Science > Physics > New Breathtaking Confirmation of Special Relativity
| Topic: |
Science > Physics |
| User: |
"Pentcho Valev" |
| Date: |
13 Oct 2005 01:38:03 AM |
| Object: |
New Breathtaking Confirmation of Special Relativity |
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
It seems that special relativity says the following: if something does
not carry information, it CAN move with a speed greater than c. But if
it does carry information, then - sorry - c remains the limit. In other
words, Einstein limited his predictions to information carriers, not
just to anything, and therefore Einstein remains great. Needless to
say, the next step will be some synthesis between special relativity
and the theory of information so there will be funds, grants etc. in
the years to come. More quotation:
"But very little experimental work has been done to support this
theoretical analysis, and experimental physicists would like to see
actual physical proof from the lab that supports the theory."
Pentcho Valev
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| User: "François Guillet" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 02:57:51 PM |
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"Pentcho Valev" <pvalev@yahoo.com> a écrit dans le message de news:
1129185483.854691.298860@g49g2000cwa.googlegroups.com...
| "Einstein's Special Theory of Relativity states that information cannot
| travel faster than the speed of light in a vacuum.
Not sure. Here is instantaneous information transfer :
"These experiments demonstrate that useful quantum information could be
transferred through quantum channels via de-excitation of one sample of
photoluminescent material quantum entangled with another."
http://arxiv.org/abs/physics/0503052
FG
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| User: "Harry" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 03:26:07 AM |
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"François Guillet" <guillet.francois@wanadoo.fr> wrote in message
news:434ebc40$0$7846$8fcfb975@news.wanadoo.fr...
"Pentcho Valev" <pvalev@yahoo.com> a écrit dans le message de news:
1129185483.854691.298860@g49g2000cwa.googlegroups.com...
| "Einstein's Special Theory of Relativity states that information cannot
| travel faster than the speed of light in a vacuum.
Not sure. Here is instantaneous information transfer :
"These experiments demonstrate that useful quantum information could be
transferred through quantum channels via de-excitation of one sample of
photoluminescent material quantum entangled with another."
http://arxiv.org/abs/physics/0503052
FG
Popper and Peres disagreed with that interpretation, if I remember well; and
there remains the loophole bug (according to Gisin, as to date no single
experiment managed to close simultaneously the detection and the locality
loopholes)...
Harald
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| User: "Russell" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 12:51:09 PM |
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Harry wrote:
"Fran=E7ois Guillet" <guillet.francois@wanadoo.fr> wrote in message
news:434ebc40$0$7846$8fcfb975@news.wanadoo.fr...
"Pentcho Valev" <pvalev@yahoo.com> a =E9crit dans le message de news:
1129185483.854691.298860@g49g2000cwa.googlegroups.com...
| "Einstein's Special Theory of Relativity states that information cann=
ot
| travel faster than the speed of light in a vacuum.
Not sure. Here is instantaneous information transfer :
"These experiments demonstrate that useful quantum information could be
transferred through quantum channels via de-excitation of one sample of
photoluminescent material quantum entangled with another."
http://arxiv.org/abs/physics/0503052
FG
Popper and Peres disagreed with that interpretation, if I remember well; =
and
there remains the loophole bug (according to Gisin, as to date no single
experiment managed to close simultaneously the detection and the locality
loopholes)...
More to the point, the cited arxiv paper has not undergone
peer review and IMHO does not appear to be publishable.
The authors are reporting a result that is inconsistent with
basic quantum mechanics -- there is *no* quantum mechanical
justification for a molecule (or atom) to undergo stimulated
emission when its entangled partner -- not the molecule itself --
is stimulated. The authors need to address this more basic
inconsistency before they can say anything at all about special
relativity.
It is telling that neither author (AFAICT) is a physicist, and
no consultation with the LSU physics department is acknowledged.
