Incorrect assumptions about the speed of light

I keep reading posts on the newsgroup about the speed of light being absolute
and maximal.
I believe it is worth pointing out two current opposing opinons

1. the speed of light is not constant and is changing along with the universe
and space, time, gravity. A provocative idea currently quite hotlly contested
but one which does explain the unevenness of space.

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

Both of the published opinons are in keeping with the general theory of
relativity.

clear skies

You know, what bugs me is; if you are driving at the speed of light, and turn
on your headlights, well...
rat
~( );

email: remove 'et' from .com(et) in above email address

Arobinson319:

I keep reading posts on the newsgroup about the speed of light being absolute
and maximal.

Well, it certainly isn't absolute; photons have been slowed down to
speeds of a few meters per second, perhaps less, in experiments
conducted in the past several years.

I believe it is worth pointing out two current opposing opinons

1. the speed of light is not constant and is changing along with the universe
and space, time, gravity. A provocative idea currently quite hotlly contested
but one which does explain the unevenness of space.

I regret that membership in the American Association for the
Advancement of Science is required to read this entire article from 27
August, 2003, but here is an extract:

"...Known as Lorentz invariance, that principle implies that all
particles of light , or photons, travel through empty space at the same
speed regardless of how much energy they pack. In recent years,
however, various quantum gravity theories have suggested that because
of the underlying frothiness of spacetime, Lorentz invariance might not
hold, in which case light of different wavelengths would travel at
slightly different rates. Researchers might be able to measure the tiny
speed differences by studying light from enormous extragalactic
explosions known as gamma ray bursts--or so theorists predicted in
1998.

"But the new studies put the kibosh on that tantalizing idea. Floyd
Stecker, a theoretical astrophysicist at NASA's Goddard Space F light
Center in Greenbelt, Maryland, and colleagues studied gamma rays from
the hearts of the galaxies Markarian 421 and Markarian 501, some 450
million light -years from Earth. En route the rays pass through a haze
of infrared photons that fill intergalactic space. If Lorentz
invariance were violated, the gamma rays would zip right through the
haze. According to special relativity, however, the highest energy
gamma rays should collide with the infrared photons to make
electron-antielectron pairs. This process should soak up gamma rays
above a well-defined cutoff energy--just what the researchers observed,
Stecker reports in a paper to be published in the journal Astroparticle
Physics .

"Gamma rays from the Crab Nebula also bear out Einstein's theory,
gravitation theorist Ted Jacobson and colleagues at the University of
Maryland, College Park, report in the 28 August issue of Nature . The
rays come from extremely energetic electrons spiraling in the magnetic
fields inside the gargantuan cloud of gas. If Lorentz invariance were
violated, the electrons would slam up against a virtual speed limit
slower than the speed of light . From the energy of the gamma rays,
however, Jacobson and colleagues deduced that the electrons were
traveling within a 10-billion-billionth of the speed of light --even
stronger evidence that Einstein was right."

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an
object moving slower than the speed of light cannot accelerate to faster that the
speed of light"

It has been my understanding that some particle -- especially in the
jets emitted from certain QSO's -- may give the appearance of moving
and superluminal speeds, but that they do not. This oversimplification
(my fault, entirely) will no doubt be explained by a more knowledgable
reader.

Both of the published opinons are in keeping with the general theory of
relativity.

*****

Davoud

--
usenet *at* davidillig dawt com

"Arobinson319" wrote in message
...
I keep reading posts on the newsgroup about the speed of light being
absolute
and maximal.
I believe it is worth pointing out two current opposing opinons

Any theory has differing opinions. Witness the flat earth society.

1. the speed of light is not constant and is changing along with the
universe
and space, time, gravity. A provocative idea currently quite hotlly
contested
but one which does explain the unevenness of space.

"hottly (sic) contested"? How about "proposed and rejected"? All recent
tests support the view that the speed of light in a vacuum is constant.

2. particles exist which have been measured at moving faster then the
speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the
speed
of light can never decelerate to slower than the speed of light - and an
object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

No, experiments have been carried out which reduced the speed of light
through different materials. And matter can move faster than light does in
that material. Google "Bose-Einstein" for more. Also Google "Cherenkov
radiation." Nothing has ever been observed to travel faster than C, the
speed of light in a vacuum.

