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Q & A: gravitational grooves?

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Most recent answer: 10/22/2007
Q:
if space is bent to create gravity does that space go back to being perfectly straight after that mass moves out of that space? Say earth plops down somewhere and the space around it is now bent around it creating gravity... now if earth went somewhere else does the space it was in before go back to being perfectly straight If it is still bent does that mean there will be some type of gravity even though earth has moved? Also if space doesen’t go back to being straight does that mean that after billons of trips around the sun that there will be a "grove" left by earth that it will follow?
- James
U.S
A:
There really isn't a groove or indentation left over where the Earth used to be. In fact, if you ignore the orbit and just think of the earth by itself, how would you even say where the Earth used to be. Different observers, travelling at different velocities with respect to the Earth, would point to entirely different regions as the places where they say the Earth used to be. Somebody on Earth would just point to where it is now.

However, your basic insight is correct. The gravitational effects are in some sense left in space where they can do their own thing, not directly involving their source any more. For example, as the Earth accelerates in (almost) uniform circular motion around the Sun, it emits gravitational waves which then travel out away from the Earth and Sun. These are very weak, but for some massive objects rotating very rapidly, the same effect carries away enough energy to measurably slow the rotation.

If the Earth were to blow apart into two parts heading opposite directions, gravity on the Sun would be entirely unaffected for about 8 minutes. The gravitational changes only travel at the speed of light. So that's another aspect to the way in which the gravity sits in the structure of space itself, not immediately dependent on the original source. However, none of those effects give any long-time grooves.

Mike W.

(published on 10/22/2007)

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