Many-worlds true quantum event generator

[rodsika]

Hi, what cheap device is available where a quantum choice can be made.. for example.. particle that goes to left or right path or other similar? I'd like to experience what it is like to split myself between going to work or stay at home. According to Many World Interpretation, when I observe the device. A part of me would be entangled with the particle that goes to left, and the other part of me would be on the right particle.. and two worlds will split off and evolve separately...

How do you make or time it such that say the left particle is entangled to my decision to go to office (and actually doing it).. and the other particle (right or other configuration choices) staying at home?

Also in the present of a true quantum event generator.. would there always or automatically be a split in our parts in each of the quantum choice of the devices?

 

[Fyzix]

If some version of MWI were true, you'd be splitting non stop 24/7, so no need to conduct any such experiment if you would like to "experience the splitting"...

However, MWI is very likely not true, atleast not in it's current form so I wouldn't get attached to living like it is.

 

[JesseM]

No. We'd only split if there are quantum device choices available.

It has nothing to do with "devices", all the particles that make up your body and the world around it obey quantum laws, and all possible states for any quantum system must be manifested in the MWI.

 

[rogerl]

It has nothing to do with "devices", all the particles that make up your body and the world around it obey quantum laws, and all possible states for any quantum system must be manifested in the MWI.

Many Worlds appear silly, ain't it. But how come so many physicists believe it. How many percentage of them really believe it? 50%? 80%?

 

[JesseM]

Many Worlds appear silly, ain't it. But how come so many physicists believe it. How many percentage of them really believe it? 50%? 80%?

Why do you call it silly? Just because it's counterintuitive? At a theoretical level it seems more elegant to me, as it says that measuring devices are governed by the same laws as systems being measured, and all systems follow the same quantum laws at all time, but it doesn't require the addition of any new hidden variables as in Bohmian mechanics. Historically theoretical elegance has tended to be a better guide in physics than "common sense" intuitions about what predictions seem weird to us.

 

[rodsika]

It has nothing to do with "devices", all the particles that make up your body and the world around it obey quantum laws, and all possible states for any quantum system must be manifested in the MWI.

Hi, in a typical day, how many worlds does a single human spawn? Hundreds or billions? Also what is the smallest living thing that can create worlds? Bacteria or ants?

 

[ExecNight]

Well MWI suggests for every random event, the universe splits into available options. I think "Random Event" is the key here. Because some things can't be mathematically modeled right now doesn't mean they are random.

Actually i will go as far as saying, almost everything above atomic level can be very well mathematically modeled from the beginning of the universe. Your conciousness is a product of this material world, so considering your actions as random is absurd :)

 

[JesseM]

Hi, in a typical day, how many worlds does a single human spawn? Hundreds or billions? Also what is the smallest living thing that can create worlds? Bacteria or ants?

There aren't really clearly-differentiated "worlds" as I understand it, just a single wavefunction for the entire universe which can be seen (in the same way as any normal quantum wavefunction) as a superposition of different position states, a superposition of different momentum states, etc. How familiar are you with the standard (non-MWI) idea that every quantum system is modeled as having a single state vector which can be expressed as a sum (superposition) of eigenvectors for any observable like position or momentum? The basic idea behind the MWI is that we should use the same rules for the entire universe as the rules we use when modeling the evolution of quantum systems between measurements, that measurement itself shouldn't involve any special new rules like "wavefunction collapse".

 

[JesseM]

Well MWI suggests for every random event, the universe splits into available options. I think "Random Event" is the key here. Because some things can't be mathematically modeled right now doesn't mean they are random.

Actually i will go as far as saying, almost everything above atomic level can be very well mathematically modeled from the beginning of the universe. Your conciousness is a product of this material world, so considering your actions as random is absurd :)

But any chaotic system will exhibit sensitive dependence on initial conditions, which should mean that if you turned history back a bit and made some tiny micro change at the atomic level, then when you played history forward again with the altered initial condition, the new history would eventually start to diverge macroscopically from the original version.

 

[cgk]

Why do you call it silly? Just because it's counterintuitive? At a theoretical level it seems more elegant to me, as it says that measuring devices are governed by the same laws as systems being measured, and all systems follow the same quantum laws at all time,

I was of the impression that almost all interpretations (except maybe for the Kopenhagen one) have these features.

but it doesn't require the addition of any new hidden variables as in Bohmian mechanics.

...you mean apart from the states of all split worlds themselves? Also, I don't think the hidden variables are the problem people care about... (rather the lack theirof). But in Bohmian mechanics they again have a somewhat counterintuitive nature (pilot wave etc) and their violate locality. On the other hand, there is little reason to believe that a quantum theory interpretation should be fully local (think of EPR-type entanglement).

Historically theoretical elegance has tended to be a better guide in physics than "common sense" intuitions about what predictions seem weird to us.

While that is certainly true, I'm somewhat doubtful about MWI being called elegant. It's a far stretch.

I also wonder if really a majority of physicists believe it. If I hear about it, it's usually in the sense of a discussion about a kind of novelty thing (aka ``see, interpretations are so free, we can't even exclude the MWI on a rational basis...'')

 

[ExecNight]

But any chaotic system will exhibit sensitive dependence on initial conditions, which should mean that if you turned history back a bit and made some tiny micro change at the atomic level, then when you played history forward again with the altered initial condition, the new history would eventually start to diverge macroscopically from the original version.

Yes but for the butterfly effect, you first need to send a butterfly back in time. That's not possible, so there goes the chaos theory :)

Every initial condition starts from a single condition in our universe. These initial conditions are one, so every outcome can be mathematically modeled. Including this message you are reading right now.

 

[JesseM]

I was of the impression that almost all interpretations (except maybe for the Kopenhagen one) have these features.

Copenhagen (or 'shut up and calculate', which also involves wavefunction collapse) is the default one that all other interpretations want to argue against, I think. And from what I understand the only alternative interpretations that are mathematically well-defined and taken seriously by a lot of physicists are variants of the MWI (including decoherent histories) or variants of Bohm's interpretation, other alternatives like the transactional interpretation are mostly just conceptual and don't have any clear mathematical definition.

...you mean apart from the states of all split worlds themselves?

Typically a hidden variable is defined as any information about the state of a system beyond what's in the wavefunction, the MWI is understood not to have anything but a single universal wavefunction so it doesn't have hidden variables.

Also, I don't think the hidden variables are the problem people care about... (rather the lack theirof).

But I was talking about theoretical elegance--a theory that doesn't contain extra hidden variables is simpler at a theoretical level than one that doesn't, even if it's more complicated in terms of the number of real-world entities are supposed to exist.

But in Bohmian mechanics they again have a somewhat counterintuitive nature (pilot wave etc) and their violate locality. On the other hand, there is little reason to believe that a quantum theory interpretation should be fully local (think of EPR-type entanglement).

