What Is Physics?

We can consider the founding father of physics to be Sir Isaac Newton (1642–1726). Newton’s physics became known as ‘classical physics’ and reigned until Einstein questioned the basis of understanding in physics by asking a key question like, “What if the speed of light is finite?” In another challenge to Newtonian classical physics, Einstein’s general theory of relativity led to explaining the bending of light in a gravitational field. This was first observed in a total solar eclipse on May 29^th, 1919 by a team led by Sir Arthur Eddington. These different areas of physics marked a transition from a Newtonian understanding of the universe to an Einsteinian one. Newtonian mechanics was an approximation still valid at speeds much less than the speed of light, which remains a defining boundary between the two.