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Empirically Confirmed Superluminal Velocities?



 
 
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  #1  
Old October 24th 03, 04:19 AM
Robert Clark
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

wrote in message news: ...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

You're aware of the discussions on sci.physics.relativity that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement. This is because of the uncertainty of
synchronizing clocks in two different locations. The standard SR
method of using light-signals requires the assumption of the constancy
of the one-way speed of light. [1]
I was interested to see that in some descriptions of the experiment
of Wang et.al. using lasers in cesium gas, that the light pulse was
said to exit the chamber before it entered:

"Can c, the speed limit of the universe, the speed of light in vacuum,
be exceeded? In July, 2000, the science-oriented news media were full
of reports that pulses of laser light had broken the speed-of-light
barrier. Physicists L. J. Wang, A. Kuzmich, and A. Dogarliu of the
NEC Research Institute in Princeton, NJ, had a paper about to be
published in the prestigious journal Nature describing an experiment
in which not only had laser pulses traveled faster than light, but had
actually emerged from the apparatus before they had entered it." [2]

It occurs to me that this is what would appear to happen if the
entrance and exit were synchronized using light signals but the actual
signal to be measured was traveling superluminally or if light signals
provided an inaccurate means of synchronizing clocks. What would be
needed to see if the signal pulse was being propagated superluminally
would be to have the pulse reflected back to the source and seeing if
the total travel time was less than the time for light to make the
round trip.

Another experiment might have made such round trip measurements.
These were experiments by Ranfagni et.al. of microwaves propagating in
a wave guide:

"In the new experiments, led by Anedio Ranfagni of the Italian
National Research Council in Firenze, the setup looks innocent enough:
The team sent microwaves (3.5 cm wavelength) through a narrow,
ring-shaped opening onto a large and nearby focusing mirror, which
collimated the waves into a beam propagating back from the mirror,
beyond and behind the source. They "modulated" the microwaves with
rectangular pulses (sharp "amplify" and "attenuate" commands, in rapid
succession) and detected the pulses at positions between 30 and 140 cm
from the source, along the beam axis. The slope of their plot of
arrival times vs. distance led to an apparent propagation speed of 5
to 7% above c, although beyond about 1 m, the speed approached c, all
of which agreed with previous predictions." [3]

The experimenters claim some speeds exceeding c in the reflected
waves but it is difficult to tell here if any of these speeds are for
a round trip signal back to the source.


Bob Clark



1.)Conventionality of Simultaneity
http://plato.stanford.edu/entries/sp...e-convensimul/

2.)Faster-than-Light Laser Pulses?
by John G. Cramer
http://www.npl.washington.edu/AV/altvw105.html

3.)Faster than a Speeding Light
http://focus.aps.org/story/v5/st23
  #2  
Old October 24th 03, 05:32 AM
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

In article , (Robert Clark) writes:
wrote in message news: ...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

You're aware of the discussions on sci.physics.relativity


I'm certainly not aware of any discussions on sci.physics.relativity,
nor do I have any interest in these.

that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement. This is because of the uncertainty of
synchronizing clocks in two different locations. The standard SR
method of using light-signals requires the assumption of the constancy
of the one-way speed of light. [1]
I was interested to see that in some descriptions of the experiment
of Wang et.al. using lasers in cesium gas, that the light pulse was
said to exit the chamber before it entered:

"Can c, the speed limit of the universe, the speed of light in vacuum,
be exceeded? In July, 2000, the science-oriented news media were full
of reports that pulses of laser light had broken the speed-of-light
barrier. Physicists L. J. Wang, A. Kuzmich, and A. Dogarliu of the
NEC Research Institute in Princeton, NJ, had a paper about to be
published in the prestigious journal Nature describing an experiment
in which not only had laser pulses traveled faster than light, but had
actually emerged from the apparatus before they had entered it." [2]

It occurs to me that this is what would appear to happen if the
entrance and exit were synchronized using light signals but the actual
signal to be measured was traveling superluminally or if light signals
provided an inaccurate means of synchronizing clocks. What would be
needed to see if the signal pulse was being propagated superluminally
would be to have the pulse reflected back to the source and seeing if
the total travel time was less than the time for light to make the
round trip.

Another experiment might have made such round trip measurements.
These were experiments by Ranfagni et.al. of microwaves propagating in
a wave guide:

"In the new experiments, led by Anedio Ranfagni of the Italian
National Research Council in Firenze, the setup looks innocent enough:
The team sent microwaves (3.5 cm wavelength) through a narrow,
ring-shaped opening onto a large and nearby focusing mirror, which
collimated the waves into a beam propagating back from the mirror,
beyond and behind the source. They "modulated" the microwaves with
rectangular pulses (sharp "amplify" and "attenuate" commands, in rapid
succession) and detected the pulses at positions between 30 and 140 cm
from the source, along the beam axis. The slope of their plot of
arrival times vs. distance led to an apparent propagation speed of 5
to 7% above c, although beyond about 1 m, the speed approached c, all
of which agreed with previous predictions." [3]

The experimenters claim some speeds exceeding c in the reflected
waves but it is difficult to tell here if any of these speeds are for
a round trip signal back to the source.

