Many Worlds Interpretation existence

[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!