Stephen Hawking is one of a very few contemporary scientists whose name is readily recognized by the public at large. Part of his fame stems from his discoveries in theoretical physics, but much of it has to do with the worldwide success of his book A Brief History of Time. In the years following its publication, Hawking's fame only increased, as he made appearances in many popular television programs. He has also had the rare distinction of being the subject of a feature film, The Theory of Everything (2014).
While lauded for his landmark discoveries that led to the defining theory of how the very large-scale universe behaves, Einstein's activities as a pacifist and Zionist drew considerable criticism. However, Hawking notes in the back matter that Einstein was much more interested in the enduring truths of his equations than in the passing realms of politics. Einstein was also uncomfortable with both determinism (the belief that actions are determined by preceding events or natural laws) and indications that the formation of the universe was based on random events. To this idea, Einstein is quoted as having said, "God does not play with dice!"
Sir Isaac Newton
In the back matter following Chapter 12 of A Brief History of Time, Hawking characterizes Newton as unpleasant and vicious in the face of opposition. Newton's main contribution to science was his Philosophiæ Naturalis Principia Mathematica (1687), which established the foundation of modern physics based on the works of Galileo, Copernicus, and German mathematician Johannes Kepler. Newton is most well-known for his three laws of motion and the law of universal gravitation, which hold true for all matter except at the subatomic (or quantum) level. His work in optics and mathematics also significantly contributed to the "Scientific Revolution" in Europe (roughly from 1550 to 1700) when modern science emerged. Later in life, as Hawking notes, Newton left science for the more lucrative job of catching counterfeiters and ordering the hanging of criminals.
Galileo was a staunch Catholic, which placed him in the crosshairs of the Inquisition (the process of combating heresy established by the Catholic Church) following publications of his observations that ultimately separated science from theology. Despite having been placed under house arrest for life, his final work, Dialogues Concerning Two New Sciences, was smuggled out and has since been acclaimed as "the genesis of modern physics."
Roger Penrose, a colleague of Hawking, is noted for his work on black holes. Together they developed an understanding of Einstein's general theory of relativity, indicating both the origin and ending of the universe. The collaboration between Hawking and Penrose has been, according to Hawking, a particularly fruitful one. In 1970, Hawking and Penrose together proved that "there must have been a big bang singularity" at the origin of a universe such as ours that continues to throw matter apart so that (as has been observed) the universe continues to expand, propelled by that primordial burst.
Copernicus made his landmark contribution to the science of astronomy by establishing a heliocentric model, in which Earth and other planets orbit the sun. This replaced the long-standing geocentric model (in which Earth is stationary at the center, with the sun and other planets moving around it) that had been in place for almost two millennia. By removing God's creation from the center of existence, Copernicus set himself up to the ire of the Catholic Church and its authorities. His On the Revolutions of Heavenly Spheres was completed in 1530, but it was not released until shortly before his death in 1543. The model solved some—but not all—of the discrepancies of the geocentric Aristotelian–Ptolemy model that argued the sun, moon, and planets orbited Earth. It was not until the 1600s that Galileo used the hypothesis developed by Copernicus to explain their observations on the movements of the planets; the law of universal gravitation established by Newton further supported the Copernican model.
Hubble made a series of painstaking measurements of the light emitted by distant objects in space to come to the conclusion that our galaxy is only one of a great many galaxies. In 1929 Hubble observed that distant galaxies are moving away from us, leading to the explanation that the universe is expanding. The idea, according to Hawking, is that if this is so, then it suggests that at some time in the past, everything in the universe was much closer together.