Consensus about Van Flandern's ideas on speed of gravity?

[quantum123]

Ever since the Weber bar, there have been a lot of gravitational waves detectors all around the world: LIGO, VIRGO, GEO 600, and TAMA etc that promise to demonstrate gravitational waves. So far the result has been null. This reminds me of psychics who always claim to be able to detect harmful vibrations. Yes, neat mathematics, but what are we talking about here?

 

[rbj]

Ever since the Weber bar, there have been a lot of gravitational waves detectors all around the world: LIGO, VIRGO, GEO 600, and TAMA etc that promise to demonstrate gravitational waves. So far the result has been null.

or, at least, not exceeding noise from geologic, tidal phenomema, whatever.

which has more gravitational effect on you? the semi-truck passing by or a super-nova on the other side of the Milky Way?

 

[quantum123]

That sounds awfully familiar - yes, the Michelson Interferometer and the ether.

 

[Hans de Vries]

Ever since the Weber bar, there have been a lot of gravitational waves detectors all around the world: LIGO, VIRGO, GEO 600, and TAMA etc that promise to demonstrate gravitational waves. So far the result has been null. here?

The trend of ever more sensitive detectors will likely continue.

Advanced LIGO:

http://www.ligo.caltech.edu/advLIGO/scripts/summary.shtml

"The Advanced LIGO interferometers proposed here promise an improvement over initial LIGO in the limiting sensitivity by more than a factor of 10 over the entire initial LIGO frequency band. It also increases the bandwidth of the instrument to lower frequencies (from ~40 Hz to ~10 Hz) and allows high-frequency operation due to its tunability. This translates into an enhanced physics reach that during its first several hours of operation will exceed the integrated observations of the 1 year LIGO Science Run. These improvements will enable the next generation of interferometers to study sources not accessible to initial LIGO, and to extract detailed astrophysical information. For example, the Advanced LIGO detectors will be able to see inspiraling binaries made up of two 1.4 M neutron stars to a distance of 300 Mpc, some 15x further than the initial LIGO, and giving an event rate some 3000x greater. Neutron star - black hole (BH) binaries will be visible to 650 Mpc; and coalescing BH+BH systems will be visible to cosmological distance, to z=0.4."


The original target sensitivity was reached last year after some 3 to 4 years
of steady improvements, Time to take the next step. Stronger lasers (200W
instead of 10W) Larger and heavier test masses (34 cm vs. 25 cm,
40 kg vs. 11 kg) and much more.Regards, Hans

 

[pervect]

That sounds awfully familiar - yes, the Michelson Interferometer and the ether.

Given Taylor & Hulse's 1993 Nobel prize winning observations, it would be *extremely* surprising if gravitational radiation did not exist, as the measured decay of the pulsar orbits is within .5 percent of the value expected due to gravitational radiation.

 

[Stingray]

Ever since the Weber bar, there have been a lot of gravitational waves detectors all around the world: LIGO, VIRGO, GEO 600, and TAMA etc that promise to demonstrate gravitational waves. So far the result has been null. This reminds me of psychics who always claim to be able to detect harmful vibrations. Yes, neat mathematics, but what are we talking about here?

The fact that gravitational waves have not been observed yet by these detectors was expected. There are theoretical estimates of the gravitational wave strengths from various astrophysical phenomena. Given what we know about how common these events are, nothing currently running was given a significant chance of detecting anything.

I am most familiar with LIGO, so I'll give you the story there. The current design has a sensitivity right on the edge of what might be useful. It was considered possible but unlikely that it would see anything within a few years. A major upgrade ("advanced LIGO") was always planned, and that is expected to detect a signal fairly quickly.

Advanced LIGO was not built directly because it would have been too hard. The current detector - while inadequate - was still extremely difficult to design and build. Even after a very careful design, it took several years for people to figure out how to remove all of the unexpected noise sources from the working instrument. The experience gained in first building something simpler was considered essential before proceeding. There have also been various technological advances which make certain upgrades much simpler (and cheaper) now.

 

[tehno]

More interesting example

Thanks for clarifying that point pervect. Now, how would you treat a situation where one of two nearby non rotating massive bodies disintegrates - causing an abrupt decrease in the mutual gravitational attraction - or if you choose - in the local spacetime curvature. In either case, the surviving object will be affected - if the change is not communicated by gravitational radiation - what is the nature of the wave is involved?

Yogi,how about of central collision of two identical mass black holes approaching each other with same acceleration and terminal speed with regard to the distant observer?

 

[yogi]

Yogi,how about of central collision of two identical mass black holes approaching each other with same acceleration and terminal speed with regard to the distant observer?

