Einstein's Theory of Relativity - Time is not what we think it is
According to Einstein:
The motion of an object through space and the motion of that object through time always add up to the speed of light.
Let's think about what that means.
If you are standing absolutely still in one place, (Ok, so that's not actually possible because the Earth is rotating, whizzing round the sun etc, but if it were possible...) then you are not moving through space at all, so all of your movement is through time.
If you then get into a car and start travelling along a road, some of your movement is now through space and a bit less of it is through time so, for you, time slows down a bit. At the kind of speeds we can manage on earth, this effect is so small that we don't notice it.
If we were then to climb on board a spaceship and set off through the galaxy at fifty million miles an hour, we might not notice much of a difference but for every two hours that passed, according to the clock on board our ship, three hours would have passed on Earth, because we would be moving so fast that around a third of our motion would be through space and two thirds through time, so our clock would only tick at two thirds the speeds of the ones back on Earth.
This gives rise to the famous limerick
There was a young lady named Bright
Who could travel much faster than light;
She set off one day,
In a relative way
And came back the previous night
Arthur Henry Reginald Buller, Punch December 1923
and to Science Fiction tales in which space travelers go off-world for a few weeks and come back to find that everyone they knew on Earth has grown old and died during their absence, and they get to meet their great great great grandkids. Science Fiction is difficult to write when you grasp this idea. Unless you get around the problem by travelling through wormholes or have special warp drives that sniff at the limits imposed by the mere fabric of spacetime, Starbase would be long gone by the time you'd boldly been.
So where are we going with this? Well, let's look at some implications.
First, if something could travel as fast as the speed of light, then all its motion would be through space and none of it would be through time, so time would stand still.
Actually, we know that something does travel at the speed of light. Light travels at the speed of light. So for a photon, time does not exist. We'll come back to this later.
The sub-atomic particles within the atoms that make up everything, including us, travel at fantastic speeds, which means that there may well be discrepancies between our own perception of spacetime and that of the materials we are built from.
It is also important to mention that although, within the universe, nothing can travel faster than the speed of light, the universe itself can expand faster than the speed of light because it is not itself bound by the laws that govern its contents, ie it is beyond spacetime. According to the Big Bang Theory, the universe got from stupefyingly small to bogglingly big in less than the blink of an eye and continues to expand at a rate that would leave a mere photon struggling on the starting line!
(For a really good explanation of relativity, wormholes etc using analogies starring Bart and Lisa Simpson, read The Fabric of the Cosmos by Brian Greene.)
Return Home Return to Reality