Now, it is of course possible for non-physicists to discover
new physics; if the experiments really do show what they claim,
this is an important finding. Unfortunately, there is no error
analysis at all, and the two figures containing unmassaged data
are decidedly unconvincing. Experimenter bias is likely and
was not controlled for, despite this being easy to do.
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| User: "Russell" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 05:00:09 PM |
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Fran=E7ois Guillet wrote:
"Pentcho Valev" <pvalev@yahoo.com> a =E9crit dans le message de news:
1129185483.854691.298860@g49g2000cwa.googlegroups.com...
| "Einstein's Special Theory of Relativity states that information cannot
| travel faster than the speed of light in a vacuum.
Not sure. Here is instantaneous information transfer :
"These experiments demonstrate that useful quantum information could be
transferred through quantum channels via de-excitation of one sample of
photoluminescent material quantum entangled with another."
http://arxiv.org/abs/physics/0503052
The results don't look very convincing to me. Where is
the error analysis? We are merely told that some of the
experiments worked better than others... heh.
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| User: "Harry" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 06:05:43 AM |
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"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129185483.854691.298860@g49g2000cwa.googlegroups.com...
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
Aargh! Those news reporters confuse everything...
SNIP
Harald
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| User: "Pentcho Valev" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 06:22:08 AM |
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Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129185483.854691.298860@g49g2000cwa.googlegroups.com...
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
Aargh! Those news reporters confuse everything...
News reporters? "In this week's issue of "Nature" magazine, Mark A.
Neifeld, a UA Electrical Engineering and Optical Sciences Professor,
and Duke University physicists Michael D. Stenner and Daniel J.
Gauthier present..."
Pentcho Valev
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| User: "Harry" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 06:56:32 AM |
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"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129202528.185670.240970@g14g2000cwa.googlegroups.com...
Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129185483.854691.298860@g49g2000cwa.googlegroups.com...
"Einstein's Special Theory of Relativity states that information
cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
Aargh! Those news reporters confuse everything...
News reporters? "In this week's issue of "Nature" magazine, Mark A.
Neifeld, a UA Electrical Engineering and Optical Sciences Professor,
and Duke University physicists Michael D. Stenner and Daniel J.
Gauthier present..."
Pentcho Valev
Pencho, SRT does not directly "state" anything about "information". Thus, if
you want to critique those professors, please cite their claims instead of a
copy of their words (never heard of the "telephone game"?). Now what do you
think, did the experiment bring anything else than a *Non Breathtaking*
confirmation of wave theory?
Harald
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| User: "Pentcho Valev" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 10:54:01 AM |
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Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129202528.185670.240970@g14g2000cwa.googlegroups.com...
Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129185483.854691.298860@g49g2000cwa.googlegroups.com...
"Einstein's Special Theory of Relativity states that information
cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
Aargh! Those news reporters confuse everything...
News reporters? "In this week's issue of "Nature" magazine, Mark A.
Neifeld, a UA Electrical Engineering and Optical Sciences Professor,
and Duke University physicists Michael D. Stenner and Daniel J.
Gauthier present..."
Pentcho Valev
Pencho, SRT does not directly "state" anything about "information".
Now it does.
Pentcho Valev
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| User: "Harry" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 02:48:32 AM |
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"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129218841.673172.204190@g49g2000cwa.googlegroups.com...
Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129202528.185670.240970@g14g2000cwa.googlegroups.com...
Harry wrote:
"Pentcho Valev" <pvalev@yahoo.com> wrote in message
news:1129185483.854691.298860@g49g2000cwa.googlegroups.com...
"Einstein's Special Theory of Relativity states that information
cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental
physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
Aargh! Those news reporters confuse everything...
News reporters? "In this week's issue of "Nature" magazine, Mark A.
Neifeld, a UA Electrical Engineering and Optical Sciences Professor,
and Duke University physicists Michael D. Stenner and Daniel J.
Gauthier present..."
Pentcho Valev
Pencho, SRT does not directly "state" anything about "information".
