On 16 Apr 2016, at 01:46, Bruce Kellett wrote:
On 16/04/2016 12:20 am, Bruno Marchal wrote:
On 14 Apr 2016, at 14:31, Bruce Kellett wrote:
It is interesting that you have not answered my question about
what exactly you mean by 'counterfactual definiteness' so that we
know what you mean when you say that a theory is not
counterfactually definite.
It is hard to define, especially if we avoid being technical. But
we have a good example: QM-with-collapse (or QM with a single
universe). Like Einstein already explain at the Solvay Meeting: if
QM (with a single universe) is correct, we can't ascribe an element
of reality knowing a result that we would obtain with certainty if
we would make some measurement, but will not do. Then Kochen and
Specker proved that QM (+ a single universe) is precisely like
that. The proof does not apply to the many-world, although it might
apply to some too much naive rendering of the many world (notably
if we interpret wrongly the singlet state as I have explained in
previous post).
I do not understand what you are saying. Are you claiming that
ordinary QM with collapse is counterfactually definite because
Einstein realism does not apply?
I say the contrary: t is NOT counterfactual making Einstein realism
not able to be applied.
I.e., we cannot know with certainty what would have been the outcome
of an experiment that was not performed? (This is also the
consequence of the Kochen-Specker result that no set of hidden
variables can predict the results of all possible spin measurements
on a spin 1/2 particle.) I would have thought that this was one
possible definition of counterfactual indefiniteness.
I would be OK too.
What additional fact about MWI changes this conclusion?
None. Except that with a single physical reality that
counterfactualness entails non locality, but the same
conunterfactualness with eother computationalism and/or QM-without
collapse does not entail physical nopn locality, but only its
statistical *appearances* in the memory of the machine testing it.
Since in MWI all possible experiments are performed in some word or
other, I would have thought that experimental outcomes are available
for all possible experiments -- nothing is actually indefinite
It is relatively to you knowledge of a state. If you measure the
position very precisely, you "soul" is attached to an infinity of
"body/representation" with many definite, but different, momenta.
If you measure something the result is definite only relatively to one
representation among many. If you look at the transfer of information
in the 3p picture of the entire quantum teleportation, you can see
that the information is spread locally at all times. It is even
somehow made explicit if you are using Bob Coecke's use category to
describe such quantum events.
http://arxiv.org/abs/quant-ph/0402130
http://arxiv.org/abs/quant-ph/0402014
-- even though not all outcomes occur in this one world that we
happen to inhabit at the moment.
There is no real sense to say that we inhabit a world. We are all the
times in an infinity of worlds/situation, which differentiate or not
relatively to what we interact with.
An electronic orbital is a sort of map of the set of all words we are
relatively to the possible energy of that "electron".
But by the linearity of the tensor product, we share the worlds only
with the person we interact with.
You might look at the Rubin's paper (provided by Scerir). Or Bob's
Coocke.
I will comment your other post with more detail perhaps later. But I
do not really grasp your
<<
A and B perform their measurements at spacelike separation, but each
chooses the measurement orientation outside the light cone of the
other. There are four possible combinations of results, corresponding
to four worlds in the
MWI: |+>|+'>, |+>|-'>, |->|+'>, and |->|-'>.
Since each observer has a 50% chance of getting |+> and 50% of getting
|->, and the two measurements are completely independent of each
other, it would seem that each of these four worlds is equally likely.
>>
The expressions |+>|+'>, |+>|-'>, |->|+'>, and |->|-'> does not
describe the superposition in which the observer will self-localize
in: it is not the singlet state, which describe an infinity of worlds
where all pair of particles of Bob and Alice are correlated.
The whole point is that the result of the measurement does not
describe the state we measure, but the partition of the sort of worlds
to which we *relatively* belong.
It is a bit long to verify by hand, but the linearity of tensor
products and of the evolution makes the correlated state remaining
correlated, and when one of them make a measurement, it just tell Bob
in which partition of the multiverse he *and "his" Alice" belong.
Only if the states of Alice and Bob electron where counterfactually
definite before the measurement would this entail a crazy spooky
action at a distance. You talk like if Bob or Alice are well defined
relatively to each other, but that is not the case: they both get
random event, just correlated in all universes, and they can't know
which one it is, only the partition of the multiverse given by the
singlet state.
Bruno
Bruce
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