I Many Worlds Interpretation existence

[PeterDonis]

There is no "claim" by defining absolute simultaneity by synchronized clock readings.

The term "absolute simultaneity" already has a definition--you can't just decide to use your own instead of the standard one.

What really bothers you is that "thing" is at two place. What bothers you is non-locality.

I have said nothing whatever about non-locality in response to you. I'm just responding to your incorrect claims about "absolute simultaneity". You are claiming that, if I start out two synchronized clocks at the same event and then let them separate, spatially separated events where they both read the same proper time provide "absolute simultaneity". That's not correct. (Also see further comment below.)

I am not either going to retract that time is absolutely measured by clock, proper clock. It would be nice if you could stop pretend to contradict what the entire edifice of relativity stands on.

The word "absolutely" is wrong. What "the entire edifice of relativity stands on" is that proper time is measured by clocks. But proper time is not "absolute"--it's just arc length along a timelike worldline. Such an arc length is invariant, yes--it's the same regardless of our choice of coordinates. But "invariant" is not "absolute". It's just "invariant".

It may not be, only an experiment could sort it out.

The prediction of QM is quite clear: the measurements should commute. (Provided that the electrons are not allowed to interact further when they come back together--further interaction would change their joint quantum state.) Given the initial entanglement and no further interaction, the prediction for the measurement results is the same regardless of where in spacetime the measurement events are--they can be spacelike separated, timelike separated, null separated, or even the same event.

A further comment: you seem to think that the proper time of the two electrons once they separate has something to do with determining the measurement results. It doesn't. Electron spin states are stationary, so they don't change with time; that means that, given the initial entanglement, it doesn't matter how much proper time elapses for each electron before a measurement on it is made. The QM prediction for the measurement results remains the same.

 

[vanhees71]

To my mind, as an experimental physicist, every interpretation of quantum theory is as good/bad as every other interpretation as long as it is incapable to predict physical consequences on the basis of which its truthfulness can be proven. All adherents of all interpretations should understand that these interpretations are to a large extent based on personal psychological predispositions. It makes no sense trying to pick other interpretations into pieces (this reminds of religious disputes); a scientific approach means to think of or to provide experimental consequences that might “prove” that one’s own interpretation might be closer to the truth.

Well, there's however one constraint also from a physical (and not philosophical) point of view: An interpretation must not contradict the very model/theory it is claiming to interpret. The assumption of an instantaneous collapse, e.g., contradicts the very foundation relativistic local QFT is built upon and thus should be rejected as a valid interpretation of relativistic QFT (including the very successful Standard Model, how incomplete it indeed might be).

 

[tom.stoer]

That means, I know when using a certain measurement device that every outcome - after selecting the preferred basis - will actually occur (according to MWI). Why do I then always have the "feeling" that the results of an intended measurement are uncertain?

What exactly is uncertain and when?

Before the measurement it is uncertain in which branch "Jestocost" will be in after the measurement. But according to MWI Jestocost is branching as well, so all branches are populated by one Jestocost.

(strange wording; did I get what you are asking for?)

What branches at the end?

All of them.

In a typical Stern-Gerlach-experiment measuring spin w.r.t. z-direction it will look like

$$|s_x = +1\rangle \,\otimes\, |\text{initial pointer}\rangle \,\otimes\, |\text{initial Jestocost}\rangle \,\to\, |s_z = +1\rangle \,\otimes\, |\text{pointer indicating +1}\rangle \,\otimes\, |\text{Jestocost observing +1}\rangle + |s_z = -1\rangle \,\otimes\, |\text{pointer indicating -1}\rangle \,\otimes\, |\text{Jestocost observing -1}\rangle $$

where I neglected several other subsystems like the environment.

What even Everett didn't grasp: There are no means to re-establish Einstein's comfortable and deterministic classical world.

He did!