Now it does.
Funny, but not to-the-point
[reinserted:]
Now what do you
think, did the experiment bring anything else than a *Non Breathtaking*
confirmation of wave theory?
Well?
Harald
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| User: "brian a m stuckless" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 06:01:38 AM |
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DARK travels FASTER than LiGHT.!!
[With AFFiNE studded HUB GAPs].!!
brian a m stuckless.
<> >><> >><> >><> >><>
Pentcho Valev wrote:
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
It seems that special relativity says the following: if something does
not carry information, it CAN move with a speed greater than c. But if
it does carry information, then - sorry - c remains the limit. In other
words, --
DARK travels FASTER than LiGHT.!! [With AFFiNE studded HUB GAPs].!!
-- Einstein limited his predictions to information carriers, not
just to anything, and therefore Einstein remains great. Needless to
say, the next step will be some synthesis between special relativity
and the theory of information so there will be funds, grants etc. in
the years to come. More quotation:
"But very little experimental work has been done to support this
theoretical analysis, and experimental physicists would like to see
actual physical proof from the lab that supports the theory."
Pentcho Valev
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| User: "brian a m stuckless" |
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| Title: DARK travels FASTER than LiGHT.!! [With AFFiNE studded HUB GAPs].!! |
13 Oct 2005 06:01:39 AM |
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DARK travels FASTER than LiGHT.!!
[With AFFiNE studded HUB GAPs].!!
brian a m stuckless.
<> >><> >><> >><> >><>
Pentcho Valev wrote:
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
It seems that special relativity says the following: if something does
not carry information, it CAN move with a speed greater than c. But if
it does carry information, then - sorry - c remains the limit. In other
words, --
DARK travels FASTER than LiGHT.!! [With AFFiNE studded HUB GAPs].!!
-- Einstein limited his predictions to information carriers, not
just to anything, and therefore Einstein remains great. Needless to
say, the next step will be some synthesis between special relativity
and the theory of information so there will be funds, grants etc. in
the years to come. More quotation:
"But very little experimental work has been done to support this
theoretical analysis, and experimental physicists would like to see
actual physical proof from the lab that supports the theory."
Pentcho Valev
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| User: "Will Janoschka" |
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| Title: Re: DARK travels FASTER than LiGHT.!! [With AFFiNE studded HUB GAPs].!! |
13 Oct 2005 10:50:37 AM |
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On Thu, 13 Oct 2005 11:01:39, brian a m stuckless
<bastuck@nf.sympatico.ca> wrote:
DARK travels FASTER than LiGHT.!!
[With AFFiNE studded HUB GAPs].!!
brian a m stuckless.
Of course it does. It was there before the LiGHT.
-will-
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| User: "Mahmoud In My Dinner Jacket" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 05:27:19 AM |
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Hoorah for some fast women!
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 10:21:34 AM |
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I don't why the release is made as if this effect had been suddenly
discovered. Information always travels at the GROUP velocity. This is
dw/dk where w is 2*pi*frequency and k is 2*pi*wavenumber. The phase
velocity is w/k.
Radio waves travel with a phase velocity faster than c in the
ionosphere, but travel with a phase velocity which is slower. In fact
it can be shown that the group velocity in an ionised medium is in fact
kc^2/w In other words if the phase velocity is 2c the group velocity
will be c/2. Snells law follows the PHASE velocity, information
transfer follows the group velocity.
This has been known for a very long time (before WW2) and I don't know
why it is suddenly being raised now.
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| User: "Tom Roberts" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 01:35:59 PM |
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wrote:
Information always travels at the GROUP velocity.
Not true.
Information in a wave travels at the front velocity. In most cases for a
normal medium this is the same as the group velocity, but in regions of
anomalous dispersion it is not. In a medium with anomalous dispersion
the group velocity is >c, but the front velocity is never >c for EM
radiation.
