Free Astronomy Magazine November-December 2021

25 ASTRO PUBLISHING NOVEMBER-DECEMBER 2021 The reason why no mass-endowed body, from the lightest subatomic particle to the largest of stars, can- not exceed nor even reach the speed of light was explained over a century ago by Albert Einstein in his Theory of Relativity. The more the speed of a body increases, the more energy it takes to accelerate it fur- ther. As it approaches the speed of light, the mass tends to infinity and requires almost infinite energy to increase the speed by an infinitesi- mal amount. Even the smallest mass existing would need more energy than is available in the entire uni- verse to reach the speed of light. Conversely, all massless particles, such as photons, are forced to travel at the speed of light. This fact makes some scenes from other TV series bizarre, where humans are seen interacting with entities made up of pure energy that remain es- sentially stationary in space. The reason why massless particles them- selves cannot exceed the speed of light is also explained by the Theory of Relativity: the more its speed in- creases, the more time slows down (said in a nutshell) and, at the speed of light, time stops. For the photon and other massless particles, time does not flow − everything happens instantaneously. To overcome the speed of light, time would have to slow down even further, but being already stationary at this point it cannot do so any further and can- not begin to flow backwards. Over the last century, the Theory of Relativity has received hundreds of experimental confirmations relat- ing to dozens of different physical phenomena. If it were possible for