Is it possible one day maybe to harness gravity to our benefit or is that impossible I'm new to science I have no training but I'm fascinated how the universe works thanks
Getting back to the original question, and away from the lies and red herrings raised by the god [who is never wrong

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Gravity can be a great help and/or a hindrance as already stated and detailed in a number of posts.
The ultimate dream of controlling gravity, would be controlling spacetime as in the Alcubierre drive which would give us "Star Trek" like technology.NB: and let me say at this time, although difficult in the extreme, and totally beyond any capabilities we have at this time, or could dream of having in the near future, it is not against the laws of physics and GR.....
We have two models of gravity: Newtonian which tells us that mass attracts each other with a force that varies as the inverse square of the distance between them.eg: The Earth/Moon system would see the attraction quadruple if the distance was halved and see the attraction lessened to a quarter of the present if the distances were doubled.
It works perfectly fine with most Solar System operational space craft.
Then of course we have Einstein and his spacetime curvature in the presence of mass.
With gravity assists that was mentioned, we are using the momentum of the planet and its gravity to obtain a boost in speed relative to the Sun.
This enabled us to see Voyager's 1 and 2 gather enough momentum to leave our Solar System and the gravitational clutches of the Sun.
Gravity Assists can either be used to speed up or slow down a craft,s velocity relative to the Sun.
Gravity/Spacetime is warped and twisted in the presence of mass and even made to "ripple" similar to waves in a pond after throwing a rock in, when to massive bodies interact, or collide.
Gravity will even slow down time both mechanically and biologically in relation to an outside reference frame.
Yet in knowing all that, and in being able to take advantage of what we do know about gravity, as yet cosmology/physics is unable to say exactly what gravity is and why it occurs, other than it exhibits itself when matter/energy warp/curve or twist spacetime.
A great Physicist said.....
Matter/Energy tells spacetime how to curve: Spacetime tells matter/energy how to move:
John Archibald Wheeler: