# Question about the Many-Worlds Interpretation

#### Captain Morgan

I get the basics of the interpretation, but I don't understand one specific element. If there are parallel worlds, where is this parallel world? Is it like a stack of newspapers, each page being a different world, where the entire, connected newspaper is the universe? What I'm asking is if this parallel world located in our universe. I'm going to assume its not in our observable universe, but what about as a whole? Is there something I'm missing, or am I confusing two theories?

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#### bcrelling

The way I've heard it:

The possibilities of the way events can unfold diverges like branches on a tree, For the MWI there is a new spread of branches every time a probability wave is collapsed. However we never have access to these other worlds once they have diverged from us.

I think the stack of newspapers analogy you quoted is more to do with the "block universe" hypothesis.

#### bhobba

Mentor
Hi Captain

Yea its a weird thing to get your mind around.

The worlds it splits into is really described by the math - analogies from everyday usage like where are they etc are not really appropriate. What actually happens is the wave-function of the whole universe keeps on evolving unchanged but is now able to be, for conceptual understanding, separated into a number of different 'parts' where each part is considered a new world depending on the possible outcome of the observation. In its modern incarnation this happens when what is called decoherence occurs - the outcome of which is technically called a mixed state. A mixed state is a sum of the actual outcomes of the observation where the 'weightings' of that sum is the probability of that outcome occurring. In other interpretations it is assumed an observation picks one of the possible outcomes and it evolves from then on. In MW an observation does nothing - everything keeps evolving as is but each outcome is considered a world. Its very very neat mathematically and extremely beautiful - but not to everyone's taste so to speak.

Thanks
Bill

#### bhobba

Mentor
For the MWI there is a new spread of branches every time a probability wave is collapsed. However we never have access to these other worlds once they have diverged from us.
Actually the beauty and allure of MW is no collapse occurs. Everything just keeps evolving - but after decoherence occurs the system is in a mixed state that is the sum of the possible outcomes. Noting at all happens - the universe keeps on evolving - but is now able to be conceptually separated into a number of 'parts' where each part is the outcome of the observation and considered a separate world.

Thanks
Bill

#### Quantumsatire

Very difficult to surmise. I feel like each time an outcome occurs, it exists in its own "observable universe" like system that is part of a greater Universe. Of course this deviates a little from mathematical MWI, I believe.

#### Double-Slit

I get the basics of the interpretation, but I don't understand one specific element. If there are parallel worlds, where is this parallel world? Is it like a stack of newspapers, each page being a different world, where the entire, connected newspaper is the universe? What I'm asking is if this parallel world located in our universe. I'm going to assume its not in our observable universe, but what about as a whole? Is there something I'm missing, or am I confusing two theories?
Usually the UNIVERSE with big U is containing the entire existence with all 3 spatial and 1 time dimension too.If we consider the Multiverse then logically would be an error since how can you have something outside existence,but put that aside we can interpret is as our 4 dimensions with our rules of physics,maybe those other universes have other laws of physics,so it can't be in our UNIVERSE (with big U).It has to be somewhere outside,whatever direction that may be (we would surely need more than 4 dimensions).But since our universe is thermodinamically closed system we can't transmit any matter/energy to them.So these universes would be completely isolated forever from eachother,with no ways to communicate with them.So even if this theory is true we could never prove it 100% since it can't be proven.

#### Pseudo Epsilon

your asking their position, ie their x,y,z co-ordinates. They are not on our cartesian plane at all if they exist. Its like asking what connects two entangled photons. Its purely mathamatical.

Gold Member
Is there something I'm missing, or am I confusing two theories?
Maybe this video where Sean Carroll explains MWI (starts @01:30) could help:

Personally, I’m not a believer of MWI since, beside common objections (and no experimental proofs), I find it contradictory. If in MWI all outcomes are ‘materialized’, we ought to see some very strange behaviors somewhere in “our branch”. Imagine throwing a dice; in one (poor) branch the result must be 6 all the time!

As in this picture, the leftmost scientist will only measure “up” for all eternity... and go crazy...

And we never see this kind of oddness in “our branch”. How come?

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#### DrChinese

Gold Member
And we never see this kind of oddness in “our branch”. How come?
Oddness? For one, there's me. And have you looked in the mirror lately?

Might make more sense than you realize...

Gold Member
Oddness? For one, there's me. And have you looked in the mirror lately?
lol :rofl:

DrC you are perfectly normal. You just have to take an avocado for his word!

Now, mirrors don’t work for Vampires & Devils, and I’m cool with that (green was never my favorite color anyway).

<-- see this odd skin color…? =MWI??

