What's up with gravity wave detection?

Eric Flesch:
On Mon, 30 Aug 2004 18:48:29 -0000,
(Bilge) wrote:
Eric Flesch:
Of course not. Bosons classically manifest routinely and so their
gravitational vectors can be described. But photons have *no*
classical manifestation between emission and absorption. There is a
real difference here in their behavior "in the wild".

Say what? Neutrons and protons are fermions, i.e., spinors, not vectors.
On the other hand, the photon _is_ a four-vector.

Sorry, frightful slip, I meant baryons.

You didn't address the fact that light is a four vector, which for
whatever reason, you seemed to think was an essential feature.

"Details"? Quantum gravity is vaporware. You can't quote it as
though it were a reference.

``Aspects of Quantum Field Theory in Curved Spacetime'', Fulling, S.A.,
``Quantum Fields and Strings: A course for Mathematicians'', Witten, E.,
and others, ed., 2 volume set.

These are speculative works.

In what way do you find them speculative? In view of the fact that
you specifically referred to qed, which is a quantum field theory,
try to be specific.

You can't have it both ways here. If you want to talk about what ``QED
shows,'' you have to allow standard techniques from QED.

You mystify me. What have I said to limit the application of QED?
I'm saying that where QED's description differs from GR, QED rules.

I hate to break this news to you, but the spacetime of special relativity
from which qed derives is no less ``continuous'' than the spacetime of
general relativity. It is possible to formulate qed (and quantum field
theories, in general) in curved spacetime, e.g., see the references above.

A pity fhen that photons don't travel in continuous paths, shown by
the delayed-choice experiment.

That is not what that experiment shows and in any case, what does that
experiment have to do with anything? You mentioned qed, so obviously you
must think special relativity is ok. How does formulating qed in curved
spacetime differ in any way from formulating it curved spacetime with
a specific value for the curvature, nanely zero, in any way that matters
to your argument?

If your speculative references are modelling photon behavior to be
different than observed behavior, then they are a waste of paper.

Then it's a good thing that isn't the case.

GR is not, and was never meant to be, a description of the nature of
light.

But general relativity is a theory of the spacetime in which light
propagates. Are you suggesting that there is something special about flat
spacetime other than the particular value for the curvature, (i.e., zero)
or that spacetime is relevant to the light which propagates in spacetime?

No, I would say rather that GR is incomplete when it comes to the way
that light interacts with spacetime.

General relativity _is_ spacetime, so-to speak. Once you eliminate
general relativity, you aren't talking about spacetime any longer.
Since qed was the _last_ of the four interactions to appear, light
didn't even exist until well after general relativity appeared.

Every mirror that we've ever built, if we build the box that you
describe, toss in some photons and close the box, the photons would be
absorbed (and converted to heat) in an infinitesimal fraction of a
second.

The point being what? Then, the heat contributes to the mass.

Sure, but the mass is missing whilst "in-flight" as a photon -- the
quantum description shows the photon has no mass in the classical
sense.

So what?

Why then the insistence that the in-flight photon should exert
gravitation just as though the mass was present?

The source of the gravitational field is T^uv, not the mass.

In that sense you are right. But I am reminded of one of Bohr's
refutations of Einstein's gedankenexperimenten where Einstein's
premise of increased mass was countered by the different rates of time
flow in a differential gravitational field.

Which was what, precisely?

It was the last one, after which Einstein no longer tried to pick
holes in Bohr's model. Here is an accounting from Pagels' "The Cosmic
Code": Einstein imagined one had a clock in a box present so that it
would open and close a shutter very quickly on the light-tight box.
Inside the box was also a gas of photons.

What does that have to do with general relativity? All you've quoted is
an ancient and irrelevant thought experiment about quantum mechanics.
Stop jumping from topic to topic.

[...]
confirmed it. After this, Einstein never disputed the consistency of
the new quantum theory.

No one, least of all me, is disputing quantum mechanics. I'm disputing
your understanding of quantum theory and general relativity, not to mention
qed.

[...]
So, if I place a radioactive source which decays by positron emission
in a thermally insulated box, then what do you predict the mass of the
box to be,

(1) before any of the nuclei decay,

(2) after all of the nuclei have decayed and the positrons have
anihilated with electrons in the walls of the box,
via e+ e- - \gamma\gamma (In the interest of simplicity, I'll
skip the bremsstrahlung prior to any anihilation which is only
relevent if you have a very convoluted answer to this question),

(3) times in between (1) and (2)?

I expect (ignoring neutrinos) that the box will weigh less the more
"in-flight" radiation there is inside the contained box, so W(1)=W(3)
and W(2) is less. Do tell me about any such experiment which has been
done -- citation please.

In other words, what you are saying is that energy, momentum and
angular momentum are not conserved.

You've already
turned a simple, straightforward question into a something much
more complicted than was necessary.

Actually, my objection is that it all is simpler than currently
modelled. If one accepts that the "in-flight" photon has no classical
existence and so does not exert gravitation, then a great many
physical processes can be described more simply.