The overall time evolution is perfectly deterministic (but of course quantum), whereas from the "intra-branch" or frog perspective there is an apparent collaps and an apparent probabilistic evolution.

Unfortunately Everett was not able to discuss with Einstein.

What Everett didn't also understand: You are sitting in some arbitrary branch an think that your thinking within this branch is of any relevance for an overall understanding.

He did!

Every branch will be populated by one Jestocost.

 

[tom.stoer]

Well, there's however one constraint also from a physical (and not philosophical) point of view: An interpretation must not contradict the very model/theory it is claiming to interpret. The assumption of an instantaneous collapse, e.g., contradicts the very foundation relativistic local QFT is built upon and thus should be rejected as a valid interpretation of relativistic QFT (including the very successful Standard Model, how incomplete it indeed might be).

The instantaneous collapse is problematic if and only if you combine it with an ontic interpretation, i.e. that "there is an external reality" and that "in this external reality something really collapses instantaneously".

The collapse is harmless if the collapse is applied to a mathematical representation of your (!) knowledge about the system; then this collapse is nothing else but a reset of your (!) knowledge after performing and observing an experiment. Then the collapse is strictly local; nothing "out there" really collapses b/cr your (!)knowledge is not "out there".

The collapse according to Everett might be problematic if one combines a quantum system with a classical background spacetime. If it's possible to unify quantum system and spacetime into one Hilbert space than this problem goes away (other problems survive, and new problems will enter the stage, e.g. the problem of time evolution in a quantum gravity theory).

 

[Lord Jestocost]

The overall time evolution is perfectly deterministic (but of course quantum), whereas from the "intra-branch" or frog perspective there is an apparent collaps and an apparent probabilistic evolution.

Every branch will be populated by one Jestocost.

Thus, all my current thinking results always from my current "intra-branch" or frog perspective. Or does my mind not belong to the deterministically evolving world Everett has in mind.

 

[tom.stoer]

Thus, all my current thinking results always from my current "intra-branch" or frog perspective. Or does my mind not belong to the deterministically evolving world Everett has in mind.

What is "your mind"?

In the sense of microscopic (quantum) objects and processes it (your mind) undergoes a branching as well, therefore it (your mind) always has this frog perspective as well. In the sense of some "non-physical entity" quantum mechanics can't tell you anything about your mind.

 

[AlexCaledin]

... In the sense of some "non-physical entity" quanten mechanics can't tell you anything about your mind.

- but Feynman tells/hints (in the "Lectures") that the physicist's mind (whatever it may be) is a little part(icipant) of Nature's growing knowledge/choice.

 

[Lord Jestocost]

The overall time evolution is perfectly deterministic (but of course quantum), whereas from the "intra-branch" or frog perspective there is an apparent collaps and an apparent probabilistic evolution.

Let's try it again (as German is my mother language, it's really difficult to express my thoughts in English):

The overall time evolution is perfectly deterministic and that must apply to me, as a conscious observer, too (I assume that a conscious observer is part of the world Everett has in mind, so the conscious observer cannot simply jump out of it). So, why should there be - from my "intra-branch" or frog perspective - an apparent collaps and an apparent probabilistic evolution? To my mind, here seems to be a severe logical inconsistency.

 

[PeterDonis]

The overall time evolution is perfectly deterministic and that must apply to me, as a conscious observer, too

You're misstating this. A correct statement is: The overall time evolution is perfectly deterministic and that must apply to the physical process that underlie the existence of me, as a conscious observer, too. But according to the MWI, the mapping between the physical process--the unitary evolution of the wave function--and you, the conscious observer--the actual experience you have of observing a particular measurement result--is not one-to-one. You are implicitly assuming that it is, and that assumption is incompatible with the MWI. According to the MWI, one unitary evolution can correspond to many "conscious observers" in the sense of particular experiences of particular measurement results.

 

[tom.stoer]

why should there be - from my "intra-branch" or frog perspective - an apparent collaps and an apparent probabilistic evolution? To my mind, here seems to be a severe logical inconsistency.