Well, MWI advocates do argue that their interpretation allows locality to be restored, since Bell assumed in his proof that each measurement would have a unique outcome but this is obviously no longer true in the MWI.

While that is certainly true, I'm somewhat doubtful about MWI being called elegant. It's a far stretch.

Again, just at the theoretical level of equations and such, not in terms of predictions about what exists in the world. But as I said history has tended to show that theoretical elegance is a better guide than trying to minimize the number of entities that exist in the real world, for example if you cared about minimizing the number of real-world entities you'd have been led to favor the view that our galaxy was an isolated "island universe" surrounded by empty space over the view that it's just one of a vast number of galaxies (perhaps infinite) whose existence have very little effects on our lives on Earth.

I also wonder if really a majority of physicists believe it. If I hear about it, it's usually in the sense of a discussion about a kind of novelty thing (aka ``see, interpretations are so free, we can't even exclude the MWI on a rational basis...'')

I've often seen physicists express the view that it's the simplest theoretically, but remain agnostic about whether the other terms in the universal superposition really "exist" in exactly the same sense we do (see Stephen Hawking's comments in the last paragraph of the 'Reception' section here for example)

 

[JesseM]

Yes but for the butterfly effect, you first need to send a butterfly back in time. That's not possible, so there goes the chaos theory :)

Every initial condition starts from a single condition in our universe. These initial conditions are one, so every outcome can be mathematically modeled. Including this message you are reading right now.

But QM only allows you to model a wavefunction, which assigns different amplitudes to different position/momentum states in a giant superposition, but doesn't pick one out as the "real" state. And your original comment was about the MWI, was it not? Do you disagree that in the context of the MWI, starting from a system in a specific position state, the future evolution would lead to a superposition of different position states for the particles, and that small early differences in particle positions for different elements of the superposition should later lead (via the butterfly effect) to bigger differences at the macro-scale for different terms in the superposition?

 

[ExecNight]

But QM only allows you to model a wavefunction, which assigns different amplitudes to different position/momentum states in a giant superposition, but doesn't pick one out as the "real" state. And your original comment was about the MWI, was it not? Do you disagree that in the context of the MWI, starting from a system in a specific position state, the future evolution would lead to a superposition of different position states for the particles, and that small early differences in particle positions for different elements of the superposition should later lead (via the butterfly effect) to bigger differences at the macro-scale for different terms in the superposition?

Like i said, everything above atomic level can be mathematically modeled. How is wavefunction relevant here? Yes well, we can't calculate exact positions of particles and so use probabilities.

Also yes, these probabilities create a superposition. And no real state is picked, true. Can you be more specific how does any of this creates a butterfly effect? In the sense of being a random and unexpected event in the mathematical model of the universe.

 

[Demystifier]

At a theoretical level it seems more elegant to me, as it says that measuring devices are governed by the same laws as systems being measured, and all systems follow the same quantum laws at all time, but it doesn't require the addition of any new hidden variables as in Bohmian mechanics. Historically theoretical elegance has tended to be a better guide in physics than "common sense" intuitions about what predictions seem weird to us.

Even though MWI does not require additional variables, it does require additional postulates (and there is no consensus on - which ones) in order to explain/derive the Born rule. So it is not really simpler than Bohmian mechanics.

 

[Dmitry67]

I would rather say, there is no acceptable definition of Born rule in MWI, because Born rule talks about the propabilities while MWI is deterministic.

But there is at least some hope that the 'apparent probability' would somehow 'emerge' from the behavior of the complex (and may be conscious) systems. So there is a hope that QM as we know it is complete already (or course, without gravity/very high energy stuff)

 

[Fyzix]

Dmitry, you know that your consciousness hypothesis has no foundation, so saying that it gives rise to hope that the current MWI is correct, is a little bit misleading.

I can also say that there is hope that there will emerge a completely local and deterministic quantum interpretation that will have no problem with Bells Theorem.
Does this statement give hope to this?

Besides MWI also got problems with relativity (check Jeffrey A Barrett)

 

[Dmitry67]

1. My hope has some foundation. For example, most of the scientific community agree on Block Time, hence there is nothing special in the moment of time called "NOW". The "NOW" phenomenon is not explained by physics, but is moved the the realm of the yet-to be-explained consciousness.

2. When I google
Jeffrey A Barrett mwi relativity
I find this thread and few links to Barrett works
what exactly are you talking about
Could you provide a description of that "problem"?

 

[rodsika]

My interests in the Many World was brought about by this movie I just watched called Source Code. If you still haven't seen it. Go watch it this sunday. It's incredibly good and very poignant. The movie is about Many World Interpretation. A train exploded in the morning. Then hours later, a man consciousness was sent back in time into a parallel Many World to determine the name of the bomb detonator. He did it several times.. visiting different Many World branches in the process. Of course I won't tell you the end to avoid spoiler but if you watch it, it will surely spark you interests in Many World Interpreation and combination with General Relativity as well as Consciousness Reseach. There is a possibility the movie may even be true.. it's because consciousness is still*a mystery. What if consciousness can be sent across Many World branches using some help from GR. That is what the movie is all about. It can happen. Give comment about Many Worlds after after you watch it!

 

[ExecNight]

Your conciousness isn't something magical. Its electrical and chemical reactions to stimuli. Therefore while the stimuli remains the same, it will stay where it is. Plain and simple.

Can anyone please tell me about something in this universe that is purely random and is not a product of the big bang(initial condition).

I can't comprehend this thought process. For examples sake; How come weather activity is random? It is not, its just very complex and too many variables are in effect (Butterfly Effect) it doesn't mean its random.. It just means we can't calculate it.

Now this belongs to the Quantum Forum, as the question is, like i asked before how superposition and wavefunction probability calculations affect the macro world. Do they create randomness? How?

 

[JesseM]

Like i said, everything above atomic level can be mathematically modeled.

And like I said, a chaotic system cannot be precisely predicted without knowledge of the exact state of the "atomic level".

Also yes, these probabilities create a superposition. And no real state is picked, true. Can you be more specific how does any of this creates a butterfly effect? In the sense of being a random and unexpected event in the mathematical model of the universe.

Are we talking in terms of the MWI or not? If we are, do you disagree that if we have a model of, say, weather patterns, then if we run the model twice with slight differences "at the atomic level" the large-scale behavior of the weather patterns will eventually be quite different on the two runs? Do you disagree that in the MWI these slight difference "at the atomic level" would actually be manifested in different terms of the superposition (different 'worlds')?

 

[ExecNight]

And like I said, a chaotic system cannot be precisely predicted without knowledge of the exact state of the "atomic level".

