Two star appear in an otherwise empty void exactly ten light-years apart...?

Question

Two star appear in an otherwise empty void exactly ten light-years apart. An observer on each star would only know the existence of their star until ten years later when they finally see the light of the other star in their skies. Since these stars have mass, then they also have gravity. The gravity of these two stars would interact with each other and create an attractive force.

Though it takes ten years to see light from the other star, would not the gravity of each star reach to the other's instantaneously? In other words, the reaction of mass at a distance (gravity) occurs at infinite speeds.

Hope I have stated this clearly enough...just one of my ponderings for today.

I guess it was always my understanding that even though waves, such as electromagnetic and gravitational waves, propagate at the speed of light, the reaction of mass at a distance was instantaneous.

Hope someone out there can set be in the right direction.

Answer 1

no, gravity has the same speed as light.

look here:
http://en.wikipedia.org/wiki/Gravitation
http://en.wikipedia.org/wiki/General_relativity
http://en.wikipedia.org/wiki/Gravitational_radiation
http://en.wikipedia.org/wiki/Graviton

here is the web site of the people looking for gravitational radiation.
http://einstein.phys.uwm.edu/

Answer 2

Oh well. You are asking a question that can not be answered except theoretically. Current dominant theories state that nothing can travel faster than light.

One answer mentions gravitons. Gravitons are a theoretical concept to explain how gravity works. They are conceptually similar to light, so must follow the rule that nothing is faster than light. Nobody has captured a graviton.

But what if existence is instantaneous? It is beyond our current mathematics to explain how instantaneity might be transmitted to the universe.

But what if the transmission of existence is not instantaneous, just a lot faster than the speed of light? How could this be tested? The major gravitational changes that are taking place occur so far away - in the center of the Milky Way galaxy, that it is not possible to obtain data during our lifetime that correlates to the occurrence of a current event. Scientists are at work trying to detect gravity waves.

Suppose a pair of black holes had grown at the center of the Milky Way from what had been a binary star system. Finally, one black hole falls into the other and is converted into energy that blasts out into space in a Galactic Jet. The millions of star masses that the destroyed black hole contained would blast out in a negative gravity wave as their mass converted into energy.

How could we use this event to understand how gravity worked or to further our understanding of Astrophysics?

If the event was observed by telescopes, and the detection of a gravity wave occurred at the same time, then that would be evidence that light and gravity travel at the same speed. But if the gravity moment changed at the instant of mass conversion, we would not know why it changed, and the event would not be observed in the light spectrum until perhaps a thousand years later.

;-D This would make it inconvenient to use as evidence of the superior speed of gravity.

PS. There are lots of things in scientific theories that are there because the math requires them. They have not actually been seen or sensed. That is why experiments are conducted in the first place: to verify the existence of something predicted by a mathematical necessity of the theory.

Answer 3

The speed of gravity has not yet been measured to extreme accuracy, but several experiments have so far narrowed it down to within about 1-10% that of the speed of light. This suggests to the scientific community at large that the propagation of gravitic waves will in fact be shown someday to be that of light speed.

If it were shown that gravitic effects are instantaneous (which Newton's theories assumed, but the idea troubled even Newton himself), then it would completely disprove General Relativity theory, since then it would be possible to send information instantaneously throughout the universe given sufficiently sensitive measuring equipment. This violates the basic tenet that no information may be transmitted faster than the speed of light, otherwise it would break relativistic causality, similar to being able to travel back in time and kill your younger self.

If gravitic effects are thought of as a compression wave, then a finite speed is in fact easy to grasp. No compression wave travels through a medium at infinite speed. If you have a solid rod billions of miles long, and you push on one end of it, this push is not felt at the other end for quite some time (equal to the speed of sound within that rod, which makes sense because sound is also a compression wave).

Answer 4

It is one of my doubts six months back. As I started to read more higher concepts in Physics, I got a clear Idea regarding this.
For instance, if you take two charges accelerating in some direction, then they will produce EM waves and the influence of one charge over the other will be felt only when the EM wave from one of the charges reaches the other.
There is a similar analogy with Gravitational force. The effect of one mass on the other will travel at a speed of light towards the other and when this reaches the other, the influence is felt and not readily. (Note that nothing can travel with a speed more than the speed of light in Vaccum)
Now to test you let me ask you a simple but extremely conceptual question.
Suppose I fix a rod from the surface of the earth to just before the surface of sun(approx. 1 A.U long). (Note this experiment is imaginary). Now, from earth I push one end towards sun, When will the other end hit the surface of sun?
(Don't consider melting of Rod)
Options: a)0s b)8minutes c)more than 8minutes
Answer is c). Because when you push the rod, then the effect on the rod will move in longitudinal waves. Guess the speed. It will the same speed that the sound travels in that rod. So, it will take more time than the light has taken to cover the distance. So answer is (c).

Answer 5

Sorry, the effect of gravity is not instantaneous. Gravitional interaction is believed to be mediated by exchanges of "gravitons". These travel at the speed of light. The earth is orbiting the sun and sunlight takes about 30 minutes to reach earth. If the sun dissapeared, earth would still orbit the sun for another 30 minutes.

Answer 6

Yes. Gravity is a force of compression. It's force is similar to hydraulic force and is felt immediately. Gravity's hydraulic fluid is the mass of the universe. The stars would feel each other's gravity 10 light years before they saw each other's light.

Now that we have more knowledge, it is probably time to revisit Newton's experiments and resulting postulations concerning gravity.

Two seemingly opposing theories are that gravity and a vacuum cannot co-exist and nothing can travel faster than the speed of light. The speed of light theory does not take the vacuum into consideration. There is nothing that would prevent complex matter, if it could exist, from traveling faster than the speed of light in a vacuum. This is how the universe was created.

The compression of the stars attempts to create a vacuum around their surface. The universal mass fills it instantaneously, much faster than the speed of light, holding true that a vacuum and gravity cannot co-exist and holding true that nothing can travel faster than the speed of light in space. Space is not a vacuum.

Answer 7

The folks above are right, any form of information can travel no faster than the speed of light.

And light from the Sun takes 8 minutes, not 30, to travel to Earth.

Answer 8

No, gravity spreads at the speed of light as well.