The World
Calvin (on Hobbes' shoulders reaching into a mailbox): Ah! I got the letter I wrote to myself!
Hobbes: What did you write?
Calvin: "Dear Calvin, Hi! I'm writing this on Monday. What day is it now? How are things going? Your pal, Calvin."
Calvin (to Hobbes): My past self is corresponding with my future self.
Hobbes: Too bad you can't write back.
- Calvin and Hobbes, April 19 1995
Time is cyclic. The universe explodes out from the big bang, cools down and develops stars, galaxies, planets and life – and then the expansion gradually slows and turns around into a contraction. Eventually the clouds of dead stars and dissolved galaxies implode inwards into a big crunch, which bounces back into a new big bang identical to the old. All past information vanishes and things begin anew exactly like it once did. The history of the universe is dots on a big circle. But what exists at the center of the cosmic circle? Here, outside time, lies Ex Tempore.
Ex Tempore is literally the center of the universe, a small self-contained world that follows its own time direction. It lies outside the time of the universe, but using parachronic travel it is possible to reach Ex Tempore from the universe, or vice versa. Parachronic travel can reach any point on the great circle of time; from the perspective of Ex Tempore all of history is the same distance away.
Time travel of any kind – even the smallest observations – changes history. A time traveler may visit the world a year after his departure, gather some souvenirs and return home, finding it unchanged. But if he returns to that future he will find it changed – his time travel has changed the future. Going back a few moments will not lead to any huge change, but the farther back the greater the ripple effects. Going back a few years and giving a few stock tips will change the economy, affecting the lives of millions in subtle ways. Going back a century can change the world utterly. Crush a few bugs in the cretaceous and you will get a nasty surprise when you get home.
There are no paradoxes in time travel; you can kill your grandfather as he was a child, and you will not disappear – but if you return to your own time you will not find a trace of your existence. Time travelers can never truly go back to the same future since they change all history after their visit. Even worse, in the new history that occurs after the time travelers intervention, other travelers may appear and travel even further back, undoing the whole story and causing an entirely new history to play out.
In many ways history appears like many parallel timelines, like in the many worlds theory of quantum mechanics. But at any moment there is just one current timeline, and that is what is being changed. A past timeline is impossible to reach.
Ex Tempore is the only safe place from being wiped out when somebody changes the remote past. It has become a refuge for many beings, both humans and extremely alien. It is a vantage point, a reservation, a museum and the palace of the true rulers of the universe.
Parachronic Time
With the Lord a day is like a thousand years, and a thousand years are like a day.
-- 2 Peter 3:8b
Time is a confusing subject, because it is not a single phenomenon but actually at least two.
The time experienced by the beings living in the universe is called (by the human society of Ex Tempore) “tempus time”. It flows from big bang to big crunch, subject to the ordinary adjustments due to relativity (it is slowed near light speed and heavy masses) and seems to exhibit strict causality: causes always precede their effects.
Beings in Ex Tempore experience time just as if they existed in the universe, and the laws of physics seem to be completely identical. But the local time runs in a completely different direction compared to tempus time; this time is called aevum time. Two travelers from the same universe, departing to Ex Tempore with their timeships billions of years apart will arrive at the same instant as seen in Ex Tempore since they both started at the exact same moment in aevum time (and travel to and from Ex Tempore takes a constant time). Changes to history happen according to aevum time, which is also strictly causal. As long as no travelers from within or Ex Tempore change the timeline it will remain the same for as long aevum-time passes before anybody leaves from Ex Tempore to it.
The origin of Ex Tempore is somewhat mysterious, but the laws of parachronic physics seems to imply that a cyclic timestream logically has to have an invariant point like Ex Tempore. In a way it is the dual of the universe. It might have been a natural phenomenon, but by now it has be thoroughly redesigned and reshaped by advanced civilizations. Some cultures have suggested that aevum time is truly linear, with no beginning or end. Others favor the theory that it is also cyclic like tempus time – there is only a finite amount of matter in the universe, so eventually all possible permutations of events will have been played out and the situation returns to a previous state. Yet others speculate that there exists something beyond Ex Tempore, a kind of meta-parachronic physics enabling time travel within Ex Tempore and maybe a way to reach a yet more fundamental place with its own time – aeternitas.
Civilization
'Oh, fools,' said I, 'thus to prefer dark night
Before true light,
To live in grots and caves, and hate the day
Because it shows the way,
The way which from this dead and dark abode
Leaps up to God,
A way where you might tread the sun, and be
More bright than he.'