Being unable to predict the system doesn't mean the system is random. It just means we don't have the variables and the means. There is no Chaos :)

Are we talking in terms of the MWI or not? If we are, do you disagree that if we have a model of, say, weather patterns, then if we run the model twice with slight differences "at the atomic level" the large-scale behavior of the weather patterns will eventually be quite different on the two runs? Do you disagree that in the MWI these slight difference "at the atomic level" would actually be manifested in different terms of the superposition (different 'worlds')?

I disagree with MWI because what i am trying to say is, no matter how many times you start the same system with same inital condition. It will always end up giving you the same result. Because i suggest that in this system there are no random events. So while there won't be any difference at all no different world will spawn.

 

[JesseM]

Being unable to predict the system doesn't mean the system is random. It just means we don't have the variables and the means. There is no Chaos :)

Chaos has nothing to do with randomness and I never said it did, so why do you bring it up?

I disagree with MWI because what i am trying to say is, no matter how many times you start the same system with same inital condition. It will always end up giving you the same result.

The MWI is deterministic, but what is evolving deterministically is a wavefunction which includes a superposition of multiple position states. Do you disagree that if we start a quantum system with the same initial conditions multiple times, then the wavefunction will evolve into a superposition of different position states, even if the initial state was a position eigenstate where every particle had a precise position to begin with? Do you disagree that if the system is a chaotic one, then even if the different elements of the superposition had only small "microscopic" differences a short time after the initial state, after a longer time the different elements of the superposition would inevitably start to have sizeable macroscopic differences due to the butterfly effect?

 

[ExecNight]

The MWI is deterministic, but what is evolving deterministically is a wavefunction which includes a superposition of multiple position states. Do you disagree that if we start a quantum system with the same initial conditions multiple times, then the wavefunction will evolve into a superposition of different position states, even if the initial state was a position eigenstate where every particle had a precise position to begin with?

Yes all agreed.

Do you disagree that if the system is a chaotic one, then even if the different elements of the superposition had only small "microscopic" differences a short time after the initial state, after a longer time the different elements of the superposition would inevitably start to have sizeable macroscopic differences due to the butterfly effect?

This is the point we disagree it seems. So i should ask you, for QM to be effective in Macro World the particles we are talking about need to be in a non-isolated state. And if i got this all correct if there is no isolation the wavefunction collapses.

When the wavefunction collapses there is only one observable outcome left in the Macro World as a particle. This is what we observe.

So for discussion's sake, you claim that this observation comes from a random event. I don't know if this is proven. Is it? Or the particle we observe is exactly what we would expect how a particle behave instead of a wavefunction would in the first place?

 

[Dadface]

Is there any empirical evidence that can give the MWI any credence?

 

[JesseM]

This is the point we disagree it seems.

So you agree that the system will be in a superposition of different position states where the position of individual particles differ slightly, but you disagree that the butterfly effect implies that in a chaotic system, if you run it forward from different states where the position of individual particles differs slightly, these small initial differences lead to large differences later on?

So i should ask you, for QM to be effective in Macro World the particles we are talking about need to be in a non-isolated state. And if i got this all correct if there is no isolation the wavefunction collapses.

Huh? Not in the MWI, the whole point is it rules out the idea of "collapse" under any circumstances. And with no collapse, all macro systems would be like the Schroedinger's cat thought-experiment (where we imagine an entire cat can be kept totally isolated from the outside environment until the box it's in is opened), in giant superpositions of macroscopically different states (like "alive cat" and "dead cat").

When the wavefunction collapses there is only one observable outcome left in the Macro World as a particle. This is what we observe.

You're talking about the Copenhagen interpretation, not the MWI. But we can still discuss the issue of chaotic systems in this context, as long as we are willing to have a thought-experiment like Schroedinger's cat where a large macroscopic system can remain totally isolated for a while, until it is finally observed and "collapses". My assertion would be that if the cat's brain is sufficiently chaotic for sensitive dependence on initial conditions to apply (plausible given how many nonlinear effects there are in brains), then even if the experiment is not specifically designed so the cat lives or dies based on the decay of a radioactive particle, it would still be true that if enough time is left between the moment the cat is sealed in the box and the moment it's opened, then at the moment before the box is opened and the cat's wavefunction is collapsed, according to QM the cat would be in a superposition of macroscopically distinct states, like "sitting in North corner", "sitting in South corner", "walking in the middle of the box", "sleeping in the middle", etc.

So for discussion's sake, you claim that this observation comes from a random event.

What "observation"? I said nothing about observation, and again there is no concept that anything special happens upon observation in the MWI.

 

[rodsika]

There aren't really clearly-differentiated "worlds" as I understand it, just a single wavefunction for the entire universe which can be seen (in the same way as any normal quantum wavefunction) as a superposition of different position states, a superposition of different momentum states, etc. How familiar are you with the standard (non-MWI) idea that every quantum system is modeled as having a single state vector which can be expressed as a sum (superposition) of eigenvectors for any observable like position or momentum? The basic idea behind the MWI is that we should use the same rules for the entire universe as the rules we use when modeling the evolution of quantum systems between measurements, that measurement itself shouldn't involve any special new rules like "wavefunction collapse".

Are you saying that this idea of worlds splitting whenever there are quantum choices are wrong? No version of Many World that uses this concept? I was reading a book called "Schroedinger Rabbits: The Many worlds of quantum" and I came across these passages:

"According to Everett, you see a single version of reality because the countless divergent versions of patterns of neuron firings in your brain very rapidly cease to affect one another, just as 2,345- Angstrom calculations in the computer described above are affected only by light very close to that particular wavelength. Other versions of reality - which of course include other versions of your brain - quicly become imperceptible to your own version.

However, thanks to de Witt, the false image of universes actually splitting quickly became associated with many-worlds. Famously, John Wheeler ultimately rejected his pupil Everett's theory has having too much conceptual baggage. Perhaps the notion of the universe repeatedly splitting was the major part of that baggage."

 

[JesseM]

Are you saying that this idea of worlds splitting whenever there are quantum choices are wrong? No version of Many World that uses this concept?

I wouldn't say "no version" involves such a notion of splitting worlds, but I don't think most MWI advocates imagine any clearly-defined distinct "worlds", talking about worlds is usually more like an approximate way of talking about the fact that the wavefunction contains a superposition of macroscopically different states. See for example the Stanford Encyclopedia article on MWI which says:

The MWI consists of two parts:

A mathematical theory which yields evolution in time of the quantum state of the (single) Universe.
A prescription which sets up a correspondence between the quantum state of the Universe and our experiences.
Part (i) is essentially summarized by the Schrödinger equation or its relativistic generalization. It is a rigorous mathematical theory and is not problematic philosophically. Part (ii) involves "our experiences" which do not have a rigorous definition.

...

The concept of "world" in the MWI belongs to part (ii) of the theory, i.e., it is not a rigorously defined mathematical entity, but a term defined by us (sentient beings) in describing our experience. When we refer to the "definite classically described state" of, say, a cat, it means that the position and the state (alive, dead, smiling, etc.) of the cat is maximally specified according to our ability to distinguish between the alternatives and that this specification corresponds to a classical picture, e.g., no superpositions of dead and alive cats are allowed in a single world.

