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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: gravitational fields
From: Frank Reed
Date: 2008 Mar 16, 00:10 -0400
From: Frank Reed
Date: 2008 Mar 16, 00:10 -0400
Bill writes: "Off topic, but allow me put it another way--an old question. Our Sun is gone in a nanosecond. Light continues to come our way for approx. 8 minutes. What happens to gravity (Sun's) the moment it ceases to exist?(Not a star size; red yadda yadda vs. ... trick question)." Ok, I can't resist. General relativity, the best model of gravitation that we have, is incapable of answering this particular hypothetical question. Why? Because the setup violates mass-energy conservation, and this is explicitly required by GR. But you can do similar problems, and of course, when you do, the theory says that changes in the gravitational field propagate at the speed of light. There's no theoretical reason to believe otherwise, and there is also some observational evidence that confirms this specific feature of the model. Again, I would be happy to chat more about this, but I worry about annoying people with off-topic material, so again, if you want more, join me at Compuserve SciMath (see previous post for the address). -FER --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
