Comments:

Photons have no rest mass they are pure energy. from e=mc^2 they can be assigned a "mass".

So are you saying that gravitational waves could be assigned mass on the same basis?

As I understand it photons ride on the electro-magnetic realm and gravitational waves on the timespace fabric. I don't know what the relation is between the two. If you do can you enlighten me?

Earth based gravity detectors are not sensitive enough and are prone to vibrations caused by traffic, people walking etc.

When we get to put up the long baseline interferometers in space I feel that we will quickly find gravity waves.

I don't think that we are critical enough of Quantum Theory even though it makes accurate projections. Some of the supposed consequences I don't fully embrace.

What does quantum theory say in these matters?

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Somebody please correct me if I'm wrong, but I believe e=Mc^2 describes the relationship between mass and electromagnetic energy. Since gravity is not electromagnetic, it says nothing about gravity.

And again, correct me, but...If a photon had mass, it couldn't move at the speed of light, or more accurately it's mass would become infinite at c. You could theoretically "convert" it to a predictable mass M=e/c^2.

Again, we're talking about another basic force outside the pale of the electromagnetic. Perhaps the term "gravity wave" is an imperfect one? Is there really a wave function there? Way over my head...

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"Good against remotes is one thing. Good against the living, that's something else." (Han Solo)

Somebody please correct me if I'm wrong, but I believe e=Mc^2 describes the relationship between mass and electromagnetic energy. Since gravity is not electromagnetic, it says nothing about gravity.

And again, correct me, but...If a photon had mass, it couldn't move at the speed of light, or more accurately it's mass would become infinite at c. You could theoretically "convert" it to a predictable mass M=e/c^2.

Again, we're talking about another basic force outside the pale of the electromagnetic. Perhaps the term "gravity wave" is an imperfect one? Is there really a wave function there? Way over my head...

The correct term is gravitational wave. Gravity waves belong to geophysics. See Einstein@home, LIGO. VIRGO. GEO600, etc,
Tullio

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Thanks, Tullio. I stand corrected.

My point was that using the term "wave" is perhaps confusing to those of us who aren't professionals, because we think in terms of electromagnetic waves--light, radio, or whatever. It was just an idle thought, and I don't know that there's a better or more accurate term, in any case.

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"Good against remotes is one thing. Good against the living, that's something else." (Han Solo)

My point was that using the term "wave" is perhaps confusing to those of us who aren't professionals...

That term and associating 'speed of action' appears to be confusing for everyone!

To my confused mind, the suggestion of the existence of 'gravity waves' that distort time and space suggests a finite 'speed' to which mass can impart it's gravitational effect...

And yet there is this apparent 'infinite speed' for the action of gravity whereby you must assume the instantaneous positions of orbiting bodies to get the celestial mechanics to work...


Here's a good question for anyone with the knowledge:

For a group of orbiting bodies such as our solar system, you can sum all the mass to give an 'aggregate' mass at the 'centre' of the solar system.

Do the orbits work correctly if the orbit for any planet is calculated for orbiting the aggregate mass at a fixed central position?

Or must the position of that centre be recalculated for the instantaneous location of all the orbiting bodies?

How quickly is that change in position of that centre 'communicated' to the orbiting bodies?


Regards,
Martin

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
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My point was that using the term "wave" is perhaps confusing to those of us who aren't professionals...

That term and associating 'speed of action' appears to be confusing for everyone!

To my confused mind, the suggestion of the existence of 'gravity waves' that distort time and space suggests a finite 'speed' to which mass can impart it's gravitational effect...


Regards,
Martin

G"k-wave and G"k-shield stuff;

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2003 Conference on Gravity;

Experiments, Devices, Wave creation, Potential uses.

Conference_2003

Things have come a long way in a few years.

I can just picture some aliens sitting somewhere on a very dark planet and saying "Until our scientists prove that we can artifically produce light, I'm only going to believe in gravity waves...."

This is one of the big mistakes in human thinking. Only what we can see exists.

And if aliens are visiting us regularly, why are we looking into deep space for signals? Is anyone looking closer to home?

