# Gravitation Speed/Acceleration/Velocity

1. Aug 13, 2004

### Olias

Light leaves the Sun, it takes *8 minutes to reach earth, how long does a Gravitational Signal take to get from the Sun to Earth?

Does Space have a Velocity?..what is the derived speed of Gravity through a near Vacuum, one that has no Matter , actually does gravity signals become null?

2. Aug 13, 2004

### VantagePoint72

The speed of gravity is the same as the speed of light, and likewise is constant. Space doesn't have a velocity, disturbances such as gravity have a velocity. Should the sun suddenly disappear from the sky, we would see it and feel it happen at exactly the same time.

3. Aug 13, 2004

### Nereid

Staff Emeritus
That's according to GR, which has met all experimental/observational tests so far with flying colours.

Olias, can you think of an experiment which, in principle, could test whether the speed of gravity is c or not?

4. Aug 13, 2004

### pervect

Staff Emeritus
Gravity has no more problem propagating through empty space than light does.

As far as the speed of gravity goes, one has to be careful how one asks the question. One might ask "what would happen if the sun would suddenly disappear". The answer is that "The sun can't suddenly dissappear"! (It violates some important conservation laws).

But one can sensibly ask "what would happen if I blew up the sun". The answer is that the change in gravity would propagate outwards at the speed of light.

There are other questions one could ask as well, but this is probably a long enough response for now.

5. Aug 13, 2004

### VantagePoint72

That propagation being the essence of gravity waves. Imagine a binary pulsar system. The motion of two massive bodies around each other would mean that the strength of the gravitational field is changing in a given direction. In GR terms, this means that that the amount of curvature of spacetime is changing. As you can visualize these wave-like disturbances radiating outward, it's easy to make the comparison with light and see why gravity should travel at the finite speed of c. (btw, that wasn't directed at you pervect, just an addendum on my previous post for Olias)

6. Aug 15, 2004

### Olias

Yes, I actually am leaning towards Gravitational Waves being the fixed standing waves of a 'Pure Fluid', which are Low-Energy, obviously the Lowest Energy Possible, Absolute.

7. Aug 15, 2004

### Nereid

Staff Emeritus
How do these concepts help you devise an experiment from which you can determine the 'speed of gravity'?

8. Aug 24, 2004

### Olias

Lets define empty space?..whats Gravititating?..if there is "nothing" there to communicate, what do we look for..is there a transformation of Gravitational Signals, ie without, er... 'Matter Content'?

should ask if Photon goes from one atom to another, then this is a 3-D spacetime (two-body-communication)..what about a single photon without any atoms in near vicinity to communicate, wont the photon get confused!

Last edited: Aug 24, 2004