I have my own theories, but I'ld like to hear other oppinions about how this kind of scenario could turn out. This is one part of a story I'm developing.
Setting: We are talking about a medieval / fantasy setting around the year 1300-1600.
At some point in the history of this world, it’s inhabitants start to experience something strange: They dream about their own future - all at the same time. This is a global effect and affects all people who were sleeping (and able to dream) during that exact moment where this strange event was triggered. Everyone dreams about the exact same period of time and the dream feels real and detailed. If someone would die during that period of time, they’ld suddenly wake up like after a horrible nightmare - if not, they’ll continue to sleep normally but still have quite a good memory about the dream when they wake up later.
Some will quickly realize that the dream wasn’t just a dream, but instead an accurate depiction of what would happen if they didn’t have that dream. In other words: The dream depicted the future exactly, but since many people now know their own future they can act accordingly and basically change it instantly. Since this causes most dreams to not match reality after a few weeks, some might forget about it. Who knows.
But then, a few months later - it happens again. This time, it’s at 13:11, and they only dream 3 years of their future. But these global precognitive dreams keep happening in irregular (and sometimes quite short) intervals. In fact, in some rare occasions, they even dream about having such a precognitive dream! People start to notice and talk about it. Some will probably panic - others will make use of those informations.
I’m not sure if I explained it well enough, so a few pointers:
- Every global trigger of this event has an apparently random interval (there is a reason for the triggering, but that’s out of topic). Let’s assume that it can happen at any time of the day (0:00 until 23:59) and that the intervals range between a few days to a few years.
- Every person asleep and able to dream during a triggering, will have such a precognitive dream. This basically means that during such an event, one side of the world is affected more than the other.
- People who are awake during that event are completly unaffected.
- Every person’s dream has the same ‘length’. They all dream 20 years of their lives, or 15 years - or maybe just 2 days. Each trigger has a random duration (with tendency to multiple decades), but that duration then is the same for everyone dreaming - even if suddenly woken up inbetween.
- People who dream about their own death will wake up right afterwards, as if they had a horrible nightmare. They'll remember everything up to the point where they pass out, basically. Otherwise, people who don't die will continue to sleep normally. Dying doesn't have any real influence besides the way those people tend to wake up (it's probably quite a bit more traumatizing)
- The precognitions are absolutely accurate. But just the fact that some people dreamt about it already changes the future by itself. If no one would’ve had those dreams, everything would happen exactly as predicted.
- Those dreams happen instantly, as soon as the event was triggered. Interrupting a person that is just having that dream is basically impossible.
- The dreams are a reflection of "what would have happened". It's not a dream in the common sense, where it might can be influenced from outside or things like that. It's basically just a taped version of the future displayed as dream.
- Edit: The dream feels realistic, but the person will not inherit any mental illness caused by future events. The dream itself can still be horrible / shocking enough to scar the person though, if someone is that unlucky. Here it works pretty much like our own dreams: The worst you can have is a horrible, realistic nightmare. I'm not sure how this kind of thing can affect a person's mind.
- They can have precognitive dreams about precognitive dreaming. But this would remain quite rare and can be ignored for this question.
Theese dreams continue to happen and don’t have any apparent end. The intervals are not predictable. How could the people in such a world react and develop?
As sidenotes, my own thoughts about this kind of scenario:
Mass hysteria/panic? Depending on religious aspects?
I think technological advancements would be much, much faster, since an inventor (or a customer) knows the tool already and can re-invent it ahead of time.
Ethics/Morale would be affected. Now a murderer in the future, is known in the past. A man/woman who is unfaithful would have to pay the price before even doing it. A conflict between two friends/family members/parties would alredy affect things in the past, etc.
Ambitions might change. Someone who realizes that they don't want to meet the same end try to find other means of living.
All the newborn children in those dreams basically will never exist (?), since the exact sitations/details change.
Edit: Added another point about mental scars / effects.