How Does Gravity Influence Light's Path in General Relativity?

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Discussion Overview

The discussion revolves around how gravity influences the path of light in the context of General Relativity (GR). Participants explore the implications of mass on the geometry of space-time and how this affects both planetary orbits and the trajectory of photons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that massive bodies like the sun alter the geometry of their surroundings, leading to curved paths for planets and potentially for photons as well.
  • Another participant questions whether photons would follow the same curved paths as planets, specifically asking if they would be "stuck" in a curve forever.
  • A participant clarifies that the geometry of space-time is influenced by the energies of both the sun and the moon, indicating that both masses are necessary for closed geodesics.
  • There is a discussion about whether the paths of light are closed or merely curved, with one participant expressing confusion about the nature of geodesics created by the sun.

Areas of Agreement / Disagreement

Participants express differing views on the nature of geodesics and the influence of mass on light's path. There is no consensus on whether photons can be considered to follow closed paths like planets.

Contextual Notes

The discussion highlights the complexity of gravitational effects on light and the dependence on multiple masses, suggesting that assumptions about fixed geometries may not hold true.

nemia
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Hi All
I understand that in GR big masses like sun just change the geometry of their neighbourhood, which means that some lines will be transformed to elliptic forms so the Earth will use the new line and then will be forever turning around the sun.
Is this true?
Does this mean that even a photon will be stuck in that curve forever ?
thanks
 
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Hi A.T.
That is not my question.
What I understand is that gravity changes the geometry so the planets will use the new straight lines which are so curved to become closed.
no if a photon uses the same trajectory as the planet will it be turning forever around sun?
 
If the mass is great enough, yes. Such a situtation is a "black hole".

If you are talking about "orbits" of planets, the space-time geometry is determined by both masses (more correctly "energies"). The joint energies of the sun and moon are sufficient to form a closed geodesic which the Earth follows around the sun. The energy of the sun is not sufficient, alone, to form a closed geodesic.
 
Thank you very much I think I understand.
it depends on both masses not only the sun one.
so there is not a fixed geometry with fixed geodesics?
I thought that the sun for our example will create new geodesics that every other corps will use.
Do you mean for the moon the line becomes an elliptic form but for the light it will be a slightly curved line but not closed?
 

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