The (your) perspective before the measurement is

$$|s_x = +1\rangle \,\otimes\, |\text{initial pointer}\rangle \,\otimes\, |\text{initial Jestocost}\rangle $$

whereas after the measurement there are two mutually invisible "intra-branch" perspectives; one of these (yours) perspectives reads

$$|s_z = +1\rangle \,\otimes\, |\text{pointer indicating +1}\rangle \,\otimes\, |\text{Jestocost observing +1}\rangle $$

So for "Jestocost observing +1" it seems as if the original state has collapsed to one component in which "+1" is realized.

"Mutually invisible" means that this branch structure which appears due to decoherence remains stable w.r.t. time evolution and - of course - mutually orthogonal such that no interference can occurre anymore.

 

[AlexCaledin]

... the physical process that underlies the existence of me, as a conscious observer...

- that's not necessary so; it may well be this way: The (whole) conscious existence is the Process that is using the physics as the organizer for events.

 

[Lord Jestocost]

You're misstating this. A correct statement is: The overall time evolution is perfectly deterministic and that must apply to the physical process that underlie the existence of me, as a conscious observer, too. But according to the MWI, the mapping between the physical process--the unitary evolution of the wave function--and you, the conscious observer--the actual experience you have of observing a particular measurement result--is not one-to-one. You are implicitly assuming that it is, and that assumption is incompatible with the MWI. According to the MWI, one unitary evolution can correspond to many "conscious observers" in the sense of particular experiences of particular measurement results.

I understand what you are saying, that's not the point. Again, what is MWI good for – from the viewpoint of an experimental physicist; there is no hint in all comments which might indicate that MWI might be closer to the truth than any other interpretation. Instead of “collapse” I hear now a lot about some “explosive increases” of world branches. Is there any idea to prove something? Sorry, with your permission: When I say that “consciousness creates reality”, I am at the same level of trueness.

 

[Boing3000]

The term "absolute simultaneity" already has a definition--you can't just decide to use your own instead of the standard one.

And what is the definition of absolute time ?

The word "absolutely" is wrong. What "the entire edifice of relativity stands on" is that proper time is measured by (proper) clocks. But proper time is not "absolute"--it's just arc length along a timelike worldline. Such an arc length is invariant, yes--it's the same regardless of our choice of coordinates. But "invariant" is not "absolute". It's just "invariant".

Now you are just re-arranging words. Invariant means absolute, because everybody agree with such a quantity.

The prediction of QM is quite clear: the measurements should commute. (Provided that the electrons are not allowed to interact further when they come back together--further interaction would change their joint quantum state.) Given the initial entanglement and no further interaction, the prediction for the measurement results is the same regardless of where in spacetime the measurement events are--they can be spacelike separated, timelike separated, null separated, or even the same event.

I was also under that impression. But the detector and the electron have space-like trajectories. And Bell didn't prove QM does not care, he proves the correlation is instantaneous. And there is only two "instantaneous" possible, the proper time of detector or the proper time of electrons... and entanglement is not a property of detector (and photon have zero proper time), so I happen to prefer the later possibility.

A further comment: you seem to think that the proper time of the two electrons once they separate has something to do with determining the measurement results. It doesn't. Electron spin states are stationary, so they don't change with time; that means that, given the initial entanglement, it doesn't matter how much proper time elapses for each electron before a measurement on it is made. The QM prediction for the measurement results remains the same.

I know that. I think it MAY be interesting to perform an experiment to see if it's true.
I also think that having entangled state that do evolve with time would also be a quite interesting case. But from what you write, I guess those cannot exist.

I like to args about logic possibility (that's why I like Bell's inequality). Correlation is validated by experiments. Perfect correlation exist only at space-time located event.
But you may also think the wave function is real, and that's where the information is stored "in limbo" waiting for detector to extract it "from there". Like this is also perfectly simulable by computer program. That's possibility one ... we live in a simulation.

