The twentieth century brought forth some of the greatest scientists the world has ever know. Physicists such as Niels Bohr, Max Planck, and Albert Einstein made extraordinary discoveries about light, atomic structure, and time which would uncover some of science’s greatest mysteries. Despite the importance of these theories and discoveries, most people find them difficult to understand as they can become quite complex. Luckily, Carlo Rovelli wrote a book to explain said ideas on physics to those who are completely unaware of the subject matter. His book Seven Brief Lessons on Physics summarizes the most interesting and important discoveries over the past century while explaining how it fits into the bigger picture of our understanding of the universe. Rovelli begins by explaining Einstein’s education. Einstein spent a year in Italy, after abandoning his high school and going to some university lectures for fun. After that, he began studying physics and soon wrote three major theories: one was about atoms, one on quantum mechanics, and the other about special relativity. However, his theory of relativity was flawed as it didn’t properly correspond with the law of gravity. Einstein was then inspired to write his theory of general relativity. The theory combines special relativity and Newton’s law of gravity, as it integrates the two to make an explanation of gravity as a geometric property of space and time or spacetime. This also gave light to how time passes slower when there are more gravity and vice versa. Einstein’s theory completely changed our perception of time and showed how gravity affects space-time.The next chapter focuses on quantum mechanics and quantum theory. Rovelli begins by explaining how Max Planck gave birth to quantum mechanics. Planck attempted to divide energy into small packets where he discovered that electromagnetic energy could only be emitted in a quantized form. Einstein showed that light truly is quantized as he discovered the idea of energy quanta and photons. Bohr then theorized that when electrons jump from one orbit to another with lower energy, a light quantum is emitted. Rovelli explains that quantum mechanics does not explain where particles are but rather the probability of where they are. These particles can only be located during a collision and therefore scientist uses these complex mathematical formulas to determine where particles are in between collisions. Rovelli then takes us from particles to the universe as he explains how humans understand the structure of our universe. People began by making general assumptions about the universe. Many saw the earth merely the ground below us and the sky was above. Anaximander was the first ever astronomer. He discovered that Earth is suspended in space and advocated the idea of an open universe worldview which would soon replace the closed universe view. The next great astronomer would be Aristotle. He recognized that the Earth was not flat, but rather a sphere. What he failed to discover was that the Earth revolved around the Sun as he believed the sun and the cosmos revolved around the Earth which was at the center of the universe. This geocentric theory of Aristotle would continue until Copernicus would create the heliocentric theory meaning that the sun is at the center. From then on humans began discovering more and more in astronomy and we can now see solar systems light years away. Rovelli explains how we as humans currently understand the universe as ever-expanding whose boundaries we cannot observe. Seven Brief Lessons on Physics by Carlo Rovelli explains how the great physicists of the 20th century helped to shape our understanding of the universe today. He does this by going through scientists such as Albert Einstein and Neils Bohr’s discoveries and then explaining the ideas in layman’s terms. Rovelli’s book has helped me to better understand physics and some of the more complex theories of the 20th century. I find he does this well when relating these theories to the real world as well as making analogies to guide the reader. I find Einstein’s theory of relativity a fascinating discovery in the book. It completely changes how we as humans perceive time and the dynamic of space. I recall watching the movie Interstellar which has Einstein’s theory play a prevalent role as the astronauts travel to different planets with different gravities which lead to drastic consequences. Rovelli helped me to understand the scientific portion of this movie even more so now, and I can’t wait to watch it again with my newfound knowledge.