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Hanno, 

You asked a question about gravitation yesterday. You may have intended to send this as a private message, but either way, since this is off-topic, I will reply in more detail with a private message, and we can continue this conversation by email if you wish. If anyone else is interested, please let us know.

For a hint of the "madness" that comes from speculations about the speed of gravity, I invite you to look up Tom van Flandern who was everywhere online back in the early days of the online universe (late 80s, early 90s). He posted frequently to the Compuserve message boards and later on Usenet message boards, like sci.physics, peddling some very peculiar ideas. He was a talented mid-level expert in the "mechanics" of celestial mechanics computations who worked at the US Naval Observatory in the 1970s and directly contributed to almanac calculations, but went off the deep end when he decided that he was smarter than all the rest of the world's physicists combined ...and then some. He ended up on the loony fringe of science. And it all started with his speculations about the "speed of gravity". Nonetheless, there were some very good replies to his "speed of gravity" ideas over the years that you may find useful. It's a subtle issue, and the short answer to your question is that "there is no short answer".

Frank Reed
Conanicut Island USA

PS: I'm going to use this message as an opportunity to "retire" my long-standing signature to messages (my initials "FER"). Instead I'll be signing with my full name and location (and possibly other info) whenever I can remember to do so.