In popular descriptions of quantum teleportation I see time and again
that it is explained by spooky action at a distance which is also simultaneous.
Now I know from relativity that if the action is simultaneous in one
frame the effect appears _before_ the cause in other frames.
If I am going to believe in time reversal for one frame it is no big
step for me to believe in time reversal for all frames, the effect
occurring in the past light cone of the cause.
If you explain it that way you can get away with spooky action at a
distance.
any comments?
Chris
In popular descriptions of quantum teleportation I see time and again
that it is explained by spooky action at a distance which is also simultaneous.
...
Now I know from relativity that if the action is simultaneous in one
frame the effect appears _before_ the cause in other frames.
...
Chris
Events that are on each others light cone are effectively
simultaneous (the metric separation is zero), and that is true for
all observers.
The very fact that we can see this time reversal in the theory, together
with the fact that these processes cannot be used to send information
faster than light, is a good reason to think that there is no action at
a distance, spooky or otherwise. In particular, the time reversal
immediately raises the question of who is the actor, and who the actee[*]
Quantum mechanics tells us what results we'll get. It doesn't say
anything about how it works, and popular science descriptions are
usually just misleading.
Sylvia.
[*] Spell check says that this isn't a word, but what does it know?
You are correct, of course, that QM does not offer any mechanism
for this behavior, and I agree that the popular descriptions are
little or no help. But I do think that this is something worth thinking about in order to get a deeper understanding, perhaps beyond QM.
I've been studying QM since the early 1970's, and it is only in the last decade or so that there has been much interest in the "interpretation"
of QM and what it implies about the mechanisms of particle
propagation. I think this is long over due.
On 6/13/22 10:43 AM, Richard Livingston wrote:
Events that are on each others light cone are effectivelyYes, for such pairs of events the metric separation is zero, and that
simultaneous (the metric separation is zero), and that is true for
all observers.
applies for all observers (it is really independent of observer and coordinates).
But that is not at all what "simultaneous" means. Rather, that is a
lightlike interval.
Simultaneous means at the same time, and that is a coordinate-dependent concept (because a coordinate system defines what one means by "time")
-- for a given coordinate system all events with the same value of the
time coordinate are simultaneous with each other. In an inertial
coordinate system, for each such value the locus of events is
necessarily a 3-D spacelike hypersurface. In general, for different coordinate systems these loci are completely different.
Tom Roberts
On 14/06/2022 17:15, Tom Roberts wrote:
Simultaneous means at the same time, and that is a
coordinate-dependent concept (because a coordinate system defines
what one means by "time") -- for a given coordinate system all
events with the same value of the time coordinate are simultaneous
with each other.
No, that is fundamentally upside down:
The "time" we experience is *proper* time, which is the (physical)
time clocks and everything tick *locally* (i.e. at and per
themselves), and is *universally* (an invariant of the geometry and)
one and the same for every observer, clocks and everything,
i.e. not even restricted to inertial motion or observers.
So, it is *proper* time that is (physical) "time" and, not per
chance, modulo more speculative research on time itself, it is the
primary parameter of any dynamical system.
OTOH, coordinate-time is an artefact of coordinate systems, i.e. of
a choice of reference frame, and it is a *relative* notion
that introduces distortions such as time dilation and length
contraction for the trajectory of any particle that is not simply at
rest in that frame.
Part of the problem is that the thinking can not go much beyond pure speculation until and unless we get experimental results that are either inconsistent with QM, or are consistent with it, but not fully described
by it, in the latter case indicating that QM is incomplete.
Sylvia.
On Thursday, June 16, 2022 at 2:27:54 AM UTC-5, Sylvia Else wrote:
...
Part of the problem is that the thinking can not go much beyond pure
speculation until and unless we get experimental results that are either
inconsistent with QM, or are consistent with it, but not fully described
by it, in the latter case indicating that QM is incomplete.
Sylvia.
Agreed, but part of the problem has been that there has been little thinking (except by a very few) about what quantum mechanics implies about our concepts of time and causality, nor how the Born Rule works. There are
two ways to discover deeper theories about such things. One is by an experiment that gives an unexpected result (e.g. the Lamb shift) that inspires a theory. The other is a speculation that permits an experimental test. (And then there are the speculations that are inherently untestable, e.g. the so called many worlds interpretation of QM.)
I suspect out current impasse in physics is due to an unexamined assumption in our theory. While it would be nice for an experiment to lead us in that direction, until then we can speculate and try to test those ideas. But first
we have to admit that there is something that needs a deeper understanding.
Rich L.
...
Still, we don't actually know that there is anything underneath quantum mechanics (QM) that exists. Unless there are infinite layers of
mechanism, there must be a point at which it just does what it does,
with no more explanation being possible.
Perhaps QM has reached the bottom level, and that's just how the
universe is.
Sylvia.
On 6/15/22 1:18 AM, Julio Di Egidio wrote:
On 14/06/2022 17:15, Tom Roberts wrote:
Simultaneous means at the same time, and that is a
coordinate-dependent concept (because a coordinate system defines
what one means by "time") -- for a given coordinate system all
events with the same value of the time coordinate are simultaneous
with each other.
No, that is fundamentally upside down:No, it is not. It is what these words mean, and what is required for determining simultaneity for spatially-separated objects.
one and the same for every observer, clocks and everything,No. Each observer, object, or clock's proper time is completely
independent of the proper time for other observers, objects, or clocks.
But the subject was simultaneity, for objects separated spatially. For
that, the proper time of any object is useless -- a given observer,
object, or clock can only apply its proper time to events located along
its worldline, which does not include objects separated spatially.
OTOH, coordinate-time is an artefact of coordinate systems, i.e. ofYes. Necessarily so. "Simultaneous" is a relative concept. (Simultaneity
a choice of reference frame, and it is a *relative* notion
is of course only one aspect of a coordinate system.)
The coordinate system does not induce "time
dilation and length contraction" -- they are generated by certain
measurement procedures applied to objects moving relative to an inertial coordinate system.
On Monday, June 20, 2022 at 3:05:28 AM UTC-5, Sylvia Else wrote:
For example, in
something like the two slit experiment, how does the photon end up in
only one spot always, as opposed to only statistically on average one
spot?
For a given photon we calculate a wave function that can be used
to predict the probability distribution of photon destinations.
But even this has a problem with entanglement experiments and Bells Inequality.
But there are enough hints that our physics is not complete yet that I'm hopeful that we can still dig a little bit deeper.
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