Upending Our Understanding of the Universe

It is by far the most famous equation in the history of science - and one of the shortest: E=mc2. Derived by Albert Einstein in 1905, the equation describes the relationship between mass and energy, stating that the total energy contained in a given piece of matter is equal to its mass times the speed of light squared. Given that the speed of light is a whopping 299,792,458 metres per second, this means that a single gram of matter contains some 89 Terajoules of energy - enough to power 17,000 homes for a year. Put another way, while the Little Boy atomic bomb dropped on Hiroshima on August 6, 1945 contained 64 kilograms of enriched uranium fuel, only a tiny fraction of this - around the mass of a paperclip - was converted into pure energy. Put it yet another way, a typical adult male weighing in at around 90 kilograms if completely annihilated would produce a release of energy equivalent to about 1,400 times that of the combined energy released by the bombs dropped on Hiroshima and Nagasaki. Thus, despite just sitting there on the toilet watching this video, you contain an incredible amount of energy. But how did scientists manage to measure something as inconceivably speedy as light, and what on earth does the speed of light have to do with mass and energy? The story of science’s quest to understand the mysteries of light is a fascinating one, full of brilliant figures, frustrating dead ends, and revolutionary discoveries that completely upended our understanding of time, space, and our place in the universe. Since the dawn of history, humans have understood that light is very fast indeed. After all, when lightning strikes, the light seems to arrive near-instantly, while the thunder can take several seconds to catch up. Just how fast, however, long remained a subject of considerable debate, with many ancient philosophers including Aristotle arguing that the speed of light was infinite. In the 10th and 11th centuries, Islamic scientists Ibn Al-Haytham and Ibn Sina suggested that the speed of light was finite, but too fast to measure using existing methods. It was not until 1638 that the great Italian scientist Galileo Galilei devised the first mildly practical, if inconclusive, method for measuring the speed of light. In Galileo’s experiment, two people carrying covered lanterns would stand a pre-measured distance apart. One experimenter would uncover his lanterns, while the other would uncover his the moment he saw the light from the first, with the delay between the first and second signal being measured. The two experimenters would then move farther apart and repeat the procedure. In theory, this method would compensate for both experimenters’ reaction times, allowing the actual speed of light to be measured. At the time, however, Galileo was under house arrest and almost nearly blind, and was unable to actually carry out his experiment. It was not until 1667 that members of Florence’s Accademia del Cimento finally tried out Galileo’s method. Unfortunately, even at great distances the delay between the two lantern signals was so small as to be unmeasurable, leading the Academy to conclude that the speed of light lay somewhere between 10,000 kilometres per hour and infinity. Given the lack of experimental evidence to the contrary, the theory of infinite speed would hold sway for many decades, vigorously supported by leading enlightenment thinkers like French philosopher René Descartes, Five years later, however, a 28-year-old Danish astronomer named Ole Rømer arrived in France to take up a position at the Paris Academy of Sciences. His first assignment... This is an abridged version of a video on our channel TodayIFoundOut which you can check out and subscribe to here:    / @todayifoundout