Actually all the above experiments yield results fully consistent with
the existing theoretical predictions, based on classical
electrodynamics (even QM is not really required) and fully consisten
with relativity. You should read the scientific publications, not
writeups in popular media. There are all sorts of funny htings you
can do with pulses which change shape across small distnaces.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"
  #3  
Old October 24th 03, 07:11 AM
Bilge
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

Robert Clark:
wrote in message news: ...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"


You're aware of the discussions on sci.physics.relativity that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement.


That is not the case.

This is because of the uncertainty of synchronizing clocks in
two different locations.


It's completely unnecessary to synchronize anything.

  #4  
Old October 25th 03, 11:29 AM
Robert Clark
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

(Bilge) wrote in message ...
Robert Clark:
wrote in message news: ...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the same"

You're aware of the discussions on sci.physics.relativity that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement.


That is not the case.

This is because of the uncertainty of synchronizing clocks in
two different locations.


It's completely unnecessary to synchronize anything.


It is well known among researchers in the foundations of relativity
the need to synchronize clocks at two locations for comparing times at
those locations.
See this post by Stephen Speicher:

From: Stephen Speicher )
Subject: Speed of light
Newsgroups: sci.physics.research, sci.physics.relativity
Date: 2003-06-24 20:06:03 PST
http://groups.google.com/groups?selm...st.localdomain


Bob Clark
  #7  
Old October 25th 03, 10:01 PM
EL
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

Randy Poe wrote in message . ..
[EL]
Hi Bilge.

Why is it so difficult for people to imagine group velocities as wave
envelopes!

All decent empirical wave-group-velocity measurements show that they
are much lower than phase velocity in the same dispersive medium.


Except in negatively-dispersive media, where both theory and
experiment show the opposite.

- Randy


[EL]
Bring back the grudge and let us grind.
What is the merit in being a beautifully coloured parrot?
The merit is to admire the colourful feathers (mostly in a mirror).
However, a parrot is a sound mimicking bird with a bird's brain.

Dispersion is another word for scattering.
Scattering if you did not know is like what happened to the Jews all
over history.
Scattering is like holding a handful of seeds and then tossing them
for random distribution during planting processes.
A dispersive medium is a medium as media are defined in being either
homogenous or not and isotropic or not.
The quality of a medium indicates if it was able to induce scattering
or not.

Now try to imagine pinball the game and look for Pachinko.
The many steal marbles are supposed to be scattered randomly by design
to induce a factor of luck.

The dispersion of light and this means its scattering among air
molecules or any transparent or semitransparent medium should make you
understand that the waves are being physically scattered by deflection
and reflection on the particles of that medium.

Of course by now you should have realised that negative-dispersion is
an expression coined by an idiot.

The phenomenon being the heart of this debate is definition dependant.
In optics dispersion is also defined as the Rate of Change of the
Refractive Index over wavelength scale at a specific wavelength.

Therefore, that definition implies that a wavelength scale must be
constructed by arbitrating a periodical interval indicating wavelength
increments against which we plot the refractive index to extract a
rate of change of that RI with respect to the change in wavelength
about the wavelength in question to illustrate a dispersion figure.

If my sentence was too complex for you to understand, here it is again
in different words.

We have a specific frequency of a wave of light.
We put a point on a graph's x-axis to represent that frequency and we
extend our scale to the left and to the right.
The graph's y-axis then represents the refractive index.
This means that in that specific material the refractive index is
frequency dependant.
By plotting all the different refractive index values we illustrate
the scattering of the refractive index about (before and after) the
frequency at question.

What does the idiotic negative-dispersion supposed to mean!

Pick up any respectable reference that tabulates the refractive index
of materials and try to find any negative value.
The overwhelming majority of indexes have a value between 1 and 2 and
they are POSITIVE VALUES.

Now the rate of change of positive values over positive intervals is
quite unlikely to make sense being negative.
A faster rate and a slower rate are simply seen in the aggregation/
dispersion of the plotted points of the refractive index against the
wavelengths.

So please educate yourself before defending idiots because it only
makes an idiot out of you too.

EL
  #8  
Old October 25th 03, 11:19 PM
Randy Poe
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

On 25 Oct 2003 14:01:38 -0700, (EL) wrote:

Randy Poe wrote in message . ..
[EL]
Hi Bilge.

Why is it so difficult for people to imagine group velocities as wave
envelopes!

All decent empirical wave-group-velocity measurements show that they
are much lower than phase velocity in the same dispersive medium.


Except in negatively-dispersive media, where both theory and
experiment show the opposite.

