scerir
Jan2-09, 06:00 AM
Ian Macmillan:
> I have to say that I am confused about the term
> "a-causal" from "s", which I understood to mean
> "without cause", or lately in arbitrary time
> assignment, to refer to where an event is influenced
> by a "future" condition. I confess ignorance about
> the introduction of causality in this context.
Schrodinger wrote: "Franz Exner (to whom
I am personally indebted for his exceptionally great
support) was the first who contemplated the possibility
of an acausal conception of nature."
He also wrote: "In my opinion this question [acausality
in nature] does not involve a decision as to
what the real character of a natural happening is,
but rather as to whether the one or the other
predisposition of mind be the more useful and convenient
one with which to approach nature. [...].
We can hardly imagine any experimental facts which would
finally decide whether Nature is absolutely determined
or is partially indetermined. The most that can be decided
is whether the one or the other concept leads to the simpler
and clearer survey of all the observed facts."
As for the weird behaviour of the bi-particles
it is incorrect to say that the experimenter’s
arbitrary choice of measuring the state of the idler
particle, at wing A, somehow CAUSED the collapse
of the state of the signal particle at wing B.
Only nonlocal, instantaneous, uncaused correlations-
-at-a-distance are predicted by quantum theory.
And as many exps have shown, there is no before
and no after.
The conclusion might be that, while an individual event
only happen, i.e. at wing A, its INTERPRETATION might
depend on another individual event happening, in the
past or even in the far future, at wing B.
Now imagine we do not like this a-causal interpretation
of quantum correlations and imagine we want to check
whether another, causal interpretation would be possible,
i.e. an interpretation according to which a measuremnt
at wing A, performed on the photon a, would CAUSE
a specific collapse, at wing B, of the wavepacket of the
photon b. To check this we need a source of bi-photons,
a specific SPDC source, for that purpose. Unfortunately
we realize very soon that such a specific SPDC source, but
preserving quantum correlations, simply cannot exist
(unless John Cramer will be successful with his "bilking"
experiment.)
At least this is my humble idea of all that.
s.
[[Mod. note -- There is also another very common usage of "acausal",
meaning simply "outside the light cone". For example, we might say
that the correlation between observations at events A and B is acausal
to mean that neither of A or B is contained in the other's future light
cone, i.e. that speed-of-light signals sent from one of {A,B} can't
reach the other. -- jt]]
> I have to say that I am confused about the term
> "a-causal" from "s", which I understood to mean
> "without cause", or lately in arbitrary time
> assignment, to refer to where an event is influenced
> by a "future" condition. I confess ignorance about
> the introduction of causality in this context.
Schrodinger wrote: "Franz Exner (to whom
I am personally indebted for his exceptionally great
support) was the first who contemplated the possibility
of an acausal conception of nature."
He also wrote: "In my opinion this question [acausality
in nature] does not involve a decision as to
what the real character of a natural happening is,
but rather as to whether the one or the other
predisposition of mind be the more useful and convenient
one with which to approach nature. [...].
We can hardly imagine any experimental facts which would
finally decide whether Nature is absolutely determined
or is partially indetermined. The most that can be decided
is whether the one or the other concept leads to the simpler
and clearer survey of all the observed facts."
As for the weird behaviour of the bi-particles
it is incorrect to say that the experimenter’s
arbitrary choice of measuring the state of the idler
particle, at wing A, somehow CAUSED the collapse
of the state of the signal particle at wing B.
Only nonlocal, instantaneous, uncaused correlations-
-at-a-distance are predicted by quantum theory.
And as many exps have shown, there is no before
and no after.
The conclusion might be that, while an individual event
only happen, i.e. at wing A, its INTERPRETATION might
depend on another individual event happening, in the
past or even in the far future, at wing B.
Now imagine we do not like this a-causal interpretation
of quantum correlations and imagine we want to check
whether another, causal interpretation would be possible,
i.e. an interpretation according to which a measuremnt
at wing A, performed on the photon a, would CAUSE
a specific collapse, at wing B, of the wavepacket of the
photon b. To check this we need a source of bi-photons,
a specific SPDC source, for that purpose. Unfortunately
we realize very soon that such a specific SPDC source, but
preserving quantum correlations, simply cannot exist
(unless John Cramer will be successful with his "bilking"
experiment.)
At least this is my humble idea of all that.
s.
[[Mod. note -- There is also another very common usage of "acausal",
meaning simply "outside the light cone". For example, we might say
that the correlation between observations at events A and B is acausal
to mean that neither of A or B is contained in the other's future light
cone, i.e. that speed-of-light signals sent from one of {A,B} can't
reach the other. -- jt]]