Dear rambus2005:

wrote in message
oups.com...

Randy M. Dumse wrote:
.

In GR, it is mass-energy that gravitates, and not just
mass. Even photons (and even pressure!) participate.
If you put two photons in a mirror box, its mass
would increase (a tiny, but non-zero, amount). Fill
the mirrored box with many photons, and externally,
you can't tell the difference between the box with
photons in it and the box with an equivalent mass.

Nice post. A small correction, though, the "box full
of photons" is a bad example. What you are
measuring is the effect of the increased "pressure
radiation" which manifests itself as a measurable
force, not the increased mass of the system.

In the center of momentum frame, two or more photons have rest
mass. The center of momentum frame resides within the box. Are
you sure the basis of your objection is entirely valid and
complete?

David A. Smith

wrote in message
oups.com...
Nice post. A small correction, though, the "box full of photons" is a
bad example. What you are measuring is the effect of the increased
"pressure radiation" which manifests itself as a measurable force,
not the increased mass of the system.


Thanks. I hear, and appreciate, your objection. I even worried a bit
about putting it as I did. Notice I had choosen mass-energy, as opposed
to the more correct stress-energy, to more easily be understood by the
current audience. I also included a pressure comment to keep the door to
larger concepts open. So you are right that in this example pressure
plays the major role.

But I don't know if I am comfortable saying the mass of the system does
not increase. I feel if I left out the box completely, and the "system"
was just the two (antiparallel) photons it would still have mass.

But given the box is closed, you don't know what's inside. You can
measure the mass of the system. Weight it, or try to accelerate it. In
either case, it exhibits mass. Calling it mass, or calling it "pressure
radiation manifesting itself as a measurable force" seem just two ways
of looking at the same thing due to equivalence.

Would you call the "mass without mass" of Wheeler's geon due to pressure
radiation? I wouldn't. Would radiation thrown down a black hole increase
it's radiation pressure component? or does it just become "mass".

So I don't see the mirrored box as a terribly bad example, just one
complicated by the presence of the mirrored box, to make it is easier to
conceptualize two photons as a system. The mirrors help us imagine them
remaining in close proximity.

--
Randy M. Dumse

Caution: Objects in mirror are more confused than they appear.

wrote in message
ups.com...
| Sorcerer wrote:
| "Danny Dot" wrote in message
| ...
| |I am a lowly engineer in aerospace, but have taken a few advanced
physics
| | questions.
| |
| | My question is, if two photon's pass really, really, really close to
each
| | other -- will their paths be changed by one interaction with the
gravity
| of
| | the other.
|
| No.
| Photons are not billiard balls, although they share some things in
common,
| such as momentum. What makes a photon different is that they can pass
| right through each other. That isn't so strange, though, they can pass
| right through glass too, a billiard ball cannot.
| Androcles
|
| Actually billiard balls can pass thru glass and photons cannot!
|
| The first case should be obvious, unless you have bullet-proof glass.
| (I make a joke!) And then you go get more glass.
|
| In the second case, photons are thought to be absorbed by the
| atomsin the medium, and the the excited atoms radiate new
| photons. John Fox, Am. J. Phys., 33,1 (1965), calls this an
| extinction process. The new photons are not, strictly speaking,
| the originals, but replicas. I'd guess that a little energy is lost
| in each absorption/re-emission event.

The difficulty with such a theory is prismatic refraction and internal
reflection. The relation between the incident ray and the resultant ray
is well defined by Snell's Law, so your model is that of a tunnel
in which a car enters one end and pushed a different car out from
the other, but the replica cars are sorted by colour and emerge at
different angles determined by the tunnel faces. There is no
evidence of energy loss in that process.
If the light heats the glass then the glass will certainly absorb
energy. However, the re-radiation is omnidirectional, does not obey
Snell's Law and is delayed in time, the glass gradually cooling
long after the sun went down.

|
| In my humble opinion there is a lot of wrong think about
| so-called photons. Here is an alternate description of how
| atoms disturb one another at a distance electromagnetically.

All we can do is construct theory based on observation. No
two people think alike, there WILL be many wrong thinks.
The best think is the one that cannot be rejected by empirical data,
but there is no guarantee of correctness.



| Ritz's (1908) ballistic emission theory held that charges emit,
| more-or-less continuously, what he called fictitious particles.

