
Too many worlds - prostoalex
http://aeon.co/magazine/science/is-the-many-worlds-hypothesis-just-a-fantasy/
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jessriedel
Not really sure what the purpose of this piece is. My research concentrates on
figuring out what exactly is missing from MWI to make it a complete, sensible
theory, so I am very happy to entertain criticisms of it. But the author don't
make much attempt to understand the arguments of MWI proponents. It's
basically just MWI bashing.

He mostly attacks the popular-level work of Tegmark, or other big-name MWI
proponents like Hawking who don't actually publish on this stuff. Tegmark is a
fantastically smart guy with deep insight on a lot of stuff, but his approach
to the measurement problem simply isn't as clearly and exhaustively laid out
as people who concentrate on this full time. In particular, you really need to
address guys like David Wallace, for whom articulating MWI from a technical
background is part of their core research.

It would be like attacking sloppy language in a popular book by a world-famous
cancer researcher regarding evidence for natural selection. The cancer
researcher has a pretty good grasp on what constitutes evidence for natural
selection, but even he can slip up and (say) fall into a just-so story if he's
not careful. Attacking that guy is not a good way to engage with relevant
philosophy.

Anyways, I have a technical comment on this:

> This picture really gets extravagant when you appreciate what a measurement
> is. In one view, any interaction between one quantum entity and another – a
> photon of light bouncing off an atom – can produce alternative outcomes, and
> so demands parallel universes.

This isn't right in general. There definitely needs to be some sort of
amplification (and hence, usage of negentropy) to get the production of
branches in the wavefunction. Systems that have thermalized don't branch any
more.

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drcode
This article seems silly: Both the Copenhagen and Multiple Worlds
interpretation (as far as I understand, as a non-physicist) yield the same
objective answers, so deciding on one interpretation or the other is really a
matter of "taste" for the physicists involved... in a way, each physicist can
arbitrarily decide for themselves which interpretation they find most useful
for their work.

Now Mr. Philip Ball comes along, who isn't a thoretical physicist AFAIK, and
says that the MWI people are doing it wrong.

In this article, the only concrete argument he gives for why MWI is "wrong" is
because it blurs the idea of "self", which the author finds distasteful. But
science doesn't "care" about tastefulness, all it cares about is hypotheses,
experiments and repeatability. Unless the author can cite an experiment that
shows MWI to be invalid (or alternatively can make a formal argument as to why
it represents a needlessly complex hypothesis, ala Occam's Razor) he is not
basing his argument on a scientific foundation.

~~~
eridius
MWI isn't scientific to begin with. As you said, it's indistinguishable from
Copenhagen as far as prediction and testability is concerned. The only reason
to prefer MWI is for whiffy non-scientific reasons, and that's what this
article is challenging.

~~~
AReallyGoodName
If you can't distinguish MWI from any other interpretations results than
doesn't that also indicate that the other interpretations have just as many
issues?

In fact given the name is suffixed with interpretation I really don't get the
authors point. We have a way of thinking about things, nothing more, hence
that suffix.As you point out it's scientifically indistinguishable from other
interpretations. So why pick on MWI. Why not write the exact same speil about
the Copenhagen interpretation which is no more or less testable (if it was
we'd be able to distinguish its results from the other interpretations)

~~~
eridius
Because the complaint isn't that it isn't testable. Since we're talking about
non-testable properties of these models, the only way in which they differ is
in how we think about them, which puts this in the realm of philosophy. And
the article is arguing that the philosophical implications of MWI are
problematic.

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kmicklas
This article is complete garbage - full of ad hominem attacks and
philosophical whining. The author rejects MWI for apparently completely
emotional reasons and seems to take the idea of there being multiple worlds in
a much too concrete manner.

~~~
meowface
Philosophical whining isn't so bad if the philosophical logic is actually
sound. This article is a product of someone who knows little of either
philosophy or physics attempting to use the former to refute ideas of the
latter.