For a metric which isn't time dependent, energy is conserved. The
rest depends only upon the equivalence principle, which has so far
been violated in experiments sensitive to parts in 10^13.

On Tue, 31 Aug 2004 01:47:02 -0000,
(Bilge) wrote:
You didn't address the fact that light is a four vector, which for
whatever reason, you seemed to think was an essential feature.

T'was you who used that term to describe light, not me, and in any
event the four vector relates to spacetime transforms which is not my
point which is regards to the nature and behavior of the individual
photon.

Eric Flesch:
(two books on QG) are speculative works.

In what way do you find them speculative? In view of the fact that
you specifically referred to qed, which is a quantum field theory,
try to be specific.

I was specific, but you snipped that part. My whole reply was:
"These are speculative works. What has quantum gravity ever predicted
which has been observationally confirmed? (which is the topic of this
thread)" To that I will add that they present progress-thus-far on an
experimentally unverified hypothesis. Specifically, the "graviton"
does not exist and so will never be found. I do however think that
gravitational waves should be detectable, but they have no particle
analog. I expect the tension of the universal brane would dampen
gravitational waves from far-away places to where they do not reach
us. Too much is made of the "similarity" of gravity and light, when
gravity is likely, instead, to use a 4th spatial dimension to
propagate in addition to the usual three. OK, is that specific enough
for you? (and off-topic to my original point, altho perhaps more
on-topic to the thread title)

A pity fhen that photons don't travel in continuous paths, shown by
the delayed-choice experiment.

That is not what that experiment shows and in any case, what does that
experiment have to do with anything?

It shows that GR stress-tensors do not model photon behavior and so
cannot be used, as they so often are, to claim that the in-flight
photon exerts gravity.

You mentioned qed, so obviously you
must think special relativity is ok. How does formulating qed in curved
spacetime differ in any way from formulating it curved spacetime with
a specific value for the curvature, nanely zero, in any way that matters
to your argument?

It makes no difference, I suppose. You're obviously very learned and
skillful, Bilge (you could have picked a nicer nick), but physical
models are just descriptions. Think of the reality of being a photon.
You are emitted from place A. You are absorbed at place B. And what
is your experience in between? You are travelling at the speed of
light, you know. What is the time dilation involved? Did you not
have time to view the passing scenery? No time to exchange gravitons?

This is the point, the in-flight photon has *no time* to interact with
spacetime whilst on its journey. There is no classical existence
whilst travelling at c. No continuous travel, no precise vector. The
photon can only depart and arrive. Its experience is that of stepping
across, analogous to conduction between bodies in contact. And the
wave description of its flight is the mapping of that vectorless
conduction into our 4D spacetime manifold. Model that, "Bilge".

All you've quoted is
an ancient and irrelevant thought experiment about quantum mechanics.
Stop jumping from topic to topic.

I was replying to Carlip's "demonstration" that light is attracted to
mass, showing that gravitational equivalence to time flow accounts for
it. Never mind, then.

No one, least of all me, is disputing quantum mechanics. I'm disputing
your understanding of quantum theory and general relativity, not to mention
qed.

I'm not a professor of QM as you appear to be. Your knowledge is
greater than mine. That doesn't prohibit that I might have a correct
thought which you did not yourself arrive at. Think about it. There
are problems with current theory, such as the inability to unify QM
and gravity. Is it not sensible to investigate changes in the model,
consistent with observation, which might bring that unification
closer? Any simplication is bound to be favorable. My idea on light
is a simplification.

I expect (ignoring neutrinos) that the box will weigh less the more
"in-flight" radiation there is inside the contained box, so W(1)=W(3)
and W(2) is less. Do tell me about any such experiment which has been
done -- citation please.

In other words, what you are saying is that energy, momentum and
angular momentum are not conserved.

It depends on what frame you use. The key is what the null geodesic
represents. It is, in fact, the straightest of lines. When spacetime
is bent by a mass, you (presuming your thought is similar to others'
in your profession) seem to think that there is a "straighter" line
than that, by which the curvedness of the geodesic can be described.
But what is spacetime curvature all about, other than a redefinition
of straightness in local places? We can view the curvature from a
distance, but even our lines of sight follow those geodesics.

If we take the gravitational contours to represent true straight
lines, then angular momentum is still conserved. But this would lead
to some interesting results, it is true. Using advanced technology,
we could build this device:

Say we can construct a pinhead-sized black hole using electrical
current (so it evaporates when the current is shut off). We place
this in the engine room of a spaceship. Now we release photons at it
at such a trajectory that they go half-way around the black hole and
come back with a return vector opposite to the emitted vector. That
means we have double recoil in one direction only. We could move our
spaceship without any external emission.

Ridiculous? Remember that any sufficiently advanced technology seems
like magic to learned men of a previous era. Think about it.