[EL]
Bring back the grudge and let us grind.
What is the merit in being a beautifully coloured parrot?
The merit is to admire the colourful feathers (mostly in a mirror).
However, a parrot is a sound mimicking bird with a bird's brain.


Nice poetry, if unfathomable. Shall we discuss physics?


Dispersion is another word for scattering.


Incorrect.

Dispersion in wave physics means wavelength-dependence of the speed of
propagation. A medium can be dispersive but, in theory, lossless.
Scattering is inherently lossy. It refers to energy being sent in many
other directions away from the line of propagation.

Normal (positive) dispersion does have the tendency to spread signals
out in time, but this is a different phenomenon than dispersion.

Scattering if you did not know is like what happened to the Jews all
over history.
Scattering is like holding a handful of seeds and then tossing them
for random distribution during planting processes.


Again, nice poetry, but not very closely related to either dispersion
or scattering as the terms are used in physics.

A dispersive medium is a medium as media are defined in being either
homogenous or not and isotropic or not.


A dispersive medium is one in which speed depends on frequency. As we
all know from prisms, glass is a dispersive medium. Most real media
area, though the slope depends on the details of the interaction
between the energy and the molecules of the medium. Most of the time,
the slope of a speed vs. wavelength curve is positive, i.e., the speed
increases with wavelength, or decreases with frequency. Low frequency
waves propagate faster. You can see this in water with storm systems,
with low frequency components traveling reaching shore far ahead of
the rest of the system.

But there are materials which exhibit an opposite slope over some
wavelength regimes, with higher frequencies having higher speeds. This
is not magic, but it leads to a different effect on the shape of a
multiple-frequency pulse as it propagates.

What does the idiotic negative-dispersion supposed to mean!


Indicated above.


Pick up any respectable reference that tabulates the refractive index
of materials and try to find any negative value.
The overwhelming majority of indexes have a value between 1 and 2 and
they are POSITIVE VALUES.


Dispersion refers to slope. How low frequencies move compared to high
frequencies is what leads to the effect.


Now the rate of change of positive values over positive intervals is
quite unlikely to make sense being negative.


Huh? You're saying it doesn't make sense for a positive value to
decrease? Why the hell not?

http://en.wikipedia.org/wiki/Dispersion_(optics)
http://www.corning.com/opticalfiber/...ture_page2.asp
http://adsabs.harvard.edu/cgi-bin/np...ptCo.179..107W

- Randy

  #9  
Old October 26th 03, 07:07 AM
EL
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?

Randy Poe wrote in message . ..

Huh? You're saying it doesn't make sense for a positive value to
decrease? Why the hell not?


[EL]
Because less positive and more positive is still positive and I am
talking about refractive indexes.
The refractive index may increase or decrease away from the tested
frequency (wavelength) about which dispersion is being measured but in
all those cases dispersion is positive, absolute or simply unsigned.
What you are talking about is not negative dispersion at all but we
may describe it better as the rate of dispersion.
Since dispersion itself is the rate of change in the refractive index
then what you are talking about is the rate of the rate of change,
which is irrelevant to group velocity.



http://en.wikipedia.org/wiki/Dispersion_(optics)


[EL
Just as an example to demonstrate how silly you can be Randy I copied
the contents of that link and here it is.
{{{
Dispersion (optics
From Wikipedia, the free encyclopedia.
Find out how you can help support Wikipedia's phenomenal growth.

(There is currently no text in this page)
}}}

So you are referring me to a page that has no text in it which means
that you did not even read the content of the links you supplied.

Stop fabricating responses and get serious please.
I do not even know why you are being so enthusiastic defending those
idiots while you are much better a parrot than that.

Please invest your precious time in mathematics where you know better.

Regards.

EL
  #10  
Old October 26th 03, 08:10 PM
Mark Palenik
external usenet poster
 
Posts: n/a
Default Empirically Confirmed Superluminal Velocities?


"Bilge" wrote in message
...
Robert Clark:
wrote in message news:

...
I'll add here as a comment that the issue of group velocity is
generally misunderstood, perhaps due to the fact that lower level
textbooks don't explain it well. Group velocity *is not* signal
velocity. Under some circumstances, when the dependence of phase
velocity on frequency over the bandwidth of the signal is weak, group
velocity is a good approximation to signal velocity over distances
short enough so that the pulse shape does not change appreciably in
propagation. That's all. The conditions listed above are reasonably
well satisfied in most practical situations, but they totally fail
under anomalous dispersion situation.

Mati Meron | "When you argue with a fool,
| chances are he is doing just the

same"

You're aware of the discussions on sci.physics.relativity that to
determine if a signal travelled superluminally what would be required
is a round-trip measurement.


That is not the case.

This is because of the uncertainty of synchronizing clocks in
two different locations.


It's completely unnecessary to synchronize anything.


Besides, as long as two clocks are synchronized from the frame in which the
experiment is being carried out, the measurement they give for the speed of
light should be C.


 




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