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Light and Gravity
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I.Vecchi
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Joined: 05 May 2005
Posts: 124

PostPosted: Wed Jun 21, 2006 1:36 pm    Post subject: Re: Light and Gravity Reply with quote

Chalky ha scritto:

...

Quote:
It is difficult to see how you can avoid ftl information transfer from
observable ftl pulses since the presence or absence of the pulse
conveys one bit of information - the basic building block of all
digital communication systems.

It's more complicated than that. Ref. [1], which I am perusing,
provides a a good entry point. I quote:

"Anomalous dispersion is the event in which the group index of
refraction of an optical pulse in a medium becomes less than one, thus
producing a group velocity greater than c or even negative velocities.
...
It has been shown that in regions of anomalous dispersion between [!!!]
two gain peaks, the pulse suffers no distortion ... . At this point
information must be defined. There has been much discussion as to the
appropriate definition of information and how its definition will
affect causality.
...
Even though the gain-assisted pulse peak can be transferred
superluminally, gathering information from the pulse is another issue.
The detector might be able to recognize the presence of the pulse
sooner than if the pulse had progressed through the vacuum, but
recognizing the height or width of the pulse takes more time. As the
beam passes through the medium, quantum noise is added to the signal.
Using a signal-to-noise ratio (SNR) to define whether or not
information has been conveyed, it can be shown that the information
indeed takes longer to process in the presence of quantum noise.
...
In regions of anomalous dispersion, between two gain peaks, group
velocities of pulses can exceed c . So far there has been no conclusive
evidence that causality is violated. Either the detector must wait for
a certain SNR to be reached, thus delaying the confrmation that a
signal has been received, or the medium must respond to the optical
change, thus distorting the shape of the pulse.. ...There is still no
evidence that causality is violated or that information has been sent
superluminally."


IV

[1] Brian Winey "A Review of Superluminality in Regions of Anomalous
Dispersion" at web.pas.rochester.edu/~bwiney/superluminalitypaper.pdf

-----------------

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"Dance, dance off the row!"
Graffiti at Heidelberg's Uni Mensa, 1987.
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Thomas Johnson
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Joined: 30 Apr 2005
Posts: 73

PostPosted: Wed Jun 21, 2006 11:42 pm    Post subject: Re: Light and Gravity Reply with quote

Uncle Al wrote:
Quote:
2) Magnetism. The theoretically most magnetically polarized test
mass would be aligned undecatiplet manganese. Its active mass
fraction would be 5x10^(-5), polarized electron mass/total mass. The
most extreme real world magnets approach 10^(-7).

Just for future reference, your numbers are incorrect here.

A solid of Mn(2+) with 5 electrons somehow aligned would give you 5
electrons/55 nuclear particles.

taking the electron/proton mass ratio as a starting point, you would
get a ratio of spin mass to nuclear mass of

1836/5 or about 367.

Inverting this gives you a ratio of about 5x10^(-5).

Real world magnets would include polarized iron, which for arguments
sake lets say has 1 electron/nucleus (it has 2.22 Bohr
magnetons/formula unit). This would give you 1x10^(-5) (since the mass
is roughly the same as Mn).

I don't know how you define "extreme", or how you calculated 10^(-7),
but I wouldn't agree with either.

Thomas.
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Chalky
science forum beginner


Joined: 13 Jan 2006
Posts: 20

PostPosted: Thu Jun 22, 2006 6:40 am    Post subject: Re: Light and Gravity Reply with quote

I.Vecchi wrote:
Quote:
Cl.Massé ha scritto con ammirevole chiarezza:

...

The speed of light is the maximum speed (for information travel.) It is
rather a property of space-time.
Now, permittivity and permeability are
effective quantities that allow to use the same equations for
electromagnetic field in any medium, transparent or no. They aren't
fundamental constants, and may be set to 1 in vacuum in an appropriate unit
system. In a medium, they model the average behaviour of a field.

The sticky point here is that there are media where EM pulses with
group velocity exceeding c have been observed ([1]). It is claimed
that c is still the maximum speed for information transfer, because it
is allegedly impossible to extract information from such pulses so as
to implement information transfer at speeds exceeding c.

[1] http://physicsweb.org/articles/world/16/12/3/1 and references
therein.

In fact, the title and subtitle of this particular reference read:
Clear message for causality
Experiment confirms that information cannot be transmitted faster than
the speed of light.

It is stated there that when a binary pulse is encoded onto infinitely
smooth, predictable pulses, that binary pulse is observed to travel at
<c. (The figure 1 referred to therein is confusing because the author
does not indicate which graph represents a 1, which graph represents a
0, or even which graph represents the information before propagation,
or which graph represents the information after propagation.)

C
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Uncle Al
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Joined: 24 Mar 2005
Posts: 1226

PostPosted: Thu Jun 22, 2006 6:41 am    Post subject: Re: Light and Gravity Reply with quote

Uncle Al wrote:
Quote:

Thomas Johnson wrote:

Uncle Al wrote:
2) Magnetism. The theoretically most magnetically polarized test
mass would be aligned undecatiplet manganese.

First,

What is "undecatiplet" Mn?

There are five unpaired d-electrons in a manganese octahedral or
tetrahedral ligand field. Spin multiplity is 2N+1. In the extremely
unlikely event you can get solid manganese metal to perfectly polarize
and perfectly align, 2N+1 = 11. More realistically you'll need an
Mn(+2) salt. Now the active atoms are expanded in space and diluted
by counterions' mass - much worse as a test mass. Terrestrial magnets
are hopeless as EP violation probes.

No element other than manganese has as high a ratio of spin to mass
unless you want to polarize H atoms in a megatesla+ field so they
don't recombine. Strong thermodynamic aguments suggest any EP
violation larger than 10^(-10) difference/average is fairy dust. Even
then, only a parity anomaly is allowed by prior observation.

A Google search shows the word "undecatiplet" is only used in posts to
newsgroups by Mr. Schwartz. Google scholar doesn't show the word being
used at all.

Learn some chemistry and stop whining. Ignorance is not a virtue. If
you use materials in the lab, know something useful about them.

"Introduction to Ligand Fields," Figgis.

The Mn example was illustrative of the best possible theoretical case,
spin/mass. As stated, real world magnets are limited to about 50
parts-per-billion active mass by the mechanism of their magnetism.
Adelberger claimed a tenth mole of polarized electrons net in

http://www.aip.org/pnu/2006/775.html

A tenth mole of electrons is 0.055 mg. If we allow him 100 g of test
mass that gives 550 parts-per-billion active mass. Already hopeless
at face value. Now you go look up how much the thing really massed,

http://mist.npl.washington.edu/eotwash/spin.jpg

[snip more whining]

A parity Eotvos experiment opposing P3(1)21 and P3(2)21 quartz has no
less than 999,726,000 parts-per-billion active mass - the relative
spatial configuration of atomic nuclei in the crystal lattices. It is
at least 1.8 million times more concentrated in active mass than the
magnet experiment. Why bother trying an experiment that has a 6.3
orders of magnitude larger signal source? Suppose it didn't work.

Every possible gravitation theory without exception must either
postulate or ignore the Equvalence Principle. There is no third
case. If the EP is true there will never be a net signal in its
challenges. If the EP is false then there must be a parity anomaly
(with whatever else might be in there). The odd-parity maths of any
teleparallel or other EP-violating theory demand it. The only EP test
that has never been reported is a parity test.

If you wanted to do the next logical EP test, what would you choose?
Chiral string theories have an EP parity violation; achiral string
theories do not. A simple experiment in existing apparatus could
vastly prune the 10^500 acceptable vacua. It is the only empirical
test of string theory known to date - and it only attacks a founding
postulate. Postulates cannot be defended or they would not be
postulates. It could happen.

Somebody should look.

http://focus.aps.org/story/v17/st21
Phys. Rev. Lett. 96 221302 (2006)

"Because CPT involves space and time operations, it turns out that any
violation of CPT invariance would disrupt the spacetime symmetries
embodied in relativity theory."

If space is anisotropic, (consistent with teleparallel theories of
gravitation),

1) Angular momentum is not conserved through Noether's theorem.

2) A parity Eotvos experiment will have non-zero net output for
sufficiently parity divergent mass distributions (atomic nuclei
arrayed in opposed enantiomorphic crystal lattices).

3) Single crystal solid spheres of enantiomorphic space group
P3(1)21 and P3(2)21 quartz are extremal parity divergent test masses
in theory and by quantitative calculation.

Somebody should look.