The other more occam's like possibility is to probe that. There IS a connection between those spin orientation and space time. It occurs to me a long time ago that you could make the beam (of photon, that's easier) goes trough vast amount of twisted space (black matter, black hole sling shot), and then get them back to the same place (and most probably not parallel). Then the instantaneous correlation is not even the most spooky thing. The spooky thing is the significance of same angle.

Thus modifying your previous statement: "it doesn't matter how much proper time space elapses for each electron(photon) before a measurement on it is made". It is true ? If so how do you decide detector have the "same" angle ? (I wonder if a simple trip to the moon and back (or ricocheting between satellite) would not twisted the photon spin in some way)

 

[Lord Jestocost]

So for "Jestocost observing +1" it seems as if the original state has collapsed to one component in which "+1" is realized.

Why?? Why do I - together with the measuring apparatus and the system itself - not simply remain in a superposition state which evolves according to the appropriate Schroedinger equation in course of time?

 

[tom.stoer]

I understand what you are saying, that's not the point. Again, what is MWI good for – from the viewpoint of an experimental physicist; there is no hint in all comments which might indicate that MWI might be closer to the truth than any other interpretation.

There will never be such a hint.

In the strict sense all interpretations are equivalent from an experimental / phenomenological perspective. That's why they are different interpretations of the same underlying mathematical theory. Otherwise they would be different theories.

So different interpretations provide different explanations of the same mathematical and experimental facts.

 

[tom.stoer]

Why?? Why do I - together with the measuring apparatus and the system itself - not simply remain in a superposition state which evolves according to the appropriate Schroedinger equation in course of time?

You have to be careful what you mean by "I".

Look at the formulas: The overall state including you as a macroscopic quantum system behaves exactly in that way, i.e. according to unitary time evolution. But in addition the measuring device (plus the decoherence effects due to interaction with environment) results in a selection of a preferred basis and emergent stable branches (so-called einselection).

So from the global perspective unitary time evolution according to the Schrödinger equation remains valid, superpositions remain intact, collapse does not occur. From the frog perspective only one branch (out of all branches) remains visible (within one branch) i.e. interference between branches does not occur; from the frog perspective this looks like a collapse which is in accordance with our observations.

This is what Everett et al. try to achieve: unify universal validity of unitary time evolution with an apparent collapse.

 

[PeterDonis]

that's not necessary so; it may well be this way: The (whole) conscious existence is the Process that is using the physics as the organizer for events.

This looks to me like just a different way of describing the same thing using vague ordinary language, not a different way the world could be. I don't see how it affects the main point I was making.

 

[PeterDonis]

the detector and the electron have space-like trajectories.

No, they don't. Their worldlines are timelike.

Bell didn't prove QM does not care, he proves the correlation is instantaneous.

He proved no such thing. I don't know where you are getting your understanding from, but it appears to be flawed. You need to either give references specifically supporting these statements of yours, or stop making them.

having entangled state that do evolve with time would also be a quite interesting case. But from what you write, I guess those cannot exist.

Where did I say that?

Perfect correlation exist only at space-time located event.

What does this even mean?

ow do you decide detector have the "same" angle ?

Um, by recording that angle when you make the measurement, and then comparing the information afterwards?

 

[Lord Jestocost]

No physical process - regardless of how irreversible it ever might be - isn’t able to reduce interference terms to exactly zero. Thus, in principle (and that’s what physics is about) the entire information which an observer possesses at the beginning of the measuring process remains “conserved” in course of the measuring process. No entropy increase can take place and thus, no conversion of a pure state to a mixed state can take place in a physical sense. Thus, if one takes quantum theory seriously in a pure physical sense, there is – so to speak - neither a “splitting” or a “collapse” of information possible.

Therefore, the many worlds interpretation means in effect: We are - in a classical sense - never living in a real reality.

