go back to step 2." More is sometimes less.

3. I would say that Occam favors the MWI over all the other realist interpretations, since the other ones seem to require additional axioms.

1. Yes, but to me the fact that you are forced to accept all the excess of MWI should be a proof that QM does not tell us what actually happens

2. From what you say I understand that you like QM and think it is simple, but that is not enough to make it right. Plenty of nice and simple theories have been ruled out already.

3. I am certain Ockham would disagree, the facts are that there are two interpretations - one requires multitude of unobservable universes while the other doesn't yet both agree with experiments. Ockham's Razor is not about axioms: entia non sunt multiplicanda praeter necessitatem, "entities must not be multiplied beyond necessity," how is MWI not in violation of this principle?

It's the same matter. The worlds are just correlations between subsystems. At any point on the curve that represents the time evolution of the state of the universe, there's infinitely many decompositions into subsystems, and infinitely many bases to choose from. A "split" between classical worlds is just the observation that a short segment of the curve can be described as an interaction between subsystems that makes their states correlated. (I disagree with that FAQ answer about conservation of energy).

Worlds are just correlations? Correlation is a concept which only makes sense when applied to two measures of quantities and it is a measure of quantity itself, how can it be a world how can it have material existence? How for example is an electron a correlation and a correlation between what?

 

[WaveJumper]

PTM19, you are raising some very good points that i totally agree with. However, realism in MWI is not the same as the realism found in our observations. I think MWI is about more or less abstract universes, where determinism is preserved and there is only a weak form of realism implied. By weak realism i refer to the idea that there exists some sort of reality outside of measurements, but we are limited in our ability to fully describe it(though we collectively agree on it). Strong realism(the ability to know what the objects of measurements really are) is incompatible with MWI, imo. I fact, don't think strong realism is compatible with QT as it is today, at all.
While i don't agree with the MWI, i think of it as a mere framework model that solves some of the gnarling problems of QM, without further delving into the details of the universe we appear to live in. But on the whole, i agree with you that it seems too extravangant a solution, kind of like killing a mosquito with a nuclear bomb.

 

[Fredrik]

I don't understand what you mean by anti-realist, ensemble doesn't have anything to say about realism, why do you think it does?

It says that neither pure nor mixed states represent the properties of an individual system. That's as anti-realist as anything can get.

Realism is the belief that objective reality exists independent of measurements, is this the realism you are talking about?

No.

I agree that that kind of realism is consistent with the ensemble interpretation.

Again, what kind of realism are you talking about? It seems to me that by realism you mean the statement that QM math describes real world but why would you call it "realism"?

Yes, that's what I mean. It's the term that Isham used in his QM book. Do you have a better one?

Why is this assumption so important to you?

It isn't. It's just interesting. I used to think QM couldn't possibly be a description of anything, not even a fictional universe, and I used to think that the MWI was an ill-defined mess of inconsistent nonsense. Now that I understand the MWI much better than before, I understand that it's neither an ill-defined mess, nor something that can be ruled out. That makes it interesting.

Here is what one normally should do - one should make a hypothesis, not assumption, that QM without any additional axioms describes what really happens. Then one performs an experiment and sees that the outcome of an observation is not a mixed state therefore the hypothesis is ruled out. End of story.

This doesn't make much sense. QM makes the same predictions about results of experiments regardless of whether it also "tells us what actually happens". That doesn't change because you call it a hypothesis instead of an assumption. And if it had, we wouldn't be talking about an interpretation of QM anymore. We would be talking about a similar but different theory.

You on the other hand assume that QM without any additional axioms describes what really happens

Look, either it does or it doesn't. I'm just exploring the possibility that it does. Why does that bother you so much? I'm not used to seeing such an extreme shut-up-and-calculate attitude.

and then when it doesn't agree with experiments you argue that it is the experiment which is flawed

Huh?! Do you think there are experiments that are inconsistent with the MWI?

