The Force of Gravity: Instantaneous or with a Delay?

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Discussion Overview

The discussion explores the nature of gravity, specifically whether it acts instantaneously or with a delay, and the implications of gravitational waves. Participants consider theoretical scenarios involving isolated atoms and the propagation of gravitational effects across vast distances, as well as the broader implications of gravity waves in relation to other forms of radiation.

Discussion Character

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

Main Points Raised

  • One participant proposes a thought experiment involving two atoms and questions whether they would "observe" each other instantaneously or after a delay, suggesting a distinction between feeling and seeing each other.
  • Several participants assert that gravity is not instantaneous and propagates at the speed of light, referencing Einstein's theories.
  • There is a discussion about the implications of creating matter out of nothing and whether this could lead to other unexpected phenomena.
  • One participant speculates that every instance of matter distorts spacetime and produces gravitational waves, questioning if these could be measured despite current technological limitations.
  • Another participant raises the idea of a gravitational Doppler effect and discusses the difference between static gravitational fields and gravitational waves, noting that only accelerating objects radiate gravitational waves.
  • Questions are raised about the relationship between mass, acceleration, and the emission of gravitational waves, particularly in scenarios where an object's motion is equivalent to the expansion of spacetime.

Areas of Agreement / Disagreement

Participants generally agree that gravity propagates at the speed of light and is not instantaneous. However, there are multiple competing views regarding the implications of gravitational waves, the conditions under which they are emitted, and the theoretical scenarios presented, leaving the discussion unresolved.

Contextual Notes

Some claims depend on specific definitions of gravitational fields and waves, and there are unresolved questions about the nature of gravitational effects in hypothetical scenarios involving motion and spacetime expansion.

robertm
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Say you had a universe, like our own in every way except that the total matter in existence was one single atom. Now say you introduced another atom of roughly the same dimensions into this universe as far from the original atom as spacially possible.

How long, if any time at all, would it take for either atom to "observe" the existence of the other? Meaning: Is the force of gravity an instantaneous force, or does the force travel ie... as in a gravity wave?

If the atoms are say 100 million light years apart, would either be aware of the other's existence until 100 million years after the 2nd atom was introduced, or would they somehow instantly experience the distortion of spacetime due to each others mass?

Would they be able to "feel" each other before they could "see" each other?
 
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Gravity is not an instantaneous force and propagates at the speed of light. Otherwise, information would travel instantaneously.
 
According to Einstein, gravity propagates at the speed of light.

On the other hand, nobody know what would happen if you suddenly created matter out of nothing. If you can do one impossible thing, maybe you can do other impossible things. ;)
 
Gravity is not an instantaneous force. As you said, gravity waves from the second atom will travel to the first at a finite speed, namely, the speed of light.
 
Phlogistonian said:
On the other hand, nobody know what would happen if you suddenly created matter out of nothing. If you can do one impossible thing, maybe you can do other impossible things. ;)

Ha Ha. Very funny. :wink: Well good you all have so far confirmed what i was thinking. Thanks guys!
On the subject of gravity waves...

I was thinking, we can only (theoretically) maybe detect extreme examples of ridiculous manifestations of matter (black holes, binary neutron stars, type 2 supernova) but, if the theory holds true would i be correct in assuming that every instance of matter occurring in spacetime would distort spacetime and produce "gravity waves" that could theoreticaly be measured even if our current technology does not allow it? So does this mean we are even more so swamped with gravitational waves than we are with EM radiation?

Say we had "eyes" that could "see" a certain wavelengths of gravity waves instead of eyes that can detect EM radiation. How would our experience of the physical world be different/similar? Would we be provided with more information or less?
 
robertm said:
Well good you all have so far confirmed what i was thinking. Thanks guys!

Anytime.

On the subject of gravity waves...

I was thinking, we can only (theoretically) maybe detect extreme examples of ridiculous manifestations of matter (black holes, binary neutron stars, type 2 supernova) but, if the theory holds true would i be correct in assuming that every instance of matter occurring in spacetime would distort spacetime and produce "gravity waves" that could theoreticaly be measured even if our current technology does not allow it? So does this mean we are even more so swamped with gravitational waves than we are with EM radiation?

It is true that every massive body in the universe will theoretically emit gravity waves as it moves, even if we cannot detect those waves because they are so weak. Whether this means we are more swamped by gravity waves than by E&M waves, I am not sure.
 
Hmmm... i wonder what would happen to a mass' gravitational field if, in relation to the total extent of spacetime surrounding it, it had no motion. ie... an object's only motion is equivalent in direction and magnitude to the expansion of spacetime.

My point being: is the distortion of spacetime reliant on mass AND acceleration, or simply mass?

Would it even emit gravity waves?
 
G01 said:
Anytime.



It is true that every massive body in the universe will theoretically emit gravity waves as it moves, even if we cannot detect those waves because they are so weak. Whether this means we are more swamped by gravity waves than by E&M waves, I am not sure.


so does that mean that there is a gravitational Doppler effect?
 
There is a difference between a static gravitational field and gravitational waves. Everything has a gravitational field. But only accelerating objects radiate gravitational waves and only if the motion is not spherically symmetric.
 

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