Flowermountains

Everything is Relative

This is part two in my quest for the holy grail: the meaning of life. For part 1, see here. Now I will shed some light on the issue of light itself, going back a rough century to the time of Einstein’s great theories. Why light? Since it is this particular phenomenon that triggered Einstein into completely changing the way people (read: scientists) see space, time, and the universe as a whole.¹

What happened? Well, some years earlier, other people had shown that the speed of light is a constant, no matter how you look at it, it’s always the same. So, what would happen if you’d run after a departing beam of light, fast enough to catch up? What would you see? Would light “stand still”? Apparently things are not that easy, and Einstein concluded that, no matter how fast you would run, you wouldn’t gain an inch! The speed of light is still constant, no matter how you look at it, no matter how fast you go. This and some other stuff led to Einstein’s theory of relativity. In short, the idea is that when you travel with constant speed in a closed chamber, there is no way for you to determine at what speed you are moving. Any experiment you run will result in the same findings, whether you are at rest, or moving at any constant speed. Motion is relative, and only defined in comparison with something else. Still following? Now the interesting part starts.

This theory has some interesting implications. Most importantly, the notions of “space” and “time” as being universal, like we’re used to, are not exactly true. Let’s start with time. Suppose you take two exactly identical, very precise clocks, and you send one of them on a tour around the earth in a very fast airplane while leaving the other one behind. Upon the return of the airplane, you compare the two clocks. You would then, to your surprise probably, find that according to the clock in the airplane a little less time has passed since departure. You can imagine this as follows. Remember high school geometry? When an object moves in three dimensions, it’s speed is divided between the three axes. When it moves at constant speed, any change in direction will cause the portion of speed along each axis to change, but the total speed (the sum of the partial speeds) remains the same. Now, change the object’s three dimensional space into a four dimensional version, with the fourth dimension being time. According to Einstein, every object always moves at constant speed through the four dimensional spacetime, and this constant speed is equal to the speed of light! When an object is at rest, all of it’s movement in concentrated along the time-axis. However, when moving, some of the time-motion is diverted to movement through space! Thus, also the notion of time is relative. Reasoning one step further, this also means that, when travelling through space at light-speed, there is no movement through time anymore. Light is timeless.²

Some similar reasoning leads to the conclusion that also space is relative: objects that move very fast seem to be slightly shorter than when they would be at rest. However, I don’t think this is very important to the rest of the story so I won’t delve into this.

Maybe it’s wise to take a break here. This stuff requires some time to settle in. In fact, I’m getting slightly confused again myself. Next time we’ll see how all this influences the idea of “force” and why we have still some problems with that. By the way, as a small reference, most of what I explain here is based on a book by Brian Greene, called “The Elegant Universe”. If this stuff interests you, I can really recommend this book. It almost reads like a novel.

¹Being a social scientist who is studying science, I could easily go into a discussion about the relation between scientific ‘truth’ and ‘what is really out there’. You know, everything is socially constructed in some way. There is no neutral, objective science. Oh well. I’ll save this for later.
²I think this also explains why light always seems to move at the same speed, no matter how fast you go. Speed, after all, is depending on our notion of time.