What is the difference between Lorentz's and Einstein's theories of relativity?

Lorentz's theory of relativity was developed in the late 19th and early 20th century, while Einstein's theory of relativity was published in 1905 and 1915. Both theories deal with the concept of relative motion and the constancy of the speed of light, but there are some differences between the two.

Lorentz's theory, also known as Lorentz ether theory, suggested that a medium called ether permeates all of space, and that the speed of light is constant with respect to the ether. This means that the speed of light would appear to be different for observers who are in different states of motion relative to the ether. Lorentz also proposed a set of equations, called the Lorentz transformation, which describe how measurements of space and time in one reference frame are related to measurements in another reference frame.

Einstein's theory of relativity, on the other hand, rejected the notion of ether and proposed that the laws of physics are the same for all observers who are in uniform motion relative to each other. According to Einstein, there is no absolute reference frame against which all motion can be measured. The speed of light is always measured to be the same, regardless of the state of motion of the observer or the source of the light. Einstein's theory also introduced the concept of spacetime, in which space and time are viewed as two aspects of a single entity, and described the curvature of spacetime in the presence of massive objects.