The Shalimar Treaty

[AngleWyrm]

Our physics predicted nothing could travel faster than the speed of sound. One argument against it was that if you were the target of a supersonic bullet, you would hear the bullet hit, then you would hear the bullet travelling downrange, then you would hear the bang of the bullet leaving the gun; you would witness events going backwards in time, which seemed to present a temporal paradox. This is exactly what happens. The target witnesses the arrival of the bullet, and can even have the time to radio back to the gunner and announce that the firing is still in the target's future (measurable and recordable as such with a tape recorder). But of course the firing is in the gunner's past, so it is meaningless to ask the gunner not to fire.

The best argument against gravity having speed that I've read was by Sir Aurthur Eddington: "If 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 S', and Jupiter attracts the Sun towards its previous position J', 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."

[Slick]

Galileo proved that light moved faster than sound and he probably was't the first to prove it. No modern phyisics predicted that the sound barrier was impossible to break. The term "sound barrier" was coined in the World War II era when countries were trying to make airplanes go faster than sound. They knew it was possible, but were encountering extreme difficulties as they approached the speed of sound. Aerodynamic forces on the airplanes was so great that it caused many failures, crashes and deaths. Hence the term "barrier".

Regarding the question on "terminal speed of gravity". I find it interesting that you quote from the first article that appears in a google search for "speed of gravity" even though it does not represent the vast majority of scientific acceptance; which is that gravity is transmitted at the speed of light. Their pic is nice too. Instantaneous transmission of gravity is correct under Newtonian physics, but not under relativistic physics. If gravity was transmitted instantaneously, I could vibrate a mass to send signals everywhere in the universe instantaneously using gravity as a carrier. This would violate the theory of relativity. The theory of relativity may one day be proven wrong, or I should say incomplete; because its predictions have been observed and verfied many times over and so far it has been shown to be consistent for all observable tests performed. Indeed, NASA has used and does use relativistic physics in its calculations. Even as "slow" (relative to the speed of light) as our Mars missions have travelled, their trajectories were calculated using relativistic physics. If they relied on Newtonian physics, they would be off course. Until the theory of relativity is shown to be wrong, incomplete or it is replaced by a superior theory that more closely agrees with observation and is tested to verify its correctness, I'll consider Einstein to be correct.

[AngleWyrm]

Thanks for clarifying the sound-barrier. That makes much more sense.

I read that article on "speed of gravity" several years ago; that it is now on top of the google search is interesting to me. However discussing credibility of the author avoids the subject material. They called Galileo a worker of black magic when he showed that a grape and a grapefruit fall at the same speed.

Is it true that the calculation of planetary locations must take the force of gravity to be instantaneous?

[Slick]

I don't think so.

Here's the "argument": 'If the sun were to suddenly disappear, it would be unrealistic for the earth to continue to orbit nothing for another 8 minutes.'

I see some problems with this line of thinking:

- First, these same people wouldn't have a problem thinking that the earth would still see the sun for another 8 minutes as the light continued to travel to the earth. But somehow gravity seems different to them. It's probably because we have indisputable proof of the speed of light and the layman can witness its effects. Gravity has yet to be actually measured, which is why I said above that it was theorized to travel at the speed of light (based on principles). Scientists find measuring the speed of gravity acurately very difficult, but they are trying; and the prevailing theory is that it travels at the speed of light under the limits of the theory of relativity. So for some people, no-can-see, no-can-believe. And that's fine with me.

Second, under our current understanding of physics, the sun just can't disappear. So, it's one of those garbage-in-garbage-out arguments. We know of no way to instantaneously remove mass, so of course there is no theory about what happens next.

Last, orbits of planets around the sun are actually ellipses. Also, the sun is actually pulled and moved slightly by each planet. The sun's "orbit" is less than its diameter so it kinda just wobbles a little in response to each planet, but we can measure it. Since our source information (light) travels at the speed of light, we can't see instantaneous effects, if they existed. In a practical sense, the speeds of planets, the sun, the solar system, the galaxy, the local supercluster, etc., are small compared to the speed of light so it limits our accuracy of measurment.

I don't think I am avoiding the subject material. The credibility of the author is certainly important. For every theory out there, there's somebody who is convinced it is wrong and has a counter-theory. Yes, occasionally these people who we consider to be nut-cases sometimes, rarely, are the true geniuses who are actually correct. This doesn't mean that I should believe every counter- or conspiracy- therorist. The process is well established for objectively presenting a new theory, testing it, and adopting it if valid. People with these outlandish theories all claim the same thing: I can't prove it because the scientific community won't grant me any $$$ to use their XXX (equipment, satellite, telescope, collider, reactor, fill in the blank). Most of these guys are just that, nut-cases who are hell bent on trying to get their inane experiments (and their wallets) funded. The scientific community is portrayed by these people as extremely closed-minded, status-quo, establishmental, and rigid. My impression is that this is as far from the truth as possible. The reason why these nut-cases are ignored is because their theories are fundamentally flawed. The last thing the "real" scientists would want is to be on the wrong side of the fence if/when a new correct understanding of the universe is proven. Good theories are tested every single day. Experiments are being done as we "speak" to learn the fundamentals of our universe. That is what the XXX (equipment, satellite, telescope, collider, reactor, fill in the blank) *is* being used for.

[AngleWyrm]

Hypothesis: The effect known as gravity is instantaneous. Null hypothesis: The effect of gravity displays a finite transit delay (presumably comperable to speed of light).

Experiment: If light and gravity both arrive from the sun, then earth's trajectory through space should be a tangent to the center of the observed position of the sun, eight minutes west of current position. On the other hand, if gravity does not travel, then earth's trajectory should be a tangent to the sun's current position, eight minutes east of observed.

Is there a method of measuring earth's current trajectory by ameteur equipment? Could it be plotted via planetary positions or the like?

[Slick]

Not as of yet, no accurate method for determining gravity really exists. That method sounds to me like it would work, however its effect is very very small. The determination of gravity would obviously have to be a vector; strength and direction and be made extremely accurately such that the error in measurement is small compared to the value.


Since gravity has no maximum range, the earth is also being pulled by everything else in the universe (closer than the age of the universe x the speed of light). Since the force of gravity drops by the inverse square law, effects from mass outside our solar system will probably be too small to detect for a very long time, if ever.

There are other effects too that would affect the results:

Curvature of space - currently postulated, but measurement inaccuracy is far too large compared to numbers that we would need. At least our local section of space is "flat" i.e. not curved to the best of our measurements.

Dark matter - matter that does not give off light. Rocks, dust, gas, etc. Some scientists have postulated exotic forms of mass (wimps - weakly interacting, massive particles), but these too haven't been observed. But dark matter does exert gravitational forces. Based on rotational dynamics in the galaxy, there has to be a huge amount of dark matter; far more than the luminous matter that we can see. Not sure how much is in our solar system; or if it has a significant effect.

"Dark energy" - I really don't want to go there. Possible, but unobserved, and rather controversial. If it exists, though, it could/would affect gravity.

Expansion of space - the exact rate is debated, but it has upper and lower bounds based on observations. I'd have to see the numbers, but my guess is that this is too small to have an effect on our local orbit around the sun.

And of course the catch all - how can we know if there is something else that is currently totally unknown by us???