Hi,
two weeks back I wrote about the movie Arrival. I did not really get into the problems that arise when somebody knows the future, I will try to settle this today.
Alright, lets say that you just acquired the ability to know what will happen in the future. Cool huh?
First problem, do you have free will (meaning if you can choose to do something or there is no way to actually choose anything)? Lets start with the answer: yes, you have free will. Basically two things can happen, if you truly know what will happen then you can not choose any other option which means that by knowing the future you and everybody else will lose free will if you could choose something else than what the ability tells you then it would not be telling the future. Something else could happen though, you could know all the possibilities that arise from your decisions and the decisions of others. Funny would be if you would see it for the decisions of others, then the ability would be useless for longterm predictions where people all across the globe would interconnect with their decisions (do animals have free will, which ones do and which ones do not?). You could for example see that in 40 years there are couple (a lot) of lines that go to Third World War but there would be so many people involved in changing couple of important people that you could hardly do anything with it. At the same time if your brain would be organized in the mess you would immediately know what option you need to take to optimize whatever you want to optimize. Much easier would be if everybody else lost their free will and you alone had it.
The real fun begins if you consider no free will aka determinism. You know exactly what will happen but you can not change it. Imagine standing on cross roads, you know you will turn to left, its the future and you can not decide otherwise but there does not seem to be anything that would actually prevent you from turning right. If you do it, it means that the ability was telling you exactly that from the beginning but then you would turn left…
Lets consider thought experiment:
There is a robot that has very strict type of thinking. It is standing in a hall way that splits into two corridors, left and right (it is driving towards the left). Nothing miraculous can happen there, nothing that would prevent the robot to go where it is programmed to go.
You are at the headquarters and know where the robot will turn or simply what will happen there. You tell this information to the robot and the robot will turn exactly the other way. For example you know that he will turn left. You send him the information and he according to his program turns right which means that your ability is not working and this simply can not happen, you can not tell him the direction because he would do the opposite. What will you tell him? What is the future?
There is one more line of code in the robot: if you get the information “you did not decide”, you will turn left. This is to make it harder, the future would switching between left and right indefinitely, meaning the robot would not do anything and we do not want it. The only solution that I came up with is that he will actually not decide, you will send him the information: “You will start going left but when you will get this information you will turn right. After hearing this you will turn left but when you hear this information you will turn right again…” it will continue and then it depends how the robot is made. If it waits until the stream of information halts then it wont ever decide and you will speak to him forever. If it will take the information and while it processes the next part it will start to act accordingly to it (meaning the opposite way), the robot will slowly move towards left or right. At some point it will be on the threshold which raises a problem of course and I guess there is nothing stable to tell him without destroying the ability that you gained, you know what he will do but you can not tell him.
The last part would be the same scenario as if the robot could teleport from the beginning but if you have to say the information then it will result in a paradox. In normal non-robot life you would probably run into more complicated scenarios where knowing the future would not alternate you decision which is the whole problem we are dealing with. But if you would not and your ability would HAVE TO work then… ???
BOOM!
Dragallur
Clearly there is face in the upper middle part of the picture on the left. There is definitely sign of both eyes, of nose and mouth, thats more than one needs to 
recognise face in something, consider the following one on the right. Do you see the black thick circle filled with yellow color, two ellipses and curved line extended in the ends? Yeah me too.
as you can see below it was just the low resolution of Viking spacecraft.
Science and rationality 