HD Flack, "Chiral and achiral crystal structures"
Helv. Chim. Acta 86 905 (2003)
http://www.flack.ch/howard/cristallo/cacs.pdf
http://www.flack.ch/howard/cristallo/Howard.Flack.html
http://en.wikipedia.org/wiki/Flack_parameter

M. Petitjean, "On the root mean square quantitative chirality and
quantitative symmetry measures"
J. Math. Phys. 40(9) 4587 (1999)
http://petitjeanmichel.free.fr/itoweb.petitjean.html
http://www.mazepath.com/uncleal/qzdense.png
Theoretical slope is -2 exactly. Intercept depends on structure.
CHI=1 is maximum geometric parity divergence
CHI=1-[10^(-15)], 1 cm diameter quartz solid sphere
CHI=1-[10^(-16)], 3 cm diameter quartz solid sphere

D. Yogev-Einot and D. Avnir "Quantitative Symmetry and Chirality of
the Molecular Building Blocks of Quartz"
Chem. Mater. 15 464 (2003)
"Pressure and temperature effects on the degree of symmetry and
chirality of the molecular building blocks of low quartz"
Acta Cryst. B60, 163--173 (2004)
http://chem.ch.huji.ac.il/employee/avnir/topics.html

--
Uncle Al
http://www.mazepath.com/uncleal/
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Tom Roberts
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Joined: 24 Mar 2005
Posts: 1399

PostPosted: Thu Jun 22, 2006 6:43 am    Post subject: Re: Light and Gravity Reply with quote

Chalky wrote:
Quote:
It is difficult to see how you can avoid ftl information transfer from
observable ftl pulses

Actually it's rather easy and well known: in media with anomalous
dispersion the group velocity can be >c, but this is due to an
interference among the various components of the wave, and those
components must _already_ be present. Those individual components travel
<c, and that is the fastest that a modulation of the wave can travel.

For an excellent demonstration, see
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html

Tom Roberts
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Thomas Johnson
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Joined: 30 Apr 2005
Posts: 73

PostPosted: Fri Jun 23, 2006 3:22 am    Post subject: Re: Light and Gravity Reply with quote

Uncle Al wrote:
Quote:
http://focus.aps.org/story/v17/st21
Phys. Rev. Lett. 96 221302 (2006)

"Because CPT involves space and time operations, it turns out that any
violation of CPT invariance would disrupt the spacetime symmetries
embodied in relativity theory."

If space is anisotropic, (consistent with teleparallel theories of
gravitation),

1) Angular momentum is not conserved through Noether's theorem.

2) A parity Eotvos experiment will have non-zero net output for
sufficiently parity divergent mass distributions (atomic nuclei
arrayed in opposed enantiomorphic crystal lattices).

Can you direct us to a reference in the peer-reviewed literature that
backs this claim up? Has anyone published on the concept of using
crystals in an Eotvos experiment?

The phrase "sufficiently parity divergent" is not very precise. If you
use Petitjean's formalism (as only you do in this arena), you have a
choice of CHI=1 (a chiral chrystal) or CHI=0 (a non-chiral crystal).
So, is CHI=1 sufficient? If so, show the work that links CHI to an
expected experimental result. If not, then this experiment is a waste
of time.

Quote:
3) Single crystal solid spheres of enantiomorphic space group
P3(1)21 and P3(2)21 quartz are extremal parity divergent test masses
in theory and by quantitative calculation.

Somebody should look.

You keep stating this, "Somebody should look". Besides Adelberger (who
did an experiment before you started working on the project) and Jun
Luo, who else should look?

Quote:
From http://www.mazepath.com/uncleal

"The full parity Eötvös experiment in quartz is COMPLETED in PR China
as you read this."

It then makes a comment suggesting that Prof. Jun Luo did the
experiment.


Quote:
HD Flack, "Chiral and achiral crystal structures"
Helv. Chim. Acta 86 905 (2003)
http://www.flack.ch/howard/cristallo/cacs.pdf
http://www.flack.ch/howard/cristallo/Howard.Flack.html
http://en.wikipedia.org/wiki/Flack_parameter

M. Petitjean, "On the root mean square quantitative chirality and
quantitative symmetry measures"
J. Math. Phys. 40(9) 4587 (1999)
http://petitjeanmichel.free.fr/itoweb.petitjean.html

D. Yogev-Einot and D. Avnir "Quantitative Symmetry and Chirality of
the Molecular Building Blocks of Quartz"
Chem. Mater. 15 464 (2003)
"Pressure and temperature effects on the degree of symmetry and
chirality of the molecular building blocks of low quartz"
Acta Cryst. B60, 163--173 (2004)
http://chem.ch.huji.ac.il/employee/avnir/topics.html

These are nice references, but none of them has anything to do with
gravity or EP. The deleted reference does not make a connection
between chirality and EP either.

