In the theory of general relativity, space-time is not considered to be made up of any particular substance or material. Instead, space-time is a conceptual framework that combines three dimensions of space and one dimension of time into a four-dimensional continuum.
According to general relativity, mass and energy cause the curvature of space-time. Think of space-time as a fabric or a rubber sheet that can be warped by massive objects like stars or planets. The presence of mass or energy creates a curvature in space-time, and objects move along paths determined by this curvature.
The concept of the fabric of space-time is often used as an analogy to help visualize the effects of gravity. Objects with mass create a "dip" in this fabric, causing other objects to move towards them due to the curvature of space-time.
However, it's important to note that the fabric analogy is just an illustration and shouldn't be taken literally. Space-time itself is not a tangible substance or material that can be physically touched or observed. It is a mathematical framework that describes the interplay between space, time, and gravity according to Einstein's theory of general relativity.