|Ex Tempore and the Ex|
Ex Tempore is located at ”the center of the universe”, although that statement has no real meaning. For all practical purposes it is a small world of itself, a bubble of space and time unconnected to the rest of the universe, reachable only through phasing.
The geometry of Ex Tempore is a tiny closed universe, currently about 1,500,000 kilometers across. A ray of light will eventually return to its origin unless blocked, and in principle one could see one’s own back by looking with a telescope. At present most matter in Ex Tempore is organized (if that is the word) into a spherical jumble roughly the same size as the Earth – a complex three dimensional labyrinth of ecosystems housed within diamond domes, ruined stone cities, lattices of computronium, intricate megastructures and fields of debris. Most of it is inhabited, but the inhabitants are often so strange that it is hard to distinguish them from the architecture.
Ex Tempore is dominated by the advanced mainliners, cultures of awesome power and understanding that have run things for millennia or more. Their internal politics and interactions shape the environment like natural forces. Up until 5000 Aevum years ago the structures of the Ex were organized into a toroidal band reaching around the world, but for unclear reason they were reshaped into a sphere.
Other mainline cultures are less abstract than the advanced, but still truly alien. Most are incomprehensible to humans – and each other – without advanced interpretation. Most of the mainline cultures have a reasonably working relationship, although there are many complicated political and cultural conflicts dating back centuries or millennia. Most disregard the timestream and turn inwards towards Ex issues, but some take a vague interest and at least observe the changes going on, sometimes copying or acquiring information and objects (sometimes beings or whole cultures) that catch their interest.
The peripherals are newcomers, beings who have reached Ex Tempore from their own timelines or been snatched there by the inhabitants. Some are well on their way of settling down into the mainline, others are still confused newcomers and some are bewildered individuals, cut off from their homeworlds forever.
Inhabitants of Ex view the universe of the timestream extremely different from its own inhabitants. In Ex, the universe is a flickering thing, never stable, never solid like Ex. The mainliners tend to regard themselves and Ex as more real than the universe, and the fate of its inhabitants of little concern. If a certain action causes a billion beings to die in one way, and not doing it still leads to them dying (albeit later on), is there any reason not to chose the first action if it has some desirable outcome? Is there any point in helping a being in the timestream, when that being will anyway have lived its entire life in less than an instant of Ex Tempore time? The peripherals have a firmer connection to the timestream and in general do care about it. Often this results in elaborate schemes of changing it in some suitable way, schemes which often allow the peripherals to enjoy the best fruits of the histories. It is hard to resist the temptations of a changing history, especially when mistakes can be unmade. At least that is what they think in the beginning, until they cause their own first burst and are faced with the consequences of their actions.
Why does not every peripheral take advantage of the libraries and information that can be gained from the more helpful mainliners to become Advanceds to further their aims? Actually, quite a few peripherals do this both individually and as a group. The problem is that as they become Advanced their perspective shifts beyond recognition, and quite soon their goals, identity and culture is no longer anything like what it once was. Also, by simply taking advantage of the advanced cultures the less advanced cultures tend to become assimilated and loose most of their uniqueness. Many cultures realize that if they want to remain themselves that have to develop from within rather than being uplifted to godhood. Also, the cultures that refrain from radical change tend to be the ones that remain accessible, the rest become part of the mainline melting pot.
Divina natura dedit agros, ars humana aedificavit urbes (De re rustica, III.1)
Gravity is directed towards the cores, enormous spherical structures near the center of Ex that likely house some of the most advanced mainline cultures, existing within a computing matrix of quantum black holes. Gravity increases towards the cores, and becomes too great for humans to easily handle around 2000 kilometers away. Most human (and other Earth-derived peripheral) habitats exist 5000 kilometers away, where the gravity is normal Earth gravity.
Ex is not unlike the old Norse idea of the world-tree Yggdrasil: habitats, often self-contained ecosystems the size of small continents, hang in the branches of immense trees of supporting structure, transport systems, cooling and information conduits. The supporting trunks and branches, many tens of kilometers across, extend from the cores outwards reaching heights of over 12,000 kilometers. At several levels geodesic spheres distribute load between the branches.