One cannot deny that a continuous stream of light reaches us
from the sun or a glowing tungsten filament, I'd be hesistant to
call that fictitious. Also it is a simple matter to control the
radiation from the filament with a rheostat. It doesn't bother
me whether they are called corpuscles, fictitious particles or
photons, a rose by any other name would objectively still stink
or subjectively smell as sweet.




| It would be fairly easy to picture vibrational disturbances
| being impressed on the outgoing fluxes of fictitous particles.
| (Real particles with gaps between them might be permissible.)
|
| If you have a gazillion atomic sized Ritzian* e/m radiators all
| doing their thing, their emission fluxes, with vibrational
| disturbances impressed, spread out in more or less all
| directions, in buck-shot (or water spray droplet) fashion,
| rather than bulltet-like fashion, and pass amongst one another
| mostly unscathed.
|
| Every now and then (quite frequently, actually) some of these
| "wave-like" disturbances arrive at a given chunk of space in
| phase with each other, and constructive interference produces
| a strong enough wave action (at that place and time) that
| can induce a "measurable" atomic disturbance.
|
| *Ritz theorized that atoms produced e/m radiation as a result
| of their electron orbits vibrating with respect to their atomic
| magnetic fields. (No spin-flips or shell hopping required!) This
| would be similar to the well known e/m radiation produced by
| molecular vibrations.

As I understand you, what you propose is essentially an aether theory
macroscopically and a particle chain-collision theory microscopically,
the particles (or virtual/fictitious particles) pervading all of space.

As a mathematical model it has merit, but as a physical model it requires
a substance, matter, mass, or at least "something", call it what you will.
"Virtual" or "fictitious" doesn't quite work for me.

Based on empirical data and some knowledge of radio, it does
seem to me that the some-"thing" is/are the magnetic and electric fields
interchanging, each giving rise to the other alternately and containing
a finite and fixed quantity of energy which manifests itself as the
alternating fields.

http://www.androcles01.pwp.blueyonder.co.uk/AC/AC.htm

Thus a "photon" can be any size, will radiate either as a single
ripple on a pond, diminishing in amplitude as it spreads ever wider,
OR as a focussed beam with no change in amplitude, and of course
as something in between.


An energy source such as radio antenna broadcasts, but will focus
the energy into a beam by a parabolic dish for transmission to
a distant point without attenuation of the amplitude.
The wave goes omnidirectionally but diminishes in amplitude,
the photon goes unidirectionally without attenuation.

Low frequency photons are large, like tsumanis, passing through
multiple holes or slits like a boiled egg though an eggslicer
while high frequency photons are small as with ripples on a
puddle and pass through a single slit like a peppercorn in an
eggslicer, without diffraction, as optical light through the
door mesh of a microwave oven.

Thus we have both a wave model and a particle model and
the question to ask is how a molecule focuses its energy into
a beam-like entity to join with others, as with a laser.
That answer may be in phased array radar if we have TWO
photons emitted in opposite directions.

|
| For more on Ritz's emission theory, please see:
| http://www.shadetreephysics.com/crit/1908a.htm
| http://www.shadetreephysics.com/ritz.htm
|
| Bob Fritzius
| Electrical Engineer gone bad

For understanding the shape of light curves:
http://tinyurl.com/rv9z4
(automation of the same curves Vladimir Sekerin produced, in gif format)
Androcles

Randy M. Dumse wrote:
wrote in message
oups.com...
Nice post. A small correction, though, the "box full of photons" is a
bad example. What you are measuring is the effect of the increased
"pressure radiation" which manifests itself as a measurable force,
not the increased mass of the system.


Thanks. I hear, and appreciate, your objection. I even worried a bit
about putting it as I did. Notice I had choosen mass-energy, as opposed
to the more correct stress-energy, to more easily be understood by the
current audience. I also included a pressure comment to keep the door to
larger concepts open. So you are right that in this example pressure
plays the major role.

But I don't know if I am comfortable saying the mass of the system does
not increase. I feel if I left out the box completely, and the "system"
was just the two (antiparallel) photons it would still have mass.