I have always had the feeling that gravitational radiation might not be adequate to explain all the circumstances which can be proposed - Einstein himself had doubts while considering the problem. So When the subject comes up on these boards I try to tease answers out of pervect and others. In doing so I try to break the problem down into a simple physical situation - for example, the total conversion of the engery contained in a positron and electiron that combine to create two gamma ray photons - all the energy is accounted for in the product - the gravitatinal field of the electron and positron is extinquished - how is this reported to an external observer - I see this as analogous to the interaction of two black holes

Pervect stated that, in the cases of massive bodies, w/o rotation, theory predicted no gravitational radiation - but the destruction of the G field for an electron and positron is a reality which is communicated to outside observers (other masses). Interestingly - positrons and electrons do have an inherent spin h bar/2 - but this angular moment is picked up by the photon spin - so I still can't find anything left over to fund the collapse of the gravitational field

 

[tehno]

When two black holes "central collide",with all identical parameters of mass and speed,obviously they create new stationary black hole.
(Part of) The difference of energy prior and after the event being converted into?

 

[pervect]

A body can't suddenly disappear, but it could be exploded. To approximate the gravitational wave emission, you'd have to calculate the quadropole moments for the system - and calculate the third time derivative of the quadropole moments.

Let me go into this in more detail.

Suppose we have two bodies, both with mass m, and positions as a function of time of f(t) and -f(t) (so that the center of mass is at the origin). We further assume that y=z=0 for both bodies.

If we want to apply the approximation I mentioned previously, first we calculate

Ixx = 2*m*f(t)^2

We then reduce this so that the trace is zero

Qxx = (4/3)*m*f(t)^2
Qyy = -(2/3)*m*f(t)^2
Qzz = -(2/3)*m*f(t)^2

Take the third time derivative, squaring, and collecting terms, I get radiated power proportional to:

$${\frac {32}{3}}\, \left( 3\, \left( {\frac {d f}{dt}} \right) {\frac {d^{2} f}{d{t}^{2}}} +f \left( t \right) {\frac {d^{3} f}{d{t}^{3}}} \right) ^{2}$$

I don't think I've seen this particular result in a textbook anywhere, hopefully I've carried out all the steps correctly.

It looks like we have on term that's proportional to velocity * acceleration, and another term that's proportional to distance * rate of change of acceleration. These terms are added together and squared.

 

[tehno]

Differential equations of motion for such problems can not be solved explicitely.Even in the case of classical mechanics when the energy of the system is conserved.Even worse,we would have sort of damping
due to energy loss of gravitational radiation here.

 

[yogi]

.Even in the case of classical mechanics when the energy of the system is conserved.Even worse,we would have sort of damping
due to energy loss of gravitational radiation here.

Isn't that what pervect derived - the damping consequent to the radiated power. The loss of gravitational energy to space is manifested by radiation reaction forces that dampen the motion within the system. While it is true that the quadrapole energy flux formula does not come from an exact solution of Einstein's equation - the approximations are consistent with the observations.

But I still wonder about my original query - in a matter system that by definition does not lead to gravitational radiation (because of symmetrical destruction, with no velocity or unbalanced acceleration or rotational components) there will nonetheless be an information signal heralding a diminution in the gravitational field experienced by nearby masses.

 

[quantum123]

The fact that gravitational waves have not been observed yet by these detectors was expected.

Yes, they were expected but was never announced in the first place. If it were announced, do you think the project would have been given a go-ahead? Lots of promises are given everytime in the attempt to get money. And such words are given only after the project fails to give any results. There is a feeling of deception.

 

[Stingray]

Yes, they were expected but was never announced in the first place. If it were announced, do you think the project would have been given a go-ahead? Lots of promises are given everytime in the attempt to get money. And such words are given only after the project fails to give any results. There is a feeling of deception.

There was no deception. If you go into the relevant papers, it was always made clear how hard it would be to detect gravitational waves. I've also spent the last 8 years or so around people heavily involved with LIGO. They have always emphasized that it would be surprising if the 1st generation machine detected anything interesting.

 

[pervect]

Differential equations of motion for such problems can not be solved explicitely.Even in the case of classical mechanics when the energy of the system is conserved.Even worse,we would have sort of damping
due to energy loss of gravitational radiation here.

I'm not sure if I mentioned it in this thread or another, but formulas I gave earlier are the gravitational equivalent of the Lamor radiation formulas for electromagnetism. The goal is to get a reasonable approximate answer in analytical form.

People can and do get better results with numerical simulations of black hole collisions directly from the Einstein field equations - but you won't find that sort of detail in a PF post, you'll have to go to the source papers. Attempting to insure that these sorts of numerical simulations are accurate is a difficult task. I gather that there has been a lot of progress in the field of how to make "good" numerical simulations in General Relativity, but I don't know much about the details.

I don't think there are many numerical simulations of "head on" collisions however, that would be a rather unlikely scenario and given the amount of effort involved, the researchers are interested in simulating events that might actually happen. Most of the simulations I've heard of are various forms of inspirals.

