I posted this earlier under a different subject heading, please don't
ignore me this time!

Hi,

I have a question about general relativity. It is based off of the
Feynman Lectures. Suppose you have a tower on a planet. And at the
top of the planet you drop a photon to the Earth. As it leaves, the
photon kicks the tower in one direction and then speeds to the
surface. At the surface, the photon strikes with an increse in
energy, a higher frequency, and thus a higher momentum. It kicks the
tower/Earth in the opposite direction than before. But this kick is
stronger than the one at the tower when it left. So there is a net
momentum transfer in the opposite direction. But this doesn't make
sense. you could make the Earth more compact, so that the difference
in kick gets more and more. Until finally you could build a space
ship where all you do is shine a bit of light in one direction, and go
careening off into space somewhere. But this net "motion exnihilo" is
weird. Clearly I'm missing something. But what? You have the same
thing in
Newtonian mechanics. Where on the tower you drop a ball and it falls
to the earth, striking with greater momentum than when it left. But
when you look at this from a non-inertial reference frame, you see
what's happening. The momentum picked up by the ball is exactly
counterballanced by the momentum picked up by the Earth/tower. This
is because the force acting on the ball is exactly equal in magnitude
to the force of the ball on the Earth, but opposite in direction, and
the impulse of force over time is the same, and they both cancel out.
But with a photon, you don't have that luxury. For a photon to
"accelerate" the Earth upwards, there would have to be some "advanced
warning" that the photon was coming, travelling faster than light.
And this apparently, is excluded. How do you resolve this [apparent]
paradox? One thing is by the equivalence principle, this should be
the same
as a rocket accelerating upwards in outerspace, and firing a photon
from the top to the bottom. I haven't thought enough about this case
though. Am I looking at the Earth/tower system from the
wrong frame? Am I misunderstanding the conservation of three momentum
with four momentum? What's going on here? Thanks...

(Joe) wrote in message . com...
I posted this earlier under a different subject heading, please don't
ignore me this time!

Ok, pardon top post, your scenario below is clear and IMO
true.

Joe, there is a gedanken (thought experiment) used commonly
in relativity involving a "light box". What we do is fill
a box with light, that has prefectly reflecting walls on
the interior and weigh it.

You'll find the "light pressure" pushing up on the top of
the box is less than the "light pressure" pushing down on
the bottom of the box, for the reasons you very well
described, that wee bit of difference in the energy of
light as it changes altitude, makes a pressure difference,
entirely due to "photon" momentum.

Congradulations Sir I'm giving you an A+ , the + is for
posting again.
You should examine the Pound-Rebka experiment, you'll
understand it, after-all you just described it!
Regards and Luck
Ken S. Tucker
PS: hope you post more often, are you a student?

Hi,

I have a question about general relativity. It is based off of the
Feynman Lectures. Suppose you have a tower on a planet. And at the
top of the planet you drop a photon to the Earth. As it leaves, the
photon kicks the tower in one direction and then speeds to the
surface. At the surface, the photon strikes with an increse in
energy, a higher frequency, and thus a higher momentum. It kicks the
tower/Earth in the opposite direction than before. But this kick is
stronger than the one at the tower when it left. So there is a net
momentum transfer in the opposite direction. But this doesn't make
sense. you could make the Earth more compact, so that the difference
in kick gets more and more. Until finally you could build a space
ship where all you do is shine a bit of light in one direction, and go
careening off into space somewhere. But this net "motion exnihilo" is
weird. Clearly I'm missing something. But what? You have the same
thing in
Newtonian mechanics. Where on the tower you drop a ball and it falls
to the earth, striking with greater momentum than when it left. But
when you look at this from a non-inertial reference frame, you see
what's happening. The momentum picked up by the ball is exactly
counterballanced by the momentum picked up by the Earth/tower. This
is because the force acting on the ball is exactly equal in magnitude
to the force of the ball on the Earth, but opposite in direction, and
the impulse of force over time is the same, and they both cancel out.
But with a photon, you don't have that luxury. For a photon to
"accelerate" the Earth upwards, there would have to be some "advanced
warning" that the photon was coming, travelling faster than light.
And this apparently, is excluded. How do you resolve this [apparent]
paradox? One thing is by the equivalence principle, this should be
the same
as a rocket accelerating upwards in outerspace, and firing a photon
from the top to the bottom. I haven't thought enough about this case
though. Am I looking at the Earth/tower system from the
wrong frame? Am I misunderstanding the conservation of three momentum
with four momentum? What's going on here? Thanks...