There has never been any coherent transport system through Ex, since most civilizations prefer to deal with each other virtually (or not at all). Some sections have elevators climbing rails, others employ flying vehicles and others sport systems akin to pneumatic tubes. The supporting structure often contains spaces that can be traversed by foot or vehicle, but there are plenty of surprises for the unwary. One system which is fairly unified is the entropy management network, a vast network of cooling pipes branching throughout the Ex and leading downwards into the cores and to radiator wanes high in the outermost branches. The larger conduits are traversable by special vehicles (“coolant behemoths”) run by the Scyllae
Some regions are utterly inaccessible, like the Gortus. The Gortus is a reflecting polyhedron 700 kilometers across between two of the cores, with a negative apparent gravity. It is believed that it actually consists of a pocket of physics based on different physical constants and inhabited by truly alien beings. Some habitats hang suspended from cables hundreds of kilometers long, with no visible entrances.
The receiving areas, sometimes called the bays, are the destinations and departures of many timeships. This is also where new arrivals are often transported. They are enormous chambers covering with phasing inhibitor equipment. The “human” bays at Namaqua are 100-kilometer chambers with golden pillars reminiscent of the colonnades of Cordoba reaching up to a transparent roof kilometers above. Transport is managed through fast threaded vehicles described as “melting green wedding cakes mixed with porcelain tanks” by one of the visitors. The golden surfaces also act as phasing inhibitors, making departure hard unless allowed by the ruling intellects.
There are plenty of small settlements outside the Ex, not unlike space stations or orbital habitats. Some are inhabited by isolationist mainliners, others by peripherals from space-based cultures. There is even a junkyard of old starships drifting in orbit around a massive placeholder device.
Ex Tempore is not run by law, but by etiquette.
Ex Tempore is organized by a fragile consensus. All the less advanced cultures know that the Advanceds could call the shots, but they are often uninterested in doing so except when their own survival and lofty interests are at stake. The Advanced cultures also know that there is a terrible risk in getting into conflict; while some gladly compete and plot against each other, a real physical conflict with clarketech weapons is too awful to contemplate. Last time it occurred billions of Ex inhabitants died nearly instantly, and wrecked the long-term plans for thousands of powerful cultures. At the same time it is practically impossible to police the Advanceds and most of the cultures have practically nothing in common. The situation is terribly unstable, but at the same time nobody who wants to stay in Ex Tempore wants to get into trouble.
The result of this has been the emergence of the Consensus. It can best be described as “Don’t rock the boat, don’t upset the neighbors”. The Advanceds try to not to upset the power balance and interfere with each other, the less advanced cultures try to keep the advanced from interfering with them. Several cultures and groups have spent much time acting as peacemakers, setting up trade and agreements to minimize the risk of hostilities. The Council and Schedule is one of their creations, a way of airing the discussions of Ex broadly.
The Schedule is one of the few public services in Ex that everybody pays attention to.
In the past, consortia of mainliners have prevented peripherals (and each other) from accessing the timestream by use of phasing inhibitors, nanotech surveillance/attack systems and other means. Such restricted epochs tend to end when the original consortium breaks up due to internal or outside strife. In the current period, the advanced mainliners have taken a decidedly passive approach; they allow everybody free access to the timeline, and seem more interested in watching the children play than doing anything themselves.
The problem with free access to the timeline is that anybody can reach in and change things, possibly wiping out travelers and erasing interesting epochs. One group can easily sabotage for another group, by sending back travelers or objects into the past that easily lead to childish escalation of history-disruption. This is the reason for the Schedule: different cultures announce when they are going to interfere with the timestream, and in what way. Often new announcements are followed by debate in the Council as other cultures disagree with the likely results, various simulations are tested and deals are made (“If you get to wipe out the Roman Empire, then we get to try out industrializing China”).
The Schedule provides “timeslots” for different cultures to manipulate the timestream. On the largest scale the Schedule simply rotates the access to the timeline between different cultures: humans get a century of access, then the strigae, then the trilos, and so on. Each major change resulting in an interesting timeline leads to a finer division of access into shorter slots. Often the slots are further subdivided internally for different tasks. Other cultures often request use of unused future parts of the timelines for independent projects like entropy management, mass mining or supercomputing.
Since regions sufficiently far from each other does not cause any causal interference certain projects can be done in parallel if some care is taken. While humans are naturally most interested in the Earth there are a few other places in the universe (billions of light-years distant) where other lifebearing planets are explored. The orthoxantho are from one such parallel region and are involved with another schedule.
The problem with the Schedule is the fragility of history. It is not uncommon for accidental changes to produce future time travelers jumping back and damaging interesting history. This immediately leads to loud recrimations against the guilty even if they did not themselves have anything to do with the problem.