As you yourself stated in another thread the theory is not just mathematics, what is also needed is interpretation which links mathematics with real world. And it is this part that I object to, it's the interpretation of MWI that postulates additional unobservable universes created every second

Did you mean "it is not this part that I object to"? That would make more sense. The stuff that links the mathematics to results of experiments is a part of the definition of QM. It's not a part of the "interpretations" of QM, which are attempts to interpret QM as a description of what actually happens.

And no new matter gets created in the MWI. That's just a myth that's being spread by people who have misunderstood it. (It's no better than the "First there was nothing. Then it exploded" misrepresentation of the big bang theory).

- this is an extreme violation of Ockham's razor since there is absolutely no reason for all those baroque extensions other then to save the assumption which doesn't lead anywhere anyway.

I don't think you would be saying these things if you understood the MWI. The mathematical model is very simple.

One other important thing is that the approach MWI takes to save the above assumption can be used to save any pseudoscience from contradictory experiments, if you can postulate arbitrary unobservable universes any result can be explained.

The MWI is that assumption (if we're still talking about "QM tells us what actually happens"), and the claim you're making is completely false. The MWI is just an interpretation of QM, so it has nothing to do with crackpot theories that make predictions that disagree with experiments.

1. Yes, but to me the fact that you are forced to accept all the excess of MWI should be a proof that QM does not tell us what actually happens

It's very clear that it isn't.

2. From what you say I understand that you like QM and think it is simple, but that is not enough to make it right.

If you think that I think that QM needs an interpretation, you must have missed the 20 or so posts where I've been saying that it doesn't. (Which is understandable if you're not a regular reader of the QM forum).

3. I am certain Ockham would disagree, the facts are that there are two interpretations - one requires multitude of unobservable universes while the other doesn't yet both agree with experiments. Ockham's Razor is not about axioms: entia non sunt multiplicanda praeter necessitatem, "entities must not be multiplied beyond necessity," how is MWI not in violation of this principle?

Didn't I explain that already?

Worlds are just correlations? Correlation is a concept which only makes sense when applied to two measures of quantities and it is a measure of quantity itself, how can it be a world how can it have material existence? How for example is an electron a correlation and a correlation between what?

Between the states of the subsystems, or equivalently between the "measured" operator on the system and an "einselected" observable on the environment. For example, between the two spin-z eigenstates of a silver atom and two states of the environment that include physicists that remember getting a specific result.

I should add that this is actually just a way to define the interesting worlds, the ones in which the environment can contain stable records (e.g. memories in a physicist's brain) about results of experiments. A "world" (interesting or not) is defined by a basis for the Hilbert space of the universe. The Hilbert space of the universe is the tensor product of the Hilbert spaces of the subsystems, so to specify a basis for the bigger space is to specify a basis for all of the smaller spaces. Decoherence theory tells us that the interaction between a system and its environment will make the density matrix of the universe almost diagonal in a particular basis. So the interaction selects a basis with a special property. This is called "einselection". There are many more worlds than the einselected ones, but decoherence theory tells us that they won't contain stable records of measurement results, and therefore no conscious observers. (Consciousness involves changing states of memory, and a memory is a stable record of a measurement result).

(There's still a lot I don't know about decoherence theory, so I probably won't be able to explain this much better).

 

[PTM19]

Edit: I didn't see your later edits when I replied.

It says that neither pure nor mixed states represent the properties of an individual system. That's as anti-realist as anything can get.

Ok, I now understand what you mean - with ensemble interpretation QM is anti-realist, in that it doesn't describe reality. Yes, I agree with that, the problem is realism to me has a particular meaning - that the physical reality exist independently from observation, so I took your statements to mean that ensemble interpretation somehow precludes the possibility of such realism.

This is roughly what I mean by realism:
http://en.wikipedia.org/wiki/Philosophical_realism#Realism_in_physics

Look, either it does or it doesn't. I'm just exploring the possibility that it does. Why does that bother you so much? I'm not used to seeing such an extreme shut-up-and-calculate attitude.

It doesn't bother me and I am strongly against shut-up-and-calculate attitude, but my goal here is to show the shortcomings of MWI. The main point was that an assumption which does not agree with experiments unless one introduces outlandish postulates to save it should be considered as ruled out.