On the other hand, DeWitt did seem to have a more technical definition of a "world" in terms of a choosing a preferred basis (like the position basis) and then considering each possible eigenstate of that basis to be a distinct "world" even if the differences were microscopic--see this section on DeWitt's version from another Stanford Encyclopedia article on variants of Everett's interpretation. Note though the section on the difficulty of choosing which basis should be the preferred one (starting with the paragraph that begins "The preferred basis problem is arguably a more serious problem for a splitting-worlds reading of Everett").

 

[rodsika]

I wouldn't say "no version" involves such a notion of splitting worlds, but I don't think most MWI advocates imagine any clearly-defined distinct "worlds", talking about worlds is usually more like an approximate way of talking about the fact that the wavefunction contains a superposition of macroscopically different states. See for example the Stanford Encyclopedia article on MWI which says:

On the other hand, DeWitt did seem to have a more technical definition of a "world" in terms of a choosing a preferred basis (like the position basis) and then considering each possible eigenstate of that basis to be a distinct "world" even if the differences were microscopic--see this section on DeWitt's version from another Stanford Encyclopedia article on variants of Everett's interpretation. Note though the section on the difficulty of choosing which basis should be the preferred one (starting with the paragraph that begins "The preferred basis problem is arguably a more serious problem for a splitting-worlds reading of Everett").

About this Prefered Basis problem, the question is why we get observables like position, momentum, spin and related. Why. What other observables can we get from Hilbert Space.. are you talking about observables like position-size, momentum-color, etc as the weird combination of observables that can be acquired (in any combination)*in*Hilbert Space? Pls. give other valid examples of what weird observables possible which we don't get in our world but available in Hilbert Space.
*
But then reading about preferred basis problem. I came across it in*Max*Tegmark article that says Decoherence has solved why things appear*classical, which I presumed is related to the preferred basis problem?* (see the thread "Predictivity Sieves questions" which*came as a result of my research in your preferred basis connection)*Can you share a very good site that introduced the preferred basis problem? Thanks.

 

[JesseM]

About this Prefered Basis problem, the question is why we get observables like position, momentum, spin and related. Why. What other observables can we get from Hilbert Space.

No, the point is that some observables like position and momentum don't commute, so you have to decide whether the position basis or the momentum basis is to be "preferred" in order to break down the universal state vector into a set of eigenstates which you call "worlds" in DeWitt's version of the MWI.

But then reading about preferred basis problem. I came across it in*Max*Tegmark article that says Decoherence has solved why things appear*classical, which I presumed is related to the preferred basis problem?* (see the thread "Predictivity Sieves questions" which*came as a result of my research in your preferred basis connection)*Can you share a very good site that introduced the preferred basis problem? Thanks.

You could take a look at this thread, and there's some discussion of the preferred basis problem starting on p. 9 of this paper. But you can find more references just by typing the words "preferred basis everett" (not in quotes) into google scholar or google books.

 

[JDude13]

Hi, what cheap device is available where a quantum choice can be made..

A flourescent light flickering is performing a quantum experiment.
However most things are quantum experiments. There could be minute changes in the brightness of an incandescant bulb which are too small to differentiate between.

Any electronic device which generates a random number can be dependant on a few if not one quantum mechanical factor.

 

[rodsika]

No, the point is that some observables like position and momentum don't commute, so you have to decide whether the position basis or the momentum basis is to be "preferred" in order to break down the universal state vector into a set of eigenstates which you call "worlds" in DeWitt's version of the MWI.
You could take a look at this thread, and there's some discussion of the preferred basis problem starting on p. 9 of this paper. But you can find more references just by typing the words "preferred basis everett" (not in quotes) into google scholar or google books.

I've read the threads you mentioned. But Collin Bruce seems to be describing it differently in Schroedinger Rabbit. He seemed to be saying that the problem of preferred basis is how to map the Hilbert space to the geometry of our own space-time. What has this got to do with momentum? Anyway he said (he was describing the Hilbert Space):

"... How to decide which way to draw the axes needed? Why should the directions of the various axes we chose correspond in any way to the directions of our particular three-dimensional space?

The matter gets even more puzzling if we take into account that, according to the mathematics, half the axes respresent imaginary numbers - numbers like the square root of minus one. This problem of deciding a preferred axes is called the problem of the preferred basis, and physicists wrangle fiercely over whether a unique preferred basis to map Hilbert space to the geometry of our own space-time arises naturally from the mathematics, or must be put in by hand"

Now pls. connect what he is saying to what you are saying above that "No, the point is that some observables like position and momentum don't commute, so you have to decide whether the position basis or the momentum basis is to be "preferred" in order to break down the universal state vector into a set of eigenstates which you call "worlds" in DeWitt's version of the MWI."

What do you mean by commute and what has this got to do with mapping Hilbert space to the geometry of our own space-time? I have actually studied about preferred basis problem years before and I thought it was just about why classical states are preferred (which was done alleged by Environmental Superselection). Many thanks.

 

[JesseM]

I've read the threads you mentioned. But Collin Bruce seems to be describing it differently in Schroedinger Rabbit. He seemed to be saying that the problem of preferred basis is how to map the Hilbert space to the geometry of our own space-time. What has this got to do with momentum? Anyway he said (he was describing the Hilbert Space):

"... How to decide which way to draw the axes needed? Why should the directions of the various axes we chose correspond in any way to the directions of our particular three-dimensional space?

Momentum and position eigenstates are axes in Hilbert space, each one forming a different "basis". It's like how in 3D space you can have coordinate system #1 made up of x-y-z axes, as well as coordinate system #2 made up of x'-y'-z' axes pointing in different directions, and you can use either coordinate system to describe points and vectors in that space.

What do you mean by commute and what has this got to do with mapping Hilbert space to the geometry of our own space-time?

If two observables commute (like position and spin), then one meaning of that is that in terms of the Hilbert space, you can find a set of basis vectors such that each vector is an eigenvector of both those observables. If they don't commute, then an eigenvector of one will be a superposition of different eigenvectors of the other, and vice versa. So, another way of stating the preferred basis problem is that you have to pick a complete set of commuting observables as your basis, if the vectors are position eigenvectors (definite position states) then they won't be momentum eigenvectors (each vector will be a superposition of different momentum states) and vice versa.

A more intuitive physical meaning of commuting vs. not commuting is that that if two observables commute, you can measure one without disturbing the value of the other--if you measure position, then immediately after that (a negligible time interval) measure spin, then immediately after that measure position again, then if the time between measurements is arbitrarily small the second position measurement will be arbitrarily close to the first one (in the limit as the time goes to infinity the change in position goes to zero). But if you measure position, then immediately measure momentum, then immediately measure position again, then no matter how small the time intervals the probability distribution for position will be significantly changed, by an amount which can be calculated from the position/momentum uncertainty relation.