 

[scrutinizer]

duh

"van flanderns ideas are not widely accepted"...neither were Debroglies, in fact, they didnt accept his ideas as a phd thesis.

" ...belive that Van Flandern has actually been published, so that while his ideas may be full of errors and far away from the mainstream..."

State the "errors" and give refuting arguments...I have found none...science is not about making claims like this without backing them up, leave that to politics.

sheesh, get back to basics guys.

THERE IS NO DELAY (NO "SPEED" OF GRAVITY, IT IS INSTANTANEOUS)...SIMPLE EXPERIMENTS HAVE SHOWN THIS; AND CONSERVATION OF ANGULAR MOMENTUM PROVES THIS.

If it were not so, orbits would not be stable, the Earth is NOT attracted to the point where the sun USED to be, (the spot where light tells us it now is).

Also, the GR description of gravity assumes a force which is not explained, the ball on the trampoline will go nowhere without it.

"...Yet, anyone with a computer and orbit computation or numerical integration software can verify the consequences of introducing a delay into gravitational interactions. The effect on computed orbits is usually disastrous because conservation of angular momentum is destroyed. Expressed less technically by Sir Arthur Eddington, this means: ÒIf the Sun attracts Jupiter towards its present position S, and Jupiter attracts the Sun towards its present position J, the two forces are in the same line and balance. But if the Sun attracts Jupiter toward its previous position SÕ, and Jupiter attracts the Sun towards its previous position JÕ, when the force of attraction started out to cross the gulf, then the two forces give a couple. This couple will tend to increase the angular momentum of the system, and, acting cumulatively, will soon cause an appreciable change of period, disagreeing with observations if the speed is at all comparable with that of light.Ó (Eddington, 1920, p. 94) See Figure 1.


Understanding the very meaning of the “speed of gravity” requires resolving any confusion that may remain between these two unrelated concepts. The “speed of gravity” refers to whatever causally links the source of gravity to the 3-space acceleration of a target body. Dividing the distance between a source of gravity and a target body by the “speed of gravity” answers the question: “If a source of gravity accelerates, how much time will elapse before the target body responds?” In Figure 3 and Table I of our previous paper [1], we showed this is much less than the light-time between the two bodies in the case of binary pulsars. Further points relevant to electrodynamic analogies and retarded potentials raised by Marsch & Nissim-Sabat [+12] and Ibison et al. [+13] were already answered by this author. [+14] In brief, retarded potentials omit transverse aberration, the largest physical manifestation of propagation delay, and therefore cannot address questions of interest here. We will elaborate in the next section.

S. Carlip has now also commented on our previous paper. [+15] Carlip argues for the consistency of some of these experiments with the geometric interpretation of general relativity, assuming that gravity propagates at lightspeed. However, neither experiment (5) or (6) on the above list (if independently verified) is consistent with the geometric or lightspeed interpretations of GR, although they are consistent with the field interpretation of the same equations in flat space-time. [+16,+17] In brief, Carlip (following recent practice) repeatedly blurs the distinction between changes in gravitational fields and gravitational waves, thereby arriving at conclusions applicable only to the latter, but claiming they also apply to the former.

http://www.ldolphin.org/vanFlandern/gravityspeed.html

http://metaresearch.org/cosmology/gravity/speed_limit.asp

 

[Antenna Guy]

THERE IS NO DELAY (NO "SPEED" OF GRAVITY, IT IS INSTANTANEOUS)...SIMPLE EXPERIMENTS HAVE SHOWN THIS; AND CONSERVATION OF ANGULAR MOMENTUM PROVES THIS.

If it were not so, orbits would not be stable, the Earth is NOT attracted to the point where the sun USED to be, (the spot where light tells us it now is).

? - If the speed of gravity were instantaneous, wouldn't the Earth be pulled toward were the Sun is now (rather than "the spot where light tells us it now is")?

(Edit: nevermind - on second read, I think you're saying the same thing)

Regards,

Bill

 

[D H]

THERE IS NO DELAY (NO "SPEED" OF GRAVITY, IT IS INSTANTANEOUS)...SIMPLE EXPERIMENTS HAVE SHOWN THIS; AND CONSERVATION OF ANGULAR MOMENTUM PROVES THIS.

General relativity does indeed have gravity propagating at the speed of light. It is also correct that using this aspect and this aspect alone of GR yields a poor model of even the solar system, let alone the universe. This, however, is a straw man argument.

GR predicts other effects beside a finite speed of propagation. Ignoring these other effects but incorporating the finite speed of propagation will lead to incorrect results. The problem is not in the theory; it is in the erroneous application of the theory. These other results nearly (but not quite) cancel the effects that result from finite propagation speed.

 

[gonegahgah]

Can't they just get a long asteroid that is spinning end over end and just send a fairly simple detector up close to it and moving in a parallel path at one of the ends and read the results closer to home? What problems would exist for this sort of experiment?