We are approaching the last possible phase of stellar evolution and the last step in fighting gravity wars
Before we get to that last step, need to look at a little more closely.
The Newtonian view of gravity was that all masses exert an attractive force on all other masses and the strength of the force decreases with with the inverse square of the distance between objects.
Is this a good description of gravity? For relatively weak gravitational fields it is marvelously good - it explains almost every motion of the planets and moons of planets PERFECTLY and its good enough to send probes to Jupiter and beyond with extraordinary precision.
But, it does not explain everything and there are many alternative theories of gravity. To understand the mostly widely accepted one, we start with
This is very surprising and counter-intuitive.
You can never catch up to a photon. Imagine two rocket ships, one flying toward the Sun at nearly the speed of light, one away from the Sun at nearly the speed of light. Ask them to measure the speed of the photons streaming away from the Sun and they measure the same km/sec. This is not at all what happens when considering relative velocities of cars on the freeway.
This is a radical concept!
So, time is stretched out by a factor of 5 for your friend in the rocketship. His/her clocks run at 1/5 the speed of yours.
So, your friend at 0.98c will have a 1-foot ruler that looks like it is only 2.4 inches long to you.
There have been many experiments, mostly on elementary particles moving near the speed of light in accelerators that have directly measured the increases of mass, dilation of time and contraction of space. Other experiments have compared the time passage on very accurate clocks while moving in airplanes in the opposite directions. Even the discovery of cosmic rays was made possible by the fact that the half-lives of the particles was effectively extended by time dilation long enough for the particles to reach the surface of the Earth.
He got away from the idea of a force and instead looked at an interpretation of gravity in terms of its effect on space and time.