The front velocity is so-named becuase it is the speed with which the
front of a wave travels when its source is turned on. This is also the
speed with which changes in the source propagate. That is, of course,
directly related to information transfer, because it is the propagation
speed for any modulation of the source (the only way to transfer
information via a wave).
This is why certain experiments that display group velocities >c do not
violate SR.
Many discussions of waves are limited to phase and group velocity, and
do not include the front velocity. I don't know why.
Tom Roberts tjroberts@lucent.com
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 02:22:40 PM |
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In article <jOx3f.20$Ej6.2@newssvr17.news.prodigy.com>, Tom Roberts <tjroberts@lucent.com> writes:
ianparker2@gmail.com wrote:
Information always travels at the GROUP velocity.
Not true.
Information in a wave travels at the front velocity. In most cases for a
normal medium this is the same as the group velocity, but in regions of
anomalous dispersion it is not. In a medium with anomalous dispersion
the group velocity is >c, but the front velocity is never >c for EM
radiation.
The front velocity is so-named becuase it is the speed with which the
front of a wave travels when its source is turned on. This is also the
speed with which changes in the source propagate. That is, of course,
directly related to information transfer, because it is the propagation
speed for any modulation of the source (the only way to transfer
information via a wave).
This is why certain experiments that display group velocities >c do not
violate SR.
Many discussions of waves are limited to phase and group velocity, and
do not include the front velocity. I don't know why.
I often wondered about it too. Perhaps it is because you can write
neat closed formulas for phase and group velocity, thus have something
which can be assigned at tests:-) The math of front velocity tends to
be more complex. But I would say that in terms of intuitive
obviousness, it is the front velocity that is the easiest to grasp.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Timo Nieminen" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 02:33:50 PM |
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On Thu, 13 Oct 2005 wrote:
Tom Roberts <tjroberts@lucent.com> writes:
Many discussions of waves are limited to phase and group velocity, and
do not include the front velocity. I don't know why.
I often wondered about it too. Perhaps it is because you can write
neat closed formulas for phase and group velocity, thus have something
which can be assigned at tests:-) The math of front velocity tends to
be more complex. But I would say that in terms of intuitive
obviousness, it is the front velocity that is the easiest to grasp.
Shake a slinky, and it's easy to see the phase velocity. What with
evrybody ignoring dispersion (except when they can't) and pretending that
every wave is monochromatic, no wonder most people don't outgrow that
picture.
If the slinky was whacked with a hammer rather than shaken regularly, it
might be a different story.
A nice paper came out in PRL the day before a lecture. So nice that the
lecture ended up being a reading/discussion of that (and another) paper.
Fore-runners with light pulses in water. Coincidentally, the author ended
up a visitor with our dept for 6 months; he was pleased that his paper was
of use.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 03:00:01 PM |
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In article <20051014052721.A69614@emu.uq.edu.au>, Timo Nieminen <uqtniemi@mailbox.uq.edu.au> writes:
On Thu, 13 Oct 2005 wrote:
Tom Roberts <tjroberts@lucent.com> writes:
Many discussions of waves are limited to phase and group velocity, and
do not include the front velocity. I don't know why.
I often wondered about it too. Perhaps it is because you can write
neat closed formulas for phase and group velocity, thus have something
which can be assigned at tests:-) The math of front velocity tends to
be more complex. But I would say that in terms of intuitive
obviousness, it is the front velocity that is the easiest to grasp.
Shake a slinky, and it's easy to see the phase velocity. What with
evrybody ignoring dispersion (except when they can't) and pretending that
every wave is monochromatic, no wonder most people don't outgrow that
picture.
Yes, true. But then they get hopelessly confused later. The point
is, our basic concept of velocity is this of mechanical velocity. An
object is in point A at a given time, how long before it gets to point
B. Phase velocity doesn't represent anything like this. It describes
a motion of a pattern within something that doesn't need to get from A
to B, since it already is "here, there and everywhere". So, as I
said, people get confused and when they later hear that phase velocity
may be faster than c, it just doesn't add up for them. You can teach
them to use the formulas, but they still don't really grasp it.
