Gravity ~ Acceleration ~ Centrifuge & GR

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Discussion Overview

The discussion centers on the equivalence of gravity and acceleration, particularly in relation to time dilation effects as described by General Relativity (GR). Participants explore the implications of artificial gravity generated by centrifugal motion and consider various scenarios involving gravitational and velocity time dilation.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that gravity and acceleration are equivalent, including their effects on time dilation.
  • Others argue that artificial gravity from centrifugal motion should be considered equivalent to gravitational effects.
  • There is a discussion about whether gravitational time dilation can cancel out under certain conditions, such as at the gravitational balance point between two planets or at the center of the Earth.
  • One participant mentions that gravitational time dilation is more related to gravitational potential than gravitational force, suggesting that it does not cancel out like force does.
  • Participants explore the concept of gravitational time dilation at various points, including the balance point and the center of the Earth, with references to the Schwarzschild solution.
  • There is a question about whether gravitational potential is represented by slope or depth, with some clarification provided regarding the importance of depth in relation to time dilation.
  • One participant raises a scenario involving a centrifugal wheel and its effects on perceived gravity and potential, questioning how these factors interact with time dilation.

Areas of Agreement / Disagreement

Participants express multiple competing views on the relationship between gravitational and centrifugal effects, as well as the nature of time dilation. The discussion remains unresolved regarding the specifics of gravitational potential and its representation.

Contextual Notes

Participants note limitations in their discussions, such as the simplifications made by excluding frame dragging and special relativity effects. There is also mention of the complexities involved in calculating time dilation in various gravitational contexts.

  • #31
Janus said:
Let's two centrifuges, They have different length arms, and spun such that a clock at the end experiences each feels 1g. The clock on the centrifuge on the longer arm will run slower, even though it feels the same g-force as the other clock. Or you could arrange it so that the speed of the ends of the arms are the same for each centrifuge. In this case both clocks will run at the same rate, even though one will feel a greater g0force than the other.

Thanks Janus. Just reiterating what I think you've explained. Correct me if wrong.
Are you saying that the time dilation for an object in a centrifuge is based purely on the speed it is traveling (SR) and that there is no gravitational (GR) time dilation to be counted?
And so the time dilation is independent of the radius of the centrifuge?
 
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  • #32
gonegahgah said:
Thanks Janus. Just reiterating what I think you've explained. Correct me if wrong.
Are you saying that the time dilation for an object in a centrifuge is based purely on the speed it is traveling (SR) and that there is no gravitational (GR) time dilation to be counted?
And so the time dilation is independent of the radius of the centrifuge?

That's one correct way of looking at it.

An alternative way of reaching the same mathematical result is to integrate the centripetal acceleration as if it were a gravitational field, from the center out to the relevant radius, giving the equivalent gravitational potential difference between those points, and hence derive the corresponding time dilation.

Regardless of whether you're using the SR velocity or the equivalent gravitational potential, the time dilation does not depend on the acceleration. As Janus pointed out, you can have the same time dilation for different accelerations, or different time dilations for the same acceleration.
 

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