"The fact that light travels at a finite, but very high speed, was first discovered in 1676 by the Danish astronomer Ole Christensen Roemer...his value for the speed of light was 140,000 miles per second, compared to the modern value of 186,000 miles per second...
Einstein made the revolutionary suggestion that gravity is not a force like other forces, but is a consequence of the fact that space-time is not flat, as had previously been assumed: it is curved, or 'warped', by the distribution of mass and energy in it. Bodies like the Earth are.not made to move on curved orbits by a force called gravity; instead, they follow the nearest thing to a straight path in a curved space, which is called a geodesic. A geodesic is the shortest (or longest) path between two nearby points...
Up to the beginning of this [20th] century people believed in an absolute time...However, the discovery that the speed of light appeared the same to every observer, no matter how he was moving, led to the theory of relativity - and in that one had to abandon the idea that there was a unique absolute time...Thus time became a more personal concept, relative to the observer that measured it..."
Einstein's revolutionary suggestion (second para above refers), in my understanding, extends Newton's law(s) of gravity. It's just that Einstein's general theory of relativity, predicted a slightly different motion, from Newton's theory.
Hawking points out that, the general theory of relativity, is only one of two basic partial theories explaining the universe, however. The other, quantum mechanics, is not entirely consistent with relativity (at least that was the case in 1999)..
Roger Penrose and Stephen Hawking demonstrated that Einsteins's general theory of relativity implied, that, the universe must have a beginning (from a point of singularity) and perhaps, an end.
Reference: 'A Brief History Of Time' by Professor Stephen Hawking, Bantam Books, (1999, original 1988).
I have a later paperback edition and the quotes are from pages, 21, 33-34 and 159.
Issac Newton (1643-1727)
Physicist, mathematician, astronomer, author, inventor - English polymath
Albert Einstein (1879-1955)
Theoretical physicist - German born
Roger Penrose (born 1931) English/British
Mathematician, Nobel Laureate in Physics
Stephen Hawking (1942-2018) English/British
Theoretical physicist and cosmologist
When Steve Harley (1951-2024) wrote some of his lyrics, he could touch upon some deep ideas and questions, in my view. Music and science make appropriate bedfellows, I may have referred to this before. All the best. X