I recall, years ago, a discussion with Ed Green (he seems to have
dropped out of here, a pity) on this topic. A question I asked was
"how would you define the speed of the Mississipy river, between St.
Louis and New Orleans.
If the slinky was whacked with a hammer rather than shaken regularly, it
might be a different story.
Yes.
A nice paper came out in PRL the day before a lecture. So nice that the
lecture ended up being a reading/discussion of that (and another) paper.
Fore-runners with light pulses in water. Coincidentally, the author ended
up a visitor with our dept for 6 months; he was pleased that his paper was
of use.
Of course he was, any author would be.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Timo Nieminen" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 03:17:53 PM |
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On Thu, 13 Oct 2005 wrote:
The point
is, our basic concept of velocity is this of mechanical velocity. An
object is in point A at a given time, how long before it gets to point
B. Phase velocity doesn't represent anything like this. It describes
a motion of a pattern within something that doesn't need to get from A
to B, since it already is "here, there and everywhere". So, as I
said, people get confused and when they later hear that phase velocity
may be faster than c, it just doesn't add up for them. You can teach
them to use the formulas, but they still don't really grasp it.
A handful of problems, which is all that they'd usually get, and some blab
about v_p * v_g in hollow conducting waveguides, isn't enough to get it
across.
I should do an animation of constant phase lines in a waveguide - should
communicate better than words/equations. Even better, maybe I should
encourage on of my students next year to do it. A nice and believable
example of v_p > c.
Some of this year's students did some nice stuff on v_g > c due to
anomalous dispersion. It's nice when one does some good clear
graphs/animations and tells the rest all about it (they have to do an oral
presentation to go with the work, so this part isn't optional).
At least it should get across the idea that wave propagation isn't a nice
neat world of perfect sine waves. That, and an inkling of the Real Thing,
is about all, IMHO, that we should expect from the generic physics
student.
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 03:38:41 PM |
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In article <20051014060437.U76720@emu.uq.edu.au>, Timo Nieminen <uqtniemi@mailbox.uq.edu.au> writes:
On Thu, 13 Oct 2005 wrote:
The point
is, our basic concept of velocity is this of mechanical velocity. An
object is in point A at a given time, how long before it gets to point
B. Phase velocity doesn't represent anything like this. It describes
a motion of a pattern within something that doesn't need to get from A
to B, since it already is "here, there and everywhere". So, as I
said, people get confused and when they later hear that phase velocity
may be faster than c, it just doesn't add up for them. You can teach
them to use the formulas, but they still don't really grasp it.
A handful of problems, which is all that they'd usually get, and some blab
about v_p * v_g in hollow conducting waveguides, isn't enough to get it
across.
Not even close to enough.
I should do an animation of constant phase lines in a waveguide - should
communicate better than words/equations. Even better, maybe I should
encourage on of my students next year to do it. A nice and believable
example of v_p > c.
Yes, by all means, you should do it. A picture is often worth much
more than a thousand words.
Some of this year's students did some nice stuff on v_g > c due to
anomalous dispersion. It's nice when one does some good clear
graphs/animations and tells the rest all about it (they have to do an oral
presentation to go with the work, so this part isn't optional).
Excellent, that puts the natural human inclination to show off to a
very good use.
At least it should get across the idea that wave propagation isn't a nice
neat world of perfect sine waves. That, and an inkling of the Real Thing,
is about all, IMHO, that we should expect from the generic physics
student.
If you manage to do this, you did more than enough. The perfect sine
wave case is very far removed from the real world. If and when taught
as "the picture" instead of just an introduction to the picture, it may
be doing more damage than good.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 04:33:37 AM |
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This is true. However in the case of LINEAR disturbance the front and
group velocities are the same. ASfter all a front may be described in
terms of a Fourier Transform. A Fourier Transform quite clearly travels
at group velocity. In radio terms, you start modulating a wave at one
end, the modulations containg the information and the modulation
travels at group velocity towrds the receiver.
