Force of gravity between photon and earth

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Discussion Overview

The discussion revolves around the force of gravity between a photon and the Earth, exploring theoretical approaches to calculate this force using gravitational equations and concepts from relativity. Participants consider both classical and relativistic frameworks, as well as experimental evidence related to photon behavior in gravitational fields.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • One participant proposes using the gravitational force equation F=(GMm)/(r^2) by first converting the energy of a photon (E=hf) into mass equivalence (E=mc^2) to find the force between a photon and the Earth.
  • Another participant challenges this approach, noting that the observed deflection of light due to gravity is twice what would be expected from Newtonian calculations, referencing early tests of General Relativity (GR).
  • Repeated inquiries are made about how to accurately calculate the gravitational interaction between a photon and the Earth.
  • A suggestion is made to review the Mossbauer Effect experiments, which measured the energy gain of photons in a gravitational field, as a relevant experimental context.
  • It is noted that both Newtonian and relativistic calculations for bending light are available, indicating the complexity of the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the method for calculating the gravitational force between a photon and the Earth, with multiple competing views and approaches presented.

Contextual Notes

The discussion highlights the limitations of applying classical mechanics to photons, the dependence on relativistic effects, and the unresolved nature of the calculations proposed.

cragar
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If I wanted to use F=(GMm)/(r^2) to find the force between a photon and the Earth
could I use E=hf and then find the energy the plug it into E=mc^2 then use the to find
the mass equivalence and then plug it into the first equation.
would this work.
 
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Not really, the observed deflection is twice that. That was one of the early tests of GR.
 
so then how would we calculate it .
 
Review the google websites discussing the famous Mossbauer Effect experiments by Pound and Rebka at Harvard in 1959, where they measured the energy gain of the 14 keV photons from iron-57 falling from the top of the physics building to the basement.
 
cragar said:
so then how would we calculate it .

Bending Light gives both Newtonian and relativistic calculations.
 

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