Dear Joe:

"Joe" wrote in message
om...
I posted this earlier under a different subject heading, please don't
ignore me this time!

Hi,

I have a question about general relativity. It is based off of the
Feynman Lectures. Suppose you have a tower on a planet. And at the
top of the planet you drop a photon to the Earth. As it leaves, the
photon kicks the tower in one direction and then speeds to the
surface. At the surface, the photon strikes with an increse in
energy, a higher frequency, and thus a higher momentum. It kicks the
tower/Earth in the opposite direction than before. But this kick is
stronger than the one at the tower when it left. So there is a net
momentum transfer in the opposite direction. But this doesn't make
sense.

Sure it does.

you could make the Earth more compact, so that the difference
in kick gets more and more. Until finally you could build a space
ship where all you do is shine a bit of light in one direction, and go
careening off into space somewhere. But this net "motion exnihilo" is
weird. Clearly I'm missing something. But what? You have the same
thing in
Newtonian mechanics. Where on the tower you drop a ball and it falls
to the earth, striking with greater momentum than when it left. But
when you look at this from a non-inertial reference frame, you see
what's happening. The momentum picked up by the ball is exactly
counterballanced by the momentum picked up by the Earth/tower. This
is because the force acting on the ball is exactly equal in magnitude
to the force of the ball on the Earth, but opposite in direction, and
the impulse of force over time is the same, and they both cancel out.
But with a photon, you don't have that luxury. For a photon to
"accelerate" the Earth upwards, there would have to be some "advanced
warning" that the photon was coming, travelling faster than light.
And this apparently, is excluded. How do you resolve this [apparent]
paradox?

The net energy of the system is conserved. No paradox. The energy of the
light is unaffected by the light's position in the gravity well, from the
POV of the release point (or any other single point observing multiple
positions of light and resulting energy states).

One thing is by the equivalence principle, this should be
the same
as a rocket accelerating upwards in outerspace, and firing a photon
from the top to the bottom. I haven't thought enough about this case
though. Am I looking at the Earth/tower system from the
wrong frame? Am I misunderstanding the conservation of three momentum
with four momentum? What's going on here? Thanks...

David A. Smith

This light box may explain something. If I put a light box on the
planet, it is obviously apparent that it can't acclerate the Earth.
This is because the force on one side of the box is direclty
counterbalanced by the force of the ground on that side of the box.
However, if there is more light in the box, increasing that force, to
the point where it causes structural failure of the ground, then it
will accelerate to the center of the Earth. And yet, in my naivitee,
I think of light bouncing back and forth between the top and bottom.
As it bounces off the top, it imparts less momentum than when it
bouncess off the bottom! Shouldn't this cause a net force in the one
direction, accelerating the planet? What counterbllances it? (You
can tell my intelligence drops the more I keep my mouth open.) I tell
you the truth, I've fled to the internet to escape grades. I
appreciate the comment, but it makes me afraid of asking even stupider
questions.

[I think I know where it comes from, it must be the light box acting
on the planet. But this appears to be wiggling out of my question.]

Another question that I have is about the parallel between a rocket
ship and a uniform gravitational field. Let's assume the rocket ship
is thrusting in outer space, at uniform acceleration. This
corresponds to uniform thrust. Now, I take a mass up to the top of
the space sip, and "drop" it. Suddenly, the "mass" of the space ship
is less, because it is not accelerating what you "dropped". But this
means there is a sudden lurch of the craft, because it is moving at
constant thrust. This is different with gravity (isn't it?), if the
space ship is on the ground, and I drop something from the top, there
is no sudden lurch! Notice depending on the size of this object, and
the ratio that it takes up with to the rest of the craft, this lurch
could be enormous! But there is no accompanying lurch on ground.
This means that for the equivalence principle to be true, the space
ship must adjust its thrust to compensate for the dropped object. Now
I can be a devil! Suppose I'm in a space ship, and for some reason I
suspect I am. I can do real hell to the pilots in the conspiracy to
keep me believing this by tossing things around, which way and that,
and seeing if they can compensate their thrust to match! If I do real
hell out of this, can I ask if there really are pilots that smart to
keep up with this charade? Can they really adjust thrusters in
strength, omnidirectional, etc. to do this? In fact, what would be
interesting, is too see if it is even CONCIEVABLY POSSIBLE for a space
ship and pilot to do this. In otherwords, if the information that I
had dropped something from the top had to travel FASTER THAN LIGHT to
get to the controllers who then send a signal from their computer to
the thrusters, etc. I don't know. (I wich I was a GOD.)

