## question regarding dark energy and accelerated expansion

Question regarding dark energy and accelerated expansion. If gravitational force were somehow diminished at large distances----ie lower gravitational constant at huge distances--might this explain the increase or accelerated expansion seen. If this were true, would it be necessary to evoke a completely separate factor--ie dark energy --to explain this. For this to be even considered , one would have to humbly admit that not all is known of gravity-----less of a leap than the same statement re dark energy----????

Randall Rosenthal

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 Recognitions: Gold Member Science Advisor This is not a simplifying explanation. We already have MOND as an alternative theory of gravity that predicts it becomes stronger with distance.

 Quote by rrosenthal Question regarding dark energy and accelerated expansion. If gravitational force were somehow diminished at large distances----ie lower gravitational constant at huge distances--might this explain the increase or accelerated expansion seen. If this were true, would it be necessary to evoke a completely separate factor--ie dark energy --to explain this. For this to be even considered , one would have to humbly admit that not all is known of gravity-----less of a leap than the same statement re dark energy----????
Yup...... People have thought of that.....

http://en.wikipedia.org/wiki/F%28R%29_gravity
http://arxiv.org/abs/1205.5266

The next step would be to come up with models of modified gravity (dozens of theorists doing pages and pages of math), figure out exactly what observations you should see with modified gravity (more theorists doing more pages and pages of math), and the punchline is that the observations look more like dark energy than modified gravity, but modified gravity isn't totally dead yet.

## question regarding dark energy and accelerated expansion

As you already know that in general relativity, dark energy arises due to a comparitively large value of the cosmological constant, But the complete explanation of dark energy is beyond the direct scope of general relativity. When you say that-" If gravitational force were somehow diminished at large distances----ie lower gravitational constant at huge distances--might this explain the increase or accelerated expansion seen. If this were true, would it be necessary to evoke a completely separate factor--ie dark energy --to explain this?". If you consider gravity alone, then if G is small at large distances, it would only reduce the effect of gravity. But, this doesn't explain why the universe is accelerating. If we assume your point to be true then the universe should now be in a steady state. BUT IT IS NOT. Therefore, there must be a repulsive force responsible for the expansion. This gives rise to the WIMP theory,axion assumption(i.e nambu-goldstone theorem) etc.

 Recognitions: Gold Member Science Advisor Er ... your point is not even wrong, but, is an unnecessarily confusing mix of unrelated ideas.

 Tags constant, dark energy, gravitational