# Expanding Universe - weakening gravity?

Please excuse the simplistic approach to the following question.

If one accepts that the universe is indeed expanding could this not be simply because the relative strength of gravity has or is diminishing?

Instead of suggestions of dark energy and or dark matter to make equations make sense could it just be gavitational weakening?

I am sorry if this question appears ill informed but I wished to dsicuss this issue all the same.

In support the hypothesis a friend did some math for me to relate universal expansion to local circumstances ( Earths orbit)

At the same time if you consider the observed universe radius of 13.5 Billion LYr and that Earth is 8.5 LMin from the sun then a 1 LYr change in the universe radius would equal 1.1979E-15 LYr change in Earth's orbit. That would be equal to 11.33 meters.

Since the fastest observed recession body seems to be around 0.95 c that would mean in one year we should see something on the order of 10 3/4 meters change in Earth's orbit.

Even though this figure of 10.75 meters is an abstract figure and could have a significant error margin. in that the measurement could be from 0.001 meters to 1000 meters or so.....I find it amazing that the figure has come in so low.
Taking universal expansion figures and applying them to Earths orbit.
Following the logic it seems concievable that a weakening of gravity could be responsible for the universes expansion.

Is this worth pursuing?

## Answers and Replies

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Chronos
Gold Member
No. Local gravitational effects are far stronger than the force of expansion. The planets [at least those left after the sun goes red giant] will remain in orbit around the sun long after the rest of the universe recedes out of view.

my contention:

If the force that holds the universe together ( gravity ) diminishes then the angular momentum of matter with in this universe would be flung outwards thus increasing the size of the universe with out increasing it's mass.

A microscopic change in local conditions *could* indicate a a reason for this increase in size universally.

If one assumes the veracity of newtonian gravity then wouldn't this contention make sense?

Local gravitational effects are far stronger than the force of expansion.
I would contend that the force of expansion is actually a lacking in force rather than an increase of force.

hypothetically any way.......

Chronos
Gold Member
Gravity gets weaker with distance, inverse square law thing.

maybe i should put it this wasy:

Assume that we have a stable non-expanding universe. Then for some reason gravity starts to weaken universally.....(sharing a common source) What would be the effect?

Chronos
Gold Member
planetary orbits would fly apart, galaxies would fly apart, nothing dramatic.

Scott;

I think you have a good point. Everyone knows that all systems are giving up mass/energy through EMR. Therefore, the gravitation effect would decrease over time since a systems mass decreases over time.

Chronos said:
Gravity gets weaker with distance, inverse square law thing.
I agree with Chronos...

I do not think gravity draws from a "universal source", but from many distinct sources interacting with each other. "Local systems" interacting amongst its own elements are less likely to change verses interactions between other systems that are more distant from each other.