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http://www.therageclub.com

Read this book on gravitational wave research:
Gravity's Shadow
Tullio

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I can just picture some aliens sitting somewhere on a very dark planet and saying "Until our scientists prove that we can artifically produce light, I'm only going to believe in gravity waves...."

This is one of the big mistakes in human thinking. Only what we can see exists.

Yeah.....except try telling your version of the truth to the scientists who are working on multi-million dollar gravity wave detectors. Since gravity waves are a pretty fundamental part of modern physics theory, scientists are betting they will eventually make confirmed detections of them.

I guess with all the money and effort they're putting into detecting gravity waves, they must not believe they exist, right?... ;)

Anyway...uhhh.....exactly what's wrong with only being sure something exists if you can physically detect it??

I guess if we use your logic, then you should have no trouble believing in the purple dragon in my garage...

And if aliens are visiting us regularly, why are we looking into deep space for signals? Is anyone looking closer to home?

It would be nice if aliens were visiting us regularly. Then we wouldn't have to worry about doing SETI! ;P

Your Hypothesis has already been considered. What you are thinking of is called the Heisenberg Uncertainty Principle. That is not a factor in science of gravity waves.

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Where did you read that electromagnetic radiation has an inverse square distance rule? T'ain't so. Distance is a factor, but not necessarily inverse-squared.

In the case of visible light, stars do have an inverse-square relationship for their brightness, but that's because we assume the permeability, etc., of free space is a constant. Maybe it's not. We really don't know.

However, some electromagnetic waves (like some radio waves) go around the earth with almost no lessening of their strength. The main reason they get weaker is because of interference from all the other sources cancelling them out along the way.

It's mainly an issue, therefore, of other EM radiation cancelling the signal out as it goes through the medium.

If you were in intergalactic space and wanted to use your cell phone, depending on the directivity index of your transmitter, it would work great over billions of miles.

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Where did you read that electromagnetic radiation has an inverse square distance rule? T'ain't so. Distance is a factor, but not necessarily inverse-squared.

In the case of visible light, stars do have an inverse-square relationship for their brightness, but that's because we assume the permeability, etc., of free space is a constant. Maybe it's not. We really don't know.

However, some electromagnetic waves (like some radio waves) go around the earth with almost no lessening of their strength. The main reason they get weaker is because of interference from all the other sources cancelling them out along the way.

It's mainly an issue, therefore, of other EM radiation cancelling the signal out as it goes through the medium.

If you were in intergalactic space and wanted to use your cell phone, depending on the directivity index of your transmitter, it would work great over billions of miles.

Nope, you're wrong. No idea where you read that electromagnetic waves don't obey the inverse-square law.

"Tain't so", eh?

http://en.wikipedia.org/wiki/Radio_propagation

Your cell phone example simply isn't true. A cell phone signal is not powerful enough to remain readable by a conventional Earth-based receiver billions of miles away.

Dozens of articles have been written about signal strength and receiver sizes on the SETI Institute website. The further away a signal is generated, the more powerful it must be to be detected and the larger the receiver must be.

This is one reason why radio SETI is mainly working to detect a targeted signal rather than omnidirectional radio leakage (like our old television broadcasts). Even if there was constant radio leakage comparable to our "I Love Lucy" from some far away civilization, we don't yet possess a radio telescope large enough to detect such leakage due to the fact that radio loses power the further it travels.

There may be a billion civilizations within 10,000 light years all leaking radio into space and we would not be able to detect them with the SETI tools currently available.

BTW:

Radio does not necessarily get weaker by other radio sources "canceling them out"; radio *does* get weaker as it passes through dense objects like interstellar dust and nebulae. This is one reason why the SETI Institute believes that radio SETI may not be practical beyond a certain distance.

Other sources "canceling out" potential ET signals would only happen if there were so many natural radio sources in the observable sky that they would obscure artificial signals. This isn't the case with radio waves as, compared to other parts of the electromagnetic spectrum, the radio spectrum is comparatively "quiet".

... It is not an electromagnetic force. Therefore, I go back to my question of why and how do we know (believe) that its effect would travel at the speed of light.