#### AkInfinity

LOL many worlds hypothesis is most nonesense. It's ridiculous this view is promoted; over say the de Broglie -eineseint view (which although i do not think is correct) at least makes sense

#### phinds

Gold Member
The thing that I just find unacceptable about the MWI is this: where does the matter/energy COME from when all of a sudden the entire universe splits in two? I mean, the MWI proponents DO seem to be saying that there really ARE two universes where there was one, so how was the matter/energy of the 2nd one created?

Are there any MWI proponents out there who can help me understand why this thought doesn't kill the MWI? I mean, clearly it doesn't since there is no possibility that all those believers just haven't thought of that problem.

#### bhobba

Mentor
The thing that I just find unacceptable about the MWI is this: where does the matter/energy COME from when all of a sudden the entire universe splits in two?
But it dossnt split or change - it simply keeps evolving deterministically. However after decoherence it can be divided into subsystems where each subsystem is a world.

Thanks
Bill

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#### phinds

Gold Member
But it dossnt split or change - it simply keeps evolving deterministically. However after decoherence is can be divided into subsystems where each subsystem is a world.

Thanks
Bill
I have no idea what thought you are expressing.

#### bhobba

Mentor
I have no idea what thought you are expressing.
After decoherence a pure state is transformed into an improper mixed state of the form sum pi |w>|bi><bi|<w| where |bi> is the outcome of the observation an |w> is the rest of the world including you. Pi positive, sum pi =1. In conventional interpretations a particular |w>|bi> is selected via observation with each of the pi considered the probability of getting that outcome, and everything keeps on evolving from that. However in many worlds nothing at all happens - the wave function of the universe just keeps on evolving but each |w>|bi> is considered a world. With each observation the universe is considered as 'partitioned' into a number of different worlds, but actually nothing at all happened - its just to get a grasp on it we have considered each of the 'parts' of the mixed state a separate world. This raises the issue of exactly how probabilities comes into MWI and you will find a lot of literature on that - it is a major issue in the interpretation.

It is a misconception to think energy etc all of a sudden came into existence - in fact nothing happened other than the universe as a whole continued to evolve totally deterministically. This is an unbelievably neat and mathematically beautiful interpretation. It has an enormous amount to commend it which is why many people hold to it. But can you stomach this exponentially growing copies of you and the rest of the universe with each observation? As one person said - is nature this extravagant? I personally find it a bit too 'weird' (for want of a better word) for my tastes and simply assume an observation picks out one of the |bi> after decoherence.

But recently have been giving it a second thought after looking a bit into the idea of eternal inflation:
http://en.wikipedia.org/wiki/Eternal_inflation

One cant help but get the sneaky feeling they are somehow connected.

Thanks
Bill

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#### phinds

Gold Member
I still have no idea what you are saying, except that it SEEMS to be on the order of "well yes, the universe splits in two but it doesn't REALLY split in two".

If there are two of me, are they both made out of matter? If so, where did it come from? If not, then the whole thing seems to be a meaningless contradiction.

#### bhobba

Mentor
I don't entirely follow what your issue is. After decoherence the universe is conceptually split into a number of 'parts'- each part is considered a world. Its interpretive - the particles that make up you are considered duplicated in each world. Where were they before? - they were part of the state of the entire universe but now can be considered to be composed of each of the worlds. It a bit like when an atom spontaneously emits a photon - where was the photon before? The system continues to evolve deterministically but now a photon has been detected. Same thing - because of decoherence the state of the universe after decoherence is of the form sum pi |w>|bi><bi|<w|. The interpretation simply conceptually considers each |w>|bi> a new world and in each world the particles that made up the rest of the world are duplicated - but its simply a part of the universe as whole just like with emission of the photon.

I found the following that may help:

'Each different version of a thing, and every “parallel world” may see itself as holding all of its energy and matter, but from an outside perspective (where the “many-worldness” becomes important) it’s just part of a greater whole. Either way, energy is always conserved. So, while it’s fun to talk about “other quantum realities” and “different universes”, it’s more accurate to say that everything is happening in one universe. One, stunningly complex, weirdly put together, entirely counter-intuitive universe.'

Basically nothing happens in MWI we simply interpret it as 'splitting' into different worlds.

BTW I hate arguing for interpretations I don't hold to so I hope some guy really into MWI will contribute.

But of recent times I have chatted enough about it to actually to want to go into the details further and get a book on it - I have ordered:
https://www.amazon.com/gp/product/0199546967/?tag=pfamazon01-20

One thing that occurred to me is how do you know, as a part of a particular world, if when it 'splits', the energy of your world has decreased ie the energy of each of the particles that make up you has split according to their pi in the mixed state? You wouldn't, because what we measure is energy compared to a certain standard which has also decreased in exactly the same way.