The work has been done.

Somebody should move on with his life.

Thomas.
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Uncle Al
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Joined: 24 Mar 2005
Posts: 1226

PostPosted: Fri Jun 23, 2006 3:22 am    Post subject: Re: Light and Gravity Reply with quote

Tom Roberts wrote:
Quote:

Chalky wrote:
It is difficult to see how you can avoid ftl information transfer from
observable ftl pulses

Actually it's rather easy and well known: in media with anomalous
dispersion the group velocity can be >c, but this is due to an
interference among the various components of the wave, and those
components must _already_ be present. Those individual components travel
c, and that is the fastest that a modulation of the wave can travel.

For an excellent demonstration, see
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html

Tom Roberts

The wavepacket is reshaped (e.g., chirping) during its transmission
through the dispersive medium, moving its centroid. The statistics
are cute but no information arrives superluminally.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf
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I.Vecchi
science forum Guru Wannabe


Joined: 05 May 2005
Posts: 124

PostPosted: Fri Jun 23, 2006 12:36 pm    Post subject: Re: Light and Gravity Reply with quote

Tom Roberts ha scritto:

Quote:
Chalky wrote:
It is difficult to see how you can avoid ftl information transfer from
observable ftl pulses

Actually it's rather easy and well known: in media with anomalous
dispersion the group velocity can be >c, but this is due to an
interference among the various components of the wave, and those
components must _already_ be present. Those individual components travel
c, and that is the fastest that a modulation of the wave can travel.

For an excellent demonstration, see
http://gregegan.customer.netspace.net.au/APPLETS/20/20.html


Nice. I was just wondering what "the modulation of a wave" amounts
to, but browsing around I read of a theoretical result by Chiao and
Steinberg which clarified the issue for me. In [1] they show that group
speed of a pulse can be made greater than c with little pulse
distortion, but any point of non-analycity in the pulse (i.e. any
point around which the pulse can't be expressed by Taylor expansion)
can travel only at speed c. They interpret loss of analycity as the
input of unpredictable "new information" (the part of the pulse before
the non-analytic point tells nothing about what comes after), whose
speed therefore is shown to be bounded by c.
Actually this can be seen in the picture at [2], where superluminal
"0" and "1" pulses part ways at the top of vacuum "0" pulse.

IV

[1] R. Y. Chiao and A. M. Steinberg "Tunneling Times and
Superluminality" in 'Progress in Optics,' edited by E. Wolf, Vol. 37,
(Elsevier, Amsterdam, 1997), p. 347-406.
[2] http://physicsweb.org/articles/world/16/12/3/1/pwpia2%5F12%2D03
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Cl.Massé
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Joined: 24 Mar 2005
Posts: 149

PostPosted: Fri Jun 23, 2006 10:05 pm    Post subject: Re: Light and Gravity Reply with quote

"Chalky" <chalkyspam@bleachboys.co.uk> a écrit dans le message de news:
1150532747.796260.141510@p79g2000cwp.googlegroups.com

Quote:
It is difficult to see how you can avoid ftl information transfer from
observable ftl pulses since the presence or absence of the pulse
conveys one bit of information - the basic building block of all
digital communication systems.

The argument is valid anyway. No information can be transferred if the
zeros aren't flanked with ones, otherwise synchronization is impossible.
It's the way a hard drive works, for example, and even an asynchronous
transmission line. If the information where only one 0, it can't be known
whether it is a 0 bit or simply the sender needing to be fixed. It's the
whole idea of a protocol and of information.