 

[tom.stoer]

Therefore, the many worlds interpretation means in effect: We are - in a classical sense - never living in a real reality.

I think I got your point.

The emergence of stable, non-interfering = mutually invisible "branches" is not exact but an effective, approximate description. Therefore a component where the spin is "+1" but the pointer indicates "-1" can exist with non-zero amplitude but is highly suppressed. That means that decoherence is never perfect.

Yes, I am aware of these topics.

 

[Nugatory]

There is no problem for them sitting next to each other with at a different age. But then measuring the youngest batch before the oldest should lead to different result then the doing it the opposite.

By would you expect that? The two measurements commute.

 

[vanhees71]

The instantaneous collapse is problematic if and only if you combine it with an ontic interpretation, i.e. that "there is an external reality" and that "in this external reality something really collapses instantaneously".

The collapse is harmless if the collapse is applied to a mathematical representation of your (!) knowledge about the system; then this collapse is nothing else but a reset of your (!) knowledge after performing and observing an experiment. Then the collapse is strictly local; nothing "out there" really collapses b/cr your (!)knowledge is not "out there".

The collapse according to Everett might be problematic if one combines a quantum system with a classical background spacetime. If it's possible to unify quantum system and spacetime into one Hilbert space than this problem goes away (other problems survive, and new problems will enter the stage, e.g. the problem of time evolution in a quantum gravity theory).

Indeed, that's why I say I don't need a collapse, but just something that serves the purpose of a collapse FAPP, namely to explain, why I can prepare states of a quantum system at all, and this I can without the instantaneous collapse, just using the local interactions of standard relativistic QFT. In any case usually we consider at most experiments not larger than our lab (that can be pretty big as in the case of the huge detectors at the LHC, but it's a finite-sized setup, and the interactions of the measured particles are local, and nothing is affected instantaneously).

As I also stressed several times, I consider the formal description of QT as epistemic, i.e., as reflecting the (in general "only" probabilistic) knowledge we have about a system due to the applied preparation procedures or observations.

 

[Boing3000]

By would you expect that? The two measurements commute.

I may expect that by probing beyond the QM formalism, that ignore what commutation implies in terms of the laboratory setup.
I have stated the logic many times now. It may give hint as to what goes "behind the curtains" (rule out reality)

Maybe you know the answer to that simple question: how do experimenter align filters angle that are 15km appart ? (I have a rough idea on how they could synchronize their clock)

 

[Elroch]

Regarding the issue of the correlations being "simultaneous", this is not a well-expressed claim since simultaneity is a frame-dependent concept. It could be accurately said that the interesting situation is when there exists a frame in which the observations that provide the Bell statistics are simultaneous, but it is much better (and frame-independent) to say that the observations are at points in space-time which are space-like with respect to each other. It is this that ensures there can be no causal relationship between the events in either direction.

 

[Nugatory]

But the detector and the electron have space-like trajectories.

They do not. Their trajectories are time-like, which is something completely different.

And Bell didn't prove QM does not care, he proves the correlation is instantaneous.

Bell neither proved nor suggested any such thing. The paper is here and it says nothing abut anything being instantaneous. The closest anyone has come to supporting claim of "instantaneous" are experimental results showing that if there is a causal influence involved, the lower bound on its speed is greater than $c$. The qualifying "if" is very important.

here is only two "instantaneous" possible, the proper time of detector or the proper time of electrons... .

You have spoken of "the proper time of" various things such as the detector and the electrons several times now. What exactly do you mean by the proper time "of" something? Proper time is defined as the interval between two events on a timelike curve; any time you speak of any proper time value you are either implicitly or explicitly considering two specific events and a specific path between them. Which two are thinking of when you speak of the proper time "of" electron A? electron B?

And what is the definition of absolute time ?

That will depend on the context, but here it means the value of the time coordinate assigned by a coordinate system that has the property that the difference between time coordinates of two events is equal to the proper time on any path between these two events. Obviously no such coordinate system exists exists except as a Newtonian approximation.

