Where does the loss of gravitational potential energy goes?

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Discussion Overview

The discussion revolves around the concept of gravitational potential energy in a hypothetical closed system consisting of a star and a planet. Participants explore the implications of the star's mass loss over time and its effect on the gravitational potential energy between the two bodies, questioning where this potential energy goes and how it relates to the star's energy output.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant posits that there is a significant gravitational potential energy between the star and the planet, even at large distances, and questions where the loss of this energy goes as the star converts mass into energy.
  • Another participant clarifies that while the gravitational potential energy decreases in magnitude, it becomes larger in value, and at infinite separation, it remains zero, suggesting that the star's mass change has negligible impact on potential energy at great distances.
  • A later reply discusses the eventual gravitational attraction between the star and planet, speculating that this could lead to a collision that would release energy, but questions the current state of potential energy that has not yet been converted.
  • One participant suggests that the star radiates energy in the form of light and cosmic radiation, which could account for any perceived loss of gravitational potential energy.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravitational potential energy and its relationship to mass loss and energy radiation. There is no consensus on the fate of the lost potential energy or how it interacts with the star's energy output.

Contextual Notes

Participants acknowledge the complexities of gravitational interactions at large distances and the assumptions involved in their reasoning about potential energy and mass loss.

J. Richter
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Hi.

Imagine a closed physical system (a universe) with only one star like our Sun, and one planet like our Earth, but so far away from each other, that the gravity from both matters only has a very small effect on each other.

There is a (almost maximum) gravitational potential energy between the star and the planet, even that they are far away from each other.

The star converts mass into energy as time goes by, and the gravitational potential energy between the star and the planet gets smaller because of that.

This loss of potential energy doesn’t seem to be included in the physical processes around the star, because how is the star to know the mass of the planet so far away, and the amount of the potential energy?

My question is:

Where does the loss of gravitational potential energy between the star and the planet goes?

Regards from J. Richter
 
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J. Richter said:
There is a (almost maximum) gravitational potential energy between the star and the planet, even that they are far away from each other.
The potential is negative definite, with a maximum of zero at infinite acceleration.

The star converts mass into energy as time goes by, and the gravitational potential energy between the star and the planet gets smaller because of that.
The potential energy gets smaller in magnitude but larger in value. However, at infinite separation, the potential energy is still zero. The star's changing mass results in essentially no change in potential energy for a planet and a star separated by a very, very large distance.

This loss of potential energy doesn’t seem to be included in the physical processes around the star, because how is the star to know the mass of the planet so far away, and the amount of the potential energy?
How does the star "know" the mass of a planet that is fairly close to the star? How is a separation of 1AU any different than a separation of billions of AUs?
 
D H said:
The potential is negative definite, with a maximum of zero at infinite acceleration.
The potential energy gets smaller in magnitude but larger in value. However, at infinite separation, the potential energy is still zero. The star's changing mass results in essentially no change in potential energy for a planet and a star separated by a very, very large distance.
Thanks for your reply!

Since the star and the planet has a very small effect on each other after all, during very long time, they would be drawn towards each other because of gravity, stronger and stronger, resulting in a big collision, that would result in more heat in that universe.
But for now, this has not happened yet therefore there must be a positive (not yet released) energy between the star and the planet.

The star loses energy, and the eventual collision in the future between the star and the planet would result in a smaller and smaller crash.

Where does this potential energy go?
D H said:
How does the star "know" the mass of a planet that is fairly close to the star? How is a separation of 1AU any different than a separation of billions of AUs?
Your right, that was a clumsy way of trying to say what I meant:
It’s hard to imagine that this “lost” potential energy mentioned above, is converted into another kind of energy together with the converted mass from the sun.
 
the star is constantly radiating energy in the form of light and cosmic radiation, which should make up for any 'lost' gravitational potential.
 

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