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seen Jan 20 at 1:40

I like asking Physics questions! Would answer more if I knew more.


Sep
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awarded  Autobiographer
Sep
11
awarded  Popular Question
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awarded  Popular Question
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comment Does the amount of gravitational potential energy in the universe increase as it expands?
@Fr34K I think you are missing a minus sign, wikipedia shows the formula negated (see General formula) en.wikipedia.org/wiki/Potential_energy
Jan
27
comment Does the amount of gravitational potential energy in the universe increase as it expands?
I've awarded the bounty to @markovchain - best answer so far is "we don't know" which is perfectly honest if a bit unsatisfying!
Jan
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awarded  Benefactor
Jan
27
accepted Does the amount of gravitational potential energy in the universe increase as it expands?
Jan
24
awarded  Nice Question
Jan
24
comment Does the amount of gravitational potential energy in the universe increase as it expands?
And going back to basics (Newtonian mechanics) if the masses are unchanged, the distance between them increases, and the gravitational constant is unchanged then the total GPE increases. You are arguing total GPE decreases, how do you explain this basic break with Newtonian mechanics?
Jan
24
comment Does the amount of gravitational potential energy in the universe increase as it expands?
OK but your argument just states that an expanding universe is a closed system... I can just as well state that it is not a closed system and this thermodynamics argument doesn't apply.
Jan
24
comment Does the amount of gravitational potential energy in the universe increase as it expands?
hi, I see that dark energy may or may not exist, but I don't see how this is related to the question of whether the expanding universe increases the overall amount of gravitational potential energy. Your last sentence leaves a lot to the imagination!
Jan
20
awarded  Promoter
Jan
20
comment Time taken for gravity of a distant object to interact with a newly created particle?
Maybe I'm missing something but not one of the linked "duplicate" questions asks anything about gravitons, which is the whole point of my question.
Jan
19
comment Time taken for gravity of a distant object to interact with a newly created particle?
@EduardoGuerras yes you are right about the photon behaviour at a distance, but that is different to the virtual graviton behaviour; receiving one photon every 5 years is fine but receiving one graviton every 5 years would not be fine, as it would then take 5 years for the star to influence the particle via gravity. I think the key thing here is the difference between real and virtual particles, and the link from JohnRennie looks good on this topic.
Jan
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comment Time taken for gravity of a distant object to interact with a newly created particle?
@JohnRennie thanks for the link, looks interesting.
Jan
19
comment Time taken for gravity of a distant object to interact with a newly created particle?
@EduardoGuerras I'm not sure these are the same, the photons represent real energy emitted from the star, the virtual-gravitons do not. At a certain distance from the star I will stop seeing its photons, but I should still "see" it's virtual gravitons
Jan
19
comment Time taken for gravity of a distant object to interact with a newly created particle?
@CrazyBuddy thanks, will try to master the markup next time
Jan
19
comment Time taken for gravity of a distant object to interact with a newly created particle?
For example, it implies that the star launched enough virtual gravitons 1 year ago to be able to interact with any particle on a shell 1 light year radius! that is a lot of virtual gravitons, and the density of them a year ago would be immense. It just seems weird!
Jan
19
comment Time taken for gravity of a distant object to interact with a newly created particle?
Thanks John, I agree that the answer (a) is obvious considering relativity / curvature of space arguments, but I am struggling to visualise how it could possibly work with gravitons. It's not so much that there is no need to involve gravitons - I agree that different models handle the situation well - it is just that I struggle to understand the graviton model!
Jan
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comment Time taken for gravity of a distant object to interact with a newly created particle?
@Chris White I do not think either if these questions are duplicates, one is about FTL information exchange (which I am not covering), one is about speed of gravity transmission (which is clearly speed-of-light). I am asking a different question about the nature of gravity.