[Tyron]

Tyron  asked the Naked Scientists:
Hi Chris,
 
thanks for your input with Talk Radio 702, I always look forward to it!
 
could you possibly answer this question I have, because nobody I speak to has a clue...
*Does gravitational force travel at a particular speed?
 for example, if the sun had to suddenly be taken away we would still have light for about 8min. and 20 seconds right?
but what about our orbit around the sun, would we IMMEDIATELY go out of orbit, or would that also take time??
 
that's my ever-elusive mind boggler!
I personally think that it would be IMMEDIATELY, because I can't see how it could be something physical...
 
please help if you can.
 
many thanks
 
Tyron Crowe

What do you think?

[Madidus_Scientia]

The theory is that gravitons travel at the same speed as light, so yes, if the sun were to inexplicably vanish we would remain in our orbit for 8 minutes or so.

[lyner]

You don't need anything as unthinkable or extreme as the Sun's disappearance. You would expect a varying gravitational potential from any pair of mutually orbiting bodies, for instance two massive binary stars*. The phase of that variation would lag behind their motion but, of course, be in phase with what you saw from your observation point because the light and G variations would take the same time to reach there.

*Despite what people say, the position of the Centre of Mass doesn't tell the whole story if you are not actually at 'infinity'.