[extropy-chat] Is Many Worlds testable?

[Lee Corbin]

John Clark writes

> I don't think the MWI is more provable or un-provable then any other
> interpretation;

This seems to be at variance with what you (very skillfully) present
below. David Deutsch indeed presented (in his 1985 or 86 article
in the Davies book "The Ghost in the Atom") the argument that the
first conscious computer will have an emphatic opinion concerning
MWI, and this opinion will be that many worlds exist.

> but I want to make a prediction, I predict it will become more popular.
> It may not be science

But then, what happens after we all "remember that there was one, but
do not remember which one"?  We will all know in our bones..., er, I
mean transistors..., that the electron had to have gone through both
slots, but in different universes.  It will just be obvious.  (But anyone
reading this, please see John's great description below!)

> But actually I think MWI is testable. I've communicated with David Deutsch
> about this and he proposes an experiment to see if the MWI is right or not;

Like I said, see the old book "The Ghost in the Atom" for a lot of mediocre
essays (except the great David Deutsch one). His argument has been around
now for two decades.

> In the Deutsch test a conscious quantum computer shoots electrons at
> a metal plate that has 2 small slits in it. It does this one at a time.
> After leaving the plate the electrons hit some photographic film, but do not
> look at the photograph until later. The quantum mind has detectors near
> each slit so it knows which slit the various electrons went through.
> The quantum mind now signs a document saying that it has observed each
> and every electron and knows what slit each electron went through.

Yes!  The computer (or enhanced human) will remember this, and this
alone:  "The electron went through *one* slit, and definitely went through
that slit!".

> It is very important that the document does not say which slit the
> electrons went through, it only says that they went through one
> slit and one slit only, and that the mind has knowledge of which slit.
> After the electrons pass the plate but before they hit the photographic
> film (just place the film a long way away to give you time)
> the mind then uses quantum erasure to completely destroy his memory
> of which slit the electrons went through. The only part remaining is the
> document.

Well, the document won't quite be the only remaining part.
We will also *remember* that  there was just one electron
going through just *one* slit. For those who are scanning
this too quickly, let me explain another way:  as the universes
split (because the electron had an amplitude to go one way
and also an amplitude to go the other way), so also will we,
since we will be, in effect, conscious computers.

Then the version of me where the electron went Up knows
(i) there was just one electron, no superposition jazz (so
far as I will be able to witness), and (ii) that the electron
went Up.  Likewise the version of me (in the other universe)
who saw the electron go Down knows (i) there was just one
electron, no superposition jazz, and (ii) that the electron went
Down.

Now in a way that I cannot do now, I shall be able to simply
forget (ii) in each case. (Were it as easy to forget some people
I've known in RL!  :-)

Now, since (i) is exactly the same in both universes, and the
electron is also close enough in both universes for the two
to merge, then there becomes just one branch again. All that
I will know---and yes, the written testimony of the document
does add conviction too, I suppose---is that I saw the electron
going through just one slit.

But I have been able to forget which slit!  Since interference
*does* happen, there is only one possible conclusion:  I
was in two different universes at the same time.  They split
and then merged.

Only the insane will be unable to directly witness and deeply
feel the spitting and recombination of the universes. 

> Now develop the photographic plate and look at it. According
> to Deutsch if you see interference bands then the many world interpretation
> is correct. If you do not see interference bands then there are no worlds
> but this one and the conventional interpretation is correct.

Of course, it is absurd to anticipate that somehow the fluidic substance
"consciousness" exists after all, and we have souls, and God made the
consciousness of our souls able to prevent interference in scientific
experiments! This won't happen.

> In the Copenhagen interpretation when the results of a measurement enters
> the consciousness of an observer the wave function collapses, in effect all
> the universes except one disappear without a trace so you get no
> interference.

I hope there are some people foolish enough to bet on that---I can
always use a little more money, either now or after the singularity,
if my frozen noggin is lucky enough to survive it.

Lee

> In the many worlds model all the other worlds will converge
> back into one universe when the electrons hit the photographic film but
> their influence will still be felt, you'll see indications that the electron
> went through slot A only and indications that it went through slot B only,
> and that's what causes interference.