Many Worlds

[stevevw]

Whereas proper science commences making no 'assumptions'.
Therefore science's 'fundamental' objective reality isn't based on assumptions, (in spite of what sooo many folk here seem to think).

That is not the case I believe. Science has to start from somewhere. If it was completely open then we would have to include all phenomena. So science reduces its options down to only quantities like matter beforehand to eliminate other possibilities. This is not an opinion but a logical conclusion. Science therefore assumes a material world outside our minds as fundamental reality before any measure is taken.

How we gain knowledge of the world comes before ontology. So in positing that we can only gain knowledge about reality through empirical science is an epistemic belief rather than a scientific one.

 

[SelfSim]

That is not the case I believe. Science has to start from somewhere. If it was completely open then we would have to include all phenomena. So science reduces its options down to only quantities like matter beforehand to eliminate other possibilities. This is not an opinion but a logical conclusion. Science therefore assumes a material world outside our minds as fundamental reality before any measure is taken.

How we gain knowledge of the world comes before ontology. So in positing that we can only gain knowledge about reality through empirical science is an epistemic belief rather than a scientific one.

Again we get the tiresome philosophical word-salads!

Did you watch Yoganathan's video then read @sjastro's explanatory post #45, where he explained how energy is used in QM as the real measurable in Yoganathan's tardigrade QM system?

Whaddya mean by 'knowledge' anyway? I can give you a useful operational definition if you like(?)
(I mean, as opposed to useless circular, word-salad philosophical ones, that is).

 

[stevevw]

Well then let me lay out my argument for why I think that MWI does indeed make assumptions, even if the Schrodinger equation is no more capable of making an assumption than 1+1=2.

The assumption is that there's no such thing as hidden variables. But as Sabine Hossenfelder argues in the following video that may not be true. (Starting at 8:15) There may indeed be hidden variables, in which case there's no such thing as a collapse of the wave function, and MWI is therefore a non-starter. The particle knew from the beginning which way it was going. And in the instances where we didn't measure it, the Many Worlds don't emerge because the wavefunction never collapses.

So it seems to me that MWI does indeed make an assumption, that there are no hidden variables.

The MWI cannot get rid of the measurement problem as also mentioned by Sabine Hossenfelder.

 

[sjastro]

Here is a summary of the various interpretations with emphasis on the Copenhagen and Many World Interpretations.

In the Many Worlds Interpretation the wavefunction of the universe is defined as being ontic (real) and does not collapse.
Even though it is a deterministic interpretation it does not require hidden variables like Superdeterminism as the wavefunction is complete and evolves with time as per the Schrödinger picture mentioned in a previous post.
New universes "split off" from this time evolving wavefunction as a result of decoherence.

That's the explanation whether it's plausible is a different story.

 

[FrumiousBandersnatch]

So it seems to me that MWI does indeed make an assumption, that there are no hidden variables.

Well, it clearly makes the assumption that every idea that isn't MW isn't such a useful model, or doesn't apply, or is incorrect. Hidden variable interpretations make the assumption that interpretations that don't involve hidden variables are not as useful, applicable, or correct...

That's how hypotheses or interpretations work; they suggest one way of looking at the world is better than other ways ¯\_(ツ)_/¯

E.T.A. In other words, if MW didn't make the assumption that there are no hidden variables, it would be a hidden variables interpretation, not MW.

 

[FrumiousBandersnatch]

Here is a summary of the various interpretations with emphasis on the Copenhagen and Many World Interpretations.

View attachment 325083​

In the Many Worlds Interpretation the wavefunction of the universe is defined as being ontic (real) and does not collapse.
Even though it is a deterministic interpretation it does not require hidden variables like Superdeterminism as the wavefunction is complete and evolves with time as per the Schrödinger picture mentioned in a previous post.
New universes "split off" from this time evolving wavefunction as a result of decoherence.

That's the explanation whether it's plausible is a different story.