"jahn" wrote in message ...
"Ken S. Tucker" wrote in message om...
"jahn" wrote in message ...
[...]
Einstein's description of the gravitational redshift because his description predicts gravity affecting light during emission,
in
contrast to causing in-flight wavelength change, as required by the expansion hypothesis. In what appears to be one of the most
significant lapses in the history of science, there appears to be no record where cosmologists ever sought to determine for a
certainty whether photons actually do experience an in-flight change in wavelength while passing through a gravitational
potential
gradient.
} http://orionfdn.org/papers/arxiv-5.htm

{On the interpretation of the redshift in a static gravitational field
L. B. Okun and K. G. Selivanov
ITEP, Moscow, 117218, Russia
V. L. Telegdi
EP Division, CERN, CH-1211 Geneva 23, Switzerland
} http://dx.doi.org/10.1119/1.19382
--------------
Kind regards,
Sue...

Thanks for the refs. very interesting.
IMHO the "red shift" is a field effect, to conserve
momentum. That is not an easy *opinion* to defend in GR.

I'm basing it on the momentum transfer from light to
a mass when the light is deflected by the mass, and
the mass receives momentum from the photon.

A lossy
interation between light and matter "seems" to be
limited to subatomic wavelengths where material
entities are comparable in size....Compton scattering
and radiation recoil/reaction.

The way I see it is each subatomic particle within the
sun for example contributes to the deflection of light
by virtue of gravitating mass.

If an atom or lepton is
displaced then the wave should indeed loose energy.
In a homonogenoous dielectric, for every entity that
is being accelerated, charged or aligned another
entitiy is being decelerated discharged or mal-aligned.
So... the wavelength is reduced but no energy is
lost.
We have seen refraction in the gasses held by massive
objects. It isn't surprising at all that Einstein's field
equations can predict the density gradient of a gas
as well as the density gradient of "space-time". The
problem is:
If you say it is space-time being "squeezed"
by gravity, then you have a causality violation. If
you say an atmosphere slows the speed of light, then
it matches our experience nicely.

Ok, but that may be a simplisitic analogy.

This
should be a continuous transfer. But the question is
how does the photon deflect the mass prior to it's
arrival in the very near proximity of the mass?
After all it can't send a message ahead of itself.

It does indeed send a message before and after
itself. See Maxwell's advanced and retarded
potential. No one has ever measured the "speed of
charge" or the "speed of gravity". There are no
shock waves propagating back and forth on the
spokes of a rolling bicycle wheel as each spoke is
stretched then compressed, yet a bar of steel has
velocity factors for both transverse and longitudinal
modes.

So far I'm satisfied the speed of gravity is "c",
but the dynamical problem of matter moving at or near
light speed is one I haven't had a lot of experience
with. Others have analysed it see no problem.

A good physicist needs to spend at least as much
time on a beach as in a billard parlor. ;-)

Where should a bad physicist go? ...and will I be
arrested again?

Kind regards,
Sue...

I'm guessing it's the g-field itself that is deflected.
Regards
Ken S. Tucker

"Joe" wrote in message
om...
I posted this earlier under a different subject heading, please don't
ignore me this time!

Hi,

I have a question about general relativity. It is based off of the
Feynman Lectures. Suppose you have a tower on a planet. And at the
top of the planet you drop a photon to the Earth.

A photon can't be "dropped". Maybe a little nit-picking, but often wrong
concepts lead to wrong reasoning.

As it leaves, the
photon kicks the tower in one direction and then speeds to the
surface. At the surface, the photon strikes with an increse in
energy, a higher frequency, and thus a higher momentum.

Not really: only apparently, in the local frame. There is a lot confusion
propagated by textbooks, as many teachers (even Feynman?) didn't fully
understand it. See the AJP of a few years back where it is quite well
explained:
http://scitation.aip.org/getabs/serv... 093837402530

It kicks the
tower/Earth in the opposite direction than before. But this kick is
stronger than the one at the tower when it left. So there is a net
momentum transfer in the opposite direction. But this doesn't make
sense.

Indeed it doesn't. And it isn't really so. Result of using local differently
calibrated units.

