Gravitational Lock in GR: Earth-Venus Positioning

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Discussion Overview

The discussion revolves around the concept of gravitational locking between Earth and Venus, particularly in the context of general relativity and the implications of relativity of simultaneity. Participants explore whether the locking refers to the observed position of the planets or their actual position, considering the effects of their motion and gravitational interactions.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions the meaning of "locked" in relation to Earth and Venus, noting that both planets orbit the sun independently.
  • Another participant references the tidal locking of Venus with respect to its close approaches to Earth, suggesting a periodic visibility of the same face.
  • A different viewpoint suggests that the locking phenomenon can be a coincidence, with historical variations in the relationship between the two planets.
  • Some participants propose that while tidal locking is a well-understood concept in Newtonian physics, its implications in relativity may be negligible for planets like Earth and Venus.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravitational locking, with some suggesting it is a coincidence while others argue for a more structured understanding based on tidal forces. The discussion remains unresolved regarding the implications of relativity on this phenomenon.

Contextual Notes

There are unresolved assumptions regarding the definitions of "locking" and the specific conditions under which gravitational interactions are considered. The discussion also highlights the potential differences in interpretations based on the reference frame chosen.

tzimie
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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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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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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
 
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.
 
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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