# Reality and MWI

• I
Gold Member

## Main Question or Discussion Point

Could MWI signify that there are not necessarily a (near) infinite number of real worlds, but rather that officially we can't tell if, or to what degree, the world we are in is real?

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WWGD
Gold Member
Before quoting the first line of Bohemian Rhapsody, we may need to define terms. How do you define 'real' , in order to separate worlds that are from those that are not?

Gold Member
Before quoting the first line of Bohemian Rhapsody, we may need to define terms. How do you define 'real' , in order to separate worlds that are from those that are not?
Perhaps 'the observer' 'observes' what is 'real'. So entropy1 ends up in world A and world B, but he, or his two copies, observe different things. So which observation represents the 'real' world, if we let observation decide?

I wonder what answers the other copies gave.

WWGD
Gold Member
Perhaps 'the observer' 'observes' what is 'real'. So entropy1 ends up in world A and world B, but he, or his two copies, observe different things. So which observation represents the 'real' world, if we let observation decide?

I wonder what answers the other copies gave.
So reality is not intrinsic but dependent on the observer? What then if we swap observers and worlds, has the choice of what reality is changed?

Gold Member
So reality is not intrinsic but dependent on the observer? What then if we swap observers and worlds, has the choice of what reality is changed?
The suggestion I was making is that, since we can't determine which (subjective) world would be real, reality as variable in this sense could be dropped alltogether.

PeterDonis
Mentor
entropy1 ends up in world A and world B, but he, or his two copies, observe different things.
Yes, that is what the MWI says.

So which observation represents the 'real' world, if we let observation decide?
Both of them, according to the MWI.

PeterDonis
Mentor
So reality is not intrinsic but dependent on the observer?
No, "reality" according to the MWI just doesn't mean what you are tacitly assuming it means in that statement.

What then if we swap observers and worlds, has the choice of what reality is changed?
"Swapping observers and worlds" makes no sense. An observer is defined by the measurement results they observe; in each "world", those results are definite. You can't "swap" observer A to world B and observer B to world A; each observer is defined by the fact that they observed result A or B.

Gold Member
So reality is not intrinsic but dependent on the observer?
It's a pity I am not allowed to launch my own ideas here

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WWGD
Gold Member
It's a pity I am not allowed to launch my own ideas here
I am clearly above my depth in all possible worlds ;), so I will bow to others here.

Demystifier
2018 Award
Gold Member
I was thinking this: In MWI, to be deterministic, ALL worlds must be real, for else probability would be involved (Copenhagen). However, to me, my world is real and of another world I can't tell.

Something else: In order to know which probability a possible measurement outcome has, the factual outcome did not represent that in QM, because the outcome has become 100% certain. So, to do the probability of the outcome justice, one might consider that the outcome as obtained does not (entirely) represent reality.

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Gold Member
Reality in terms of the wavefunction can't be reconstructed from the outcomes, because the outcomes are normalized, but can be reconstructed from the amplitudes. So that is why I suggest that outcomes either don't represent reality, or they represent a different kind of reality rather than that of the wavefunction.

I adhere to MWI but I just don't like an infinite number of worlds.

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Gold Member
If an outcome of a quantum measurement could be chosen by the observer, then, since all possible outcomes are orthogonal, you virtually get a collapse as a result of that. Other outcomes are possible for other observers, so reality becomes subjective. Far-fetched, I agree...

Gold Member
Reality in terms of the wavefunction can't be reconstructed from the outcomes, because the outcomes are normalized, but can be reconstructed from the amplitudes. So that is why I suggest that outcomes either don't represent reality, or they represent a different kind of reality rather than that of the wavefunction.
Hypothesis:

To clarify above quote: I am suspecting that the wavefunction is real, not the measurement outcomes. Rather that measurement outcomes emerge as a result of the measurement.

