Assumptions
Once you establish an understanding of this mode of causality, then it is the simplest of the three to follow.
Basically there is NO causality.
You may travel backwards in time, and even interact at your own will, however you CANNOT alter anything at all, despite all attempts.
Why? because its already happened.
Basically the timeline is set, things have happened and thats how it is.
By no means do I intend to use the term Fate , since I dont subscribe to this divine omnipotence.
I also don't intend to refer to Religion at any stage either.
Events happen once, and there is no second chance.
Determined Beanz.
Lets say you have just had Beans on toast for breakfast.
You travel back in time and try to manipulate this event.
You arrive back home at 5.00am,
The usual version of you is asleep upstairs, or even brushing their teeth in anticipation of a bean-filled breakfast.
The time travelling you then makes their way to the cupboard,
spies a tin of beans, and attempts to get rid of them in the hope of changing past events,
and thereby forcing the wakening you upstairs to cook something different.
Perception 3 suggests that no matter how hard you try, those beans WILL make it to the saucepan, and into your stomach.
Thats not to say that it is your destiny to eat beans, its just what happened and so it cannot be changed.
Although you may travel backwards and interact, you know before the journey occurs what the outcome will be, so therefore you cannot change past events. In a sense any time journey is merely observational in terms of causality. It is very much like reading a book, finding critisisms, and then having decided to rewrite the book, you discover that it is word for word identical with the previous version ! Not because both books are alike, but because the version you wrote actually IS the original one. There was only ever one copy.
Future knowledge.
In the RED DWARF episode 'Future echoes' Dave Lister sees a vision of his friend 'Cat' running down the hall, with blood drooling down his chin, complaining of a broken tooth. What he has seen is an image of a time leak from the future. In order to try alter the future tooth breaking scenario, Dave rushes into his bedroom to find the 'cat' almost about to eat a mechanical goldfish, assuming that the fish causes the accident Dave jumps on the 'cat' and retrieves the fish before it even meets 'cat's lips.
Yippeee! cries Dave, he has changed future events, only to discover that during his struggle with 'cat' dave actually hit 'cat' in the mouth.
The 'cat' then proceeds to run down the hallway, with blood drooling downing his chin, complaining of a broken tooth.
In this example, Dave tried to manipulate an event of which he already knew the outcome, but instead he actually caused the accident to happen in the first place. And he wasnt even time travelling.
The mistake Dave made, was believing that since the vision was from the future, he still had an opportunity to alter it. Mistakingly thinking that events in time can occur several times. Wrong. Since time is linear, and creates no parallels, then events both in the past and future occur once only, and so have just one singular outcome.
Basically, perception 3 dictates that you may travel back in time, and mess about with events, but since these actions have already taken place before you travelled back, then the original outcome will always exist. You cannot change the past, but this doesnt make time travel pointless, consider the following examples where past interaction, although without causality, creates some strange results.
The Missing Keys.
Remember the movie Bill and Ted? During the whole film, Ted's dad, who works at the police station, had somehow lost his jailcell keys, he couldn't find them anywhere. We assume that they do exist somewhere, but he has just misplaced them. Towards the end of the film, Bill and Ted have to break free their historical friends from the station, but of course, they have no keys. Having possesion of a time travel machine, Ted decides that at some point in the future, when he has time, he will time travel back to a moment Before the keys went missing, and steal them. By bringing the keys forward in time he can hide them somewhere safe, and use the keys NOW to open the cell doors. He has only just come up with this idea, and hasnt yet even seen the keys, let alone touch them, but low and behold, in true Perception 3 style, he looks behind a signpost and there lay the missing keys!
He is currently in the middle of the key scenario, and all he knows for certain is that the keys have gone missing several days ago, only now does he realise that if he travels back to retrieve the keys, then it is actually HIM who removed them from that previous timeline, even though to him, he hasnt done it yet.
This is boss thinking, and makes for fascinating viewing. Even though the keys dont exist for a week, Ted realises that the keys can rematerialise anywhere at all, just as long has he promises at some point later on to use the time machine, go back get the keys from home, and place them wherever he happens to find them now.
We could argue " what if he forgets to keep his promise ? this will surely create a paradox !"
But it wont, perception 3 allows no paradox, and so Ted WILL eventually fullfil his task because in a weird sense,
the appearing keys proove that he already has done so.
A Promised Immortality.
In the fabulous book "Mostly Harmless" by the late Douglas Adams, the central character Arthur Dent whilst chatting with a wise old man, is reminded of the time when Arthur visited a place called 'Stavromula Beta'
(I may have got that name wrong, but it doesn't matter for sake of example).
Arthur replies "I havent been to any Stavromula Beta, Never heard of the place!"
"Oh, you havent yet, but you will." replies the wise man.
Arthur trusting these words, now discovers that he can perform any deathdefying feat without endangering his life because he knows that he lives long enough to visit this strangely named place. Despite courageous acts, Arthur does infact survive long enough to arrive at a club, which as he spots from a sign within, is called Stavromula Beta. Of course now he has to watch his step, since the wise man didn't say anything about surviving after reaching this place.
Otherwise
Meander back to my disturbed Brain.