Huh?! Do you think there are experiments that are inconsistent with the MWI?

Unless one postulates additional unobservable universes experiments are inconsistent with the assumption that "QM tells us what actually happens." (Edit: As you pointed out we should see mixed states but we don't when we do actual measurements)

As I said above to me this is enough to conclude the assumption is wrong.

Imagine for a moment that someone else say a chemist developed a nice hypothesis with beautiful math which explained most but not all experimental results and which could be modified to explain all but at a cost of spoiling the mathematical picture. What would you say if said chemist postulated existence of additional completely unobservable molecules everywhere so that they can provide what is needed to make the hypothesis agree with all experiments?

Or say a doctor developed a very nice symmetry hypothesis which explained the placement of many organs but when confronted with the fact that some organs are not placed symmetrically instead of modifying the hypothesis he insisted on postulating additional invisible organs which perfectly fulfill the symmetry.

Wouldn't you find such attempts at saving the simplicity and beauty of the math involved ridiculous? How do they differ from the MWI case? But please don't just say that I don't understand MWI without pointing out what is it specifically that makes MWI different from those cases.

Did you mean "it is not this part that I object to"? That would make more sense. The stuff that links the mathematics to results of experiments is part of the theory of QM. It's not a part of the "interpretations" of QM, which are attempts to interpret QM as a description of what actually happens.

I certainly don't see the difference, there is only math and interpretation which attempts to link math to what actually happens. "Results of experiments" is "what actually happens."

And no new matter gets created in the MWI. That's just a myth that's being spread by people who have misunderstood it. (It's no better than the "First there was nothing. Then it exploded" misrepresentation of the big bang theory).
I don't think you would be saying these things I you understood the MWI. The mathematical model is very simple.

How am I to understand it if even proponents of MWI cannot agree what it actually means. The math is not a problem - interpretation is.
From what I've read the usual description is that each measurement creates a new branch one universe separates into two, but you seem to believe all possible universes always exist.

Anyway whether they are created or not it is still true that MWI postulates an immense number of unobservable parallel universes.

The MWI is that assumption (if we're still talking about "QM tells us what actually happens"), and the claim you're making is completely false. The MWI is just an interpretation of QM, so it has nothing to do with crackpot theories that make predictions that disagree with experiments.

It has plenty to do with them in that once you admit claiming unobservable parallel universes as an acceptable explanation for contradictory experimental results you can explain pretty much anything. I've personally seen people argue that heaven and hell are not really different from parallel universes postulated by physics. The problem is that there is some truth to such claims.

It's very clear that it isn't.

Well, to me the fact the assumption "QM tells us what actually happens" forces you to accept all the excess of MWI is more then enough proof it is wrong. Obviously to you it isn't. Fine.

Didn't I explain that already?

You explained that the math is simple and works better in MWI - it doesn't require an additional axiom. Ok, but what I am saying is that it's not the math or the axiom that is problematic it's the interpretation postulating additional universes which violates Ockham's razor principle. I don't think you provided a counterargument to that.

You also stated that ensemble interpretation is at least as simple as MWI, that alone should be enough to agree that Ockham's razor favors ensemble interpretation when one considers the later doesn't require parallel universes.

Between the states of the subsystems, or equivalently between the "measured" operator on the system and an "einselected" observable on the environment. For example, between the two spin-z eigenstates of a silver atom and two states of the environment that include physicists that remember getting a specific result.

I have serious doubts if world can be defined as pure correlations - correlations cannot be fundamental since something else has to exist first for correlations to be possible. To me saying that everything is just correlations is like trying to define natural numbers with just addition without any numbers to begin with, but maybe I am wrong here, I don't have enough time to fully think it through.

