Time Flies

You wake up one morning to find yourself in a completely different bed than the one you fell asleep in.“Where on earth am I?” you think as you slowly try to open your eyes. It is therefore a great surprise when you look out the window and realize you’re not on earth at all. You are in a spaceship. In space.

After a few moments, when the shock is over, you think about how wonderful it would be to lie in your cozy earth bed. This feeling, however, is quickly absorbed by your excitement, as this means you’ll be able to explore all sorts of awesome places. The first thing you notice when you look out the window is that objects seem bluer when they are moving closer to the spaceship, and redder as you pass them. “I wonder why,” you ask.

Of course, you have never heard of the Doppler effect. According to the Doppler effect, waves can stretched out or shrink, depending on which way you are moving. In everyday life, we mostly experience this with sound waves. “Like ambulances?” you ask. And yes, this is just the same. When a car moving towards you emit a sound, it will sound more high pitched. You will observe the opposite effect, when it is passing you. The sound will suddenly drop to a much lower frequency. “So blue represents the higher frequency and red the lower,” you announce excitedly. You are absolutely right. But for this Doppler shift to be noticeable, you would have to be going really fast. And you are.

The spaceship is whizzing by at a speed of 100 000 miles per hour, or about half the speed of light. “I don’t get it, what’s the deal with this speed of light thing?” you start pondering. Well, it turns out that no matter how fast you go, you can never go faster than the speed of light. In fact, nothing that has mass will even be able to reach the speed of light. “Nothing with mass?” you ask. “What does mass have to do with things?” As you approach the speed of light, the universe will start messing with your mass, to make sure the energy required to reach the speed of light becomes infinitely large.  Basically, light itself avoids this problem by not having any mass. You look confused. “But wait, I have an idea!”

“Speed up,” you order. “We have to get as close as possible to this “speed of light” thingy. After a couple of seconds, the spaceship has reached a dazzling 99 % of the speed of light. Now it is my turn to ask, “Why does this help? What are you going to do now?” “I will go outside the space ship and fire a bullet in the same direction we’re going. That way sum of the speeds will be greater than the speed of light, and we can dismiss this cosmic speed limit.” Your face is glowing up like a child who has suddenly understood something.

Unfortunately, your idea is not going to work. Mother nature seems to be taking care of that. The speed of light is always the same relative to the observer. Let us illustrate this with an example. You are on a train moving super-fast, very close to the speed of light. As you proposed, you could fire a bullet forwards from this train. Relative to you, the bullet goes quite fast, and relative to the ground, the train is moving very quickly. Therefore, an observer on the ground would be able to see a bullet flying as fast as the sum of the two speeds. But this is not how nature works. In order to hinder you from achieving this speed, time will literally slow down relative to the observer. This means, you could bring a watch, and after the journey, it will end up showing a completely different time than another one. This is not because your watch is terrible, but simply because time went slower.

You don’t seem to like what you’re hearing and you sit down, quite disappointed. However, no more than a minute later, you jump up and scream, “What if we hit the edge?!” “Hit the edge?” I respond. “Well, I’ve heard the universe is finite (it is not infinitely large), so with this speed it may not be long until we hit the edge.” “Don’t worry,” I say. “There is no edge.” You look even more confused. “That statement didn’t make sense at all.”

It is really not that weird, though. The earth is a sphere with a finite surface area. However, it is impossible to fall off the edges. The same thing goes for space in general. We live in three dimensions, while space itself has more dimensions. We are ants on sphere, never able to experience what it must be like to escape from this hypothetical sphere. “So, how many dimensions are there?” you ask. Some scientists say four, others as much as six or seven. In fact, people working on what is called string theory believe there must be exactly 11. “What? Why eleven? How do they know?” Your string of questions gets longer and longer. “That is for another time,” I say, leaning back in my chair, dosing off into another dimension…

-William Lohrmann