fifth force

Is there a 5th fundamental force of nature ?!!
In physics, there are four observed fundamental interactions (also known as fundamental forces) that form the basis of all known interactions in nature : gravitational, electromagnetic, strong nuclear, and weak nuclear forces.
The search for a fifth force has increased in recent decades due to two discoveries in cosmology which are not explained by current theories. It has been discovered that most of the mass of the universe is accounted for by an unknown form of matter called dark matter. Most physicists believe that dark matter consists of new, undiscovered subatomic particles, but some believe that it could be related to an unknown fundamental force.
A new fundamental force might be difficult to test : One way to search for a fifth force is with tests of the strong equivalence principle, one of the most powerful tests of general relativity, also known as Einstein's theory of gravity.
In this video, we will learn about this mysterious force of nature.