According to the theory of general relativity, matter and energy are the sources of gravitational fields, and they curve or distort the fabric of spacetime around them. This curvature of spacetime is what we perceive as gravity.
The concept of curved spacetime can be a bit abstract, but the basic idea is as follows: In the presence of matter or energy, spacetime is not flat and Euclidean as we often think of it, but instead, it becomes curved or warped. Think of spacetime as a flexible rubber sheet. If you place a massive object, such as a planet or a star, on the sheet, it will create a depression or dent in the sheet. Similarly, the presence of matter or energy causes a curvature in spacetime.
Other objects or particles that come near this curved region will then follow paths dictated by the curvature of spacetime. This curvature alters the straight paths that objects would normally follow in the absence of gravity. Instead, they move along curved paths determined by the geometry of the curved spacetime.
To visualize this, imagine rolling a ball on the rubber sheet. The ball will naturally roll toward the dent created by the massive object due to the curvature of the sheet. In a similar way, objects in the presence of a massive object move along paths determined by the curvature of spacetime created by that mass.
The mathematical framework of general relativity describes this curvature through Einstein's field equations, which relate the distribution of matter and energy to the curvature of spacetime. These equations explain how matter and energy act as the sources of gravity, causing the curvature of spacetime around them.
In summary, matter and energy curve spacetime because they create a gravitational field, and the presence of this field causes spacetime to become curved or warped.