 

[Fredrik]

(Edit: As you pointed out we should see mixed states but we don't when we do actual measurements)

No, I said that if QM describes what actually happens, the universe will be in a mixed state after a measurement, and none of the terms can be dismissed without reason. But that doesn't mean that we should see mixed states! "We" are states of well-defined memories, and you only have the memory of measuring spin up in the world where the result was "up". See the stuff at the end of my previous post (added in my last edit), but read this correction first: I shouldn't have said that a basis defines a world. I think I should have said that the worlds are the terms in the density matrix, and that every possible way to express the density matrix in terms of a basis is equally valid. So not only are there infinitely many worlds (terms in the density matrix). There are infinitely many ways to describe the universe as consisting of worlds! (One for each basis).

What that stuff at the end of my previous post means is that the basis that decoherence singles out as "special" is precisely the one that describes the universe as consisting of worlds in which the physicist's brain quickly goes into a well-defined state with a memory of only one measurement result. In the MWI, this is a very significant part of the reason why we can't experience superpositions, but it's not the whole story. I think an experience can be described as the formation of a well-defined memory state, and that would imply that your memory is always in a well-defined state of remembering a specific measurement result in the world where that was the result of the measurement.

Edit: See also this post.

Imagine for a moment that someone else say a chemist...

Or say a doctor...

Irrelevant. The MWI is an interpretation of QM, not a new theory, so it doesn't make any predictions that QM doesn't.

I certainly don't see the difference, there is only math and interpretation which attempts to link math to what actually happens. "Results of experiments" is "what actually happens."

The result of the experiment isn't all that actually happens. What about the actual experiment? Didn't that happen? Didn't something happen to the silver atom as it passed through the inhomogeneous magnetic field of the Stern-Gerlach apparatus?

The difference between the two types of interpretations is huge. The first kind is what turns a mathematical model into a theory. (I define a "theory" as "a set of statements that associates a probability with each possible result of each experiment in some set of experiments". Note that a theory doesn't have to describe any aspect of reality between state preparation and measurement, not even approximately. It just has to make predictions about results of experiments). The second kind of interpretation turns the theory into a (possibly completely incorrect) description of what actually happens. The first kind of interpretation is a part of the definition of QM, but an "interpretation of QM" is always of the second kind.

How am I to understand it if even proponents of MWI cannot agree what it actually means.

I agree that it's difficult. I haven't found a definition of the MWI that really makes sense in any of the articles I've read (admittedly not that many), and I certainly haven't been able to extract one from the MWI proponents here. There's also a lot of really bad information about it on the internet.

Well, to me the fact the assumption "QM tells us what actually happens" forces you to accept all the excess of MWI is more then enough proof it is wrong. Obviously to you it isn't. Fine.

Do you often consider something proved wrong the moment you discover that it has features that rubs your emotions the wrong way?

You also stated that ensemble interpretation is at least as simple as MWI, that alone should be enough to agree that Ockham's razor favors ensemble interpretation when one considers the later doesn't require parallel universes.

I'm undecided on that, since the ensemble interpretation strongly suggests that there's an underlying hidden-variable theory, with variables weird enough to avoid the conclusion of Bell's theorem.

I have serious doubts if world can be defined as pure correlations - correlations cannot be fundamental since something else has to exist first for correlations to be possible. To me saying that everything is just correlations is like trying to define natural numbers with just addition without any numbers to begin with, but maybe I am wrong here, I don't have enough time to fully think it through.

When you have some time to spare, you might want to check out David Mermin's "Ithaca" interpretation. That one is really "correlations without correlata".

http://arxiv.org/abs/quant-ph/9801057
http://arxiv.org/abs/quant-ph/9609013

 

[SW VandeCarr]

Yes, but it is not an interpretation. Those who claim that they use only 'Shut up and calculate' are not fair enough - they are using the interpretational things (Born rule for example) to map the number they get into what they observe. When they get 0.5498585 as a result they can say only 'I get 0.549885 after my calculations'. When they say 'I get 0.549885 and hence I expect blah blah blah they DO use interpretation, they just don't admit it.

Do you need an interpretation to do the science? You do the calculation and get a result. The result agrees with experiments. What else to you need?