But given the box is closed, you don't know what's inside. You can
measure the mass of the system. Weight it, or try to accelerate it. In
either case, it exhibits mass. Calling it mass, or calling it "pressure
radiation manifesting itself as a measurable force" seem just two ways
of looking at the same thing due to equivalence.

Would you call the "mass without mass" of Wheeler's geon due to pressure
radiation? I wouldn't. Would radiation thrown down a black hole increase
it's radiation pressure component? or does it just become "mass".

So I don't see the mirrored box as a terribly bad example, just one
complicated by the presence of the mirrored box, to make it is easier to
conceptualize two photons as a system. The mirrors help us imagine them
remaining in close proximity.
Randy M. Dumse

I think Mr. Dumse's explanation good. The mirrored
box is means of conserving energy within a volume.
Carlip and Baez have posted that heating a mass
increases it's gravitational mass, and radiation within
a box is a form of heat (infared radiation) exchanging
kinetic energy within the box.
Regards
Ken

"Bill Hobba" wrote in message
...
Nice response Randy - a pleasure to read. Good to see you posting.


Thanks, Bill. I've been rather pressed of late finishing a robotics
project for the Queen of Jordan that shipped Thursday. Also was asked to
prepare a new intermediate graduate class for my university. With the
pressure off, I had a moment to look in, and saw this thread. Of course
I always like to comment on the subject of light to light attraction,
being my research interest.

You know, even from a quantum point of view, the parallel light-light
issue makes sense. If there were a quantum communicator of gravitational
attraction, a graviton, how could it make it from one photon to another
if they were parallel. Traveling at the speed of light, how could a
graviton from one reach the other?

When you think about two parallel photons (in a SR context) they fall
into the category of "elsewhere", neither being in either's future. So
it is as if neither exists to the other. Of course they don't attract.

However, if they aren't parallel, a graviton from one could make it to
the other in less than infinite time. Again, it sounds reasonable. Not
that I think this is sufficient to make a serious quantum argument, but
just a consideration on reasonableness.

--
Randy M. Dumse

Caution: Objects in mirror are more confused than they appear.

Dear Randy M. Dumse:

"Randy M. Dumse" wrote in message
...
"Bill Hobba" wrote in message
...
Nice response Randy - a pleasure to read. Good
to see you posting.
....
You know, even from a quantum point of view, the
parallel light-light issue makes sense. If there were
a quantum communicator of gravitational attraction,
a graviton, how could it make it from one photon to
another if they were parallel. Traveling at the speed
of light, how could a graviton from one reach the
other?

Virtual exchange particles travel at all speeds, not limited by
c. Additionally, the "photon behind" could receive any particle
propagating at c from the "photon in front".

When you think about two parallel photons (in a
SR context) they fall into the category of
"elsewhere", neither being in either's future.

Non-intersecting null geodesics. Yes, that does make sense.

So it is as if neither exists to the other. Of
course they don't attract.

However, if they aren't parallel, a graviton
from one could make it to the other in less
than infinite time. Again, it sounds reasonable.
Not that I think this is sufficient to make a
serious quantum argument, but just a
consideration on reasonableness.

From a much more qualified and reliable source than me!

David A. Smith

Randy M. Dumse wrote:
You know, even from a quantum point of view, the parallel light-light
issue makes sense. If there were a quantum communicator of gravitational
attraction, a graviton, how could it make it from one photon to another
if they were parallel. Traveling at the speed of light, how could a
graviton from one reach the other?

By "traveling" faster than light, of course. I don't know the detail of
quantum gravity, but in QED the photons can certainly do that. Remember
that in the momentum representation there is a 4-d delta function at
each vertex, and in the configuration space representation that involves
an integral over all space and time (implying that the photon "travels"
over all possible paths at all possible speeds, unlimited by c).

That is, of course, a perturbation theory approach. Quantum gravity is
generally, but not universally, expected to be similar.


When you think about two parallel photons (in a SR context) they fall
into the category of "elsewhere", neither being in either's future. So
it is as if neither exists to the other. Of course they don't attract.

Yes, if one could treat photons as "pointlike particles" that would be
true. But one can't. The indeterminancy of the photons' positions can
put each inside the other's lightcone (obviously their distance apart
affects the likelihood of this).


