What's up with gravity wave detection?

"Androcles" wrote in
:
|
| How long are you going to ignore me?

Until you answer my questions, moron, instead of providing a list of
experiments you copied from the FAQs. Only a ****ing lunatic would
claim...

*snip*

You are a troll, only interested in name-calling.

Looks like he's not the only one interested in name calling, eh?

"Paul Lawler" wrote in message
. 125.206...
| "Androcles" wrote in
| :
| |
| | How long are you going to ignore me?
|
| Until you answer my questions, moron, instead of providing a list of
| experiments you copied from the FAQs. Only a ****ing lunatic would
| claim...
|
| *snip*
|
| You are a troll, only interested in name-calling.
|
| Looks like he's not the only one interested in name calling, eh?

How conveniently snipped not to display his.
*plonk*
Androcles.

On Fri, 20 Aug 2004 21:50:43 GMT, "Androcles"
wrote:


"Paul Lawler" wrote in message
.125.206...
| "Androcles" wrote in
| :
| |
| | How long are you going to ignore me?
|
| Until you answer my questions, moron, instead of providing a list of
| experiments you copied from the FAQs. Only a ****ing lunatic would
| claim...
|
| *snip*
|
| You are a troll, only interested in name-calling.
|
| Looks like he's not the only one interested in name calling, eh?

How conveniently snipped not to display his.
*plonk*
Androcles.



*snicker*

You put yourself in an argument in which you cannot hope to win
because you are hopelessly ignorant regarding the topic.

Your only way out is through namecalling and killfiling.

Tell me again, Androcles. Why do you feel you can measure the effect
of a gravitational wave using Newton's force law?

The exact analogy to EM is using the static charge force quation to
judge the 'effect' of an EM wave. Of course, though, you are stupid
and will not understand what I just wrote. But it is still funny.

"Androcles" wrote in message ...
"Paul Lawler" wrote in message
. 125.206...
| "Androcles" wrote in
| :

What is the sensitivity of a gravitometer? I understood that it was
possible to detect the mass of something as small as a fridge in a
room. If that is the case, a change in gravity (wave) should be able
to be detected by moving two masses in opposite directions on the x
axis, with the meter off set on the y axis. The vector nature of the
forces would create a peak as they passed each other (pulse) but not
much help in finding the speed of the wave.

Jim G
c'=c+v

"Jim Greenfield" wrote in message
m...
| "Androcles" wrote in message
...
| "Paul Lawler" wrote in message
| . 125.206...
| | "Androcles" wrote in
| | :
|
| What is the sensitivity of a gravitometer? I understood that it was
| possible to detect the mass of something as small as a fridge in a
| room.

Ok, let's use a fridge in a room. Let's even extend to a fridge being
detectable at say one kilometer, which will require much more sensitivity,
but we'll assum it possible. That's going to need 4 fridges at 2 kilometers,
8 at 3k and 16 at 4. How many refrigerators are needed at 1 kiloparsec?




If that is the case, a change in gravity (wave) should be able
| to be detected by moving two masses in opposite directions on the x
| axis, with the meter off set on the y axis. The vector nature of the
| forces would create a peak as they passed each other (pulse) but not
| much help in finding the speed of the wave.
|
| Jim G
| c'=c+v

On Sat, 21 Aug 2004 15:44:27 GMT, "Androcles"
wrote:


"Jim Greenfield" wrote in message
om...
| "Androcles" wrote in message
...
| "Paul Lawler" wrote in message
| . 125.206...
| | "Androcles" wrote in
| | :
|
| What is the sensitivity of a gravitometer? I understood that it was
| possible to detect the mass of something as small as a fridge in a
| room.

Ok, let's use a fridge in a room. Let's even extend to a fridge being
detectable at say one kilometer, which will require much more sensitivity,
but we'll assum it possible. That's going to need 4 fridges at 2 kilometers,
8 at 3k and 16 at 4. How many refrigerators are needed at 1 kiloparsec?

Is this how you estimated things as an engineer?

*snicker*





If that is the case, a change in gravity (wave) should be able
| to be detected by moving two masses in opposite directions on the x
| axis, with the meter off set on the y axis. The vector nature of the
| forces would create a peak as they passed each other (pulse) but not
| much help in finding the speed of the wave.
|
| Jim G
| c'=c+v

"Androcles" wrote in news:TmuVc.3953
:


"Paul Lawler" wrote in message
. 125.206...
| "Androcles" wrote in
| :
| |
| | How long are you going to ignore me?
|
| Until you answer my questions, moron, instead of providing a list of
| experiments you copied from the FAQs. Only a ****ing lunatic would
| claim...
|
| *snip*
|
| You are a troll, only interested in name-calling.
|
| Looks like he's not the only one interested in name calling, eh?