Observations show expanding material that appears to move faster, but it is
an illusion. Google "Supraluminal" for more.

Hope this clarifies misinformation.

Chuck Taylor
Do you observe the moon?
Try the Lunar Observing Group
http://groups.yahoo.com/group/lunar-observing/

On 26 Sep 2003 01:00:29 GMT, (Arobinson319) wrote:

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

Nope. Tachyons are particles that some theories support. They have never been
observed, and are almost certainly unobservable if they actually exist.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

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"ar" == Arobinson319 writes:

ar I keep reading posts on the newsgroup about the speed of light
ar being absolute and maximal. I believe it is worth pointing
ar out two current opposing opinons

That's because of sloppy terminology. Of course, the terminology is
sloppy because to make it precise makes it too cumbersome to use in
normal conversation.

"The speed of light" is a short-cut for "the speed of light in a
vacuum." In some sense, even this is not-quite right. It is really
the speed of zero-mass particles in the vacuum, so the current
consensus view is that gravitons also travel at this speed.

The real point of the above is that it is better to say that there is
a certain maximum speed in our universe and we call it "c" (and we have
even defined the meter in terms of "c"). This upper limit happens to
be the speed at which zero-mass particles travel in a vacuum.

ar 1. the speed of light is not constant and is changing along
ar with the universe and space, time, gravity. A provocative
ar idea currently quite hotlly contested but one which does
ar explain the unevenness of space.

Huh?

The value of "c" *may* be saying, but I don't think there is any
strong evidence of that. Their were some measurements done which
implied that the fine structure constant may have been different by a
few parts in 10^4 (I'm doing this from memory and may be way off, but
the amount was *small*) in very early cosmological times. But that
doesn't do anything to "explain the unevenness of space."

In fact, the big problem with most cosmological theories until the
early 80s was that they couldn't explain the tremendous *uniformity*
of space, especially early in the history of the universe. That's
what made Guth's inflation so exciting; all of a sudden there was an
explanation for the uniformity of space, especially early in the
history of the universe.

You have been paying attention to all the fuss about high-precision
measurements of the cosmic background radiation, right? Those maps
they publish with all the ripples...do you know how small those
ripples are? They are *tiny*, dT/T ~ 6 x 10^-6. Ultimately, those
tiny ripples gave way to the formation of the galaxies we see today,
but space is incredibly uniform---mostly empty with an occasional bump
of matter.

ar 2. particles exist which have been measured at moving faster
ar then the speed of light however they cannot slow down to
ar slower than the speed of light. therefore a more correct
ar statement is "an object moving faster than the speed of
ar light can never decelerate to slower than the speed of
ar light - and an object moving slower than the speed of light
ar cannot accelerate to faster that the speed of light"

Uhm, you've mixed too things here, one true, the other, ahem,
"speculative." There are indeed particles which travel faster than
the speed of light _in that medium_. This is the origin of Cerenkov
radiation. A high-energy cosmic ray slams into the upper atmosphere
and produces a shower of particles whoses speed are higher than what
light can travel in the atmosphere; voile, Cerenkov radiation that can
be seen by ground detectors. Same thing happens in the water
surrounding a nuclear reactor.

But there are no _known_ particles which travel faster than "c" (which
happens to be the speed of light in a vacuum). The "tachyons" to
which you are referring a hypothetical particles and have never been
seen in the real universe (as opposed to the universe found on my
science fiction bookshelf).

regards,

roland
- --
PGP Key ID: 66 BC 3B CD
Roland B. Roberts, PhD RL Enterprises
6818 Madeline Court
Brooklyn, NY 11220

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Arobinson319 wrote:

I keep reading posts on the newsgroup about the speed of light being absolute
and maximal.
I believe it is worth pointing out two current opposing opinons

1. the speed of light is not constant and is changing along with the universe
and space, time, gravity. A provocative idea currently quite hotlly contested
but one which does explain the unevenness of space.

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

Both of the published opinons are in keeping with the general theory of
relativity.

clear skies

Arobinson319--I suggest you move this thread to news:sci.physics

What we know about nature and the "laws of physics" are based on the
empirical results of observation and experiment. There is NO evidence
that one of the fundamental constants of nature, the speed of light
is variable in time over the course of this history. We may someday
find out otherwise... but the is NO evidence to suggest that. NO evidence.

