Gravity is a natural phenomenon by which all things with mass or energy are brought toward. Another term that is often used to describe how this works is that objects gravitate toward one another. As gravitational attraction of the original gaseous matter present in the universe caused the matter to coalesce into clumps that would form stars and galaxies, it can be said that gravity is responsible for many of the large-scale structures in the Universe. Although gravity has an infinite range, its effects become increasingly weaker as objects get further away.
Gravity is most accurately described by the general theory of relativity, proposed by Albert Einstein in 1915. In his general theory of relativity, Albert Einstein describes gravity not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole’s event horizon. Except for black holes, the majority of the remaining universe will follow the laws of gravity, which is well approximated by Newton’s law of universal gravitation. This law described by Newton describes gravity as a force which causes any two bodies to be attracted to each other, with the force proportional to the product of their masses and inversely proportional to the square of the distance between them.
Gravity is the weakest of the four fundamental interactions of physics, which means that it has no significant influence at the level of subatomic particles. However, at the same time, this makes gravity the dominant interaction at the macroscopic scale, and is the cause of the formation, shape and trajectory, otherwise known as an orbit, of astronomical bodies. Scientists are attempting to develop a theory of gravity consistent with quantum mechanics, which would allow gravity to be united in a common mathematical framework under a theory of everything with the other three fundamental interactions of physics.
There is the Flyby Anomaly, which has seen various spacecraft experience greater acceleration than expected during gravity assist maneuvers.
There is the Anomalous Increase Of The Astronomical Unit, which has seen recent measurements indicate that planetary orbits are widening faster than if this were solely through the Sun losing mass by radiating energy.
The Accelerating Expansion has made it seems that the metric expansion of space might be speeding up
There are Extra Massive Hydrogen Clouds, which have been suggested by scientists studying and analyzing the spectral lines of the Lyman-Alpha Forest. Using this spectral analysis, scientists theorize that hydrogen clouds might be more clumped together at certain scales than were expect, which may indicate that the force of gravity may fall off slower than the inverse-squared law at certain distance scales.
There are also Extra-Fast Stars, which are stars on the outskirts of a galaxy are moving faster than they should according to the observed distributions of normal matter.