Enforcing the Schedule is mostly an issue of trade restrictions and ostracism; among less advanced cultures shows of power from advanceds sometimes works as a deterrent. The N’Modugno are still harassed in the virtuality by AI reminders sent by the Koon of their crimes against history.
The current Schedule is approximately as follows: the current main slot deals with low-life universes and right now variants of Earth. This slot will last at most five hundred years, then the Helionape and their allies will get a chance to work more with high-density worlds (and maybe even high density universes; the debate about that is raging among the mainliners right now. A strong coalition thinks it is too risky to create dense universes if there is any chance they will naturally produce intelligence, since nuclear matter life invasions have proven extraordinarily troublesome).
Within this big slot the current sub-slot is human history, and the goal is to give all the participating cultures a chance to play with it. The participants are mainly the other Earth-derived cultures and some mainliners like the Naos and Xantippe. There has been an agreement to try to deal with it systematically by allowing changes, then looking at the resulting timeline and if one of the interested parties finds anything they want to explore in the resulting future they have a chance to get a temporary slot. In general the goal is to change more future parts first, and then move backwards slowly – the loss of the Neanderthals due to the intervention of the N’Modugno is still an irritation.
All the different cultures are members of the Council, a virtual forum where everybody makes their official pronouncements. It can best be described as a posthuman polish parliament.
Some cultures allow all their members to participate in the Council, others restrict access or have representatives representing their members.
The basic blocs are the Noise, the Ideologicals, the Syntony and the silent majority. The Noise is simply the effect of billions of participating alien minds making incomprehensible comments and suggestions; it is a group large enough to actually act as a kind of disorganized political block that can overwhelm much of the inter-species debate if it gets upset. The silent majority on the other hand is the equally numerous species and cultures that listen in but do not participate strongly.
The ideologicals usually have a vision of how the universe should be, like maximal happiness for every being or a history expressing an aesthetic principle. Some ideologicals content themselves with creating a timeline that suits them, and after this has been done they quietly disband. Others have grander and more permanent visions that bring them into conflict with the other Ex cultures. One group that causes much trouble currently are promoting the vision of a lifeless universe as an ideal: they want to ensure the safety of Ex by making the universe stable and lifeless according to a certain elegant pattern, and fully concentrate on Ex Tempore.
The syntony seeks to create a new order, a new way of managing the council. They are little concerned about actual political decisions, but rather how they are made. In many ways they are the leaders of the debate, but usually more interested in how the debate is organized than interested in the actual subject matter.
Most humans find the Council hard to follow. Fairly advanced peripherals and extrovert mainliners, using intelligence amplification technology, AI, reality simulations and debate management tools at a frantic rate, dominate the political field. When an issue really divides the major players the speed and complexity of the debate becomes superhuman. For less important issues, it is barely manageable to follow for experienced viewers.
When Xanthippe established Namaqua she built a number of council chambers, one in each habitat. Each is a truncated eight sided pyramid, containing both virtuality baths and a large domed council chamber. The council chambers are all connected, making people standing in one visible to each other as if they were all standing in the same chamber. Controls around the walls allow access to the Council, which is projected through the dome and into the air. While Xanthippe provides these chambers for everyone, she does not regulate how other control the access. In fact, the unification conflict between Shoukakegawa and the Aquincorians largely revolved around who got to control access to the chambers. After their victory, the NRC has consolidated control over the chambers to either the local governments or to specially appointed NRC political xenoengineers who seek to make sense of the Council and make humanity’s voice heard.
How different cultures live spans everything from being hunter-gatherers on the savannah to existing as consciousness-architectures in quantum foam. The range is so vast that many cultures have nothing in common. However, somewhat similar cultures can trade and interact with more profit. A few common issues also unite most of Ex.
In a tiny universe such as Ex Tempore entropy is a problem. All processes produce waste heat, and even if energy production is simple through clarketech waste heat cannot be removed within a closed universe. If left unchecked Ex Tempore would grow hotter and more chaotic, until it was unlivable. The solution is to export entropy to the timestream: chunks of entropic matter are phased into the big crunch, and blocks of ultra-cold hydrogen ice from the eras of maximum expansion are phased into the Ex to provide cooling.
Entropy gathering is handling by a few community-minded advanced cultures that keep the cooling systems running. These Entropy Handlers sometimes request help from other cultures, and as long as the request is reasonable it is agreed to – they provide far more value through their services to most beings than their occasional request costs. Many human cultures bury their dead by sending them back to the timestream.
Another common issue is architecture. The superstructure of Ex is run mainly by the Architects of Branching Joy, a mainliner culture apparently enjoying handling the major engineering task over the last millennium.
