PDA

View Full Version : Question about gravity



SharkByte
2007-Feb-12, 04:32 PM
I remember reading somewhere a year or so ago that the speed of gravity was measured to equal the speed of light. As I read the artical I remember thinking that the way the experiment was described, it seemed like it was measuring the speed of light, not gravity, but I figured I just didn't understand all the intricacies of what they were doing or how they were interpretting the results.

There are also theories I have read that state that gravity is a field that permeates everything, everywhere at the same time and its effects are instantaniously felt everywhere at once.

If I remember correctly, it takes 8 minutes for light to reach the earth from the sun. If we could suddenly remove the sun from the solar system, would the earth continue its arc around the former position of the sun for 8 minutes or would its path immediately straiten out flinging it strait out of the solar system?

Bjoern
2007-Feb-12, 10:26 PM
I remember reading somewhere a year or so ago that the speed of gravity was measured to equal the speed of light. As I read the artical I remember thinking that the way the experiment was described, it seemed like it was measuring the speed of light, not gravity, but I figured I just didn't understand all the intricacies of what they were doing or how they were interpretting the results.


I also remember that measurement, but I don't know enough about it to comment.




There are also theories I have read that state that gravity is a field that permeates everything, everywhere at the same time and its effects are instantaniously felt everywhere at once.


First, that gravity "is a field that permeates everything" and which is "everywhere at the same time" does not imply that "its effects are instantaneously felt everywhere at once". Even if a field exists everywhere "at the same time", that does in no way imply that changes in the field propagate at an infinite speed.

Second, the idea that "its effects are instantaneously felt everywhere at once" is essentially Newton's version of gravity - which was superseced by Einstein's General Theory of Relativity (in which effects propagate at the speed of light).




If I remember correctly, it takes 8 minutes for light to reach the earth from the sun. If we could suddenly remove the sun from the solar system, would the earth continue its arc around the former position of the sun for 8 minutes or would its path immediately straiten out flinging it strait out of the solar system?

The earth should continue for 8 minutes in its "arc". Please don't try this experiment! ;-)