In these experiments quoted by Pencho what is hapenning is that a
temporary group velocity is created through non linear effects. This is
not transmissible over a distance.
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| User: "Tom Roberts" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 09:38:54 AM |
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wrote:
This is true. However in the case of LINEAR disturbance the front and
group velocities are the same.
Yes, as I said, as long as the dispersion is normal.
ASfter all a front may be described in
terms of a Fourier Transform. A Fourier Transform quite clearly travels
at group velocity. In radio terms, you start modulating a wave at one
end, the modulations containg the information and the modulation
travels at group velocity towrds the receiver.
Not in a region of anomalous dispersion. But in all cases the modulation
travels with the front velocity.
Tom Roberts tjroberts@lucent.com
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| User: "Tom Roberts" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
17 Oct 2005 12:01:45 PM |
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wrote:
This is true. However in the case of LINEAR disturbance the front and
group velocities are the same. ASfter all a front may be described in
terms of a Fourier Transform.
At any given place, yes. But if you want to discuss the propagation of
the front, this only works in a medium without dispersion. In that case,
front velocity equals group velocity.
A Fourier Transform quite clearly travels
at group velocity.
Only for a medium with zero dispersion. In the presence of dispersion,
which means the different Fourier components travel with different
velocities, this breaks down.
In radio terms, you start modulating a wave at one
end, the modulations containg the information and the modulation
travels at group velocity towrds the receiver.
Only for a medium with zero or normal dispersion (i.e. when front
velocity = group velocity). But in all cases that modulation travels
with the front velocity.
Tom Roberts tjroberts@lucent.com
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| User: "Gregory L. Hansen" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 10:13:00 AM |
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In article <1129185483.854691.298860@g49g2000cwa.googlegroups.com>,
Pentcho Valev <pvalev@yahoo.com> wrote:
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
It seems that special relativity says the following: if something does
not carry information, it CAN move with a speed greater than c. But if
it does carry information, then - sorry - c remains the limit. In other
Oh, it's one of those pumped potassium gas experiments. The group
velocity increases in the gas, meaning the point of peak intensity moves
faster than c. But the information carried in the point of peak
intensity is old news since forward points of less-than-peak intensity
already announced its arrival. The pumped gas has already been triggered
before the peak enters it.
If the leading edge of a signal could be made to go faster than c, that
would actually be interesting.
--
"No other major companies were working on [computer-controlled homes], and
that was exactly the problem. Microsoft does best when it has a
successful competitor it can copy and then crush." -- Marlin Eller,
"Barbarians Led by Bill Gates", 1998
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| User: "Tom Roberts" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 01:39:39 PM |
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Gregory L. Hansen wrote:
Oh, it's one of those pumped potassium gas experiments. The group
velocity increases in the gas, meaning the point of peak intensity moves
faster than c. But the information carried in the point of peak
intensity is old news since forward points of less-than-peak intensity
already announced its arrival. The pumped gas has already been triggered
before the peak enters it.
Yes. There used to be an interesting animation somewhere on the web that
shows how group velocity > c does not carry information, it's just due
to different frequency components of the wave interfering with each
other in an unusual way, and to do that they already need to be present.
If this peak intensity ever catches up to the front of the wave it
disappears.
If the leading edge of a signal could be made to go faster than c, that
would actually be interesting.
That is called the front velocity in textbooks that discuss it (many don't).
Tom Roberts tjroberts@lucent.com
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| User: "Dirk Van de moortel" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
13 Oct 2005 01:50:07 PM |
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"Tom Roberts" <> wrote in message news:LRx3f.21$Ej6.20@newssvr17.news.prodigy.com...