Thanks
Bill

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#### phinds

Gold Member
Interesting article ... thanks for the link.

So far, nothing I've heard changes my opinion that the MWI is just math mumbo-jumbo that has no meaning in the real world but I appreciate your attempt to enlighten me. It appears that on this subject, I am unenlightenable (but I'm good at making up words apparently)

#### Maui

The MWI(and qm in general) talks of realities, personal experience and classical mechanics talk about worlds. QM talks of wavefunctions and collapse, personal experience talks about particles in space and time. Some would even claim there is no conflict between the two.
Phinds, most quantum physicists hold more abstract ideas about the term 'world' and it is more mathematical and less classical. It's useless to argue over it, they think in terms of the formalism and you think in terms of sensory experience.

#### bhobba

Mentor
It appears that on this subject, I am unenlightenable (but I'm good at making up words apparently)
That's not my feeling - I think it just takes a bit of getting used to - that's all. I actually was more negative towards it when I started discussing it and I realised many of my objections were not valid. I am still not swayed by it but feel positive enough toward it to investigate the details further - hence forking out a bit of dosh for Wallace's book - only trouble is getting time to really give the detail a though study. I have Schlosshauer's book on decoherence and have read it but really want to give it a good study - as well as my abortive attempts to really get to grips with QFT and Renormalisation.

Ah well - at least I am retired now so can concentrate on it when I get the time.

Thanks
Bill

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#### nonequilibrium

Actually the beauty and allure of MW is no collapse occurs. Everything just keeps evolving - but after decoherence occurs the system is in a mixed state that is the sum of the possible outcomes. Noting at all happens - the universe keeps on evolving - but is now able to be conceptually separated into a number of 'parts' where each part is the outcome of the observation and considered a separate world.

Thanks
Bill
Hey,

I highlighted one of your statements.

Surely, as you say yourself, there is no collapse, i.e. there is only the Schrodinger equation, hence if you start with a pure state, you will always have a pure state, so how would the universe as a whole ever become a mixed state? Or are you talking about subsystems?

#### bhobba

Mentor
Surely, as you say yourself, there is no collapse, i.e. there is only the Schrodinger equation, hence if you start with a pure state, you will always have a pure state, so how would the universe as a whole ever become a mixed state? Or are you talking about subsystems?
This is what decoherence does - it changes a pure state into an improper mixed state by the process of tracing over the environment - you will find the detail in standard sources on decoherence such as Schlosshauer's book. The system, environment and observational apparatus as whole are in a pure state and continue to evolve as a pure state - but the system, environment and apparatus all become entangled and that's what leads to the appearance of a mixed state. It has exactly the same form as a mixed state and observationally is indistinguishable from one but is not prepared the same way as a proper mixed state (where a random system is presented for observation) so is given the name improper. This is the crux of decoherence being able or not able to solve the measurement problem - if it was an actual proper mixed state - problem solved - what you observe is there prior to observation and the measurement problem - poof gone. You can interpret it that way - and I do - but you do not have to which is the basis of the claim it doesn't solve the measurement problem. You can read about the issues involved in Schlosshauer's book.

MWI however takes a different tack - it doesn't interpret it as a proper mixed state but exactly as the formalism says - a state that is the sum of other states (interpreted as worlds) with pi's in front of each. The pi's are not interpreted as probabilities but as a sort of weight describing how much of the state contributes to each world. The state and its associated worlds continue to evolve deterministically. But since the pi's are not now interpreted as probabilities its a big issue for MWI how to get the Born rule and you will find a good deal of literature about it. In particular David Wallice, the author of the book I am getting, has done quite a bit of work on it.

Thanks
Bill

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#### AkInfinity

Phinds this will answer ur question. you dont get many worlds because is full of bs, but according tot hem every event like me typing this is a superposition of infinite worlds and when i make a dicisoin they split, so no energy is created is just that the paths separate. As you can see it is a bunch of bs, hwoever with this enterpretation the math equations work; but it also works iwth other interpretations so this isnt much proof

#### alweiss

If the many worlds picture is correct, wouldn't this mean that the Universe is not infinite(the whole universe, not the observable universe) and mean that some of our equations are false?

#### bhobba

Mentor
If the many worlds picture is correct, wouldn't this mean that the Universe is not infinite(the whole universe, not the observable universe) and mean that some of our equations are false?
No. It can be infinite or finite - it doesn't matter as far as MWI is concerned.

Thanks
Bill

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