 

[Dadface]

Let me rephrase my earlier question.Is there any experimental/observational evidence that supports these interpretations?

 

[Dmitry67]

My understanding is that to understand how world looks to YOU you break the symmetry and chose there preferred basic associated with YOU (your brain, measurement device), but there is no "objective" way to chose one basis or another. And that moment you fix the basic and frame of reference. I will check the links provided by JesseM to verify, to what extent I was right or wrong.

 

[rodsika]

Momentum and position eigenstates are axes in Hilbert space, each one forming a different "basis". It's like how in 3D space you can have coordinate system #1 made up of x-y-z axes, as well as coordinate system #2 made up of x'-y'-z' axes pointing in different directions, and you can use either coordinate system to describe points and vectors in that space.

If two observables commute (like position and spin), then one meaning of that is that in terms of the Hilbert space, you can find a set of basis vectors such that each vector is an eigenvector of both those observables. If they don't commute, then an eigenvector of one will be a superposition of different eigenvectors of the other, and vice versa. So, another way of stating the preferred basis problem is that you have to pick a complete set of commuting observables as your basis, if the vectors are position eigenvectors (definite position states) then they won't be momentum eigenvectors (each vector will be a superposition of different momentum states) and vice versa.

A more intuitive physical meaning of commuting vs. not commuting is that that if two observables commute, you can measure one without disturbing the value of the other--if you measure position, then immediately after that (a negligible time interval) measure spin, then immediately after that measure position again, then if the time between measurements is arbitrarily small the second position measurement will be arbitrarily close to the first one (in the limit as the time goes to infinity the change in position goes to zero). But if you measure position, then immediately measure momentum, then immediately measure position again, then no matter how small the time intervals the probability distribution for position will be significantly changed, by an amount which can be calculated from the position/momentum uncertainty relation.

Ok. After continuous reading of many references. I came across this paper by Maximilian Schlosshauer "Decoherence, the measurement problem, and interpretations of quantum mechanics":".. the results thus far suggest that the selected properties are in agreement with our observation: for mesoscopic and macroscopic objects the distance-dependent scattering interaction with surrounding air molecules, photons, etc., will in general give rise to immediate decoherence into spatially localized wave packets and thus select position as the preferred basis. On the other hand, when the environment is comparably "slow," as is frequently the case for microscopic systems, environment-induced superselection will typically yield energy eigenstates as teh preferred states."

So Environmental Superselection is the key to the Prefered Basis Problem. So what's the mystery left to solve? Pls. give an example of the subtle problem, thanks.

Also is this just particulars to Many World? Preferred basis problem also exist in pure Copenhagen and Bohmian Mechanics and other interpretations because Decoherence is the general mechanism that replaces wavefunction collapse.

 

[Fyzix]

1. My hope has some foundation. For example, most of the scientific community agree on Block Time, hence there is nothing special in the moment of time called "NOW". The "NOW" phenomenon is not explained by physics, but is moved the the realm of the yet-to be-explained consciousness.

I don't quite see how this would have anything in common with a consciousness somehow SELECTING to remember a world line that corresponds with Born Rule.
This introduces some sort of "collapse" through consciousness, both of which MWI was supposed to do away with...

2. When I google
Jeffrey A Barrett mwi relativity
I find this thread and few links to Barrett works
what exactly are you talking about
Could you provide a description of that "problem"?

Yes, here you go:

A final problem is that it is unclear how to formulate a splitting-worlds reading of Everett that is compatible with the constraints of special relativity. Suppose one opts for a strong sort of splitting, contrary to what Everett seems to suggest, where there are more physical systems after a typical measurement than before. If this involves somehow the creation of an entirely new universe (a complete copy of spacetime with an event structure, say) then when is the new universe created? One problem is in giving a frame-independent description of the creation event in the original universe, another is in making sense in relativity of an event that creates a new spacetime when all events, including the creation event, are supposed to be characterized by the local features of a particular fixed spacetime.

Those who favor a decoherence account of splitting worlds sometimes seem to imagine some sort of “unzipping” of spacetime that occurs along the forward light cone of the spacetime region that contains the measurement interaction. While decoherence effects can be expected to propagate along the forward light cone of the region that contains the interaction event between the measuring device and the object system, and while there is no problem describing the decoherence effects themselves in a way that is perfectly compatible with relativity, there is a problem in imagining that such a splitting process somehow physically copies the systems involved. A strong picture of spacetime somehow unzipping into connected spacetime regions along the forward light cone of the measurement event, would not be compatible with special relativity insofar as relativity presupposes that all events occur on the stage of Minkowski spacetime. And if we give up this assumption, then it is unclear what the rules are for compatibility with special relativity.

source: http://plato.stanford.edu/entries/qm-everett/#5

 

[rodsika]

https://www.amazon.com/gp/product/0199560560/?tag=pfamazon01-20
*
"Many Worlds?: Everett, Quantum Theory, and Reality"

I wonder if anyone has read the above book and whether it's worth the $84 tag. What other good books about Many Worlds are there that are available and anyone has actually read?
If Many Worlds is possible, then the current movie showing at theaters called "Source Code" can happen too. It's up to this weekend only and will show you the possibilities that can happen in Many Worlds Interpretation.

 

[Fyzix]

From reading a quick summary of this movie called "Source Code" I must say, this movie seems like crap, but other than that...
No, you could not (eventhough all possibitilies would happen in MWI) become someone elses consciousness, that would essentially make YOU disappear and be nonexistant.

Anyway, back to MWI.
It seems from your posts that you do not even possesses a basic grasp of QM, buying a book like that would not be advisable, I've been in touch with some of the authors of the papers in the book and it's quite technical.

It's aimed at people who got understanding of the subject.

Besides, you can find preprints of some of the papers online.

Here is written for the layman review of the book: http://ndpr.nd.edu/review.cfm?id=21669

 

[Dmitry67]

Those who favor a decoherence account of splitting worlds sometimes seem to imagine some sort of “unzipping” of spacetime that occurs along the forward light cone of the spacetime region that contains the measurement interaction. While decoherence effects can be expected to propagate along the forward light cone of the region that contains the interaction event between the measuring device and the object system, and while there is no problem describing the decoherence effects themselves in a way that is perfectly compatible with relativity, there is a problem in imagining that such a splitting process somehow physically copies the systems involved. A strong picture of spacetime somehow unzipping into connected spacetime regions along the forward light cone of the measurement event, would not be compatible with special relativity insofar as relativity presupposes that all events occur on the stage of Minkowski spacetime. And if we give up this assumption, then it is unclear what the rules are for compatibility with special relativity.