Harald

you could make the Earth more compact, so that the difference
in kick gets more and more. Until finally you could build a space
ship where all you do is shine a bit of light in one direction, and go
careening off into space somewhere. But this net "motion exnihilo" is
weird. Clearly I'm missing something. But what? You have the same
thing in
Newtonian mechanics. Where on the tower you drop a ball and it falls
to the earth, striking with greater momentum than when it left. But
when you look at this from a non-inertial reference frame, you see
what's happening. The momentum picked up by the ball is exactly
counterballanced by the momentum picked up by the Earth/tower. This
is because the force acting on the ball is exactly equal in magnitude
to the force of the ball on the Earth, but opposite in direction, and
the impulse of force over time is the same, and they both cancel out.
But with a photon, you don't have that luxury. For a photon to
"accelerate" the Earth upwards, there would have to be some "advanced
warning" that the photon was coming, travelling faster than light.
And this apparently, is excluded. How do you resolve this [apparent]
paradox? One thing is by the equivalence principle, this should be
the same
as a rocket accelerating upwards in outerspace, and firing a photon
from the top to the bottom. I haven't thought enough about this case
though. Am I looking at the Earth/tower system from the
wrong frame? Am I misunderstanding the conservation of three momentum
with four momentum? What's going on here? Thanks...

"Ken S. Tucker" wrote in message om...
"jahn" wrote in message ...
"Ken S. Tucker" wrote in message om...
"jahn" wrote in message ...
[...]
Einstein's description of the gravitational redshift because his description predicts gravity affecting light during
emission,
in
contrast to causing in-flight wavelength change, as required by the expansion hypothesis. In what appears to be one of the
most
significant lapses in the history of science, there appears to be no record where cosmologists ever sought to determine for
a
certainty whether photons actually do experience an in-flight change in wavelength while passing through a gravitational
potential
gradient.
} http://orionfdn.org/papers/arxiv-5.htm

{On the interpretation of the redshift in a static gravitational field
L. B. Okun and K. G. Selivanov
ITEP, Moscow, 117218, Russia
V. L. Telegdi
EP Division, CERN, CH-1211 Geneva 23, Switzerland
} http://dx.doi.org/10.1119/1.19382
--------------
Kind regards,
Sue...

Thanks for the refs. very interesting.
IMHO the "red shift" is a field effect, to conserve
momentum. That is not an easy *opinion* to defend in GR.

I'm basing it on the momentum transfer from light to
a mass when the light is deflected by the mass, and
the mass receives momentum from the photon.

A lossy
interation between light and matter "seems" to be
limited to subatomic wavelengths where material
entities are comparable in size....Compton scattering
and radiation recoil/reaction.

The way I see it is each subatomic particle within the
sun for example contributes to the deflection of light
by virtue of gravitating mass.
Yes... It creates a density gradient in the plamsa which
extends quite effectively to the earth. (aurora borealis).
No such effect is recorded for the moon with no
atmosphere... ahhh AFAIK.

If an atom or lepton is
displaced then the wave should indeed loose energy.
In a homonogenoous dielectric, for every entity that
is being accelerated, charged or aligned another
entitiy is being decelerated discharged or mal-aligned.
So... the wavelength is reduced but no energy is
lost.
We have seen refraction in the gasses held by massive
objects. It isn't surprising at all that Einstein's field
equations can predict the density gradient of a gas
as well as the density gradient of "space-time". The
problem is:
If you say it is space-time being "squeezed"
by gravity, then you have a causality violation. If
you say an atmosphere slows the speed of light, then
it matches our experience nicely.

Ok, but that may be a simplisitic analogy.
It is not an analogy:
'The Sun and the solar corona'
http://www.sp.ph.ic.ac.uk/~mkd/AndreHandout.pdf

This
should be a continuous transfer. But the question is
how does the photon deflect the mass prior to it's
arrival in the very near proximity of the mass?
After all it can't send a message ahead of itself.

It does indeed send a message before and after
itself. See Maxwell's advanced and retarded
potential. No one has ever measured the "speed of
charge" or the "speed of gravity". There are no
shock waves propagating back and forth on the
spokes of a rolling bicycle wheel as each spoke is
stretched then compressed, yet a bar of steel has
velocity factors for both transverse and longitudinal
modes.

So far I'm satisfied the speed of gravity is "c",
but the dynamical problem of matter moving at or near
light speed is one I haven't had a lot of experience
with. Others have analysed it see no problem.

The spatial displacement of a a barycenter sufficient to
observe is itself a considerable problem.
http://www.ligo.caltech.edu/


A good physicist needs to spend at least as much
time on a beach as in a billard parlor. ;-)

Where should a bad physicist go? ...and will I be
arrested again?
1. Girlie bars.
2. I don't think Feynman ever was.
http://www.wordiq.com/definition/Richard_Feynman
http://www.uky.edu/~holler/msc/roles/cargcult.html
;-)
Sue...

Kind regards,
Sue...

I'm guessing it's the g-field itself that is deflected.
Regards
Ken S. Tucker