Information transmitted faster than light?

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Discussion Overview

The discussion revolves around the concept of information transmission and the propagation of forces, particularly in the context of relativity and the speed of light. Participants explore scenarios involving communication over distances, the effects of changes in gravitational and electromagnetic fields, and the implications of instantaneous changes in mass or force.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that no information can be transmitted faster than light, referencing this as a fundamental aspect of nature.
  • There is a discussion about whether physical contact (e.g., tugging a string) would allow for instantaneous communication, with some arguing that the speed of sound in the material limits this transmission.
  • Participants propose that changes in gravitational forces propagate at the speed of light, suggesting a delay in experiencing gravitational effects if a massive object were to suddenly disappear.
  • One participant introduces the idea of a "maximally rigid ideal material" that could transmit forces at the speed of light, questioning how such a material would behave under tension.
  • There is a debate about the implications of a hypothetical scenario where a massive object disappears instantaneously, with some arguing that such a scenario contradicts the laws of physics.
  • Questions are raised about how changes in gravitational fields are experienced over distance, particularly whether changes propagate instantaneously or with a delay.

Areas of Agreement / Disagreement

Participants generally agree that information cannot be transmitted faster than light and that changes in gravitational and electromagnetic fields propagate at the speed of light. However, there are competing views on the implications of hypothetical scenarios involving instantaneous changes and the nature of force propagation.

Contextual Notes

Participants express uncertainty about the behavior of fields in response to changes in mass or force, particularly regarding whether these changes are experienced simultaneously or propagate as ripples. The discussion includes assumptions about idealized scenarios that may not align with physical laws.

  • #31
Andrew Mason said:
The change in shape of the moon would change its moment of inertia. If the moon's rate of rotation did not change, in order to conserve total angular momentum, would the location of the CM (ie. the Earth moon CM radius) not have to change as well?

The bottom line is that these kinds of changes do not appear to change the gravitational effect of these masses. Nothing has to be communicated to distant objects about such changes.

AM

Only spheres have no change in gravitational potential when they rotate.
Conservation of the dumbell Moon's angular momentum would just mean that it would rotate slower than it does now but, in our experiment, we could spin it at any rate we wanted. Why should there be a resulting first order change in the position of the Earth / Moon CM? What effect / interaction between Earth and Moon could change the radius of the Moo's orbit at the dumbell rotation rate. Tidal drag etc. would always apply but these have very long time constants c/w the spinning dumbell time.
Are you saying that there would be no periodic change of the 'dumbell' Moon gravity, measured on Earth? The field 'near' to a rotating dumbell is not isotropic so it would certainly change at the rotation rate - so how far away would you say the effect would not be noticed?
 

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