Gravitational Lock in GR

  • Thread starter tzimie
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  • #1
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Main Question or Discussion Point

When 2 bodies are locked over relatively large distances (like locked Earth and Venus), do they lock, naively speaking, to the position where another's body is seen (delay distance/c is taken into account) or to the position where other body is actually at the moment (because of Relativity of simultaneity we have to chose frame here, but there is no problem for slowly moving bodies like Earth and Venus - it could be their center of mass, or Sun, there is a little difference)
 

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  • #2
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What does "like locked Earth and Venus" mean? How are Earth or Venus "locked" in any way? They both orbit the sun.
 
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  • #3
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https://en.wikipedia.org/wiki/Tidal_locking

Venus's 583.92-day interval between successive close approaches to Earth is equal to 5.001444 Venusian solar days, making approximately the same face visible from Earth at each close approach
 
  • #4
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A pure coincidence today. It has been different in the past, it will be different again in the future.
Also, the rotation of planets with a nearly perfect rotational symmetry has no influence on the gravitational force between them.
 
  • #5
stevendaryl
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As mfb points out, some cases of celestial bodies being "locked" in this sense is a pure coincidence. However, sometimes it's not a coincidence. For example, the moon always shows the same face to the Earth because of tidal forces.

So you're asking how this notion of "locking", which is well understood in Newtonian physics, is modified by relativity. My guess would be that the relativistic corrections are completely insignificant for any actual planets.
 
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