Hi,

Some time ago I read about an experiment that showed the speed of gravitational wave propagation is equal to the speed of light. My question now is: how can a black hole exert gravitational force if the gravitational wave cannot escape it's event horizon?

greetz,
Niels

Neilsh,

I have seen a couple of other theories claiming tests that show gravity to have velocites from 9E20cm/sec (c^2), to c^c which is
9E100 cm/sec.

The one you refer to has been somewhat recent and is still contriversial in that the counter claim is it measured a different aspect of gravity but not its primary velocity.

Because gravitational waves do not propagate the gravitational force. They only carry information about changes in the gravitational field.
As the mass of a body collapses towards its event horizon the strength of it gravitational field remains constant. Once the mass passes the event horizon, no information about it can escape, including the fact that it has crossed the event horizon. To all outside observers, the gravitational field is frozen at the state it was just before the mass completely passed within its event horizon. This is why black holes are sometimes called "frozen stars".

NielsH - Gravity is immune to the no-escape clause, being that gravity itself enforces the no-escape clause. While light cannot escape the black hole, if an object falls in, the black hole exerts a greater gravitational force outside of its event horizon, and information about the change in force (gravitational wave) propagates at the speed of light.

Last I read, they did not measure gravitational waves. It was something else. So no one has seen a gravitational wave yet.

Originally posted by hlreed
Last I read, they did not measure gravitational waves. It was something else. So no one has seen a gravitational wave yet.

hlreed is correct. that experiment measured the speed of a gravitational influence, not a gravitational wave. gravitational waves are the result of quadrupole oscillations, and are a little harder to see, although the LIGO experiment is expected to see them in the next 2 years or so.

also, the speed of gravity experiment of a few months ago is hotly disputed. many experts claim that what was actually measured was the speed of light. the team that ran the experiment released their findings to the popular press instead of submitting their paper to a peer review by scientists. until the peer review has been done satisfactorily, i take any discussion about that measurement with a grain of salt.

doesn t keep me up at night or anything though, because i fully expect that when the measurement is done correctly, it will yield c as the result.

Lethe,

I too have seen many more objectors to the claim of having measured gravity as being at the speed of light. That they have mis-stated their findings.

But I will be surprised if correct testing finds it to be the speed of light for the following reasin.

Assume the sun simply vanished.

1 -Does the earth continue to orbit a non-existant mass for 8.5 minutes? or,

2 - Does it almost instantaneously go into a linear vector.?

My gut tells me that gravity has a link simular to particle entanglement and that it is like a taught rope that when broken the response is instantaneously felt regardless of distance.

It will be most interesting when they determine which it is.

I almost hate to bring this term up again but that action is believed to be linked to the Chiral Condensate.:D

MacM:

Changes to the gravitational field are thought to propagate at the speed of light. If the theory of general relativity is correct, we would need to wait 8.5 minutes after the sun exploded to feel any effects (heat, light, changes to gravity etc.).

James R.,

I agree that is the prevailing view but I am still inclined to wait and see. There are some pretty good arguements out there that that isn't the case.

Time will tell.

hmm... earth must be rotating around void for 8.5 minutes..

Just in case such testing does result in an answer my guess is that it will be 1.2E21 miles/sec.

That means the earth will only continue to orbit for 7.75E-14 seconds before flying off in a vector.

I'll only tell you why after somebody annouces that answer. But I've made it a matter of record here.

Hint: It may be viewed as anti-entrophy as in (-n) in string "Origin of Existance" and the issue of virtual particle duration being on the order of 2E-43 seconds.

Originally posted by MacM


My gut tells me that gravity has a link simular to particle entanglement and that it is like a taught rope that when broken the response is instantaneously felt regardless of distance.



Even the effect of a taut rope breaking isn't felt instantaneously, it must propagete through the rope at the speed of v = sqrt(E/D), Where E is the elasticity, or Young's modulus, of the rope and D is its density. It only seems instantanous in most everyday instances because the length of the rope is comparatively short and the value of v high.( For instance, if you used an iron wire, the value of v would be 16,400 ft/s or about 3 miles per second.)

Originally posted by everneo
hmm... earth must be rotating around void for 8.5 minutes..


No. It just takes the Earth 8.5 mins to learn that the Sun isn't there anymore....

This is correct.

And to reply to previous posts, that seem to misunderstand of the properties of gravity.

It may be true that gravity is like a probability field and reaches to all parts of the universe instantaneously, but this is not the same as saying that <b>information</b> travelling through this `field` can go any faster than light.