Something many groups find interesting is the current state of the timestream. Since humans inhabit the most interesting portion right now many humans act as consultants and analysts, explaining what is going on to various entities and cooperations such as Ashizuri. When a change has occurred it is scanned and many humans study it, pointing out events of interest or explaining their significance. If new arrivals from the timestream appear they are even more valuable both to other humans and the alien societies. They have unique memories and perspectives many are willing to pay well for.
Mindstate trade is common: Ashizuri and similar groups buy copies of the memories and personality of unique individuals for improving their virtualities. Given that many people do not wish to sell their individuality there is always a shortage, driving up prices.
The information networks of Ex are a titanic mess of standards. Every culture that arrives have their own computing paradigm and standards, which are usually crudely interfaced to the pre-existing systems of friendly cultures. Although some groups have tried to create standards (in Namaqua most notably Nova Roma Concordia and the semi-religious Strigae corporation Rising Wave Ring), the result has rather been a patchwork of systems linked through complex translation systems (many
which are temperamental or based on little-understood AI). Even worse, many systems have been designed by beings so fundamentally different that translations between them become haphazard at best.
Only part of the history of Ex Tempore is known. One reason is simply that information does get lost even in the most advanced cultures, and even when it is stored somewhere it can be nearly impossible to unearth, especially from uncooperative mainliners. But more disturbing is that much has simply been erased in long past conflicts.
There is no recorded beginning of Ex Tempore history, but the oldest records are 13 million Aevum years old. They seem to date from a period where only a single culture existed in Ex Tempore, either because they had all merged or because the previous inhabitants had been destroyed in some way.
Around 6 million years ago a great upheaval occurred among the advanced mainliners and a struggle broke out. One fraction, the Transformers, defeated the other fractions and subjugated all of Ex. The Transformers sought to use the universe as an immense computer to gather infinite information. They reached in and influenced big bang, filled the early universe with replicating technology and reshaped it in their own image. As the first attempts failed they simply learned from their mistakes and adjusted the process until they had turned the entire universe into a single processor. According to what the current mainliners tell, the Transformers to their dismay found that the result of their grand calculation was not to their liking – even infinite information was not enough for their desire. Apparently they redid their reshaping several times, always reaching the same final state. Finally they gave up, restored the other cultures that they had destroyed, and vanished.
Sometimes Ex cultures leave the universe unchanged, turning inward and spending centuries or millennia with internal politics, culture and construction. Other periods are extrovert and meddle greatly in the history.
The greatest changes were experiments in modifying the laws of physics, occurring intermittently over the last two million years. By affecting the earliest moments of big bang the symmetry breaking of physics could be affected, resulting in different values of the natural constants and particle masses. Some changes led to universes filled only with cooling homogeneous hydrogen gas or drifting black holes. In some matter was unstable, either decaying into energy over time or being converted by strange matter into more strange matter – universes where a wave of conversion spread like wildfire turning one world into another kind of world. Rather little remains of these experiments, and it is unclear how they affected Ex Tempore.
Another thing that has been extensively experimented with was the amount of life in the universe. These experiments nearly destroyed Ex Tempore several times. While the barren universes were uninteresting, universes teeming with life proved troublesome in the extreme. In a timeline where life emerges on many worlds, many intelligent species emerge and develop time travel – only to arrive at Ex Tempore simultaneously and also change their world enormously. Suddenly Ex had to manage the arrival and interference of millions of alien civilizations – and occasionally the arrivals were bent on conquest. The mainliners quickly ceased influencing the universe to create much life, seeing the safety of the Ex being threatened. Instead they settled for physical constants that allowed life to exist, but made it so rare it practically never occurred by itself. Instead a simple primordial cell could be planted on a suitable world, and the resulting biosphere and cultures could be explored in a far more orderly manner.
For a period 63,000-8000 years ago an alliance of powerful mainliners restricted access to the timestream only to operations approved by them. As this alliance broke up, a plethora or peripheral cultures got involved in the timestream and began to switch between various interesting worlds. It seems that currently the mainliners are giving them rather free reigns, perhaps because it is more interesting than doing the changing themselves.
Around 1400 Aevum-years ago, the influence on the universe concentrated on the possibilities enabled by seeding carbon-based life on the third planet of a G star in the outskirts of a spiral galaxy (the previous theme had been life in brown dwarf stars and before that quark matter entities from neutron star cores). Various variants of the history of life were played out. In the first truly successful version the species known to humans as trilobites diversified and eventually produced an intelligent species. After the trilos had been explored to the satisfaction of the mainliners, other versions of the timeline were explored. In one another interesting species was found, an intelligent avian species. 200 years ago attention shifted again, this time finding humans.
