On 21-04-2016 07:48, Brent Meeker wrote:
On 4/20/2016 10:34 PM, smitra wrote:
On 20-04-2016 07:49, Brent Meeker wrote:
On 4/19/2016 10:21 PM, smitra wrote:
On 20-04-2016 03:02, Bruce Kellett wrote:
On 20/04/2016 6:56 am, smitra wrote:
The mistake made is to invoke classical reasoning after the
measurements are made. If the choice for the orientation of the
polarizers were not made in advance, then Alice and Bob cannot
have said to have made any definite choices at all.
I think you need to learn something about decoherence , and the
emergence of the 'classical' from the 'quantum'. In the final
analysis, Alice and Bob meet to compare their results. By that
stage,
their results, and their relative magnet orientations, are definite
and classical (FAPP if you wish). And that is the end result we
have
to explain. All else is boondoggle.
Invoking FAPP is precisely where your argument goes wrong. While due
to decoherence the macroscopic world looks classical, in reality
(assuming MWI) it not classical. This means that when Bob meets
with Alice that the settings Alice chose are still not determined.
It is only when Alice communicates to Bob what her polarizer
settings were that Bob becomes localized in that particular sector
of the multiverse where this is now fixed.
What if Bob misunderstands what Alice said - does he get localized in
a different universe. Does he switch back when Alice shows him her
notebook? What if Alice and Bob don't talk directly but instead each
whispers in Bruce's ear, but they speak urdu so Bruce doesn't know
what they said until he consults a translator?
As you write below and as I've just replied to Bruce, what matters is
that this information does not spread faster than the speed of light.
But in principle, the sector of the multiverse where is is located has
a width measured in branches of the environment, that is inversely
proportional the the amount of reliable information he has about his
local information. So, if he has a lot of hair on his head and has
never counted the exact number then he is in many different branches
where this number is different.
That seems to be variety of QBism in which case we can stop
attributing existence to the wave function - it's just a summary of
Alice's (or Bob's) knowledge and it "collapses" when she gains new
knowledge.
When one invokes observers one should try to define as precisely as
possible what is meant by that. In the MWI this is relevant as one
includes the observer in the description of the quantum state. So, one
has to address how to split the degrees of freedom into environmental
degrees of freedom and the degrees of freedom that belong to the
observer. Then it seems to me that one should model the observer as a
computer that is processing information, that model that one specifies
should be taken as the definition of the observer.
So, Alice and Bob are at any instant algorithms that can be formally
represented as finite state machines. They can always be represented by
specifying some finite bitstring.
Then if information in the environment is present in the observer, then
that means that there is entanglement of the degrees of freedom in the
environment where that information can be found, and the state of the
observer as specified by its defining bitstring.
if the bitstring defining Bob is the same across several branches where
the information in the bitstring that defines Alice contains different
information about her experimental settings, then from Bob's
perspective, Alice's settings are still indeterminate. Suppose that the
information has already decohered and the atoms that make up Bob are now
in different states according to which setting Alice has chosen. But as
long as this hasn't affected the bitstring that defines Bob, then Bob is
still the same in all these different sectors.
That Bob's bitstring won't be affected is easy to see. The information
that leaks out via decoherence is not accessible a the macroscopic
level, it is hidden in the microscopic degrees of freedom. The bitstring
that defines Bob contains only information that exists at a macroscopic
level.Even if you allow for some microscopic information to leak into
Bob (information that is not visible after a coarse graining is
performed), the bitstring that defines him has some finite length and
can thus encode only a limited amount of information. The information
about Alice's settings are hidden in the environment, they cannot be
recovered from only a small part of the environment, you need pretty
much the entire future lightcone to recover it. But if only part of it
were sufficient, then Bob's bitstring could not possibly have enough
room for containing a copy of all that information.
Saibal
Brent
The person I was when I was 3 years old is dead. He died because
too much new information was added to his brain.
-- Saibal Mitra
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