The amplitudes of a measurement can reconstruct the wavefunction, so to preserve information about the wavefunction in that way, since measurements deliver single outcomes, different possible worlds have to emerge. This is not a problem, since outcomes are not reality in this hypothesis, so they are not obligated to conform to (objective) reality (however, measurement outcomes have a relation to the wavefunction).

However, in MWI the probabilities are not preserved. It is just the conspiracy coined by QM interpretations that there is always a loose screw.

I should have studied QM

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bhobba
Mentor
Unfortunately in MWI you can get bogged down in exactly what does 'real' mean:

Thanks
Bill

WWGD
Gold Member
Unfortunately in MWI you can get bogged down in exactly what does 'real' mean:

Thanks
Bill
As long as one does not get bogged down on what 'is' is...

bhobba
Mentor
As long as one does not get bogged down on what 'is' is...
I have a love/hate relationship to philosophy. I find some things interesting, and others boring or even downright maddening. I enrolled in a Graduate certificate in philosophy but I found it, as the lecturer confirmed to me, about philosophical ideas in a historical context - not the ideas themselves. That didn't actually stop me from continuing with it despite my general dislike for history, but when research assignments were required I could not go to the library (I didn't have a car at the time and my knees are totally shot so public transport was out) and contacted the disability officer to discuss how to work around it. She was on holidays or something and I could never get a hold of her so I gave it away. Later the professor contacted me and apologized - he was evidently supposed to handle it while she was away but forgot. I could return with no penalty, but this history stuff was definitely not my thing so said no thanks. I must mention however I do find the history of science, especially QM quite interesting. If they only had a graduate program in the philosophy/history of QM I would have lapped it up - but no they didn't - although their physics department had a group dedicated to the foundations of QM and were willing to enroll me in a Masters Of Philosophy in the Foundations, Philosophy, and History of QM. But a full research Masters was for me too much of a time commitment so I declined. That was when I was in my late 40's - at 64 I now think its beyond me.

Anyway the bit I find maddening about philosophy is this quibbling about everyday words to the point they even sometimes question things like 'is'. I can understand things like reality etc are hard to pin down - but 'is'? Not my bag.

Thanks
Bill

WWGD
Gold Member
I have a love/hate relationship to philosophy. I find some things interesting, and others boring or even downright maddening. I enrolled in a Graduate certificate in philosophy but I found it, as the lecturer confirmed to me, about philosophical ideas in a historical context - not the ideas themselves. That didn't actually stop me from continuing with it despite my general dislike for history, but when research assignments were required I could not go to the library (I didn't have a car at the time and my knees are totally shot so public transport was out) and contacted the disability officer to discuss how to work around it. She was on holidays or something and I could never get a hold of her so I gave it away. Later the professor contacted me and apologized - he was evidently supposed to handle it while she was away but forgot. I could return with no penalty, but this history stuff was definitely not my thing so said no thanks. I must mention however I do find the history of science, especially QM quite interesting. If they only had a graduate program in the philosophy/history of QM I would have lapped it up - but no they didn't - although their physics department had a group dedicated to the foundations of QM and were willing to enroll me in a Masters Of Philosophy in the Foundations, Philosophy, and History of QM. But a full research Masters was for me too much of a time commitment so I declined. That was when I was in my late 40's - at 64 I now think its beyond me.

Anyway the bit I find maddening about philosophy is this quibbling about everyday words to the point they even sometimes question things like 'is'. I can understand things like reality etc are hard to pin down - but 'is'? Not my bag.

Thanks
Bill
Yes, thin line between the ridiculous and the sublime in Philosophy. May be saying something brilliant or absurd, not clear where the line is.

