Actually, you CAN travel faster than the speed of light

By GrabBag | CrackpotPhysicist | 7 Oct 2020


You may have heard that it's impossible to travel faster than the speed of light. But actually, this is a totally inaccurate representation of Einstein's Theory of Relativity. It all depends on your perspective. Let me explain.

Let's say you're the pilot of a super-fast spaceship. You're going to fly a hundred lightyears to some distant galaxy.

So you push that throttle forward. Your speed increases, your theoretical rocket is generating more and more thrust, which is increasing your acceleration more and more. Looking out the windows of the cockpit, it appears as though the whole universe is flattening around you, pushing you closer to your destination and further away from the starting point. You arrive, having travelled a hundred lightyears in only one year. No laws of physics violated, no ripping holes in the space-time continuum. This is perfectly possible.

But now let's look at it from the perspective of a person watching the rocket launch from Earth. They witness the spaceship accelerate but never exceed the speed of light. It will get very close to the speed of light, but the journey will appear to take longer than a hundred years.

So there's a difference in perception between a relatively stationary thing (Earth) and a relatively fast thing (spaceship). Let's take this to the extreme. What's the perception of a beam of light travelling at the speed of light? This seems like a strange question because light doesn't have a consciousness, but this thought experiment helped Einstein understand the secret behind relativity.

If you were a beam of light emitted from a star, your life would be very short. The instant you are born, you're also colliding with an object hundreds of lightyears away. A light ray's birth and death are in the same instant. In other words, light doesn't experience time. In different other words, it experiences infinite speed.

But you've probably heard that scientists have measured the speed of light, and it has some absolute value. And if we observe really fast things from our relatively stationary vantage point, nothing ever beats light in a race. Why is this? The answer is time dilation.

Let's talk about something that happened in real life. In the Hafele–Keating experiment, scientists put super-accurate atomic clocks into airplanes and flew them around the world. At the end, the clocks in the airplanes were different from one on the ground. This experiment has been done multiple times and each result agrees with Einstein's predictions.

So time dilation is a real thing: different observers can have a different perception of time. A different perception of time leads to a different perception of speed. That's how it works.

So the next time you're on the throttle of a spaceship, travel the galaxy without worries! You can visit any destination you want in the blink of an eye! Spend an entire lifetime travelling the furthest reaches of the galaxy, then return home to a polluted wasteland! Oh, right, I forgot to mention. From Earth's perspective you never exceeded the speed of light, so your exploits took millions of years. Human civilization is long gone by the time you come back.

You'd never be able to order a package from an alien colony hundreds of lightyears away. By the time your goods arrive, you're dead. However, you could travel the entire known universe in one human lifetime with an acceleration no more than 1G, less than half of what modern day rockets are capable of (though in all fairness, no rocket today can hold that thrust for the duration of a human lifetime).

If, on the other hand, you had a wormhole to travel through, that's a different story. We'll save that topic for another day.

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