Mass is not the cause of gravity?

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Discussion Overview

The discussion centers around the validity of the gravitational force equation Fg = Gm1m2/r^2, particularly in relation to the stress-energy-momentum tensor and whether mass is the fundamental cause of gravity. Participants explore the implications of this equation in various contexts, including its application in classical mechanics and relativistic scenarios.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the fundamental validity of the equation Fg = Gm1m2/r^2, suggesting it may be flawed since it relies on mass, while gravity is related to the stress-energy-momentum tensor.
  • Another participant argues that the equation is a good approximation for many practical applications, such as rockets and satellites, where mass energy is the significant component of the stress-energy tensor.
  • A later reply acknowledges the equation's usefulness but cautions against its application in relativistic scenarios, such as light deflection or near black holes, where momentum and pressure terms become significant.
  • One participant asserts that the question of whether the equation is "just wrong" is not a binary issue, suggesting a more nuanced understanding is necessary.

Areas of Agreement / Disagreement

Participants express differing views on the validity of the gravitational force equation, with some supporting its practical utility while others highlight its limitations in specific contexts. There is no consensus on whether the equation is fundamentally flawed or merely an approximation.

Contextual Notes

The discussion reveals limitations in applying the equation to relativistic scenarios and emphasizes the importance of considering the stress-energy-momentum tensor in understanding gravitational effects.

Brady Campbell
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If the effects of gravity are relative to an objects stress-energy-momentum tensor, is the equation:
Fg = Gm1m2/r^2
fundamentally flawed since it is based off the mass of the two objects? Ignoring the "gravity isn't a force" (I understand that it is what is observed due to curves in spacetime) argument if at all possible. Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?
 
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It is accurate enough for rockets, satellites, and all sorts of other purposes. It is a good approximation for many things where the mass energy is the only significant non zero component of the stress energy tensor.
 
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Brady Campbell said:
If the effects of gravity are relative to an objects stress-energy-momentum tensor, is the equation:
Fg = Gm1m2/r^2
fundamentally flawed since it is based off the mass of the two objects? Ignoring the "gravity isn't a force" (I understand that it is what is observed due to curves in spacetime) argument if at all possible. Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?

As others have mentioned, it's a good approxiation, but don't expect it to work for relativistic flybys and/or light deflection (where the momentum components become important), or black holes (where the pressure terms become important, even dominant).
 
Brady Campbell said:
Simply put, does this formula accurately predict how "normal" objects will be effected by gravity or is it just wrong?

Neither. Take a look at http://chem.tufts.edu/AnswersInScience/RelativityofWrong.htm to see why this isn't an either/or thing where one of the alternatives is "it's just wrong".
 
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