So here’s a brain twister! If you were in a supercar of the future going at the speed of light and turned on your headlights, would the beam of light project outwards? Would the car add to its speed or would it simply not light up since there’s no relative speed difference?
The first thing to note here is that no matter how far we progress into the future, cars can never travel at the speed of light, EVER. This is because only massless particles like photons can travel at the speed of light, and objects with some mass will require infinite amounts of energy to accelerate it to the speed of light. No matter how much energy you pump in it will always travel at a speed less than the speed of light.
Rephrasing the question, “What would the situation if the car were going at 0.9999999 times the speed of light?” The answer is that things that move at the speed of light can’t even use headlights! This is where the craziness of relativity comes into play, so don’t be confused if you don’t get it the first time.
This can be explained by the idea of time dilation, but we’ll have to detract from our main question to put things in order. Take an example of two friends passing each other in two trains. If they peek through the windows at a wall clock in each other’s cabins, they will see each other clock’s run slower. This isn’t because the clocks have actually gotten slower, it’s because people moving faster than you age slower. Time isn’t some absolute thing ticking through the universe, it solely depends on the way we travel through the universe. It is, in fact, the same problem again dealing with different directions through space-time. The spacetime has a geometry that our primate brains simply can’t handle which makes us view time as something absolute. Nonetheless, it remains a fact that people moving quickly relative to you, age slowly.
And you don’t have to take our word for it. You can actually work out how much more slowly do they age. If you age for one second, then your friend in the superfast train will age according to the formula,
of your seconds, where v is their speed and c is the speed of light
Now coming back to the hypothetical car which is moving at the speed of light. Try to put the values into the same formula,
It looks like time doesn’t pass for it at all! Yes, you read that right! Time stays still for things moving at a speed of light. This means that things moving at the speed of light can’t experience things ‘happening’ the same way we can. Things can happen, they can perform actions, but they can’t experience it!
As Einstein himself once said,
“Time exists so that everything doesn’t happen at once”.
So for a vehicle traveling at the speed of light, light can never be experienced, or the switching on of the headlights. The light can travel for billions of years before a single second passes for it! So our vehicle can travel forever before an instant even began for it since it experiences no time.
I mean, like, woah.
Watch the video below for a more illustrative explanation!