Thanks for that chart - it looks useful.

ISTM that all interpretations have a plausibility problem - because QM itself is counterintuitive.

 

[SelfSim]

.. ISTM that all interpretations have a plausibility problem - because QM itself is counterintuitive.

One step further; the counterintuitivity of QM results, directly challenges the assumptions underpinning 'plausibility'.

The number of QM interpretations, alone, demonstrates science's commitment to put intuitive, 'plausible' assumptions to the test .. and not just go on believing they are true, simply because they make sense.

We're witnessing a 'hunt' aimed at ejecting any kind of long held fundamental beliefs (about reality), in QM interpretations.

 

[sjastro]

Thanks for that chart - it looks useful.

ISTM that all interpretations have a plausibility problem - because QM itself is counterintuitive.

Some interpretations are more counterintuitive and less plausible than others.
The universal wavefunction being "real" in MWI is one such point; in the CI the wavefunctions are mathematical but not completely rigorous where we can make manipulations through matrix and wave mechanics formulated in the early 20th century.
We don't have this luxury if the wavefunctions are real as it amounts to making things up.
New universes splitting off from this universal wavefunction is an unfalsifiable concept as communication between universes is not possible.

On the subject of communication the No Communication Theorem is where communication between entangled particles is not even possible making the requirement for hidden variables and therefore superdeterminism irrelevant.

The Sabine Hossenfelder video in post #56 basically justifies superdeterminism by exploiting loopholes in Bell's theorem.
I found another video by Sabine providing a broad description of how the No Communication Theorem works.
As I was watching the video I was thinking she was digging a hole for herself by making a strong case for the theorem.
At the end of the video suddenly the loophole was defined in this case the detector settings which provided the introduction for superdeterminism and the follow up video as shown in post #56.

 

[SelfSim]

Some interpretations are more counterintuitive and less plausible than others.
The universal wavefunction being "real" in MWI is one such point; in the CI the wavefunctions are mathematical but not completely rigorous where we can make manipulations through matrix and wave mechanics formulated in the early 20th century.
We don't have this luxury if the wavefunctions are real as it amounts to making things up.
New universes splitting off from this universal wavefunction is an unfalsifiable concept as communication between universes is not possible.

On the subject of communication the No Communication Theorem is where communication between entangled particles is not even possible making the requirement for hidden variables and therefore superdeterminism irrelevant.

The Sabine Hossenfelder video in post #56 basically justifies superdeterminism by exploiting loopholes in Bell's theorem.
I found another video by Sabine providing a broad description of how the No Communication Theorem works.
As I was watching the video I was thinking she was digging a hole for herself by making a strong case for the theorem.
At the end of the video suddenly the loophole was defined in this case the detector settings which provided the introduction for superdeterminism and the follow up video as shown in post #56.

Another great video .. thanks for that! Somewhere else, in these videos, Hossenfelder admitted that she's deliberately campaigning for more research into hidden variables because she says there's no-one is pursuing research in that area (even though they haven't been completely ruled out). I think its useful to keep this in mind when watching her vids.

Can't help but wonder whether neutrino behaviour might turn out to be the exception standing independently from current understanding of QM particle behaviours (ie: that QM is largely based around) .. (?) I mean they sort of stand close to the 'border' of particle and wavelike, eh? Never heard of neutrinos in the same breath as the two slit or entanglement contexts. Mind you, that's probably my own ignorance of what's going on in neutrino research ..

Co-incidentally, I read just the other day that they've nailed down the mass for a neutrino of ~0.8ev .. which (obviously) means they're sub luminal, which is interesting. {Edit/correction: that is- February 2022 upper limit of the effective electron neutrino mass, mν < 0.8 eV c–2 at 90% CL)

 

[sjastro]

Another great video .. thanks for that! Somewhere else, in these videos, Hossenfelder admitted that she's deliberately campaigning for more research into hidden variables because she says there's no-one is pursuing research in that area (even though they haven't been completely ruled out). I think its useful to keep this in mind when watching her vids.

