According to string theorist Brian Greene, after multiverses, branes - a spatially extended, mathematical concept that appears in string theory and its relatives (M-Theory and brane cosmology), a 0-brane being a zero-dimensional particle - the next big thing seems to be figuring out exactly what the underlying fabric of space and time is really made of.

There's been a succession of theories about what constitutes reality - starting with the four elements of the ancient Greeks and moving on to atoms and molecules ... then electrons, protons and neutrons ... then a menagerie of subatomic particles, including quarks and leptons ... and now the teeny, tiny vibrating strings that are the focus of Greene's theoretical work.

String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, that wants to unify the known natural forces (gravitational, electromagnetic, weak nuclear and strong nuclear) by describing them with the same set of equations.

"The really big problem in cosmology that I don't think we've cracked is a full understanding of what space and time actually are. ... We don't know what the 'atomic structure' of space and time really is," he says.

Many ideas present in modern theories about the geometry of space-time are consistent with the view that our universe is following just one of many possible cosmic scenarios, and that there could be other universes just next door that we cannot perceive.
Greene noted that this concept has often been compared to "a big cosmic bubble bath" with each universe representing just one bubble in the foam, or to piece of Swiss cheese, with each hole standing for a universe.

Maybe some very important breakthrough will answer all these questions that are preoccupying mankind.

Or maybe, just maybe, with mankind's limited perception leading us to live in a three dimensional universe in which we can only aspire to see a small fraction of what the true universe is really like, we will never do more than only skim the surfaces of true reality.

In the meantime, the deepest question could be not how the universe works, but why it exists at all.

This question is what religions and artists have tried more, and scientists less, to explain throughout the journey of mankind.