-- Henry Vaughan
The history of the universe is to a large extent affected by intelligent life, both due to its action on the world – some civilizations spread across the universe, turning stars into power plants and planets into minds – and through the history-altering of time travel.
As a rule, species go through three phases. First they slowly evolve towards intelligence, living as hunter-gatherers (or whatever their ecological niche is) with little technology and change. Then they undergo an accelerating phase as they learn more, develop more technology and change their world and themselves faster and faster. Eventually they discover all the laws of physics and make use of them (or whatever subset they find acceptable or useful), becoming a civilization as powerful as it can physically be whose only change is cultural. Of course, many species never develop or destroy themselves, and the phases may last vastly different times – some species take millions of years to do what others achieve in a few decades. But from the timeless perspective of Ex Tempore it is instant: before a certain point the species is nearly animal, after it – nearly gods.
Although advanced civilizations are powerful and fantastically diverse, many of them are surprisingly discreet. To them a cubic centimeter of matter is enough to house millions of digital minds, their machines are tiny compared to molecules and they have the patience of eons. Many have settled down into fixed patterns, having long since outgrown wild exploration and change. It is the younger civilizations that tend to make the most noise, especially when they stumble on time travel.
Time Travel and its Consequences
I know that history at all times draws the strangest consequences from the remotest cause.
-AnonymousIf you can look into the seeds of time,
and say which grain will grow, and which will not,
speak then to me.
- W Shakespeare, Macbeth, I, 3.
The discovery of parachronic travel, often called the Second Ascension, is a somewhat random process. Some species never manage, other discover it very early on. It is often not so much a result of studies of physical law as testing out an inspired guess. The underlying rules of parachronic physics are simply not deducible from normal physical processes since normal matter never does a time jump. In a very real sense it is a completely independent set of physical laws. Once the principle of parachronic phasing has been discovered, it can be developed and tested fairly easily. It usually requires at least some sophisticated electronics and sensitive detectors, but nothing extremely advanced.
The most common result of Second Ascension is the demise of the discovering civilization. Parachronic technology enables a Pandora’s box of tricks, many of which with dire military applications. Since it is fairly simple to apply once it is discovered many civilizations find themselves deluged by phasing weaponry, and sooner or later someone will use it.
Some civilizations develop parachronic travel experimentally, gradually discovering ways of sending objects forward and backward in time with little theoretical foundations. Others develop theories, showing how parachronic physics ought to work. One early result in almost any such theory created by beings realizing the essential cyclic nature of time in a closed universe is the prediction that there exists a kind of center outside the universe that could be reached parachronically. This center is of course Ex Tempore.
Ex Tempore receives all time travelers leaving their home timestream at the same time, both the first pioneer trying his crackpot invention and the last refugees from a collapsing universe. They all find themselves in the same world, and soon will discover that their own world likely has been lost forever while they were in transit.
If a time traveler arrives at any point in the timestream, everything after that moment is changed by his actions. If he accidentally bumps a vase of flowers, that little change will cause other changes – people will react differently in the room, the garbage will be different and so on – that in turn causes new changes. In the end the whole future changes beyond recognition. This includes the existence of other time travelers: sometimes they are brought into existence as a future where time travel is possible emerges, doing their own timejumps to cause changes. The original time traveler will not be erased from history if they move back even further, since they will affect a timeline at least one tesserae in the Ex Tempore future; the original time traveler will live his life normally within the timeline until he steps into his phasing machine and jumps somewhere – that will bring him into the same or even more remote timeline as the other time travelers. Sometimes the effects of a time trip prevents any other time travel, for example by causing the discoverer of parachronic technology to fail.
From the perspective of Ex Tempore the timestream is unchanging, a frozen crystal of history that can be reached into at any point – but only so long no travelers or interference from Ex Tempore occurs. Just a tiny touch anywhere, and everything beyond that time is changed. For long periods Ex Tempore does not interfere with the timestream, leaving it as it is. At other periods it nearly constantly interferes, causing the timestream to shift wildly.
Some such shifts cause time travelers from within the timestream to emerge, which usually causes a cascade of sudden shifts – a burst – and generally results in a very changed timeline, plenty of new arrivals at Ex Tempore, and some upset observing cultures that now have lost their favorite stretches of history. Usually a burst is followed by a quiet period where the new timeline is examined carefully and a new consensus on what to do is reached.