Wait, wait... He explicitly admits, that MWI *IS* compatible with relativity! The only problem for him is (bold part) *imagining* this process!

LOL!

It is like saying that "While GR is perfectly consistent with the observations, there is a problem in imagining that spacetime is not Euclidean" :)

 

[JesseM]

Ok. After continuous reading of many references. I came across this paper by Maximilian Schlosshauer "Decoherence, the measurement problem, and interpretations of quantum mechanics":".. the results thus far suggest that the selected properties are in agreement with our observation: for mesoscopic and macroscopic objects the distance-dependent scattering interaction with surrounding air molecules, photons, etc., will in general give rise to immediate decoherence into spatially localized wave packets and thus select position as the preferred basis. On the other hand, when the environment is comparably "slow," as is frequently the case for microscopic systems, environment-induced superselection will typically yield energy eigenstates as teh preferred states."

So Environmental Superselection is the key to the Prefered Basis Problem. So what's the mystery left to solve? Pls. give an example of the subtle problem, thanks.

I don't really have a detailed understanding of decoherence and its relation to the MWI, so take what I say with a large grain of salt, but from what I've read if you have the wavefunction for some quantum subsystem and a larger "environment" which interacts thermally with it, then if you calculate the wavefunction of the whole system and use it to figure out what happens to the component of the wavefunction dealing only with the small subsystem alone (not the environment), then interaction with the environment tends to drive the wavefunction of the subsystem into something close to a mixed state, a classical statistical ensemble of different eigenstates in some basis determined "naturally" by the decoherence process, rather than a "pure state" which is just a single quantum state vector that will be a superposition of different eigenstates, different from a statistical ensemble of them (in a statistical ensemble there is no interference, you're free to imagine it's definitely in one of the eigenstates and you're just uncertain about which it is). One problem here is that it only works for the wavefunction of the subsystem, the full wavefunction of the whole system composed of both the subsystem and its "environment" does not approach a mixed state (so this suggests some difficulties in using decoherence to explain how the whole universe ends up as a collection of "worlds", since the universe has no external environment...I don't really understand the "decoherent histories" approach though, maybe it has something to say about this issue). The other problem is that while the subsystem approaches something very close to a mixed state via decoherence, it doesn't do so exactly, the interference terms don't quite go to zero. Here's a quote on this from one of the most prominent MWI advocates today, David Deutsch, quoted on p. 332 of the book Minds, Machines and the Multiverse:

From the point of view of the interpretation of quantum mechanics, I think decoherence is almost completely unimportant. That's because decoherence is a quantitative matter. The interference phenomena never completely vanish; they only decrease exponentially until you can't be bothered to measure them anymore. The question of what the [interference] terms mean is still there, even if the coefficient in front of them is very small. It's like being a little pregnant. Those terms, however small, raise the same problem. If the argument is supposed to be that superpositions occur at a microscopic level but not to macroscopic objects, that's a bit like saying that you believe your bank is honest at the level of pennies but is cheating you at the level of pounds. It just doesn't make sense. It can't be that there are multiple universes at the levels of atoms but only a single universe at the level of cats.

There's also a good discussion of how decoherence relates to Everett interpretations in section 4.3 of this Stanford Encyclopedia article...on the specific subject of the preferred basis problem, they say:

The most useful application of decoherence to Everett, however, seems to be in the context of the problem of the preferred basis. Decoherence seems to yield a (maybe partial) solution to the problem, in that it naturally identifies a class of ‘preferred’ states (not necessarily an orthonormal basis!), and even allows to reidentify them over time, so that one can identify ‘worlds’ with the trajectories defined by decoherence (or more abstractly with decoherent histories).[21] If part of the aim of Everett is to interpret quantum mechanics without introducing extra structure, in particular without postulating the existence of some preferred basis, then one will try to identify structure that is already present in the wave function at the level of components (see e.g., Wallace, 2003a). In this sense, decoherence is an ideal candidate for identifying the relevant components.

A justification for this identification can then be variously given by suggesting that a ‘world’ should be a temporally extended structure and thus reidentification over time will be a necessary condition for identifying worlds, or similarly by suggesting that in order for observers to evolve there must be stable records of past events (Saunders 1993, and the unpublished Gell-Mann & Hartle 1994 (see the Other Internet Resources section below), or that observers must be able to access robust states, preferably through the existence of redundant information in the environment (Zurek's ‘existential interpretation’, 1998).

In alternative to some global notion of ‘world’, one can look at the components of the (mixed) state of a (local) system, either from the point of view that the different components defined by decoherence will separately affect (different components of the state of) another system, or from the point of view that they will separately underlie the conscious experience (if any) of the system. The former sits well with Everett's (1957) original notion of relative state, and with the relational interpretation of Everett preferred by Saunders (e.g., 1993) and, it would seem, Zurek (1998). The latter leads directly to the idea of many-minds interpretations (see the entry on Everett's relative-state interpretation and the website on ‘A Many-Minds Interpretation of Quantum Theory’ referenced in the Other Internet Resources). If one assumes that mentality can be associated only with certain decohering structures of great complexity, this might have the advantage of further reducing the remaining ambiguity about the preferred ‘basis’.

The idea of many minds was suggested early on by Zeh (2000; also 1995, p. 24). As Zeh puts it, von Neumann's motivation for introducing collapse was to save what he called psycho-physical parallelism (arguably supervenience of the mental on the physical: only one mental state is experienced, so there should be only one corresponding component in the physical state). In a decohering no-collapse universe one can instead introduce a new psycho-physical parallelism, in which individual minds supervene on each non-interfering component in the physical state. Zeh indeed suggests that, given decoherence, this is the most natural interpretation of quantum mechanics.[22]

Also is this just particulars to Many World? Preferred basis problem also exist in pure Copenhagen and Bohmian Mechanics and other interpretations because Decoherence is the general mechanism that replaces wavefunction collapse.

In Copenhagen the choice of what to measure determines what basis the quantum state will "collapse" onto a basis vector of. In Bohmian mechanics it's assumed at the outset that position has a special role, all particles have definite positions at all times and the way the positions evolve is determined by the "pilot wave", all other types of measurements are derived from the positions of "pointers" of measuring devices (see this article for more on Bohmian mechanics).

 

[Dmitry67]

The other problem is that while the subsystem approaches something very close to a mixed state via decoherence, it doesn't do so exactly, the interference terms don't quite go to zero.

I don't understand why it is important. I've heard that these terms vanish to about 10^-20 in nanoseconds, when we deal with big macroscopic systems.

The probability of having any influence of such terms is lower that to observe an violation of the second law of thermodynamics. In practice we assume that 2nd law is right, even is not "exactly" right. But who cares? The same for decoherence...

 

[JesseM]

I don't understand why it is important. I've heard that these terms vanish to about 10^-20 in nanoseconds, when we deal with big macroscopic systems.

