1. Is the the speed of light the maximum speed and why/why not?
For a particle which is created travelling slower than the speed of light, the speed of light is the fastest possible speed. The reason is that, in order to accelerate an object, you need to use energy. The more massive (or “heavier”) an object is, then the more energy it takes to accelerate it. You understand this well, as it is easier to throw a ball at 50 kilometers per hour than it is to throw an automobile at 50 kilometers an hour. As an object moves faster, it appears to gain mass (or become heavier). We don't notice this in everyday life, because this effect really only becomes noticeable when you get very close to the speed of light, but scientists have measured and verified this theory in laboratory experiments. In fact, if an object gets very very close to the speed of light, it's mass goes up so fast that it can seem to be infinitely heavy! At this point, it is impossible to gain enough energy to accelerate the object any further.
2. E.g. if you travel in a ship that are well protected from paticle hits or are flying far from all material, would it be possible to gain lightspeed (theoretically) ? and could you increase speed from there ?
No, for the reasons I describe above. It would require infinite energy just to reach the speed of light, let alone accelerate beyond it!
3. If 2 photons emitts from the same source, are not their speed, compared to each other, twice the light speed ?
No. This is a very strange thing about special relativity. Einstein's theory states that, no matter whether you are moving or standing still, light always moves at the speed of light. So, if you were on one photon and looking at the other photon, it would appear to be moving at the speed of light. This is very complicated, and I really cannot explain it via email, but good books on special relativity should be able to help you somewhat. Mathematically, the ideas behind special relativity are very simple, and can be understood with basic algebra. However, a physical understanding of what special relativity means is very difficult to achieve. I'm still not certain that I truly understand it; I just accept it as true (since repeated experiments show these theories are true).
4. In your oppinion, how far are we from common use of spacetravel, collonization and space mining etc.? 50, 250 …?
For colonization and mining of objects in the solar system, we have the technology now to be able to accomplish these things. The major hurdles are economics (space travel is very expensive, and it is hard to justify sending people to an asteroid to mine iron when it is cheaper and safer to mine iron on the Earth) and physiological (we don't know what will happen to astronauts who are in space for years at a time, both physically and mentally). In the next several decades we will probably begin to reach out within our solar system, but it will take economic pressure to establish permanent residences.
As for colonizing other stars, I personally believe that it may take thousands to millions of years, if ever, for us to reach out. The nearest star is four light-years away, but at the speeds of modern rockets, it would take us tens of thousands of years to get there. There are dreamy designs for nuclear powered rockets that may be able to go as fast as 1/10 the speed of light, but even then it would take 40 years to get to the nearest stars. And we have no clue if these stars have planets capable of supporting life! Outer space is much larger than most people imagine, and so I think it will be much longer than most people imagine before we are able to bridge the gaps between stars.
Thanks for writing!
Sincerely, Kurtis Williams