Gravity

Gravity is the most familiar of all the fundamental forces in nature but also the least understood at a fundamental level. Physicists can describe gravity and its effects, we know that it is the only fundamental force that operates at infinite range, and affects all things with mass irrespective of size, shape or electric charge. We know what it does, but so far, we can’t explain what it is.

Gravity is one of the four fundamental forces of nature, and it is well understood at cosmological scale, however there is no working theory yet to combine this understanding with the laws of particle physics explained by the Standard Model.

There are successful quantum theories explaining the electromagnetic, weak, and strong forces, but so far there is no effective quantum theory to explain gravity.

Of the 4 known fundamental forces of nature, three of them, Electromagnetic, Weak, and Strong are unified, Gravitation isn’t yet.

Gravity is by far the weakest of the 4 fundamental interactions of nature, for example, it is 1,000,000,000,000,000,000,000,000,000,000,000,000 times weaker than electromagnetism, and we don’t know why.

Three of the four fundamental forces in nature have at least one associated force-carrying particle: The electromagnetic force has the photon; the strong force has the gluon; and the weak force has the W and Z bosons. The graviton is the hypothetical elementary particle carrying the gravitation force, but so far it has not been detected experimentally.

The universal gravitational constant G, is an empirical physical constant involved in the calculation of gravitational effects, its measured value is known with some certainty to just four significant digits, however, we do not have a theoretical justification for the value of G.

Some physicists believe that gravity, the most mysterious of the 4 fundamental interactions, might not be a fundamental force of nature, but an emergent phenomenon linked to the structure of spacetime, but there is no evidence of this.

The masses of matter and antimatter are always positive, therefore it is believed that the gravitational interaction of antimatter should always be attractive, as it is the case with matter, however we still don’t know if the gravitational interaction between matter and antimatter is attractive or repulsive.