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eridius
One big complaint I have with MWI is it seems to throw probability out the
window. If every possible result of a quantum calculation actually has
physical reality, then doesn't that make all the states equally likely? The
only solution I can think of to that is to have every quantum calculation
actually spawn an infinity of worlds, of which a certain percentage of them
have a given result that matches the probability of that result in the
wavefunction. And that just seems to make MWI incredibly messy. There's a
certain conceptual cleanness in saying that the universe splits for every
decision such that all possible decisions have their own world, but saying
that every possible quantum event results in an infinity of worlds (which also
means that for every possible result there's also an infinity of identical
worlds for that state) just seems ridiculous.

~~~
Houshalter
Imagine a ball falling down a peg board. Each time it hits a peg, it has a 50%
chance of falling either direction. This creates a Gaussian distribution where
it lands. It has a very high probability of landing in the exact center, and
slightly less probability of landing to the right, and even less at landing to
the far right, etc.

See this image:
[http://ptrow.com/articles/Galton_June_07_files/GaltonBoard2....](http://ptrow.com/articles/Galton_June_07_files/GaltonBoard2.jpg)

Now imagine instead of probability, you just split universes each time it hits
a peg. One universe the ball goes to the left, and in one universe, the ball
goes to the right. Each possibility gets it's own universe.

Then the same result happens. The majority of universes have the ball land in
the middle, and very few universes have it land on the tails. But each
possibility does have it's own universe. It's just some things happen more
than others. If you pick a random universe, you are more likely to end up in
one with the ball in the middle, then on a tail.

And this doesn't require an infinite number of universes. It's a completely
discrete system.

~~~
eridius
I appreciate the example here, but this only works when every decision has 2
outcomes with a 50/50 probability distribution (or more generally, when every
decision has an even weighting between all results). I don't pretend to have a
good understanding of quantum mechanics, but my impression is that this model
doesn't match how quantum "decisions" actually work.

~~~
Houshalter
It's my understanding that that's exactly how quantum physics works. E.g. a
particle has a fixed number of things it can do each moment. E.g move left or
right, or whatever. It's the aggregate combination of all these possibilities
that produce the probability distributions we observe. But at some low level,
there's just a uniform distribution over some number of possibilities.

~~~
eridius
But move left/right/whatever by what distance?

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dkbrk
I'm not an expert in this area, so please feel free to correct me if I've made
a mistake or am completely and utterly wrong.

From what I understand, the Many-Worlds Interpretation is, in effect, the
"default" hypothesis, insofar as that it follows naturally from state
evolution according to the Schrodinger equation. The burden of proof is on the
Copenhagen Interpretation to provide some additional mechanism which
_destroys_ the quantum states we don't observe.

Take, for example, the double slit experiment with a single photon. If we
don't measure which slit it passes through, it has the pure state which we can
describe as (|left> \+ |right>), and you can solve the equations with space
and time to see that |left> and |right> overlap after they diffract past the
slits, so you get an interference pattern.

If you measure which slit it passes through, the photon's states get entanged
with the experimental apparatus. For example, |left> is now entanged with the
left detector resistering its passing, which causes an electric current to a
display, which causes photons to be emitted, which interact with the
laboratory, and some of which register on our retinas, which cause our neurons
to be in a different state, etc.. So the wavefunction is now:

    
    
        |left, measured-left, brain-saw-apparatus-say-photon-went-left, ...> + |right,...>
    

The photon is now thoroughly entanged with the state of our brain and the
entire laboratory, so when the photon diffracts after the slit the two states
|left,...> and |right,...> no longer overlap and can't interfere. It's much
the same thing as EPR, except rather than (|0> \+ |1>) getting entangled with
a second particle to produce (|0,0> \+ |1,1>), it gets entangled with all the
many degrees of freedom of the laboratory, and our brain, and the entire
world. Postulating that if we observe |left, ...> then |right, ...> no longer
"exists" is entirely analagous to particle B in EPR "observing" that if it is
in the state |0,0> then |1,1> no longer exists.

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RobertoG
It seems to me that the author just don't feel comfortable with MWI. He feels
threatened by it, in the same way people didn't feel comfortable with
Copernic, and just decide that it has not to be right. Doesn't look like a
good basis for doing science.

In my opinion, MWI is the simplest explanation. In all the others you have to
add strange components to make it works.

In David Deutsch's "The fabric of reality" there is a good philosophic defense
of many worlds. At some point he says something along the lines of: "if in the
double-slit experiment photons are interfering with ghost-photons, what it
means to say that those particles doesn't exist 'in reality'? "

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grondilu
> Here, after all, is a theory that seems to allow everything conceivable to
> happen.

That seems inaccurate. Brian Green once joked about the existence of a
universe where Sarah Palin is the president of the United states, ruling this
possibility out as incompatible with the laws of physics[1].

I'm not sure why Max Tegmark often states that every decision we make causes a
split of the Multiverse, for instance. Do we know for sure that the processes
in our brain are quantum and not classical? They can be I guess, but I doubt
they are necessarily.

1\.
[https://www.youtube.com/watch?v=NqyBKJL1eyk](https://www.youtube.com/watch?v=NqyBKJL1eyk)

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jblow
I came here to post "this article is garbage" but I see I have been beaten to
it 3 times by the only 3 other comments here. So.

~~~
Houshalter
HN needs a downvote button for articles.