 

[Dmitry67]

The result NEVER not agrees with the experiment without an interpretation! There are just 2 different things from 2 different worlds: numbers and physical objects. You need an interpretation to map them (and only MUH-compatible TOE will be interpretation-free, because there will be numbers of both sides)

 

[SW VandeCarr]

The result NEVER not agrees with the experiment without an interpretation! There are just 2 different things from 2 different worlds: numbers and physical objects. You need an interpretation to map them (and only MUH-compatible TOE will be interpretation-free, because there will be numbers of both sides)

QM is science. Interpretations of QM are philosophy (not that there's anything wrong with that). There's a plethora of interpretations out there which indicates we have no idea of what quantum "reality" is. However, you can still do the science and I disagree with the idea that you need to choose an interpretation to design experiments. If you believe MWI is "correct", how does that affect the kinds of questions you ask or the way you design the experiments?

EDIT: Ok, I grant you "shut up and calculate" can be construed to be an interpretation, but it makes no claims about what quantum reality "really" is.

 

[Dunebug7]

Personally as I said I accept ensemble interpretation and that we don't know what happens in the case of individual events - we can only make predictions about an ensemble.

But I don't see how decoherence can solve the problems of MWI I mentioned if that answers your questions.

I find decoherence troubling even in MWI.

It seems a little well you know devoid of being able to be proved. I'm not sure natural law gives a toss about our subjective biases anyway. If a woods falls in the trees and there's no one around to see it what colour is it?

I voted for LQG. Btw but what do I know?

 

[Dunebug7]

QM is science. Interpretations of QM are philosophy (not that there's anything wrong with that). There's a plethora of interpretations out there which indicates we have no idea of what quantum "reality" is. However, you can still do the science and I disagree with the idea that you need to choose an interpretation to design experiments. If you believe MWI is "correct", how does that affect the kinds of question you ask or the way you design the experiment?

That is very true. However Copenhagen interpretation I suppose at least has an experiment or two like Bell's and the two slit even if it is depressingly probabilistic; and tends to throw up more questions than answers. It's all a matter of taste though let's face it.

I suppose you are saying shut up and calculate?

________________

"If a woods falls in the trees and there's no one around to see it what colour is it?"

Well really!

 

[Fredrik]

Dmitry67:

You need to distinguish between the axioms of a theory of physics, which "interpret" the mathematics as predictions about results of experiments, and the kind of "interpretations" discussed in these threads. When we say "quantum mechanics", we're referring to a theory of physics, not to an abstract mathematical model, so the kind of interpretation you're talking about now is already included in the definition of "QM". An "interpretation of QM" is something entirely different.

It's an interpretation on top of the one that we use to make predictions about results of experiments. It's an additional set of axioms about relationships between things in the model and things in the real world, which turns the theory into a "description of what actually happens". The description is either approximately correct or completely incorrect, and there's no way to know which.

Every interpretation has its own answer to the question of whether QM is just an algorithm that tells us how to calculate probabilities of possibilities, or also an approximate description of the real world?. "Shut up and calculate" is the idea that the answer is irrelevant. "The ensemble interpretation" is the idea that the first option is correct. All other interpretations are speculations about how the second option might be correct.

 

[Jonathan Scott]

I think that the transactional interpretation is close, but I've found at least one glitch in it as currently defined, which is that if you have two entangled events with a lightlike separation, then in theory the observation you choose to make on the second one could be determined by the result of the first, making it impossible to complete the transaction until after it has completed. This is fairly easy to fix by adding additional rules, since sub-light-speed communication doesn't require any magic in this case, but I don't think nature should need that extra complexity.

My current preferred interpretation is that quantum waves are deterministic but involve two factors - a the usual structured part which gives rise to spinor and vector factors and the primary characteristics of interactions, which propagates at c, and some additional factor associated with relative phase and entanglement which propagates a transactional part in a space-like way, effectively much faster than c. As what is propagated is purely relative, it doesn't have a direction; it is just a mathematical agreement between the ends.

Yes, this is quite vague, but so is the transactional interpretation.

 

[Dmitry67]

But TI has the same issues with the collapse as CI

 

[disregardthat]

But TI has the same issues with the collapse as CI

What exactly are these issues?