A physicist came up with an excellent analogy about hidden variables.
It's like putting sand on a laboratory orbital shaker, you observe the sand shaking but it's the vibrating plate concealed by the sand which causes the sand to shake.
The vibrating plate is the hidden variable but is beyond observation.
While hidden variables might solve the measurement problem it creates another problem of not being falsifiable as they are experimentally indistinguishable from standard quantum mechanics.

Can't help but wonder whether neutrino behaviour might turn out to be the exception standing independently from current understanding of QM particle behaviours (ie: that QM is largely based around) .. (?) I mean they sort of stand close to the 'border' of particle and wavelike, eh? Never heard of neutrinos in the same breath as the two slit or entanglement contexts. Mind you, that's probably my own ignorance of what's going on in neutrino research .
Co-incidentally, I read just the other day that they've nailed down the mass for a neutrino of ~0.8ev .. which (obviously) means they're sub luminal, which is interesting.

Neutrinos also exhibit wave/particle duality but the problem with neutrinos the standard model predicts they should have zero mass.

 

[FrumiousBandersnatch]

One step further; the counterintuitivity of QM results, directly challenges the assumptions underpinning 'plausibility'.

The number of QM interpretations, alone, demonstrates science's commitment to put intuitive, 'plausible' assumptions to the test .. and not just go on believing they are true, simply because they make sense.

We're witnessing a 'hunt' aimed at ejecting any kind of long held fundamental beliefs (about reality), in QM interpretations.

That's an interesting point - one of the reasons I like MW is how the simplicity of its formulation gives rise to such a rich and conceptually challenging view of 'reality' as a vector in Hilbert space described by the universal wavefunction that gives rise to uncountable world variations. Other interpretations seem rather dull or contrived in comparison

Whether it survives long term or not, it is, as you suggest, good exercise for challenging conventional ideas of the nature of reality.

 

[SelfSim]

A physicist came up with an excellent analogy about hidden variables.
It's like putting sand on a laboratory orbital shaker, you observe the sand shaking but it's the vibrating plate concealed by the sand which causes the sand to shake.
The vibrating plate is the hidden variable but is beyond observation.
While hidden variables might solve the measurement problem it creates another problem of not being falsifiable as they are experimentally indistinguishable from standard quantum mechanics.



Neutrinos also exhibit wave/particle duality but the problem with neutrinos the standard model predicts they should have zero mass.

I guess what I'm trying to grapple with here, by introducing neutrinos into the conversation, is that neutrinos appear to not care about the normal 'environmental interactions' which is the trigger for any decoherence/collapse in the measurement issue, yes(?) .. So any references to 'neutrino slit experiments' seems very theoretical, as neutrinos don't appear to need any 'slits', or measurement devices at all, in order to decohere/collapse their superposition state(?) Ie: any old antineutrino might be all that's needed there (and that's not really an 'environmental interaction' at all)?
Reference article here:

The neutrino and its opposite, the antineutrino, are both neutrally charged particles. So here’s a riddle: If it looks like a neutrino and acts like a neutrino, doesn’t it follow that the antineutrino might be the same particle as a neutrino?

 

[sjastro]

I guess what I'm trying to grapple with here, by introducing neutrinos into the conversation, is that neutrinos appear to not care about the normal 'environmental interactions' which is the trigger for any decoherence/collapse in the measurement issue, yes(?) .. So any references to 'neutrino slit experiments' seems very theoretical, as neutrinos don't appear to need any 'slits', or measurement devices at all, in order to decohere/collapse their superposition state(?) Ie: any old antineutrino might be all that's needed there (and that's not really an 'environmental interaction' at all)?
Reference article here:

Since neutrinos have mass they have a De Broglie wavelength λ defined by the equation λ = h/p where h is Planck's constant and p the momentum.
λ defines the wave like character of a particle, the larger its value the more wave like it is.
Even though neutrinos travel near the speed of light their mass is very small compared to other leptons which also exhibit interference patterns (muon 105.7 MeV/c² vs < 0.17 MeV/c² muon neutrino).
This means the momentum of the muon neutrino used in the Fermilab double slit experiment is small making its De Broglie wavelength λ large.
The large λ value is why interference was observed in the experiment.
Note there is no need to discuss decoherence or wave function collapse in this case.