The first humans found were primitive hunter-gatherer Neanderthals, which were transplanted to a suitable habitat. A few nudges, and plenty of technological civilizations emerged to entertain and worry the peripherals involved. These first humans to arrive to Ex by their own power, the Lamplandae, quickly settled parts opened by friendly mainliners and promptly got involved in messy conflicts. To further complicate things the N’Modugno, a posthuman culture with a serious obsession about its history, sabotaged the past and nearly prevented any human timeline from appearing again. The involved peripherals instead concentrated on histories where Homo sapiens evolved to become dominant.
154 years ago the Republica Aquincorum arrived. They brought with them a large population in city-ships, an organized society and the will to settle down and prosper. Helped by some outside interests they made themselves at home and began a concerted effort to unify the other human enclaves.
This unification was met by resistance from another civilization that arrived a few decades after, the Shoukakegawans. Although still confused and shaken by their arrival they did not wish to become parts of somebody else’s big scheme, and set to resist it. As the Aquincorians consolidated, some clans of Shoukakegawa, supported by advanced technology provided by mainliner fractions, attempted a coup against them. In the ensuing conflict both sides lost heavily. Not so much personnel or territory, but rather in influence, trade and prestige. It took nearly 50 years for them to recover, and the situation remains tense to this day. The Nova Roma Concordia has reasserted itself and is ascendant, Shoukakegawa remains fragmented and many disparates are joining the unification effort. But several nonhuman species are heavily involved in the local politics, and there are problems among the Aquincorians.
Recently two major new players appeared from the same timeline: the colonization starship Magellanica from South America, and the craft of the Third British Empire of Indian Nation. Both groups have not yet integrated into the political order, and may have their own plans.
Currently Ex is relatively stable, but the mainliners know that nothing lasts forever. The human cultures in Ex are young and vulnerable.
Ex Tempore is enormously powerful but also enormously vulnerable. From its outside time position it can freely reach in anywhere in the timestream and change things. No matter how powerful something is, if it never happened it is no longer a threat. But at the same time Ex Tempore can be reached from any point in the current timestream simultaneously. This means that an advanced civilization could in principle mount an invasion, sending its army to Ex Tempore across the span of millions of years and have it all arrive in the same instant. Such invasions have happened in the past.
The technology ceiling makes most advanced civilizations meet each other on an even footing. They all wield tremendous power, but they are all on roughly the same level of technology and can do the same things. To some extent resources may determine a conflict – if you draw on the resources of the entire universe against an enemy that has far less resources, you can likely overpower him. But more often cunning and sneaky tactics determine such an advanced battle.
A war in Ex Tempore can be enormously devastating, and has several times nearly destroyed it.
If all beings in Ex Tempore were to vanish, then the timestream would be unaffected by any interventions. If that timeline were to have no civilizations doing time travel, that would be the end – no changes to history would ever occur and the universe would finally become static. To most beings involved with Ex Tempore this appears as a bad thing, although sometimes various groups seek to create a “perfect” timeline that would persist forever.
Another issue is the amount of mass brought into Ex Tempore and out of the universe. Theoretically it should be possible to bring enough mass from the universe to make the density of the universe smaller than the critical density ensuring an eventual recollapse. This would break the circle of time, and create an universe with a start and no end. It has been debated endlessly among the inhabitants of Ex what effects this would have on Ex Tempore, and the consensus is that it would likely destroy it. The fact that most advanced mainliners do not try it and actively discourage such experiments seem to support this idea. However, there are always someone interested in trying.
Why do beings from Ex Tempore visit the timestream? Although practical needs sometimes require it, usually the motivations are far more philosophical. Quite a few cultures have aesthetic motivations. Some seek out interesting or appealing times, visiting them more or less overtly and then bringing samples back home. Other try to create histories according to their ideals, desires or whims – the Immortal Chuang Empire is perhaps the most infamous example, but for every would-be world conquering project there are ten projects seeking to create a more “civilized” or more interesting history.
