Before 1905 there wasn't much to say about time. In the 17th century Newton defined time as something that continues, no matter what, without any link with reality and according to its own nature. Everybody believed that time had its influence on the environment, but if you believed that the environment had its influence on time, you really had to be mad! That changed in 1905 with Einstein's special relativity theory, in which he showed that time can be influenced. But this doesn't mean time can be changed in such a way that you can travel to the future or the past. That's what it's all about on this pages: Is it possible to travel through time, and if possible, under which circumstances? 
                It will become very clear that the speed of light has got a major influence on the possibility of time travelling. An object should move faster than light speed to travel through time. Therefore we use the tunnel effect, an effect in the quantum mechanics. That means that a ray of light or a bundle of electrons that is sent through a certain barrier arrives sooner at the other side of the barrier than if there wasn't a barrier. 
                If time travelling is possible according to the relativity theory, there will be a lot of other problems. I'm not talking about the technical problems, 'cause that's not what this is about, but I mean the paradoxes. For these problems there is no such thing as a logical explanation, no matter how long you'll search. 
 

II) Relativity

                There are 2 sorts of physics: Newton's physics and Einstein's physics. When you use formulas from Newton and formulas from Einstein's physics to calculate a certain physical value, you'll become not the same value. In 'normal' situations these differences are extremely small. But in 'extreme' situations these differences will become very big. For example: someone who's in a train that moves with an incredible high speed (like 10 000 km/second) and who measures the distance between the sleepers of the train, will measure a smaller distance than someone who stands still beside the railway. According to the physics of Newton and our intuition we'd say the distance would remain the same. In 'normal' situations that's correct: measuring in a train that moves at hundreds, thousands or even ten thousands kilometers/hour would make the difference in distance immeasurably small. Newton's laws would certainly do in these situations. But when the speed of the train approaches the speed of light, the difference will become noticeable ('extreme' situations), and we would need Einstein's physics. According to the latest experiments, Einstein's formulas seem to be the right ones.

                Einstein's special theory of relativity was finished in 1905. It's based on the constant speed of light and the fact that speed isn't absolute; when a helicopter lifts off you can also assume it's the chopper that stands still and the earth that moves. This theory describes the relation between observation of a certain phenomenon by observers that move with a constant speed related to each other. 
                The general theory of relativity was finished in 1912, but Einstein couldn't interpret his mathematical reasoning physically. He redeveloped the theory, not only based on mathematics but also on physics, and he ended up with the same result as 3 years earlier. Then he published it. This theory describes on one hand the relation between the observations of the observers that move with an accelerating speed related to each other. On the other hand it's about the influence of gravity on observations and the relation between observations that are done from places where gravity differs. Because a constant speed can be looked at as a speed with acceleration 0, the general theory of gravity includes the special one. 
 
 

Want a trip through a black hole without having to experience that pesky death? You're in luck. There's a special kind of black hole that's not just survivable, but might get you to another time, or another universe.

Black holes are, traditionally, the scariest things in the universe. Huge, mysterious, inescapable, they wander through the universe and eat everything that gets too close. "Too close" is defined by their event horizon. This is the point at which they go dark, because it requires so much energy to escape them that not even light can get away. Since not even a photon can cross the barrier, no event that happens inside the horizon can ever have an effect on people outside.

Unless, something very odd was going on in the center of the black hole. Most black holes spin - this is something that was discovered way back in the 1960s by physicist Roy Kerr. It wasn't exactly a shock, because most of the material that collapses into a black hole was already spinning. Sometimes, however, the spin on Kerr black holes goes a little above and beyond. Ever spun a glass of water, or soda bottle, so that the liquid inside swirls? Sometimes, if you spin it enough, the liquid actually parts, leaving a clear center and a spinning ring of water around it. The same kind of thing can happen in Kerr black holes. Instead of a singularity at the center, there's a ring. And you can go through the open portion of that ring without touching the gravitational crush.

What's on the other side? A lot of people have wondered. Some people think that these kind of black holes might be our key to time travel. They might be wormholes that let us hop between different points of the universe. Or they might be portals to different universes entirely. First we'll have to find a few, and then we'll need a few volunteers to go through. Preferably ones that haven't seen Event Horizon.