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Astronomy Experiment: Measure Earth's Trajectory
In a recent discussion, someone asserted that gravitic effects travel with a
finite propagation delay. Another person said that this notion would make impossible stable orbits. The logic behind both arguments seems somewhat convincing, and brings to mind an old experiment on gravity: Hypothesis: The effect known as gravity is instantaneous. Null hypothesis: Gravitic effect travels at a finite speed comperable to the speed of light. Experiment: If gravity travels similar to light, then the trajectory of planet Earth should be a tangent to the observed location of the Sun (eight minutes west of 'current' position). If gravity is instantaneous, then the trajectory of planet Earth should be a tangent to the current position of the Sun, eight minutes east of observed. Question: Do we have at our disposal equipment that can measure this difference in trajectory? Location of planets, pulsar timings? Preferably equipment that is not restricted to authority figures; usable by ameteur astronomers. |
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Interesting question, but probably instruments would need to be much
more sensitive than amateur-grade to measure what you want to measure. You might like to read some about general relativity, which describes gravity not as a field that propagates, but as a curvature of space due to massive objects. It includes the idea that rotating objects like planets and black holes sort of drag the curvature of space around. There might be something in a discussion of this that answers the question of how fast gravity (space-time distortion) propagates. This dragging would become easily measurable only near a very fast heavy spinning object, I think. I'm no expert, just basing these remarks on science articles for everyday readers. AngleWyrm wrote: In a recent discussion, someone asserted that gravitic effects travel with a finite propagation delay. Another person said that this notion would make impossible stable orbits. The logic behind both arguments seems somewhat convincing, and brings to mind an old experiment on gravity: Hypothesis: The effect known as gravity is instantaneous. Null hypothesis: Gravitic effect travels at a finite speed comperable to the speed of light. Experiment: If gravity travels similar to light, then the trajectory of planet Earth should be a tangent to the observed location of the Sun (eight minutes west of 'current' position). If gravity is instantaneous, then the trajectory of planet Earth should be a tangent to the current position of the Sun, eight minutes east of observed. Question: Do we have at our disposal equipment that can measure this difference in trajectory? Location of planets, pulsar timings? Preferably equipment that is not restricted to authority figures; usable by ameteur astronomers. |
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