Another important motivator is information gathering and curiosity. There is so much to discover even within the ridiculously tight constraints of (say) carbon-based life that visits, experiments and exploration are necessary. Recently arrived cultures often have a keen interest in their own history or nearby timelines, more remote arrivals find a challenge in learning from all the other possibilities. Although immense computing power is available in Ex and often used to run immense simulations of parts of history they can never emulate it perfectly. The sheer bulk of variables and randomness makes history inherently impossible to accurately predict over longer periods, and this contributes to its ephemeral charm.
Most of the experiments consist of introducing a tiny change and see how things play out. Mainliners often content themselves with introducing a microscopic viewing device, which they use to study the timestream with minimal interference. Changes are introduced with clinical precision, often employing a minimal use of effort. They sometime copy entire persons of interest to Ex for further interaction.
Right now the mainliners content themselves with observing while giving the peripherals free reign. Peripherals usually have a far less advanced approach, and go bodily into the timestream for exploration.
It is not uncommon to use the environment near the big crunch as an engineering workshop: anything happening there will not affect history, and advanced cultures can use it to replicate astronomical amounts of snapshot drones, computronium or to provide raw matter in Ex Tempore. Such operations are of course very vulnerable to changes in earlier history, but most big crunch workshops are anyway seen as disposable.
Even the most advanced mainliners of Ex sometimes need to bring home new resources. This is usually done using grabships, timeships equipped to project a very big phasing field around themselves to grab a large amount of matter. Usually grabships visit remote futures for water, soil or stone – or, in the case of some mainliners, planetary and stellar cores for metallic hydrogen and nuclear plasma. Among humans in Ex, most large-scale matter demands are met by Xanthippe, but most cultures still find themselves in the need of raw materials when she does not provide them. Less technically advanced cultures either buy from more advanced, or make grabs of useful resources when they are easily collected – raiding steelworks, farmlands or warehouses. This is frowned on by most of the consensus, but it is still a regular occurrence.
A common technique is the jump-buy: the traveler visits a later point in the timestream than where he intends to get his object, gathers information, jumps back into the past, uses this information for some quick stock market manipulations or other moneymaking schemes, buys the desired object and vanishes with it. This is usually approved by the consensus, provided it is done with caution. Less scrupulous travelers simply steal what they want, either directly or by jumping to a suitable point in time where they can get their hands on sellable valuables. Some play scavengers: just before a disaster will strike an area they phase in, get objects that will be destroyed anyway, and then leave. This has the added value of the excitement, which always draw a crowd of thrill-seeking supporters from across Ex.
If an action causes time travel to occur somewhere in the future a burst happens: the time travelers will start changing history until a new stable state occurs. Sometimes this involves the erasure of the entire time traveling civilization as someone jumps back before it was founded and accidentally or deliberately prevents it (or the entire species!) from happening. In addition the burst usually produces a pile of new arrivals in Ex (often of vastly different time periods), upsetting local politics and generally creating chaos. The risk of erasure of interesting cultures and species makes many Ex Tempore cultures critical of careless time jumping, and risking bursts is even more forbidden. One of the big consensus rules is to never reveal phasing techniques in the timestream.
Detecting that a phasing jump has taken place is easy for the advanced mainliners. While it is extremely hard to determine from where in the timestream it has occurred, they tend to be ready if the traveler arrives in Ex Tempore. They are also good at finding out where trips from Ex Tempore are going, and can sometimes intervene with nanosecond precision.
Occasionally when a mistake wipes out an interesting timeline it may be possible to fix the situation. This can range from a simple correction of the mistake to powerful mainline intervention. Some attempts are successful, most are not.
Note that a time traveler that arrives in the timestream and does something awful will both get away with it and not get away with it! Carl in the second example experiences the resulting timeline after his nuclear detonation, and can return to Ex Tempore after a while. But a few Aeon-hours later other travelers arrive in the timestream, changing it before it has diverged from the one they want. There will still be a Carl in this timestream (unless they change history before he arrives so that his arrival never happens – but that would in any case remove the sought after original timeline), and if he escapes and returns to Ex Tempore he will be able to meet another version of himself from the non-changed timeline!
Such twinning is relatively rare, but occurs when several groups converge on the same part of history. How this is handled depends very much on the species and culture of the traveler. Some software beings can simply merge their memories and become a single being with multiple pasts. Beings who cannot are forced to settle for some compromise.
In general, each point of history has a number of arrivals of chrononauts in its past. The latest such arrival is usually called the Last Change Point (LCP). As long as any time travelers from a future derived from the LCP moves at most back to the time just after it, that timeline remains safe. If the traveler jumps before it, the LCP vanishes and is replaced by the traveler – which usually means the end of all the changes induced by the original LCP.