 

[Neutral Observer]

I have a question.

Is the Schrodinger equation in any way similar to Feynman's "Sum over histories"? Not in terms of their mathematical structure, but rather that they both entail taking all possible paths and summing them together to get the outcome.

 

[sjastro]

I have a question.

Is the Schrodinger equation in any way similar to Feynman's "Sum over histories"? Not in terms of their mathematical structure, but rather that they both entail taking all possible paths and summing them together to get the outcome.

Both deal with the time evolution of the wavefunction when transitioning from an initial state |I> to a final state |F> and are similar.
For the Schrödinger equation the evolution of |I> → |F> can be best described as summing all random walk trajectories from which the probabilty is calculated; Feynman's "Sum over histories" is defined by the path integral formulation where there are an infinite number of paths for |I> → |F> and the probability of the transition is calculated by considering all possible paths.
Mathematically the Schrödinger equation can be derived from the path integral formulation and vice versa.

 

[Kylie]

Subscribing. This is interesting...

 

[Neutral Observer]

Both deal with the time evolution of the wavefunction when transitioning from an initial state |I> to a final state |F> and are similar.
For the Schrödinger equation the evolution of |I> → |F> can be best described as summing all random walk trajectories from which the probabilty is calculated; Feynman's "Sum over histories" is defined by the path integral formulation where there are an infinite number of paths for |I> → |F> and the probability of the transition is calculated by considering all possible paths.
Mathematically the Schrödinger equation can be derived from the path integral formulation and vice versa.

Thanks

Next question.

In Feynman's "Sum over histories" we take all the possible paths that a particle can take and we add them together. The result is that some of the paths interact constructively and some of them interact destructively. Such that what we observe, for example, is that a photon will always take the shortest path from the source to the observer, even though in theory the photon takes every path. We assume I guess that the rest of the paths simply never existed, they were preemptively eliminated by destructive interference.

In some sense the same idea holds true in QM. If we fire a photon through a double slit we'll see an interference pattern, due to the fact that some of the paths have been preemptively eliminated by destructive interference.

But the thing is that in neither of the previous two examples do we assume that the eliminated paths still exist in some alternate version of reality. However, if we introduce a detector to our double slit experiment, such that all but one of the paths is eliminated, MWI now assumes that the alternate paths still exist somewhere.

If we're going to be consistent wouldn't the logical conclusion be that the detector has somehow introduced destructive interference, presumably by entangling the photon with a complex filter known as the environment. Effectively the environment becomes the hidden variable.

Now I don't see any way, other than mathematically, to test this idea without running smack up against the measurement problem. But it just seems kind of intuitive that if destructive interference accounts for the loss of paths in other scenarios then it may well have something to do with the loss of paths in "collapse" scenarios as well.

Like I've said before, I like MWI, it raises some intriguing questions, but I just can't shake the feeling that it might be missing something.

 

[SelfSim]

... Like I've said before, I like MWI, it raises some intriguing questions, but I just can't shake the feeling that it might be missing something.

Sounds like an infinite universes problem .. which I guess, is effectively what happens whenever one invokes 'many worlds' in some explanation.
IOW, where everything is possible in an infinite/many worlds universe, hidden variables would have to be be possible once the observer/measurer adopts, (out of necessity), their own singular frame of reference, (or PoV)?
Many worlds, and a selected observation frame, implies hidden variables, I think(?)

