How did the plague years of 1665 and 1666 affect Isaac Newton’s scientific work?

When the plague forced the closure of the university in 1665, Isaac Newton returned home for approximately two years. This period of isolation provided him with the leisure to contemplate his studies, leading to a remarkably productive era of scientific discovery that he had previously kept confined to his notebooks.1

During these years, Newton achieved several foundational breakthroughs:

• Mathematics: He laid the groundwork for calculus.1
• Optics: He expanded his insights into an essay titled "Of Colours," which contained the core ideas later elaborated in his Opticks.1
• Mechanics and Gravitation: He analyzed circular motion and applied his findings to the Moon and planets. This work allowed him to derive the inverse square relation—the principle that the force acting on a planet decreases with the square of its distance from the Sun—which became essential to his later law of universal gravitation.1

Despite the significance of these contributions, Newton did not share these discoveries with the world at the time.1