Although we cannot travel at the speed of light, Albert Einstein used to think about what would happen if we could. According to Einstein’s Theory of Special Relativity, the faster you go, the slower time passes for you relative to your surroundings. This theory means that if you travelled at the speed of light, time would appear to stop.

As the graph above shows, slower objects have faster passages of time than very fast objects, for which time passes much more slowly. When an object reaches the speed of light, it will hit zero on the time axis, which means that it will not have moved at all in the time direction. In other words, when the speed of light is reached, time stops for the traveller!

# To infinity and beyond

As things approach the speed of light, they become heavier. If you were travelling at the speed limit of the universe, your mass would climb so high that it would start to reach infinity! It would require endless energy to move at that weight, which is why it’s only possible for us to reach the speed of light in our imaginations.

Zero mass

Photons, the particles that make up light, have a mass of zero. The non-existent weight of light is why it’s able to move at such incredible speed!