On speed limits and causal disconnection, with special reference to Aleksandar Vukelja

It apparently came as a shock to Einstein in about 1910 to learn that
SR and the speed limit do not apply to causally-disconnected events.


1) The end of a searchlight beam can apparently move laterally at any
speed whatever (though particular photons move radially along it at c).
This is related to rotating coordinate systems, in which most of the
Universe can sail around transversely at unlimited speed.

2) (I remember reading that) the blades of scissors can move with
unlimited relative velocity, since their motion is also causally
disconnected. (Come to think of it, perhaps this is related to the
rotational motion as in 1.) It seems to contradict SR (where the
relative motion of two particles is =c) because THE PARTICLES COULD BE
THE TIPS OF A PAIR OF SCISSORS.

3) In cosmology at large, (I also seem to remember reading that)
galaxies "move" with arbitrary relative speed because their "motion" is
not causally related. If true, this should be another way of looking
at the Robertson-Walker metric-solution, which (as the vulgar say) is
about "space stretching" rather than galaxies moving through space
(when their motion would be subject to SR).
Hence the expanding Universe can extend indefinitely beyond the
light-horizon.


It doesn't seem fair, somehow ....

"Too Many Kooks Spoil the Brothel" wrote in message
oups.com...
It apparently came as a shock to Einstein in about 1910 to learn that
SR and the speed limit do not apply to causally-disconnected events.


1) The end of a searchlight beam can apparently move laterally at any
speed whatever (though particular photons move radially along it at c).
This is related to rotating coordinate systems, in which most of the
Universe can sail around transversely at unlimited speed.

http://hermes.physics.adelaide.edu.a...Light/FTL.html
3. "Shadows and Light Spots"
http://hermes.physics.adelaide.edu.a...ght/FTL.html#3


2) (I remember reading that) the blades of scissors can move with
unlimited relative velocity, since their motion is also causally
disconnected. (Come to think of it, perhaps this is related to the
rotational motion as in 1.) It seems to contradict SR (where the
relative motion of two particles is =c) because THE PARTICLES COULD BE
THE TIPS OF A PAIR OF SCISSORS.

http://hermes.physics.adelaide.edu.a.../scissors.html
The Superluminal Scissors


3) In cosmology at large, (I also seem to remember reading that)
galaxies "move" with arbitrary relative speed because their "motion" is
not causally related. If true, this should be another way of looking
at the Robertson-Walker metric-solution, which (as the vulgar say) is
about "space stretching" rather than galaxies moving through space
(when their motion would be subject to SR).
Hence the expanding Universe can extend indefinitely beyond the
light-horizon.

http://arxiv.org/PS_cache/gr-qc/pdf/9712/9712019.pdf
| "But two particles at different points on a curved manifold
| do not have any well-defined notion of relative velocity -
| the concept simply makes no sense. Of course, in certain
| special situations it is still useful to talk as if it did
| make sense, but it is necessary to understand that
| occasional usefulness is not a substitute for rigorous
| definition. In cosmology, for example, the light from
| distant galaxies is redshifted with respect to the
| requencies we would observe from a nearby stationary source.
| Since this phenomenon bears such a close resemblance to the
| conventional Doppler effect due to relative motion, it is
| very tempting to say that the galaxies are "receding away
| from us" at a speed defined by their redshift. At a
| rigorous level this is nonsense, what Wittgenstein would
| all a "grammatical mistake" - the galaxies are not receding,
| since the notion of their velocity with respect to us is
| not well-defined. What is actually happening is that the
| metric of spacetime between us and the galaxies has changed
| (the universe has expanded) along the path of the photon
| from here to there, leading to an increase in the wavelength
| of the light. As an example of how you can go wrong, naive
| application of the Doppler formula to the redshift of
| galaxies implies that some of them are receding faster than
| light, in apparent contradiction with relativity. The
| resolution of this apparent paradox is simply that the very
| notion of their recession should not be taken literally."

It doesn't seem fair, somehow ....

Who ordered fairness anyway? ;-)

Dirk Vdm

Too Many Kooks Spoil the Brothel wrote:

It apparently came as a shock to Einstein in about 1910 to learn that
SR and the speed limit do not apply to causally-disconnected events.
[snip]

Hey stooopid, lightspeed is the fastst velocity of information
propagation. That is the whole of it, enforcing causality among other
things. Any event that does not transfer information can propagate at
arbitrary rates - infinitely fast is OK. Example: Wave function
collapse into an consistent observable in the Einstein-Podolsky-Rosen
Paradox and the Bell Inequality. Quantum eraser and quantum double
eraser experiments.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

Uncle Al wrote:
Too Many Kooks Spoil the Brothel wrote:

It apparently came as a shock to Einstein in about 1910 to learn
that
SR and the speed limit do not apply to causally-disconnected
events.
[snip]

Hey stooopid, lightspeed is the fastst velocity of information
propagation. That is the whole of it, enforcing causality among
other
things. Any event that does not transfer information can propagate
at
arbitrary rates - infinitely fast is OK. Example: Wave function
collapse into an consistent observable in the Einstein-Podolsky-Rosen
Paradox and the Bell Inequality. Quantum eraser and quantum double
eraser experiments.

Heeeeeeeeeeeeeeeeeeeeeeeey
stoooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooooopid,

-- gosh, I always wanted to do that, Uncle! --

NOW I remember why I thought it warn't fair:-
The Universe started all together in a Big Bang, right? That means
that, directly or indirectly, *everything* should be causally connected
.... at least within the light-horizon ...