# Gravitational Wave Propagation

1. Aug 12, 2011

### jlangdale

Would gravitational waves propagating through space-time at the speed of light be affected by the curvature? Or are they independent?

Why does the spinning of a binary pulsar cause a gravitational wave when there is no change in mass other than the loss of photon energy? Doesn't this object look like a point particle with a mass at the center of gravity?

What would be the source of an oscillation of gravity felt by an object C positioned 4 light minutes from a rotating binary binary pulsar? The position or orientation of pulsar pair?

Imagine a black hole curving space-time to the point that light cannot escape. Would a gravitational wave pass through the black hole or would it interfere?

Wouldn't two black holes have to combine fast enough, say approaching the speed of light, to create a sudden change in mass to create a gravitational wave?

Imagine two black holes approaching each other near the speed of light, would their combination generate a gravitational wave that could not escape the space-time curvature?

If gravitational waves travel at the speed of light and light cannot escape a black hole, are gravitational waves similarly trapped?

In the famous Sun disappearing 8 minute thought experiment, since it's impossible for the Sun to disappear without violating the conservation of energy, is it possible that an instantaneous change in the curvature of space is combatible with the 1/r^2 law?

If the Sun went supernova and a massive core was left along with an expanding mass/energy blast wave, wouldn't the Earth remain in position until 8+ minutes simply because the matter/energy cannot reach a new configuration outside the Earth's orbit faster than the speed of light?

Is it possible to verify the speed of gravity using the spring tide affects on Earth when the Moon and Sun are aligned? Would there be a significant difference in the position of the tide if the Sun was out of alignment by 8 minutes (true position)?

Would this effect be greater on the Moon if you could measure a controlled tidal affect when the Sun and Earth were in alignment?

If two objects were 10 light-seconds apart, and it takes 10 seconds for changes in gravity to travel, then another 10 seconds for the change in true mutual position to be reflected between the objects, would it then take 20 light-seconds to see the affects of gravity?

If gravity was instantaneous, would it only take 10 seconds to see the affect of changes to gravity?

If gravity travels at the speed of light through gravitational waves, it is possible that both waves meet half way in the middle at 5 light-seconds, interact and reflect back to their source for a total interaction of 10 light-seconds equaling the time it takes for light?

Jonathan Langdale

Last edited: Aug 12, 2011
2. Aug 12, 2011

### IsometricPion

Last edited by a moderator: Apr 26, 2017
3. Aug 12, 2011

### jlangdale

Thanks I'll check it out. Forgive my laziness for not searching for it (:

4. Aug 12, 2011

### jlangdale

This is a good reference, but it doesn't address the idea of measuring the speed of gravity using the Moon & the Sun, and spring tides, or maybe some tidal detection on the Moon.

5. Aug 13, 2011

### IsometricPion

The http://en.wikipedia.org/wiki/Gravitational_radiation" [Broken] should measure fractional distance changes of 10-20). The change in radius of the Earth-Moon system is about 8.9 trillion times smaller than that of the Earth-Sun system (it is ~3.93x10-26m/yr.).

I do not know enough about general relativity to know how to calculate the tidal effects numerically. However, since they are essentially "static field" effects, they would be affected by the "leading" of the "gravitational force" (i.e., they are not produced via gravitational radiation so they will follow where the velocity and acceleration of the system 8 minutes (1.25 sec.) ago would predict them to be). To estimate the deviation, one could take the jerk (time derivative of acceleration) and determine how far a projectile with constant jerk would get in the light travel time, it turns out to be ~2.5cm for the Earth (wrt the Sun), and ~2.3nm for the Moon (wrt the Earth) (these differences are approximately 1 billionth and 1 trillionth of the distance the objects move over the light travel time from the Sun and the Moon respectively). So, while there may be some effects on the Sun, Moon, and tides, I don't think any of the effects are measurable with today's technology.

Last edited by a moderator: May 5, 2017