Gregory L. Hansen wrote:
Oh, it's one of those pumped potassium gas experiments. The group
velocity increases in the gas, meaning the point of peak intensity moves
faster than c. But the information carried in the point of peak
intensity is old news since forward points of less-than-peak intensity
already announced its arrival. The pumped gas has already been triggered
before the peak enters it.
Yes. There used to be an interesting animation somewhere on the web that
shows how group velocity > c does not carry information, it's just due
to different frequency components of the wave interfering with each
other in an unusual way, and to do that they already need to be present.
I think it was this one:
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html
Dirk Vdm
If this peak intensity ever catches up to the front of the wave it
disappears.
If the leading edge of a signal could be made to go faster than c, that
would actually be interesting.
That is called the front velocity in textbooks that discuss it (many don't).
Tom Roberts
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| User: "Wilson" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 06:28:06 PM |
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On 12 Oct 2005 23:38:03 -0700, "Pentcho Valev" <pvalev@yahoo.com> wrote:
"Einstein's Special Theory of Relativity states that information cannot
travel faster than the speed of light in a vacuum. In some highly
specialized "fast-light" media, however, some experimental physicists
believe they have seen light travel faster.":
http://www.universetoday.com/am/publish/einstein_right_speed_light.html?16102003
It seems that special relativity says the following: if something does
not carry information, it CAN move with a speed greater than c. But if
it does carry information, then - sorry - c remains the limit. In other
words, Einstein limited his predictions to information carriers, not
just to anything, and therefore Einstein remains great.
Why can't the non-information carying signal be switched very rapidly on/off so
as to send a binary message at >c?
HW.
www.users.bigpond.com/hewn/index.htm
see: www.users.bigpond.com/hewn/variablestars.exe
"Sometimes I feel like a complete failure.
The most useful thing I have ever done is prove Einstein wrong".
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| User: "" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
15 Oct 2005 02:10:20 PM |
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Why can't the non-information carying signal be switched very rapidly on/off so
as to send a binary message at >c?
Because then you get a Fourier Transform. In fact a square wave has a
set of constant Fourier Terms. A Fourier Transform travels at GROUP
velocity, very much so.
There is some dispute about "Front" and "Group". In the linear case
they are the same. In the non linear case they may be different. Also
in the experiment described there is one major complicating factor (as
there is in all non linear cases) frequency doubling.
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| User: "Tom Roberts" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
14 Oct 2005 10:47:51 PM |
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Henri Wilson wrote:
Why can't the non-information carying signal be switched very rapidly on/off so
as to send a binary message at >c?
Because the propagation of "the signal was switched off" travels at
speed <= c. Ditto for "on".
The sorts of artifacts that travel with speed > c are interference
phenomena between already-present waves. The presence of the waves
provides all the information, and these interference artifacts carry no
additional information.
Stated differently: to affect the >c artifacts you must make some change
to the underlying waves, and that change travels with the front velocity
which is always <= c.
Tom Roberts tjroberts@lucent.com
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| User: "Androcles Androcles@ MyPlace.org" |
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| Title: Re: New Breathtaking Confirmation of Special Relativity |
15 Oct 2005 01:18:37 AM |
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"Tom Roberts" <> wrote in message
news:HZ_3f.300$Y6.139@newssvr24.news.prodigy.net...
| Henri Wilson wrote:
| > Why can't the non-information carying signal be switched very
rapidly on/off so
| > as to send a binary message at >c?
|
| Because the propagation of "the signal was switched off" travels at
| speed <= c. Ditto for "on".
You are a lunatic, Roberts. That stupidity would apply to sound, and it
doesn't.
Androcles.
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| The sorts of artifacts that travel with speed > c are interference
| phenomena between already-present waves. The presence of the waves
| provides all the information, and these interference artifacts carry
no
| additional information.
|
| Stated differently: to affect the >c artifacts you must make some
change
| to the underlying waves, and that change travels with the front
velocity
| which is always <= c.
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| Tom Roberts
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