According to our current understanding of physics, as described by Einstein's theory of relativity, Einstein's statement that time and space are relative is considered to be more accurate than Newton's assertion that time and space are absolute.
Einstein's theory of relativity, specifically the theory of special relativity and later the theory of general relativity, revolutionized our understanding of space, time, and the relationship between them. According to Einstein's theories, the fabric of spacetime is not fixed and absolute, but rather can be influenced by the presence of mass and energy.
In special relativity, Einstein introduced the concept of spacetime, where time and space are interconnected, and their measurements can vary depending on the relative motion between observers. This theory revealed that time dilation occurs when an object moves relative to another observer, resulting in time appearing to pass more slowly for the moving object compared to the stationary observer.
In general relativity, Einstein extended these ideas to include the effects of gravity. Gravity is no longer seen as a force acting between masses but rather as the curvature of spacetime caused by the presence of mass and energy. This theory explains how the geometry of spacetime is influenced by massive objects and how this curvature affects the motion of objects, including the path of light.
Regarding Maxwell's statement about the speed of light, it is indeed true that according to Maxwell's equations, which describe electromagnetic waves, light travels at a constant speed in a vacuum. This speed is commonly referred to as the speed of light in a vacuum and is approximately 299,792,458 meters per second (or about 299,792 kilometers per second).
Einstein's theory of relativity built upon Maxwell's work and provided a framework that explained the constancy of the speed of light in different reference frames and how it is a fundamental limit in the universe.
In summary, according to our current understanding of physics, Einstein's theory of relativity supports the notion that time and space are relative, while Maxwell's work on electromagnetism confirms that light does travel at a constant speed.