No particles (tachyons included) have ever been observed to have a
velocity greater than the speed of light.

Special Relativity
http://scienceworld.wolfram.com/phys...elativity.html

Well, it certainly isn't absolute; photons have been slowed down to
speeds of a few meters per second, perhaps less, in experiments
conducted in the past several years.

That's group velocity, not phase velocity.

Chris L Peterson wrote:

On 26 Sep 2003 01:00:29 GMT, (Arobinson319) wrote:

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

Nope. Tachyons are particles that some theories support. They have never been
observed, and are almost certainly unobservable if they actually exist.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Physics FAQ - Tachyons
http://math.ucr.edu/home/baez/physic.../tachyons.html

[Physics FAQ] - [Copyright]

Updated March 1993 by SIC; Original by Scott I. Chase.


Tachyons

There was a young lady named Bright,
Whose speed was far faster than light.
She went out one day,
In a relative way,
And returned the previous night!

-Reginald Buller

It is a well known fact that nothing can travel faster than the speed
of light. At best, a massless particle travels at the speed of light.
But is this really true? In 1962, Bilaniuk, Deshpande, and Sudarshan,
Am. J. Phys. 30, 718 (1962), said "no". A very readable paper is
Bilaniuk and Sudarshan, Phys. Today 22,43 (1969). I give here a brief
overview.

Draw a graph, with momentum (p) on the x-axis, and energy (E) on the
y-axis. Then draw the "light cone", two lines with the equations E =
+/- p. This divides our 1+1 dimensional space-time into two regions.
Above and below are the "timelike" quadrants, and to the left and right
are the "spacelike" quadrants.

Now the fundamental fact of relativity is that E2 - p2 = m2. (Let's
take c=1 for the rest of the discussion.) For any non-zero value of m
(mass), this is an hyperbola with branches in the timelike regions. It
passes through the point (p,E) = (0,m), where the particle is at rest.
Any particle with mass m is constrained to move on the upper branch of
this hyperbola. (Otherwise, it is "off-shell", a term you hear in
association with virtual particles - but that's another topic.) For
massless particles, E2 = p2, and the particle moves on the light-cone.

These two cases are given the names tardyon (or bradyon in more modern
usage) and luxon, for "slow particle" and "light particle". Tachyon is
the name given to the supposed "fast particle" which would move with
vc. (Tachyons were first introduced into physics by Gerald Feinberg,
in his seminal paper "On the possibility of faster-than-light
particles" [Phys.Rev. v.159, pp.1089--1105 (1967)]).

Now another familiar relativistic equation is E = m*[1-(v/c)2]-1/2.
Tachyons (if they exist) have v c. This means that E is imaginary!
Well, what if we take the rest mass m, and take it to be imaginary?
Then E is negative real, and E2 - p2 = m2 0. Or, p2 - E2 = M2, where
M is real. This is a hyperbola with branches in the spacelike region
of spacetime. The energy and momentum of a tachyon must satisfy this
relation.

You can now deduce many interesting properties of tachyons. For
example, they accelerate (p goes up) if they lose energy (E goes
down). Furthermore, a zero-energy tachyon is "transcendent," or
infinitely fast. This has profound consequences. For example, let's
say that there were electrically charged tachyons. Since they would
move faster than the speed of light in the vacuum, they should produce
Cherenkov radiation. This would lower their energy, causing them to
accelerate more! In other words, charged tachyons would probably lead
to a runaway reaction releasing an arbitrarily large amount of energy.
This suggests that coming up with a sensible theory of anything except
free (noninteracting) tachyons is likely to be difficult.
Heuristically, the problem is that we can get spontaneous creation of
tachyon-antitachyon pairs, then do a runaway reaction, making the
vacuum unstable. To treat this precisely requires quantum field
theory, which gets complicated. It is not easy to summarize results
here. However, one reasonably modern reference is Tachyons, Monopoles,
and Related Topics, E. Recami, ed. (North-Holland, Amsterdam, 1978).

However, tachyons are not entirely invisible. You can imagine that you
might produce them in some exotic nuclear reaction. If they are
charged, you could "see" them by detecting the Cherenkov light they
produce as they speed away faster and faster. Such experiments have
been done. So far, no tachyons have been found. Even neutral tachyons
can scatter off normal matter with experimentally observable
consequences. Again, no such tachyons have been found.