The probability of having any influence of such terms is lower that to observe an violation of the second law of thermodynamics. In practice we assume that 2nd law is right, even is not "exactly" right. But who cares? The same for decoherence...

As I understand it, it's not a matter of them having any "influence", it's more that their presence makes the notion of dividing the system's wavefunction into distinct "worlds" with distinct probabilities somewhat ill-defined conceptually.

 

[Fyzix]

Wait, wait... He explicitly admits, that MWI *IS* compatible with relativity! The only problem for him is (bold part) *imagining* this process!

LOL!

It is like saying that "While GR is perfectly consistent with the observations, there is a problem in imagining that spacetime is not Euclidean" :)

I have to ask... Are you stupid?
Read again, then reply...

 

[Dmitry67]

there is no problem describing the decoherence effects themselves in a way that is perfectly compatible with relativity, there is a problem in imagining that such a splitting process somehow physically copies the systems involved

How else the above can be interpreted?

 

[JesseM]

I have to ask... Are you stupid?
Read again, then reply...

Dmitry67's comment seems accurate to me, Schlosshauer's main criticism is that he personally finds it counterintuitive that systems would constantly be "copied" (and I think he's taking 'copying' too literally, it's just a metaphor for the different elements in the superposition), not that this would be incompatible with any known physical principles: "there is a problem in imagining that such a splitting process somehow physically copies the systems involved." His other criticism is that "A strong picture of spacetime somehow unzipping into connected spacetime regions along the forward light cone of the measurement event, would not be compatible with special relativity insofar as relativity presupposes that all events occur on the stage of Minkowski spacetime", but this is a strawman since the MWI does not offer such a "strong picture" picture of spacetime "unzipping", it says that there are superpositions of different macroscopic states in the same spacetime (though this would become trickier if we tried to incorporate different curvatures of spacetime in general relativity...without a theory of quantum gravity, what the MWI says about spacetime curvature is bound to be speculative though)

Incidentally, on the subject of how MWI advocates argue that it preserves locality, see the references in [post=1647627]this post[/post].

 

[rodsika]

JesseM,

1. In a double slit experiment.. how many worlds are there.. just 2 corresponding to the 2 slit choices or thousands corresponding to the numerous dots in the interference patterns?

2. Supposed there are 2 worlds corresponding to each slit or 1000 worlds from the dots or other similar quantum divergence. Would ALL events in the world outside the device be identical after 100 years.. I mean.. say the experiment were done in Germany.. would all the movements and behavior of every person and events in America and elsewhere be identical in the 2 worlds forever.. or are histories random such that after 100 years.. America conquered the Arabs in one world, and the Arabs occupied American in the second world (with the initial difference among them just slits in the double slit experiment) or Jerry has 2 sons in one world and 3 sons in the second world? Or is everything absolutely identical?

3. Say there are billions and billions of galaxies. And you do a single double slit experiment. Would the billions and billions of galaxies in the 2 world exist after you do the experiment versus not existing if you don't do it? I think this is what is too much in Many Worlds. Just doing a double split experiments can produce billions and billions of galaxies and if the bubble inflation is true that each bubble produce new Big Bang, then a single double slit experiments can literally produce billions of big bangs in the 2nd copy world. This is near absurdity.. maybe it's just easier to believe in Santa Clause.. :)

But you mentioned ealier in the thread "There aren't really clearly-differentiated "worlds" as I understand it, just a single wavefunction for the entire universe which can be seen (in the same way as any normal quantum wavefunction) as a superposition of different position states, a superposition of different momentum states, etc."

But if you don't do the double slit experiment. You won't produce 2 worlds. So thinking that there is a single wavefunction for the entire universe doesn't help much. Because if you do or don't do the double slit experiment, you can affect whether there is one world or 2 world in your double slit experiment.

 

[JesseM]

JesseM,

1. In a double slit experiment.. how many worlds are there.. just 2 corresponding to the 2 slit choices or thousands corresponding to the numerous dots in the interference patterns?

I already told you I don't think there'd be a clearly-defined set of "worlds" in the most common version of the MWI. If you just use "world" as a sort of shorthand for aspects of the superposition that would be visibly different to observers like ourselves, I suppose however many distinct ways the particle can hit the screen that your detector will differentiate between (both all the different spatial positions it could be detected at, and all the different times the detection could happen), that would be the number of "worlds" defined directly by the detection-event, although things like random vibrations in the particles making up the equipment could (I would think) also lead to other macro-differences due to the butterfly effect.

2. Supposed there are 2 worlds corresponding to each slit or 1000 worlds from the dots or other similar quantum divergence. Would ALL events in the world outside the device be identical after 100 years.

No, I already said in post #3 that it's not just quantum experiments that lead to multiple outcomes but the quantum nature of all physical systems, and I know you read that post because you responded in post #6, so I don't really understand why you would ask this question.

or are histories random such that after 100 years.. America conquered the Arabs in one world, and the Arabs occupied American in the second world (with the initial difference among them just slits in the double slit experiment) or Jerry has 2 sons in one world and 3 sons in the second world?

Sure. Forget the MWI for a second, suppose we had a mega-computer that could simulate the evolution of the wavefunction of an isolated Solar system for 100 years, starting from a state where the positions of all the particles were fairly narrowly defined (not necessarily a position eigenstate since we may not want huge uncertainty in their momenta either), so at a macroscopic level we could say we were starting with a single "world", do you doubt that after 100 years the calculated wavefunction would be a superposition which would assign significant amplitudes to position eigenstates with very different configurations of particles on the simulated Earth, say an eigenstate where Jerry had 2 sons and another where he had 3? Consider my comment about Schroedinger's cat in post #26:

You're talking about the Copenhagen interpretation, not the MWI. But we can still discuss the issue of chaotic systems in this context, as long as we are willing to have a thought-experiment like Schroedinger's cat where a large macroscopic system can remain totally isolated for a while, until it is finally observed and "collapses". My assertion would be that if the cat's brain is sufficiently chaotic for sensitive dependence on initial conditions to apply (plausible given how many nonlinear effects there are in brains), then even if the experiment is not specifically designed so the cat lives or dies based on the decay of a radioactive particle, it would still be true that if enough time is left between the moment the cat is sealed in the box and the moment it's opened, then at the moment before the box is opened and the cat's wavefunction is collapsed, according to QM the cat would be in a superposition of macroscopically distinct states, like "sitting in North corner", "sitting in South corner", "walking in the middle of the box", "sleeping in the middle", etc.

Do you disagree that this is what standard non-MWI QM would predict about the evolution of the wavefunction of any chaotic macroscopic system, if we could do the calculation?