See:

First speed of gravity measurement revealed

Also:

The Speed of Gravity What the Experiments Say

That also describes very nicely some of the sort of orbital simulations I tried playing with for myself where you must 'rediscover' that gravity is 'already there' for us to stay in orbit. It is the propagation of changes of the gravitational field that is at the 'speed of light'.

Further thoughts...

(Sorry, this does get rather heavyweight but should still be interesting. It keeps us in orbit!)

[edit] Whichever way we look at this, the 'speed of gravity' question appears to question the fundamental principles of science of "causality" and "conservation of energy/matter". There's something not understood or more likely I've missed something... [/edit]


There looks to be quite a 'discussion' between S Carlip (SC) and T v Flandern (TvF)...

The main parts of the argument appear to be (to my understanding):

TvF notes (amongst other examples) that the position of our sun as seen from Earth is at an angle away (and behind, described as "retarded") from the line of acceleration the Earth experiences towards the sun. That is, we see the sun as it was and where it was about 500 seconds ago, yet we experience acceleration due to gravity for the sun's present (instantaneous) position.

Indeed, you must assume an instantaneous position for calculating gravitational attraction or your orbital mechanics simply do not work.

At first glance, this appears to invalidate the fundamental principle of physics of "causality in forward time". So do we really have "Magic" and "Spooky (infinitely fast) action at a distance"?

TvF proposes that one possible answer is that gravitational fields (and also electrostatic fields) act (update) at a propagation speed of many times greater than the speed of light. (This should not be confused with the very different "gravitational waves" which can be viewed as ripples in the field whereby their propagation speed at the speed of light is uncontested.)

TvF also notes that Lorentzian Relativity allows for faster than light speed and has never been experimentally invalidated.


SC counter argues that a gravitational field updates its new position at light speed propagation from any variation due to acceleration of the source mass. With this is the implication that the gravitational field for a source mass follows exactly the position for the linear velocity of that source in forward time.

What that means for the Sun - Earth example is that for experiencing the gravity of the sun at any instant, we feel the gravity from the linear extrapolated position of the sun that is 500 seconds along the tangent from a point on its orbit from 500 seconds ago.

Hence, gravitationally we 'feel' the sun for a sun orbit that is very slightly further away and very slightly retarded transversely. Similarly, so too for the sun experiencing the gravity from the earth.

This situation whereby the gravitational pull is at a slight angle such that the earth is pulled forwards slightly (and similarly the earth pulls the sun forwards slightly in the sun's orbit) should cause the earth to gain angular momentum and be flung away. (And similarly so for the sun. ... But energy cannot be created, merely converted...) This happens for our own moon for example for an analogous 'angle of gravity' effect. The earth rotates more quickly than the moon orbits, the earth's tidal bulge is dragged ahead of the moon's orbital position, and so the skewed position of the centre of gravity from the earth as experienced by the moon pulls the moon ever faster ahead in its orbit. Hence, the moon is gaining angular momentum (from the earth) and so moves to an ever higher orbit to ultimately be flung away from the earth. (Actually, I'd expect the moon to eventually slow the earth down to a point where earth's tides and moon maintain lockstep and the moon gains no further angular momentum.)

So...

Assuming that a field of force can follow the linear velocity of the field source, and that it is only the perturbation of position due to any acceleration that then takes light speed to propagate outwards:

Does the small weakening of the gravitational effect due to the greater distance of apparent effect exactly cancel out the gain you get for the forward component felt for the small retarded position distance offset (difference between linear tangent vs following the circumference)?

My view is that the sun and earth due to gravitational light speed propagation of the new position of each other due to acceleration "appear" to take orbits that are slightly larger and slightly retarded with respect to each other.



On a related thought: Does the sun have a (multiple?) tidal bulge(s) that influences the orbits of the inner planets?...


Regards,
Martin

A few links:

Does Gravity Travel at the Speed of Light? (Steve Carlip, Matthew Wiener and Geoffrey Landis)

Speed of light

Speed of gravity

Gravitomagnetism

Lorentz ether theory

Electromagnetic radiation

See also:

UnMuseum Speed of Light

Sunlight hides a thousand-year journey that actually began in the core

Parallel thread on Einstein@Home:

Gravity Waves...