How conveniently snipped not to display his.
*plonk*
Androcles.

Plonking was irrelevant to my comment. I was not commenting on the quality
of the arguments, merely pointing out that he is not the only one engaging
in ad hominem attacks. Unless, of course, you are a licensed psychiatrist
who has examined him and are able to accurately diagnose that he is, in
fact a moron and a lunatic.

Paul Lawler wrote in message .125.202...
"Androcles" wrote in news:TmuVc.3953
:


Risking showing my naivitie, what is REALLY being discussed- a "one
of" change in gravitational field strength (pulse/wave), or a SERIES
of equal strength waves emanating from a static body?

Jim G
c'=c+v

On Fri, 20 Aug 2004 17:34:31 +0000 (UTC),
wrote:
In sci.astro Eric Flesch wrote:
You're missing the point. The stress-energy tensor is a classical
description which assumes continuous motion. But QED shows that the
photon path is the summation of all possible paths (diffraction
gratings are an application of this) and the delayed-choice experiment
shows explicitly that the travelling photon cannot be pinpointed to
any particular location in its presumed path(s). The point is that
the "travelling photon" can be modelled only by a quantum description,
and the classical stress-energy tensor does not apply.

Everything you say here is just as true of neutrons, or protons, or
any other elementary particle. Are you saying that we should therefore
not use GR at all?

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".

... You can write down a low-energy effective action for
the gravitational field without knowing details of quantum gravity.

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

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

Just trap a bunch
of radiation in a mirrored box and glue it next to a mass. The
radiation will be attracted toward the mass

No it won't be. The mass might have some miniscule effect on the
local geometry, that is all.

Are you serious? You claim that a mirrored box filled with radiation does
not weight more than an empty box?

Would you like to describe how a mirror works? How efficient mirrors
are? 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. Are you resorting to a "perfect" mirror of some kind? Would
this work the same as standard mirrors (in which photons are absorbed
& re-emitted with some efficiency) or do you prescribe a perfect
mirror which actually re-directs the same photon in some
perpetual-motion kind of way? Your illustration is fanciful. No
actual experiment has ever "weighed" in-flight radiation.

Here's a simple exercise. I assume you accept that electromagnetic radiation
is red-shifted in a gravitational field, right?

It depends on the vector. Photons departing the gravitational field
are red-shifted, certainly.

So consider a box with a
mirror at the top and one at the bottom, containing radiation in a coherent
state (you accept QED, right?) with an expectation value of momentum that's
in the purely vertical direction and an expectation value of wave packet
width (z^2-z^2) that's small compared to the size of the box. Compute
the momentum transfer to the mirrors, using however much QED you like. You
will find that the momentum transfer to the bottom, where the energy is
blue-shifted, is greater than the momentum transfer to the top. That means
``the radiation will be attracted toward 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. I suspect the same
applies here. In any event, this does not show that the "in-flight"
photon exerts gravitation.

Eric

"Jim Greenfield" wrote in message
om...
| Paul Lawler wrote in message
.125.202...
| "Androcles" wrote in news:TmuVc.3953
| :
|
|
| Risking showing my naivitie, what is REALLY being discussed- a "one
| of" change in gravitational field strength (pulse/wave), or a SERIES
| of equal strength waves emanating from a static body?
|
| Jim G
| c'=c+v

Jim, this discussion is not about the existence or non-existence of gravity
waves, but about their amplitude being great enough to be detectable. Simply
spinning the Earth in the lunar gravity produces tides and when we include
solar gravity we have neap and spring tides. If the lunar orbit were highly
elliptical we'd have higher tides at perigee than at apogee. Thus we would
have a detectable gravity 'wave'; they do exist, and can be detected.

LIGO, however, is about detecting a gravitational field from a supernova at
a distance of a kiloparsec = 3260 light years, where some quantity of matter
is
completely converted to energy (E= mc^2) and the resultant gravity field is
reduced. That would be a step pulse.
Or it could be the field from a pulsar in orbit about a neighbour that is
periodically approaching and receding from us, and that would be a
sinusoidal wave. So the answer to your question is : both. However, the
supernova (which may produce a pulsar as a remnant) is the greater.

If you want to express the problem mathematically: let delta be the smallest
amplitude detectable by the instrument used.
Let a pulse (or wave) of amplitude A be emitted at 0 and the amplitude at r
where the instrument is placed be A/r^2 = delta.
Then the amplitude at A/(r+epsilon)^2 (epsilon 0) is less than delta and
is not detectable.
LIGO has a real delta, so from that estimate the greatest imaginable A and
calculate
A/r^2 = delta
r^2/A = 1/delta
r = sqrt(A/delta)

Androcles.