Eric

Just while you lot take a deep breath, what is actually being sought?.
Not just a "one of", like a tsunami on the ocean, surely. A pulse like
that might be easily detectible when two masses pass each other, and
the vectors add. A search for a constant vibration (light vs one
photon) is another matter. Isn't that what is being looked for-
gravity wave(s) akin to light wave(s)?

Jim G
c'=c+v

"Jim Greenfield" wrote in message
om...
| Just while you lot take a deep breath, what is actually being sought?.

A pulse from a supernova (negative going because mass is lost as radiation)
or a set of ripples from a couple of pulsars spiralling into each other in
the next
10,000,000 years. Does it really matter?



| Not just a "one of", like a tsunami on the ocean, surely.

Sure. We want to play with our toys, 'one offs' are fun.

| A pulse like
| that might be easily detectible when two masses pass each other,

Yeah, real easy if you can get Shoemaker-Levy to hit Jupiter again.
I don't recall anyone claiming this detected by LIGO though.

Or did you want something bigger and closer? How about if
Charon hit our moon? We might notice a slight change in ocean
tidal levels just before we are all blown to kingdom come.
Androcles.

and
| the vectors add. A search for a constant vibration (light vs one
| photon) is another matter. Isn't that what is being looked for-
| gravity wave(s) akin to light wave(s)?
|
| Jim G
| c'=c+v

Jim Greenfield wrote:

Just while you lot take a deep breath, what is actually being sought?.
Not just a "one of", like a tsunami on the ocean, surely. A pulse like
that might be easily detectible when two masses pass each other, and
the vectors add. A search for a constant vibration (light vs one
photon) is another matter. Isn't that what is being looked for-
gravity wave(s) akin to light wave(s)?

Jim G
c'=c+v

The only oscillation that can occur requires the reciprocal oscillation
of another mass. The c.g. of that system doesn't oscillate. Any waves
emitted from this oscillation will affect surrounding masses to such an
extent that they will oscillate in response. The net sum result, i.e. by
the time all of these primary and secondary waves get to us is a null
result.
If we choose an event a bit more local, then we can indeed detect the
effect (Simply jump up and down and you become the detector) but now you
are faced with the problem of proving that it was a wave, or IOW, the
real question is, doesn't propagate at a finite speed. Gravity wave
detection is this synonymous with detection of a delay in the
gravitational interaction.

BTW, concerning your tag:

x' = x - vt
c' = x'/t
c' = (x - vt)/t
c' = x/t - v
and so,

c' = c - v

If the beam is moving to the right at c wrt K, and K' is moving to the
right wrt K (making v and c both positive values), then the speed of the
beam wrt K' will be less than c, right?
So naturally c' = c - v

Don't sweat it, an inability to add vectors has sustained special
relativity for 99 years. Having discovered that the actually resulted
from the same, I'm even more disgusted with those idiots that I was.

Richard Perry

On Wed, 01 Sep 2004 10:46:18 GMT, "Androcles"
wrote:


"Jim Greenfield" wrote in message
. com...
| Just while you lot take a deep breath, what is actually being sought?.

A pulse from a supernova (negative going because mass is lost as radiation)
or a set of ripples from a couple of pulsars spiralling into each other in
the next
10,000,000 years. Does it really matter?

[snip]

Displaying your ignorance is a favorite hobby I see.

Tell me Androcles, why is it you think that gravity is switched off
once mass is turned into energy?

On 1 Sep 2004 00:08:10 -0700, (Jim
Greenfield) wrote:

. Isn't that what is being looked for-
gravity wave(s) akin to light wave(s)?

Who knows, only one of the waves has ever been seen.

On Wed, 01 Sep 2004 10:46:18 GMT, "Androcles"
wrote:

Or did you want something bigger and closer? How about if
Charon hit our moon? We might notice a slight change in ocean
tidal levels just before we are all blown to kingdom come.
Androcles.

Really? Did you see this in a film? Do really think `gravity waves'
necessary to explain tides? Why?

Dear vonroach:

"vonroach" wrote in message
...
On 1 Sep 2004 00:08:10 -0700, (Jim
Greenfield) wrote:

. Isn't that what is being looked for-
gravity wave(s) akin to light wave(s)?

Who knows, only one of the waves has ever been seen.

You made a funny, too! Seen... light. ;)

David A. Smith

On Wed, 01 Sep 2004 06:37:22 -0500, RP
wrote:

Gravity wave
detection is this synonymous with detection of a delay in the
gravitational interaction.

You pose a difficult question since neither a gravity wave or a
graviton has actually ever been seen except in imagination. Newton and
Einstein had your problem. Newton solved it for practical purposes.
Einstein tidied it up a bit to his liking. Work on it and get back to
us.

A good classroom demonstration is to stand on a chair and attach a
rope suspended from the ceiling around your neck, Then ask for a
volunteer to remove the chair - you get gravity, simple pendulum
and perhaps some chaotic motion all out of the way at once. If you
monitor your temperature you will also see heat loss.