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See new freedom: Mageia Linux
Take a look for yourself: Linux Format
The Future is what We all make IT (GPLv3)

Just thoughts,
In my crude, non-physicist way of viewing the issue of propagation of gravitational effect itself, as separate from gravitational waves that they're searching for, I had always liked the mass curving space-time model, as in the simple bowling ball on a trampoline analogy. What this means to me in terms of propagation, is that for an observer on the moving mass (bowling ball) the observable effect on a distant object will be effectively at "time plus 2*(C/distance)", whereas for the observer situated at the distant 'edge' of the field will see the space-time (trampoline) curve change before the light of the visible movement of the mass reaches it, or "time minus C/distance", So maybe we have a hypothetical external observer where the effect would appear to be an instantaneous one, as only a hypothetical observer could be, with practical observers 'seeing' the change either long after or before the observable event.

Now to me space-time curvature implies tension, and tension implies 'fabric', which I guess also allows for the propagation of waves in similar fashion to the slapping of the trampoline. Bearing in mind the fabric is expanding, how might that alter the simplistic analogy? Might the expansion be significant enough to stretch the moving mass local observed round trip time even further, and the remote observation see the effect even further before the event [keeping speed of light as constant, just as it's s'posed to be]? or would they stay in equilibrium, stretching speed of light with the fabric.

Will frequencies practical for propagation of such gravitational waves be dependant on localised 'tension', or mass density, as it is with the perhaps overly simplistic trampoline analogy, by the spring tension and objects placed on the fabric?

Too many questions, good fun though :D

Jason.

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"Living by the wisdom of computer science doesn't sound so bad after all. And unlike most advice, it's backed up by proofs." -- Algorithms to live by: The computer science of human decisions.

Anyway...uhhh.....exactly what's wrong with only being sure something exists if you can physically detect it??

I guess if we use your logic, then you should have no trouble believing in the purple dragon in my garage...

Just wondering, how do you know it's purple? ;-)

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http://www.therageclub.com

Just wondering, how do you know it's purple? ;-)

You'll have to take my word for it.... :P

I could not let this go any longer and had to let you guys know your all wrong. Gravity is not a wave. Its a extra-dimensional subatomic particle. All matter have what are called graviton particles. The more matter = the more graviton particles. The more graviton particles in one spot = more gravitational attraction. Black holes are nothing more than holes leading to the first dimension. The singularity at the center of the black hole is the actual gateway and this is why the singularity itself has zero volume and infinite density. The black hole itself is the effect we see in our dimension. When a star collapses into a black hole it tears a hole in the dimensional barrier. When the singularity has infinite density that means it then has infinite gravity. Infinite density = an infinite number of graviton particles. The gravitons just want to go home...

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I could not let this go any longer and had to let you guys know your all wrong. Gravity is not a wave. Its a extra-dimensional subatomic particle. All matter have what are called graviton particles. The more matter = the more graviton particles. The more graviton particles in one spot = more gravitational attraction. Black holes are nothing more than holes leading to the first dimension. The singularity at the center of the black hole is the actual gateway and this is why the singularity itself has zero volume and infinite density. The black hole itself is the effect we see in our dimension. When a star collapses into a black hole it tears a hole in the dimensional barrier. When the singularity has infinite density that means it then has infinite gravity. Infinite density = an infinite number of graviton particles. The gravitons just want to go home...

While it is a theory that gravity is composed of particles, it is not the whole story. There are some papers (i'll try to find them again) that states evidence that gravity is much like light in the fact that it acts as both a wave and particles.

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There is no test as yet for gravitons such as your talking about. I do know the experiment your talking about where it was demonstrated that light is both a particle and a "wave". Quantum superposition is the cause of this effect. Its a particle while your watching it and a "wave" when your not watching it. When I say "wave" that means its not actually a wave but it exhibits properties of a wave. A single photon can interact with itself because it exists in more than one place at the same time. By observing the photon you collapse it into a single particle. I know for some of you this might not make sense but it is true. For a demonstration there is a very simply put video on the double slit experiment @ youtube.com. Just search double slit experiment. That particular test uses electrons but a similar test using photons will and has yielded the same results.

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