Isaac Newton’s fundamental work on motion and gravity may have been challenged by Einstein’s theories in the early 20th century; but the ideas and mathematical foundations laid out in *Philosophiae Naturalis Principia Mathematica*,more commonly known as the *Principia, *are still relevant. Most recently, in the European Space Agency’s mission to deploy the Philae lander on a comet, Newton’s theory of gravity played a crucial role.

“It’s all down to Isaac Newton now,” said European Space Agency senior science advisor Mark McCaughrean. “It’s down to the laws of physics.”

One of the most essential fields of study within space missions is the study of orbital mechanics. Orbital mechanics rely on the laws of universal gravitation to predict how space crafts, planets, and stars behave near one another. A look into the life of the man responsible for the fundamental theories which have made space missions, like the Rosetta mission, possible may help us appreciate how far we have come in the realm of science.

Born in 1643 in England, Sir Isaac Newton left behind a life as a farmer to study at Cambridge, where he was exposed to the beginning of the scientific revolution started by Copernicus, Kepler, and Galileo. While Newton studied the sciences, he also gained a key interest in philosophical questions.

After Newton’s graduation in 1665, he was forced to return home for 18 months due to the plague sweeping Europe at the time. During this time, thought to be his most productive, he generalized the results of the binomial theorem in mathematics, began developing his ideas of light, colour, and optics, and laid down some of the early foundations for calculus. In this period, it is said that Newton observed the falling apple that would inspire his theory of universal gravitation.

Upon returning to Cambridge, Newton’s scholarship became more widely recognized. He began to expand on his theories of light and colour, proposing that light was made up of particles and that white light was composed of many different colours. While his particle theory of light struggled against the wave theory proposed by other scientists, his ideas were still very influential, and were publishedin his book *Opticks*.

More influential was his work on planetary motion and the movement of bodies. This work was published in 1687, with support from astronomer Edmond Halley after a period of intense study, as the *Principia*. In this work, Newton laid out his famous three laws of motion and used them to make many accurate predictions of the motions of the planets, as well as detailing motion of fluids and sound waves. It was not until the end of the 19th and beginning of the 20th century that the theories of quantum mechanics and relativity would begin to bring Newton’s work into question.

While Newton was a prolific and influential scientist, he faced many challenges, particularly in the form of volatile disputes with his contemporaries. Accomplished scientist Robert Hooke initially challenged Newton’s views on light, leading to friction between the two during the 1670s and 80s. Later, Hooke accused Newton of plagiarizing his idea of a gravitational inverse square relationship, relating the force between bodies to their distance from each other, which Hooke had mentioned in a correspondence with Newton.

Similar difficulties arose between Newton and German mathematician Gottfried Wilhelm Leibniz in the early 1700s. Both men claim to have developed the theoretical foundation for the technique of calculus, a dispute which to this day has not been fully resolved.

Newton also suffered from anxiety and experienced several nervous breakdowns which interrupted his work and study.

Newton may have been a difficult scientist to work with but his crucial contributions to math and physics are just as important today as they were over 300 years ago.