(Thank goodness we already know that logical imperatives can't establish existence .. )

 

[FrumiousBandersnatch]

Many worlds, and a selected observation frame, implies hidden variables, I think(?)

ISTM that's the same as saying that MW and hidden variable interpretations are equivalent (have the same explanatory power)... [which is why they're commonly called interpretations.]

 

[sjastro]

Thanks

Next question.

In Feynman's "Sum over histories" we take all the possible paths that a particle can take and we add them together. The result is that some of the paths interact constructively and some of them interact destructively. Such that what we observe, for example, is that a photon will always take the shortest path from the source to the observer, even though in theory the photon takes every path. We assume I guess that the rest of the paths simply never existed, they were preemptively eliminated by destructive interference.

In some sense the same idea holds true in QM. If we fire a photon through a double slit we'll see an interference pattern, due to the fact that some of the paths have been preemptively eliminated by destructive interference.

The shortest photon path you are describing is a unique solution from a classical physics perspective due to the principle of least action which forms the basis of Lagrangian mechanics.
I provided a mathematical description of classical Lagrangian mechanics based on one of the most famous problems in physics posed in the 18th century the Brachistochrone problem in these posts.

Physics is Just a Model

... So the idea that our perceptions refer to anything real beyond our own minds is just a belief like any other, for example, like the belief in the resurrection of Jesus?This is the point at which I need to produce a usable definition of 'belief'. As follows: 'A belief is that which I hold to...

www.christianforums.com

Physics is Just a Model

... So the idea that our perceptions refer to anything real beyond our own minds is just a belief like any other, for example, like the belief in the resurrection of Jesus?This is the point at which I need to produce a usable definition of 'belief'. As follows: 'A belief is that which I hold to...

www.christianforums.com

Physics is Just a Model

... So the idea that our perceptions refer to anything real beyond our own minds is just a belief like any other, for example, like the belief in the resurrection of Jesus?This is the point at which I need to produce a usable definition of 'belief'. As follows: 'A belief is that which I hold to...

www.christianforums.com

Physics is Just a Model

... So the idea that our perceptions refer to anything real beyond our own minds is just a belief like any other, for example, like the belief in the resurrection of Jesus?This is the point at which I need to produce a usable definition of 'belief'. As follows: 'A belief is that which I hold to...

www.christianforums.com

Where as in Lagrangian mechanics the shortest path is a unique solution this is not the case in quantum mechanics.
There could be an infinite number of pathways all of which follow the principle of least action and does not include purely random pathways.
The pathways are probability amplitudes which need to be summed to find the optimized path.
The summing process results in both destructive and constructive interference of the probability amplitudes from which the optimized path is obtained.

But the thing is that in neither of the previous two examples do we assume that the eliminated paths still exist in some alternate version of reality. However, if we introduce a detector to our double slit experiment, such that all but one of the paths is eliminated, MWI now assumes that the alternate paths still exist somewhere.

If we're going to be consistent wouldn't the logical conclusion be that the detector has somehow introduced destructive interference, presumably by entangling the photon with a complex filter known as the environment. Effectively the environment becomes the hidden variable.

In the MWI the universal wavefunction evolves by the entanglement of the detector to the wavefunction.
The alternative version of reality is created through decoherence of this entangled wavefunction into a different universe.

Now I don't see any way, other than mathematically, to test this idea without running smack up against the measurement problem. But it just seems kind of intuitive that if destructive interference accounts for the loss of paths in other scenarios then it may well have something to do with the loss of paths in "collapse" scenarios as well.

Like I've said before, I like MWI, it raises some intriguing questions, but I just can't shake the feeling that it might be missing something.

My opinion and that’s all it is the measurement problem is solved by decoherence as quantum mechanical probabilities are converted into classical probabilities of the macroscopic world.
Of course this puts me in the 50% of people who don’t know what they are talking about according to Sabine Hossenfelder.

Here is a good explanation of Feynman’s path integral formulation.