--
~~~~ clmasse on free F-country
Liberty, Equality, Profitability.
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Cl.Massé
science forum Guru Wannabe


Joined: 24 Mar 2005
Posts: 149

PostPosted: Fri Jun 23, 2006 10:05 pm    Post subject: Re: Light and Gravity Reply with quote

"Chalky" <chalkyspam@bleachboys.co.uk> a écrit dans le message de news:
1150441167.570099.153610@r2g2000cwb.googlegroups.com

Quote:
This point reminds me of a remaining apparent problem with the
scattering and absorption/re-emission explanations of refractive index.
How are these explanations compatible with a <1 refractive index of
water at x ray frequencies?

Refractive index corresponds to phase velocity, that is, at witch speed a
surface of constant phase travels, so that the bending of light can be
calculated with it. But group velocity is the speed of travel of a pulse,
and information is transferred at group velocity. Phase velocity is
explained by interference, then it may be greater than light velocity.

This happens also for a massive particle in vacuum and for an
electromagnetic wave in a plasma. Their phase velocity are greater than c,
and the product of phase velocity and group velocity (actually the one of
the particle) is equal to c.

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Liberty, Equality, Profitability.
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Cl.Massé
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Joined: 24 Mar 2005
Posts: 149

PostPosted: Mon Jun 26, 2006 2:04 am    Post subject: Re: Light and Gravity Reply with quote

"FrediFizzx" <fredifizzx@hotmail.com> a écrit dans le message de news:
4feg1aF1j0a0rU1@individual.net

Quote:
Hmm... In what system of units is free space permittivity and
permeability set to 1? For example in gaussian cgs, eps0 = 1/4pi and
mu0 = 4pi/c^2. In natural units, hbar = c = 1, they are 1/4pi and 4pi.

As permittivity and permeability have different dimensions, we can always
set them to 1 and define the other units accordingly. Then c=1 and hbar is
a dimensioned quantity ([m kg] in SI.)

Permittivity and permeability introduce the electrical charge (or electrical
intensity according to the system), which cancels in the product. But the
coupling with charge doesn't intervene in the propagation. We can imagine a
model for which it does, like aether or quantum fluctuations, but as it is
unnecessary, the consequence is that the electrical unit drops, and there is
only the maximum speed of propagation left.

Analogously, gravitational permittivity and permeability can be defined with
mass, but that isn't an additional dimension.

--
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Cl.Massé
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Joined: 24 Mar 2005
Posts: 149

PostPosted: Mon Jun 26, 2006 2:04 am    Post subject: Re: Light and Gravity Reply with quote

John (Liberty) Bell ha scritto:

Quote:
2) From my reading of Einstein (in English translation) it appears he
always used the word velocity not speed, which begs the question why?
If there are any examples where this conclusion is contradicted (either
in original German or English translation) a reference would be
appreciated, ideally, net friendly.

"I.Vecchi" <vecchi@weirdtech.com> a écrit dans le message de news:
1150782377.098145.303560@y41g2000cwy.googlegroups.com

Quote:
As a non-native speaker, I'd say in German speed/velocity is just
Geschwindigkeit. Schnelligkeit is rather something like rapidity.
"Velocitaet" does not exist, as far as I know, except in "schwiitze
duetsch", but that does not count, although Einstein may have heard it.

"Velocity" has a Latin root meaning swift, and "speed" has a Germanic root
meaning prosperous. There is no real distinction between them, even in
physics, save for usage. Velocity is used for light perhaps only because
light is swift, while other speeds may be very low.

In his famous paper _Zur Elektrodynamik bewegter Körper_ of 1905 in "Annalen
der Physik", Einstein uses the word "Geschwindigkeit", literally meaning
"how much it is rapid", and also "rapidity". The translator is perhaps
merely a Latin language (Italian?) native speaker.

--
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FrediFizzx
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Posts: 774

PostPosted: Mon Jun 26, 2006 12:28 pm    Post subject: Re: Light and Gravity Reply with quote

"Cl.Massé" <postmaster@expeditemediagroup.com> wrote in message
news:449d7b06$0$10299$636a55ce@news.free.fr...
Quote:
"FrediFizzx" <fredifizzx@hotmail.com> a écrit dans le message de news:
4feg1aF1j0a0rU1@individual.net

Hmm... In what system of units is free space permittivity and
permeability set to 1? For example in gaussian cgs, eps0 = 1/4pi
and mu0 = 4pi/c^2. In natural units, hbar = c = 1, they are 1/4pi
and 4pi.

As permittivity and permeability have different dimensions, we can
always set them to 1 and define the other units accordingly. Then c=1
and hbar is a dimensioned quantity ([m kg] in SI.)

Been doing some more studying since I posted this. We know from
experiment in the appropiate force laws that the electric constant
divided by the magnetic constant equals c^2 (there is actually an
additional factor of 1/2 but we will ignore that). So in SI, k_e =
1/(4pi eps0) and then k_m = 1/(4pi eps0 c^2) = mu0/4pi. We set eps0 =
mu0 = 1, then we get Heaviside-Lorentz units with c = 1. However, k_e
is then 1/4pi and k_m = 4pi so it doesn't seem like we have really