I have a love/hate relationship to philosophy. I find some things interesting, and others boring or even downright maddening. I enrolled in a Graduate certificate in philosophy but I found it, as the lecturer confirmed to me, about philosophical ideas in a historical context - not the ideas themselves. That didn't actually stop me from continuing with it despite my general dislike for history, but when research assignments were required I could not go to the library (I didn't have a car at the time and my knees are totally shot so public transport was out) and contacted the disability officer to discuss how to work around it. She was on holidays or something and I could never get a hold of her so I gave it away. Later the professor contacted me and apologized - he was evidently supposed to handle it while she was away but forgot. I could return with no penalty, but this history stuff was definitely not my thing so said no thanks. I must mention however I do find the history of science, especially QM quite interesting. If they only had a graduate program in the philosophy/history of QM I would have lapped it up - but no they didn't - although their physics department had a group dedicated to the foundations of QM and were willing to enroll me in a Masters Of Philosophy in the Foundations, Philosophy, and History of QM. But a full research Masters was for me too much of a time commitment so I declined. That was when I was in my late 40's - at 64 I now think its beyond me.

Anyway the bit I find maddening about philosophy is this quibbling about everyday words to the point they even sometimes question things like 'is'. I can understand things like reality etc are hard to pin down - but 'is'? Not my bag.

Thanks
Bill
I know how you feel about philosophy but I can tell you that I really enjoyed some books.
For example:
"An outline of Philosophy" ( Bertrand Russell )
"The Principles of Psychology" ( William James ).

jedishrfu
Mentor
I enjoy the history aspect of scientific discovery. Sometimes, the way it's presented in a formal logical fashion is totally off base as to how it was really discovered.

As an example, I think Gauss was famous for having well-polished proofs that gave no indication of how he actually came upon the idea or the proof.

With respect to philosophy, I often find it confusing especially the naming and definition of philosophical systems that totally confuse me. While I can understand the need for precision in what you say (especially in law) I have trouble with the subtleties discussed in philosophy.

To be fair, I had the same difficulty in abstract topology and in biology. I guess I preferred more compact systems where things could be derived from basic principles meaning you had fewer terms to remember.

bhobba
Mentor
The point of this slight sojourn into philosophy is the use of equally real worlds in the formulation of MWI shows - and was the point I was trying to make - is riddled with philosophical issues, especially what is real. That's why I prefer Decoherent Histories rather than Many Worlds - there is no ambiguity subject to philosophical/semantic quibbling.

Thanks
Bill

The point of this slight sojourn into philosophy is the use of equally real worlds in the formulation of MWI shows - and was the point I was trying to make - is riddled with philosophical issues, especially what is real. That's why I prefer Decoherent Histories rather than Many Worlds - there is no ambiguity subject to philosophical/semantic quibbling.

Thanks
Bill
I understand the desire to 'skip' over the philosophical jargon, semantics and stoner riddles, but isn't DH just "shut up and calculate" of MWI?

WWGD
Gold Member
In a sense, as I understand it, this is sort of par for the course in Philosophy. By design it deals with topics that are open-ended, without any clear underlying structure. Once the dust clears and a definite structure, theme/focus, methodology emerges, a philosophical body of knowledge becomes a "settled area" of knowledge. This is e.g. , how the philosophical study of human behavior ultimately became the field of Psychology, etc. Seems interesting some consider Psychology to be the study of behavior ( outer manifestation) while others see it as the study of the mind ( inner processes). Maybe the difference in approach between Empiricism and Rationalism?

bhobba
Mentor
I understand the desire to 'skip' over the philosophical jargon, semantics and stoner riddles, but isn't DH just "shut up and calculate" of MWI?
Well yes. It was designed to implement Gell-Mann's idea that equally real worlds means they can all happen, the only difference being probabilities. In other words he answered what equally real means purely on simplistic grounds ie shut up and calculate. That's why the two interpretations have a lot in common, mathematically. You still do not know what world you will find yourself in, you just know the others do not also exist at the same time. But as always simplicity is in the eye of the beholder - you now must answer where did the other worlds go - each gives and takes.

Thanks
Bill

That's why the two interpretations have a lot in common, mathematically.
I thought all interpretations have the same mathematics?

Cheers