[ExI] Probability is "subjectively objective".

Lee Corbin lcorbin at rawbw.com
Tue Jul 15 04:32:49 UTC 2008


Damien writes

> At 08:13 PM 7/14/2008 -0700, Lee wrote:
> 
>>MWI has *no* problem reconciling these things.
>>(One copy of you ends up in a universe with a distant friend who reports
>>the same result you got, and the other copy of you ends up in the 
>>same universe with a copy of your friend, and once again *they* 
>>agree upon the result.
> 
> And why this curious and convenient restriction? Well, see, because
> 
>> The basic mathematical operation of QM exhibits just these two universes,
>> not four.)

Without being any expert, I think that often there is more
to it than just the math. Consider that EPR was first applied
(well, as applied as any thought experiment is ever applied)
to electron pairs.  So instead of sending photons off in opposite
directions and checking polarization, we send electrons, and
check spin direction.  Now by conservation of angular
momentum (as I understand it), if one of the electrons were to
be found spin-up, then the other would *have* to be found
spin-down.

But, predictably, it's the classic tale:  at the moment you make a
measurement here, there is a 50% chance you'll find it spin-up
and a 50% chance you'll find it spin-down.  Very far away,
your fellow experimentalist must find it to be just the opposite
to what you found.  That all seems natural enough, until you
wonder how the results of *your* measurement here flew to
your friend and determined his outcome there (or, if you are in a 
relativistic frame of reference where the thing for him happened
before the thing for you, how the results of *his* measurement
there flew to you here and determined your outcome).

But it's nonsense to suppose that anything at all flew. The only
sensible idea is that at the very instant you put the question to
your electron, your universe locally splits, just like a sheet of
plastic pinched on either side can be pulled apart.  Distantly,
your friend also pulls apart the universes, and when his split
meets your split somewhere in between, it can be argued that
there are only two universes (not four) that result because in
either of the two other (absent) universes, youse guys would
find that the law of angular momentum had been violated. And
we can't have that.

Or, in more detail, according to that high apostle of QM, Sir Roger himself,

http://lists.extropy.org/pipermail/extropy-chat/2008-January/040032.html

Lee

> As a physicist pal once put it to me:
> 
> "ALL the action in QM systems comes in the cross terms.  From algebra 
> you know (x + y)^2 = x^2 + y^2 + 2*x*y.  The squared terms are called 
> intensities and the cross terms are the amplitudes times each 
> other.  When you have a term for each atom in a bowling ball or 
> brain, it turns out that the coefficient for each of the cross terms 
> are random relative to each other due to environmental decoherence 
> and they cancel out leaving the sum of intensities, which is, by 
> definition, classical."
> 
> Which is peachy, but still looks like numerology to me (in my 
> ignorance). The "unreasonable effectiveness of mathematics" yet 
> again--and thank you, Professor Wigner.




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