removed or done anything. The 4pi factors are still there bugging us.
Wink I really don't think there is any unit system that can get rid of
these geometric factors that apply to free space.

Quote:
Permittivity and permeability introduce the electrical charge (or
electrical intensity according to the system), which cancels in the
product. But the coupling with charge doesn't intervene in the
propagation. We can imagine a model for which it does, like aether or
quantum fluctuations, but as it is unnecessary, the consequence is
that the electrical unit drops, and there is only the maximum speed of
propagation left.

Sure, but is that really the point here? I can understand the 4pi as
maybe being the surface area of a sphere and being related to the
inverse square law, but what about the 1/4pi? My research indicates
that it is possibly the ratio of two lengths related to free space EM
radiation.

Quote:
Analogously, gravitational permittivity and permeability can be
defined with mass, but that isn't an additional dimension.

OK.

FrediFizzx

Quantum Vacuum Charge papers;
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.pdf
or postscript
http://www.vacuum-physics.com/QVC/quantum_vacuum_charge.ps
http://www.arxiv.org/abs/physics/0601110
http://www.vacuum-physics.com
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ebunn@lfa221051.richmond.
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Posts: 38

PostPosted: Mon Jun 26, 2006 10:47 pm    Post subject: Re: Light and Gravity Reply with quote

In article <449acadc$0$1184$626a54ce@news.free.fr>,
Cl.Massé <postmaster@expeditemediagroup.com> wrote:

Quote:
"Velocity" has a Latin root meaning swift, and "speed" has a Germanic root
meaning prosperous. There is no real distinction between them, even in
physics, save for usage.

Lots of people who teach intro physics would be annoyed with you if you
told their students that. It's customary to hammer into students the
difference between velocity, which is a vector, and speed, which is
the magnitude of that vector.

It's true that this is a bit like training wheels on a bicycle: once
we're confident that students understand that there's an important
difference between scalars and vectors and know when to use each, many
of us no longer feel the need to insist on this verbal distinction.
Much the same is true for mass vs. weight: as long as everyone in the
room is past the training-wheels stage, I don't see any harm in saying
that something weighs 500 grams.

Incidentally, at the risk of going all metaphysical, I don't know
what it means to say that there is no distinction between two words
"save for usage": usage is everything!

Quote:
Velocity is used for light perhaps only because
light is swift, while other speeds may be very low.

To me the words velocity and speed don't carry this sort of difference
in connotation.

Quote:
In his famous paper _Zur Elektrodynamik bewegter Körper_ of 1905 in "Annalen
der Physik", Einstein uses the word "Geschwindigkeit", literally meaning
"how much it is rapid", and also "rapidity". The translator is perhaps
merely a Latin language (Italian?) native speaker.

Nowadays, people often use "rapidity" in special relativity to mean
something different, namely the inverse hyperbolic tangent of (v/c).
I'm sure that came along long after 1905, so it has nothing to do with
this; I just thought I'd mention it for completeness.

-Ted

--
[E-mail me at name@domain.edu, as opposed to name@machine.domain.edu.]
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Cl.Massé
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PostPosted: Mon Jul 03, 2006 12:29 am    Post subject: Re: Light and Gravity Reply with quote

<ebunn@lfa221051.richmond.edu> a écrit dans le message de news:
e7omnt$7aa$1@bigbang.richmond.edu

Quote:
Lots of people who teach intro physics would be annoyed with you if you
told their students that. It's customary to hammer into students the
difference between velocity, which is a vector, and speed, which is
the magnitude of that vector.

Perhaps, English speakers do what they feel like to do, but when we speak
about "velocity of light" (in French "vélocité de la lumière"), we well
speak about a magnitude. This distinction seems artificial. Why not say
"speed magnitude" and "vectorial speed". Concision have more drawbacks in
science. And what about magnetic field, force... Anyway, velocity isn't a
vector, or more precisely it is a vector in the tangent space at the given
point. Have we to coin the word "swiftness" or such like? In case of
shortage, I propose "speeditude", "velocitality", "quickage",
"velospeety"...

Quote:
Incidentally, at the risk of going all metaphysical, I don't know
what it means to say that there is no distinction between two words
"save for usage": usage is everything!

For example, usually saying "velocity of light" and "speed of sound". No
difference in meaning, but different usage.

Quote:
Nowadays, people often use "rapidity" in special relativity to mean
something different, namely the inverse hyperbolic tangent of (v/c). I'm
sure that came along long after 1905, so it has nothing to do with this; I
just thought I'd mention it for completeness.

And for curiosity, "rapid" has the same origin as "to rape" and "rapt".

--
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Liberty, Equality, Profitability.
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