Spacetime Curvature: Eliptical Orbital Paths & Keppler Laws

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Discussion Overview

The discussion revolves around the nature of orbital paths of planets, specifically addressing the elliptical nature of these paths, the implications of spacetime curvature, and how these relate to Kepler's laws of planetary motion. Participants explore the relationship between general relativity (GR) and Newton's laws in explaining these phenomena.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express confusion about why planetary orbits are elliptical if they are influenced by spacetime curvature, questioning the role of gravitational force in these movements.
  • One participant states that Kepler's laws are derived from Newton's inverse square law of gravitation and suggests that this law serves as a good approximation of GR in weak fields.
  • Another participant argues that while orbits are nearly elliptical, general relativity accounts for deviations from perfect ellipses, indicating that they are not entirely elliptical.
  • There is mention of the local effects of spacetime geometry mimicking Newtonian forces, resulting in elliptical orbits, while also noting that global effects from spacetime curvature lead to non-closed orbits.
  • A participant expresses appreciation for a demonstration related to the topic, indicating a positive reception of the explanations provided.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of elliptical orbits and the role of gravitational force versus spacetime curvature. Multiple competing views remain regarding the interpretation of these concepts.

Contextual Notes

Some claims depend on specific assumptions about gravitational forces and spacetime geometry, and there are unresolved questions about the implications of these assumptions on the nature of orbits.

Osvaldo
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Though it is hard not to believe in the spacetime curvature that cause planets to follow curved path arround massive objects, I wander how come these paths are eliptical, the object change velocity when moving arround the massive object and what is more obeys the Keppler laws. If there is not such a gravitational force (as said byexperienced physics) which would really caused these conditions, how come these orbital movements do not belong to a central force? Can somebody give a clear explanation?
 
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Kepler laws or eliptic orbit of planets is derivied from Newton's inverse square law of universal gravitation.
I understand this Newton's inverse square law of central force is a fairy good approximation of GR theory or curved spacetime around the Sun, a massive body.
 
Osvaldo said:
I wander how come these paths are eliptical
They are actually not quite elliptical. GR explains both why they are almost elliptical and also correctly predicts how much they deviate from being completely elliptical.
 
Osvaldo said:
Though it is hard not to believe in the spacetime curvature that cause planets to follow curved path arround massive objects, I wander how come these paths are eliptical, the object change velocity when moving arround the massive object and what is more obeys the Keppler laws. If there is not such a gravitational force (as said byexperienced physics) which would really caused these conditions, how come these orbital movements do not belong to a central force? Can somebody give a clear explanation?
Locally and for weak fields the space-time geometry just reproduces the same effect Newton's force would have, and would also result in an elliptical orbit:



But globally you get an additional effect from space curvature, so the orbit is not closed:
http://demoweb.physics.ucla.edu/content/10-curved-spacetime (Figure 2)
 
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A.T. said:
Locally and for weak fields the space-time geometry just reproduces the same effect Newton's force would have, and would also result in an elliptical orbit:



But globally you get an additional effect from space curvature, so the orbit is not closed:
http://demoweb.physics.ucla.edu/content/10-curved-spacetime (Figure 2)
 
Wonderful demonstration. Never saw it like the one in the video. Thanks a lot
 

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