The classical Newtonian physics treated space and time as two separate entities and time was believed to be absolute. However, Einstein’s theories of relativity clarified that space and time are interconnected and that time has a shape and has only one direction. New theories about space-time indicate that the forward direction of time is related to both thermodynamics and cosmological arrows of time.
Some of the key issues in understanding space-time include:
- The nature of space-time in and around a singularity such as a black hole
- The role of gravity in creating a beginning and an end for space-time
- Extra dimensions of space suggested by string theories and M-theory
- Is space discrete or continuous at Planck scales?
- Does space-time fluctuate at the quantum level?
There are several new background independent (No fixed space-time in the background) mathematical treatments of space-time suggested by theories such as the Twistor theory and loop quantum variables.
Steven Hawking and Sir Roger Penrose have contributed significantly to our understanding of the nature of space-time by authoring (sometimes jointly) many theories about the early universe and the state of space-time at singularities.