This is a story about spacetime...

We all know what Euclidian geometry is, right? Up & down, left & right, forwards & backwards. We know how to draw a triangle, a square. We know how to calculate the volume of a cube, a sphere, a cone. We even have methods of calculating where the points of 3-dimensional object will be, if we rotate it. We can use matrix transformations to do a rotational calculation, and work out where the corners of a spinning cube are going to be.

But what about when space gets all stretched and weird? What about non-Euclidian geometry?

If I draw two lines on a flat piece of paper, they will intersect at some point unless they are perfectly parallel. If I draw two 'straight' lines on a 'flat' hyperbolic plane, they will curve away from each other and not intersect. Even though both lines and both planes are 2-dimensional, the behaviour is very different, depending on the geometry.

Do you think you live in a 3-dimensional universe? Wrong.

So, you think you live in a 4-dimensional universe, where the 4th dimension is time? Also wrong.

You live in a 3 dimensional universe where the speed that you are travelling at relative to everything else affects the curvature of spacetime. Pretty obvious, huh?

So, if you're not moving relative to the things that you can see, then you are moving in time. If you're moving relative to something else, then you are moving in space, and ever so slightly less in time than the other object(s). Is that clear?

If I get in a rocket and fly away from the Earth at the speed of light, and fly back again at the speed of light. The whole time I was on the rocket, I was moving in space but not in time. The speed of light is the speed limit of the universe, so if I was travelling at the speed of light, then time stood still for me. However, the Earth was not moving anywhere, so it was moving at full speed through time, but not at all through space. Is this making sense?

Here's an example: let's say I travel to the moon and back. The moon is 384,400km away, so I travelled 768,800km. The speed of light is 299,792 km/s, so the round trip took me 2.6 seconds, according to your stopwatch. According to my stopwatch, my trip took me 0 seconds.

Why did it take me zero seconds to travel to the moon and back at the speed of light? It's simple really: because I was travelling through space at the maximum possible speed, so therefore I was not travelling through time at all.

Why did the person on Earth with the stopwatch record a time of 2.6 seconds for me to travel to the moon and back at the speed of light? Again, it's pretty simple: the person on Earth was not moving at all through space, so therefore they were travelling through time at the maximum possible speed.

This is the nature of spacetime: any movement through space means less movement through time, as measured by an independent observer. When you're jetting through space in your rocket, your clock doesn't seem to be ticking any slower, but the independent observer can verify that time had indeed slowed down for you when you get back to Earth and you compare your clocks.

We have just described special relativity and minkowski spacetime.

Albert Einstein is the headline act for special relativity, but it was Hendrik Lorentz who was the mathematical genius behind figuring out how objects move in minkowski space, and of course it was Hermann Minkowski who came up with the special geometry where the wonders of spacetime play out.

I got very excited a few years ago because neutrinos had been detected arriving on Earth from a distant supernova, before photons (particles of light) and this was reproduced in an experiment between CERN and Gran Sasso in Italy, 730km away. The experiment's results seemed to suggest that neutrinos were travelling 8km/s faster than light.

We all learn at school that nothing can travel faster than the speed of light. So far, special relativity has proven to be a pretty robust piece of science. Discovering something travelling faster than light would have meant tearing up the physics textbooks and going back to the drawing board.

However, the beautiful theory and equations proved to be correct. The experiment was found to be flawed due to faulty timing equipment. Damn. No time travel for us, unless maybe you're made of antimatter.

By the way, I made a little Lorentz/Lorentz joke at the start, because I was thinking of writing about chaos theory. Perhaps I'll save that delight for another day. Let's see how this one goes down before I delve into any more topics that I have a shaky understanding of.

Tags: #physics