“The whole edifice of modern physics is built up on the fundamental hypothesis of the atomic or molecular constitution of matter.” -C. V. Raman
As far as humans have figured out, there are four fundamental forces in the Universe: the three of the Standard Model (electromagnetism, the weak and strong nuclear forces) and General Relativity, our theory of gravitation. It’s the great hope of many that a quantum theory of gravitation will someday emerge, and that all four forces could be unified into a single framework. Among others, this is the dream of string theory.
But there’s another possibility: that the one force that doesn’t fit isn’t really fundamental at all. It’s possible that there’s some other fundamental entity that gravitation might emerge from. In 2010, Erik Verlinde put forth a very controversial idea that gravity might be emergent from entropy and quantum information, and just this week, he put out a paper that represents the culmination of six years of work on developing the endeavor.