What is space and time?
 

Space:

Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework.

Space is one of the few fundamental quantities in physics, meaning that it cannot be defined via other quantities because nothing more fundamental is known at the present. On the other hand, it can be related to other fundamental quantities. Thus, similar to other fundamental quantities (like time and mass), space can be explored via measurement and experiment.

Today, our three-dimensional space is viewed as embedded in a four-dimensional spacetime, called Minkowski space (see special relativity). The idea behind spacetime is that time is hyperbolic-orthogonal to each of the three spatial dimensions. 

 

Many Physicists believe that unlike ponderable matter, space has no objective existence or physical properties of its own. It may appear to have properties e.g., the permittivity and permeability of free space, or during pair production which is the creation of a subatomic particle and its antiparticle from a neutral boson. However, these properties belong to the particles themselves and not to empty space, which is simply a dimensionless location.

​

​

Time:

​

The same probably applies to time, it is simply a relative, changing point in the axis of time where matter interactions are taking place. If the Universe was empty, without matter, energy, or any interactions, then the Universe would likely not exist at all. 

 

Time travel to the future is possible but time travel to the past is not possible because it violates the second law of thermodynamics, which states that entropy or randomness must always increase. Time can only move in one direction, in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.