How about using tachyons to transmit information faster than the speed
of light, in violation of Special Relativity? It's worth noting that
when one considers the relativistic quantum mechanics of tachyons, the
question of whether they "really" go faster than the speed of light
becomes much more touchy! In this framework, tachyons are waves that
satisfy a wave equation. Let's treat free tachyons of spin zero, for
simplicity. We'll set c = 1 to keep things less messy. The
wavefunction of a single such tachyon can be expected to satisfy the
usual equation for spin-zero particles, the Klein-Gordon equation:

(BOX + m2)phi = 0

where BOX is the D'Alembertian, which in 3+1 dimensions is just

BOX = (d/dt)2 - (d/dx)2 - (d/dy)2 - (d/dz)2.

The difference with tachyons is that m2 is negative, and m is
imaginary.

To simplify the math a bit, let's work in 1+1 dimensions, with
co-ordinates x and t, so that

BOX = (d/dt)2 - (d/dx)2

Everything we'll say generalizes to the real-world 3+1-dimensional
case. Now - regardless of m, any solution is a linear combination, or
superposition, of solutions of the form

phi(t,x) = exp(-iEt + ipx)

where E2 - p2 = m2. When m2 is negative there are two essentially
different cases. Either |p| = |E|, in which case E is real and we get
solutions that look like waves whose crests move along at the rate
|p|/|E| = 1, i.e., no slower than the speed of light. Or |p| |E|,
in which case E is imaginary and we get solutions that look waves that
amplify exponentially as time passes!

We can decide as we please whether or not we want to consider the
second sort of solutions. They seem weird, but then the whole business
is weird, after all.

1) If we do permit the second sort of solution, we can solve the
Klein-Gordon equation with any reasonable initial data - that is, any
reasonable values of phi and its first time derivative at t = 0. (For
the precise definition of "reasonable," consult your local
mathematician.) This is typical of wave equations. And, also typical
of wave equations, we can prove the following thing: If the solution
phi and its time derivative are zero outside the interval [-L,L] when t
= 0, they will be zero outside the interval [-L-|t|, L+|t|] at any time
t. In other words, localized disturbances do not spread with speed
faster than the speed of light! This seems to go against our notion
that tachyons move faster than the speed of light, but it's a
mathematical fact, known as "unit propagation velocity".

2) If we don't permit the second sort of solution, we can't solve the
Klein-Gordon equation for all reasonable initial data, but only for
initial data whose Fourier transforms vanish in the interval
[-|m|,|m|]. By the Paley-Wiener theorem this has an odd consequence:
it becomes impossible to solve the equation for initial data that
vanish outside some interval [-L,L]! In other words, we can no longer
"localize" our tachyon in any bounded region in the first place, so it
becomes impossible to decide whether or not there is "unit propagation
velocity" in the precise sense of part 1). Of course, the crests of
the waves exp(-iEt + ipx) move faster than the speed of light, but
these waves were never localized in the first place!

The bottom line is that you can't use tachyons to send information
faster than the speed of light from one place to another. Doing so
would require creating a message encoded some way in a localized
tachyon field, and sending it off at superluminal speed toward the
intended receiver. But as we have seen you can't have it both ways:
localized tachyon disturbances are subluminal and superluminal
disturbances are nonlocal.

See also the relativity FAQ Faster than light.

Arobinson319 wrote:

I keep reading posts on the newsgroup about the speed of light being absolute
and maximal.
I believe it is worth pointing out two current opposing opinons

1. the speed of light is not constant and is changing along with the universe
and space, time, gravity. A provocative idea currently quite hotlly contested
but one which does explain the unevenness of space.

2. particles exist which have been measured at moving faster then the speed of
light however they cannot slow down to slower than the speed of light.
therefore a more correct statement is "an object moving faster than the speed
of light can never decelerate to slower than the speed of light - and an object
moving slower than the speed of light cannot accelerate to faster that the
speed of light"

Both of the published opinons are in keeping with the general theory of
relativity.

clear skies

Related Question!
See Physics FAQ -- Is Faster Than Light Travel or Communication Possible?
http://math.ucr.edu/home/baez/physic...Light/FTL.html