3. Say there are billions and billions of galaxies. And you do a single double slit experiment. Would the billions and billions of galaxies in the 2 world exist after you do the experiment versus not existing if you don't do it? I think this is what is too much in Many Worlds. Just doing a double split experiments can produce billions and billions of galaxies and if the bubble inflation is true that each bubble produce new Big Bang, then a single double slit experiments can literally produce billions of big bangs in the 2nd copy world. This is near absurdity.. maybe it's just easier to believe in Santa Clause.. :)

I don't know what you mean by "produce billions and billions of galaxies", both before and after the experiment there's a single universal wavefunction which can be broken down into a superposition of vast number of position eigenstates (or whatever basis you like) each of which features different configurations of particles in galaxies. Do you find the quantum rules for wavefunction evolution to be "absurdity"?

But you mentioned ealier in the thread "There aren't really clearly-differentiated "worlds" as I understand it, just a single wavefunction for the entire universe which can be seen (in the same way as any normal quantum wavefunction) as a superposition of different position states, a superposition of different momentum states, etc."

But if you don't do the double slit experiment. You won't produce 2 worlds.

Again I don't know what you mean by "produce". If you don't do the double slit experiment the particles that would have been used in the experiment are still around and in a superposition of different possible states, so if we just define "worlds" loosely as macroscopically distinguishable possibilities, it's not clear that the choice of whether to use those particles in a specific experiment or just leave them lying around in a junk heap makes any difference to the total number of "worlds".

 

[rodsika]

I already told you I don't think there'd be a clearly-defined set of "worlds" in the most common version of the MWI. If you just use "world" as a sort of shorthand for aspects of the superposition that would be visibly different to observers like ourselves, I suppose however many distinct ways the particle can hit the screen that your detector will differentiate between (both all the different spatial positions it could be detected at, and all the different times the detection could happen), that would be the number of "worlds" defined directly by the detection-event, although things like random vibrations in the particles making up the equipment could (I would think) also lead to other macro-differences due to the butterfly effect.

No, I already said in post #3 that it's not just quantum experiments that lead to multiple outcomes but the quantum nature of all physical systems, and I know you read that post because you responded in post #6, so I don't really understand why you would ask this question.

Sure. Forget the MWI for a second, suppose we had a mega-computer that could simulate the evolution of the wavefunction of an isolated Solar system for 100 years, starting from a state where the positions of all the particles were fairly narrowly defined (not necessarily a position eigenstate since we may not want huge uncertainty in their momenta either), so at a macroscopic level we could say we were starting with a single "world", do you doubt that after 100 years the calculated wavefunction would be a superposition which would assign significant amplitudes to position eigenstates with very different configurations of particles on the simulated Earth, say an eigenstate where Jerry had 2 sons and another where he had 3? Consider my comment about Schroedinger's cat in post #26:

Do you disagree that this is what standard non-MWI QM would predict about the evolution of the wavefunction of any chaotic macroscopic system, if we could do the calculation?

I don't know what you mean by "produce billions and billions of galaxies", both before and after the experiment there's a single universal wavefunction which can be broken down into a superposition of vast number of position eigenstates (or whatever basis you like) each of which features different configurations of particles in galaxies. Do you find the quantum rules for wavefunction evolution to be "absurdity"?

Again I don't know what you mean by "produce". If you don't do the double slit experiment the particles that would have been used in the experiment are still around and in a superposition of different possible states, so if we just define "worlds" loosely as macroscopically distinguishable possibilities, it's not clear that the choice of whether to use those particles in a specific experiment or just leave them lying around in a junk heap makes any difference to the total number of "worlds".

In the above questions. I'm asking in the context of DeWitt version of MWI where splitting occurs. In Jim Al-khalili Quantum: Guide to the Perplexed. It is mentioned in page 146 (where he is describing Many Worlds):"The basic idea is the following: When a quantum system is faced with a choice of alternatives such as a particle going through one of two or more slits then, rather than the wave function entering a superposition, we think of it, and the Whole Universe along with it, as splitting into a number of realities equal to the number of options available. These different worlds/universes/branches will be identical to each other apart from the different option chosen by the particle: in one universe it has gone through the upper slit, in the other it has gone through the lower slit. The universes overlap, only in that region where interference is taking place, until decoherence sets in. This then causes them to separate into non-interacting independent realities."

Note Jim Al-Khalili is a theoretical physicist. He seems to be holding the DeWitt view that splitting really occurs. He never mentions your version. So there seems to be two versions of Many Worlds, Everett original and DeWitt splitting? If so, it is not wrong to think in terms of DeWitt, isn't it? Then my questions above has to do with DeWitt version. Pls re-answer them in the context of DeWitt version just as Jim described. I'll read more of Everett original version as I reflect on your words about it. But Dewitt version is distinct from it. Thanks.

 

[JesseM]

In the above questions. I'm asking in the context of DeWitt version of MWI where splitting occurs. In Jim Al-khalili Quantum: Guide to the Perplexed. It is mentioned in page 146 (where he is describing Many Worlds):"The basic idea is the following: When a quantum system is faced with a choice of alternatives such as a particle going through one of two or more slits then, rather than the wave function entering a superposition, we think of it, and the Whole Universe along with it, as splitting into a number of realities equal to the number of options available. These different worlds/universes/branches will be identical to each other apart from the different option chosen by the particle: in one universe it has gone through the upper slit, in the other it has gone through the lower slit. The universes overlap, only in that region where interference is taking place, until decoherence sets in. This then causes them to separate into non-interacting independent realities."

Does Al-khalili say specifically that he is talking about DeWitt's version of the MWI and not other versions? As I said in [post=3236959]post #28[/post], I thought DeWitt's version was just about picking a preferred basis and saying every possible eigenstate in that basis with nonzero amplitude would be a separate "world", so the whole issue of decoherence should have nothing to do with the number of worlds, whereas Al-khalili seems to say decoherence determines the number of distinct worlds in the quote above (this seems more in line with the idea I referred to earlier that we can only talk about 'worlds' in an approximate sense, with different worlds being differentiable at a macroscopic coarse-grained level, which I think is the same idea discussed in this section of an online Everett FAQ).

Note Jim Al-Khalili is a theoretical physicist.

In post #28 I quoted from a Stanford Encyclopedia article as a basis for my understanding of DeWitt, which was also written by a philosopher of science, http://www.lps.uci.edu/barrett/ , and the other Stanford Encyclopedia article I quoted in the same post was written by a physicist (Lev Vaidman) and said in section 6:

Barrett uses the name "MWI" for the splitting worlds view publicized by De Witt 1970. This approach has been justly criticized: it has both some kind of collapse (an irreversible splitting of worlds in a preferred basis) and the multitude of worlds.

The level of discussion in those articles is typically a bit more rigorous than what you find in a typical pop physics book aimed at a broad audience (does Al-khalili talk about the preferred basis problem, for example?) If Al-Khalili says he is talking specifically about DeWitt's version and not some other version, please quote the section where he says so.