When someone is inside the timestream further change of the timestream due to outside interference or future time travelers is invisible. You have plenty of time, even if another expedition plans to erase all of your history and it will arrive one tesserae later than you did.
Some advanced civilizations use the different kinds of time to speed up computations: they send a computer from Ex Tempore into the timestream, where it calculates during countless eons and then returns to Ex Tempore with its results. It will arrive a few days after being started, with billions of years of computations finished. Some civilizations even use replicating machinery to convert a huge chunk of the universe into computing resources that returns answers; as long as they send their devices to an era after all other active changes they have no effect.
For example, John travels to 1920 and kills Hitler. As a result Germany becomes a communist state after the July revolution, and the ensuing War of the Soviets in the 40’s leads to the development of parachronic technology. A time traveler from 1950, Ivan, goes back to 1840 to ask Karl Marx what he thinks of it but accidentally infects him with a strain of flu that kills him, causing a world dominated by different political ideologies. John does not experience anything strange as he watches the revolution and war as well as the ensuing Freudian Renaissance. As long as he stays in his timeline he will not see anything amiss. If he gets into his timeship and jumps sometime (like back to 1920) he will suddenly find an entirely different 1920, where Hitler is a painter and Marx unknown.
Suppose the world where Marx died produces time travelers in turn. These may go back even further, removing all of humanity by killing the ancestors of the modern primates as they colonize the Eocene. Ivan will find a world without humans when he returns home to his era in 1950. If John, surprised by the changes in 1920, jumps to 1950 too, he might meet Ivan as the other sole human in this new timeline.
There are no parallel universes, at least not any Ex Tempore knows of. There seems to be only a single universe in the timestream, and this is what is being changed all the time by Ex Tempore and time travelers. The fact that a traveler when visiting the universe will not directly perceive any changes does not mean they occur in a parallel world to him. Rather, while he is spending many years (of Tempus time) in a certain timestream, no Aeon time passes.
Example: Suppose a traveler has landed in the radioactive ruins of the Third British Empire and is setting up a base. Some other people from Ex Tempore are going to the early days of the empire, planning to introduce some ideas that will avert its eventual downfall. The first traveler will not experience anything odd and can spend as much time as he wants studying the ruins – the other team will, from his perspective, not arrive until at the end of time. He may leave for Ex Tempore at any time, recounting his adventures there, or stay on Earth until he dies. The other team implements their plan, utterly changing future history. If they wait around to the same time as when the first traveler arrived, will they see him? The answer is no, since he has already arrived earlier in aevum time. There will be no hermit in the ruins.
A simple rule is that aevum time always trumps tempus time.
One effect of the physics of time travel is that when time travel is first discovered, it seems like a failure. In the first timestream where time travel is discovered everything phasing out seems to disappear forever – it never reappears in that timeline (but in a timeline a few aeon moments ahead, the sent objects will of course appear). This usually results in the “junk burst” – the first timeline disregards the potential for time travel, and instead quite often use it to get rid of nuclear waste, entropy and sometimes even prisoners – which results in a subsequent timeline where these objects appear out of the blue, causing serious trouble. However, this timeline in turn results in a time traveling timeline: the first experiment in time travel produces the expected result as the sent object re-appears (while it is actually the object sent from the first timeline in the corresponding time experiment), and had it not been for the junk this timeline would have been an entirely ordinary time travel timeline.
In Ex Tempore, an important issue is the Divergence Exponent. The exponent is a measure of how quickly a disturbance in a given region will lead to radical changes. Even a slightly displaced electron will eventually cause huge shifts, but there is an immense difference between displacing it in the core of the earth or in the brain of a thinking human. Different cultures measure it differently, but using major computing power it is possible to estimate it with enough accuracy to be useful – especially if the timeline has been studied carefully by snapshot drones. Using the exponent certain times and places can be marked as sensitive and likely to cause trouble if affected, while others are “safer”. As a rule, unstable and highly chaotic systems are risky, and key points in history (and the small events leading up to them) are also more divergent. Visiting Mars during the middle ages will not have as much effect as going to the crusades; even if the changes will eventually cause at least an entirely different weather state in the 1900s when the first probes arrive (and thus affect the space race), the complex shifts in sensitive battle situations will cause a far larger divergence of history. Going to Australia in the same time has an intermediate effect; it will cause subtle changes in the weather across the globe, but due to the relative isolation of the continent and its inhabitants the more marked human changes will not spread as far as fast.