Is it possible to see the future before it happens?

 Yes. But this is conditional.

What I mean by this is some things in time are set and cannot be changed and other things can be changed and learning which are which will keep you alive in a human body here on earth.

Why?

I cannot really explain why anymore than you can tell me why water or air behaves the way it does on earth. However, one can observe all these things and know that they are true.

So, seeing the future is actually possible for all human beings but it might not occur unless there is some real or imagined emergency where it is necessary to see the future for you or your family or your friends to survive through some situation.

So, it appears that Emergency situations often trigger the human ability to see or project the future in order for their life to continue unabated through whatever is happening or going to happen.

But, it also must be important to understand that there are many time lines and not just one.

How does this all work?

LIke Water and air I cannot explain how it all works but I can observe (just like watching the sun come up each morning where it isn't cloudy, foggy or raining that the sun coms up pretty unfailingly wherever you are on earth at the time if it is morning.

I tend to see time a lot like a tree with many branches and twigs. There is the trunk of the tree and as the tree grows it grows up into limbs and twigs and leaves or needles depending upon what kind of tree it is.

However, time can change to some degree and does at will over time. 

But, humans often alter time with their consciousness and minds in various ways and by their actions.

It is important to understand all this to make full sense of all of this.

Can you retroactively change time?

Yes. Under some circumstances this is possible to do.

For example, all the times cities or countries or the earth itself was blown up since 1945 with nuclear weapons or other things have been corrected in time so far except for Hiroshima and Nagasaki which were left in time as a warning to humanity of what could happen.