However, if they aren't parallel, a graviton from one could make it to
the other in less than infinite time. Again, it sounds reasonable. Not
that I think this is sufficient to make a serious quantum argument, but
just a consideration on reasonableness.

I think it is a bit too naive....


Tom Roberts

"Tom Roberts" wrote in message
news
Randy M. Dumse wrote:
You know, even from a quantum point of view, the parallel
light-light
issue makes sense. If there were a quantum communicator of
gravitational
attraction, a graviton, how could it make it from one photon to
another
if they were parallel. Traveling at the speed of light, how could a
graviton from one reach the other?

By "traveling" faster than light, of course. I don't know the detail
of
quantum gravity, but in QED the photons can certainly do that.
Remember
that in the momentum representation there is a 4-d delta function at
each vertex, and in the configuration space representation that
involves
an integral over all space and time (implying that the photon
"travels"
over all possible paths at all possible speeds, unlimited by c).

I suspect that speeds greater than c can only happen in the "virtual"
domain and only for very short "distances". IOW, it doesn't happen in
the case of parallel light travelling for great distances unless the
photons are very close together (photon bunching).

FrediFizzx

Quantum Vacuum Charge papers;
http://www.vacuum-physics.com/QVC/qu...uum_charge.pdf
or postscript
http://www.vacuum-physics.com/QVC/qu...cuum_charge.ps
http://www.arxiv.org/abs/physics/0601110
http://www.vacuum-physics.com

"Tom Roberts" wrote in message
news
I think it is a bit too naive....

Hi Tom. Really glad to see you posting here. Keep up the good work.

Yes, as couched, "Not ... sufficient to make a serious quantum
argument". Quantum is certainly not my field. But as an intuitional
tool, very satisfying.

Best Regards,

--
Randy M. Dumse

Caution: Objects in mirror are more confused than they appear.

Randy M. Dumse wrote:
wrote in message
oups.com...
Nice post. A small correction, though, the "box full of photons" is a
bad example. What you are measuring is the effect of the increased
"pressure radiation" which manifests itself as a measurable force,
not the increased mass of the system.


Thanks. I hear, and appreciate, your objection. I even worried a bit
about putting it as I did. Notice I had choosen mass-energy, as opposed
to the more correct stress-energy, to more easily be understood by the
current audience. I also included a pressure comment to keep the door to
larger concepts open. So you are right that in this example pressure
plays the major role.

But I don't know if I am comfortable saying the mass of the system does
not increase. I feel if I left out the box completely, and the "system"
was just the two (antiparallel) photons it would still have mass.

But given the box is closed, you don't know what's inside. You can
measure the mass of the system. Weight it, or try to accelerate it. In
either case, it exhibits mass. Calling it mass, or calling it "pressure
radiation manifesting itself as a measurable force" seem just two ways
of looking at the same thing due to equivalence.

Would you call the "mass without mass" of Wheeler's geon due to pressure
radiation? I wouldn't. Would radiation thrown down a black hole increase
it's radiation pressure component? or does it just become "mass".

So I don't see the mirrored box as a terribly bad example, just one
complicated by the presence of the mirrored box, to make it is easier to
conceptualize two photons as a system. The mirrors help us imagine them
remaining in close proximity.

--
Randy M. Dumse

Caution: Objects in mirror are more confused than they appear.

Very good points. There are several reasons for steering clear of
"mass" in the unfortunate "photon in the box" example.

1. As you well point out, the box is closed, so we can only observe the
increase in inertia. If one does the computations, one can show that
the increased inertia is due to the forces tangential to the vertical
box walls resulting from pressure radiation.

2. The forces at point 1 are dependent on the direction of the photons
, parallel or antiparallel . In the case of a parallel pair photons the
resulting "invariant pass" is sqrt(Sigma_E^2-(Sigma_pc)^2)=0 while in
the case of antiparallel case the "invariant mass" is Sigma_E (because
Sigma_p=0) . This fact produces a "paradox", the "mass added to the
photon box" is direction dependent which does not bode well with the
notion of mass being a scalar. This is why I call the "photon in a box"
a very unfortunate example. I emaile Baez on this, he corrected the
website a little , but not enough.