View Single Post
Old February 21 2014, 12:59 PM   #14
Rear Admiral
YellowSubmarine's Avatar
Re: Why don't they crash?

Metryq wrote: View Post
Actually, it has been measured. Astronomer Tom Van Flandern measured the "aberration" (angle) between the Sun's light and its gravity.
I wasn't talking about measuring the aberration, but the delay. The lack of aberration for gravity does not imply there wouldn't be a propagation delay if the sun vanished. If there was aberration, planets would not form stable orbits. On the other hand, if there was no propagation delay, that would allow for violations of causality, hence it's thought (but not directly measured) that there is a delay.

I was referring to a piece by Flandern (I think someone linked it here during the previous discussion?) where he explained how gravity is propagating at the speed of light while still being equivalent to Newton's view of infinite speed propagation, which is required to keep the orbits intact.

Hence my point: Stellar objects are moving without much acceleration, and pretty much predictably. Even if there's a humongous delay in the propagation of their image to you, the information reaching you is right about enough to plot your courses without aberration from their original position. Unless somebody pulls out a Picard Maneuver on you, you won't bump into anything.
Objects in mirror are bluer than they appear
YellowSubmarine is offline   Reply With Quote