 

[Nugatory]

Maybe you know the answer to that simple question: how do experimenter align filters angle that are 15km apart ?

For any practical experiment, a plumb line at each site is quite adequate. It's worth taking a few minutes to calculate the magnitude of the errors that will be introduced in this way, and compare them with the magnitude of the effect that we're looking for.

 

[Elroch]

Let's be quite clear about this: in the physics which is accepted by the body of the scientific community, there simply is not "absolute simultaneity" any more than there is "simultaneity". The word "instantaneous" rather can only usefully refer to the lack of a causal path in space-time between two events. (This happens to be definitely the case if the two points are simultaneous in any Lorentz frame).

This is true in the simplified special relativistic context and it remains in essence true in the more complex general relativistic context. It is also true that in a general relativistic context each point in space time is associated with three subdomains: the causal past, the causal future and the rest, which we can call "space-like relationships". For any two points in general relativistic space-time, if A is in the causal future of B, B is in the causal past of A and vice versa. If one has a space-like relationship to the other, the same is true of the reversed pair of points.

There is nothing much more you can say in absolute terms about their relationship in space-time without adding something beyond established physics, I believe. For example, if two points have a space-like relationship, it is easily possible to describe a feasible path for a material particle starting at one of those points that crosses a future path from the other point in as brief a proper time as you wish, indeed proper paths from both points can be found!. Eg a path from the Andromeda galaxy and one from Earth that meet with each having a proper time of say 100 years.

This can be achieved (in principle) either by extremely high acceleration or by temporarily entering a very high time dilation region, deep in a strong gravitational field (a convenient black hole, for example). So there is no meaningful definition of simultaneity for two points in space-time with such a space-like relationship: their relationship is highly arbitrary, depending on observer point of view.

To be frank any discussion of general relativity is a distraction for Bell's experiment which has all of its features in a special relativistic context.

 

[LeandroMdO]

They can also be defined in Minkowski space.

Not if you require that violations of Lorentz invariance go to zero as the lattice spacing goes to zero.

 

[Elroch]

The instantaneous collapse is problematic if and only if you combine it with an ontic interpretation, i.e. that "there is an external reality" and that "in this external reality something really collapses instantaneously".

The collapse is harmless if the collapse is applied to a mathematical representation of your (!) knowledge about the system; then this collapse is nothing else but a reset of your (!) knowledge after performing and observing an experiment. Then the collapse is strictly local; nothing "out there" really collapses b/cr your (!)knowledge is not "out there".

The collapse according to Everett might be problematic if one combines a quantum system with a classical background spacetime. If it's possible to unify quantum system and spacetime into one Hilbert space than this problem goes away (other problems survive, and new problems will enter the stage, e.g. the problem of time evolution in a quantum gravity theory).

Indeed. Concerning the "wave function collapse", when, for example, a particle passes through a two slit apparatus, the wave function is a mathematical representation of all of the information we need to make predictions about future behaviour. When the particle gets detected at a point afterwards, I understand the conditional wave function describing its past becomes highly concentrated on two paths through the slits converging at the point of detection. In Feynman's all possible paths interpretation, all possible paths that terminate at the point of detection remain possible, but the contribution of all of those that stray from the two straight lines through the slits cancel out almost perfectly. Similar cancellation leads to the vanishing of the wave function outside of the two lines from the slits as a consequence of conditioning on the detection. The summation (and cancelling) of the contributions of all possible paths is surely central to the many worlds interpretation.

Deep in the mathematics, there is probably some way to make intuitive sense of the fact that we add complex numbers (or higher dimension field values) at the ends of all possible paths to make predictions, but I remain at the level of merely knowing this works. This aspect of reality seems key to MWI.

 

[Demystifier]

Not if you require that violations of Lorentz invariance go to zero as the lattice spacing goes to zero.

Reference please!