Nothing in the cosmos can travel faster than light speed. By distinguishing cause and effect and stopping everything happening in a jumbled mess, our existence depends on it



Physics



17 November 2021

Anna Bliokh/Getty Images

TIME, various wags supposedly said, is nature’s way of stopping everything happening at once. That might not be the most useful way of thinking about things, however, not least given our confusion about how time works (see “Why does time only move forwards?“). Take a long, hard look at physics today and it isn’t time that stops everything happening at once – it is light.

The idea that light always travels at the same speed, and that nothing can travel faster than that, is hard-baked into modern physics. It is still difficult to get your head around the mind-boggling consequences. Think of travelling in a spaceship with the beam of your headlights zinging off in front of you into the vacuum of space. A stationary observer outside your ship would see those photons travelling at light speed – 299,792,458 metres per second, for those taking notes. The crux is that so would you, no matter how fast your ship was travelling in the same direction.

According to Albert Einstein’s theories of relativity, which he developed in the early years of the 20th century, space and time themselves warp to accommodate the otherwise insurmountable contradictions that arise from light’s absolute speed.

His special theory of relativity gives a mathematical explanation for the cosmic speed cap: as objects with mass accelerate to higher speeds, they require more and more energy to keep them accelerating. To attain light speed, you need infinite energy – an impossibility. Light only gets a free pass as it has no mass, as …

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