2 GENERAL PRINCIPLES OF TIME TRAVEL
The TARDIS is a machine that allows `free' movement in both the three dimensions of normal space and the dimension of time. It is movement in this latter dimension which concerns this section. Although unrestricted movement in the three dimensions of space presents us with no difficulties, the very nature of time can produce all kinds of inconsistencies, paradoxes, anomalies and violations of causality.
We see that in every day life, cause produces effect, and not the other way around. This sequence of events is called causality. The problem with time travel is that is has a tendency to create situations where effect precedes cause. Events like this are called paradoxes -- situations which should not and essentially cannot happen.
Whilst time-travelling in a TARDIS such paradoxes are kept to a minimum. The way this is achieved is two-fold. The navigational computer in tandem with the central computer checks all coordinate data which it receives, and will alter most data which is likely to put the TARDIS in a situation where problems will occur due to time travelling. This prevents the majority of temporal mishaps. To look at the next point, a basic understand of time-streams is necessary.
Time-streams will be defined technically later on, but for now only the general idea is important. Within a single time-stream it is impossible to meet time-travellers from either the past or future, and at the same time, allows one to meet the inhabitants of both past and future worlds. All time travel within a single time-stream will generally produce time loops, that is, one fulfils history instead of changing it.
The distinction between past, present, and future is only an illusion, however persistent.
There is no such thing as an absolute past, present or future. All are relative to a particular observer. An individual's memory of history, perception of present, and future destiny are all defined in their time-stream. As long as the time-steam is not interfered with, none of this will change in an unnatural fashion. Irresponsible time-travelling may interfere with any number of time-streams, regardless of how remote the interference seems. Time-streams belong to every space-time event in the universe, not just living sentient beings. However, for the purposes of this manual the term shall only apply to sentient beings.
To a single observer, the past is history: that which has happened. The present is the here and now: the events immediately happening. The future is what is yet to happen. All are illusions of reality. However, all is not lost. We may apply these terms to an individual's time-stream. Within that context, the illusion becomes real, if ephemeral. Imagine a long winding stream of water, a river, stretching from infinity to infinity. Picture this and one pictures their time-stream. Now imagine a powerful wave of water, travelling along this stream. This is an event wave, a temporal signature, the exo-space-time definition of an event. This wave is an individual. As it sweeps along the stream, the crest of the wave represents the present. The stream behind the wave, which the wave has passed by, is the past. And the parts of the stream which the wave has yet to reach is of course the future.
A clarification is required here. The time-stream is not a history of the universe. It is the history of one space-time event, one individual. That person's past is defined only for them. Someone else's future may be that person's past. Such is the illusion of time.
The analogy is not complete, however. Within the causal event horizon, every time-stream interacts in some small, often insignificant way. The causal event horizon defines a three-dimensional sphere, with an temporal signature (a time traveller in this case) in the center, with a radius equal to the age of the universe multiplied by the speed of light. The causal event horizon traverses not only distance but time, as the edge of the horizon is not the edge of the universe but images from Event One itself.
Time streams interacting is in itself not dangerous, nor is it avoidable. However, there are situations which much be avoided. At all times one's own time stream must not loop back on itself. This prevents one from meeting oneself. This is the first law of time, and the TARDIS will not under normal circumstances allow this to be broken. Even so, it is a wise practice to keep a record of when and when one visits, and avoid these coordinates if at all possible. Indeed, if a former coordinate is entered, the TARDIS will add on the amount of time passed on board (TSET) since the visit.
When two time-streams cross, but the event-waves do not collide, the past is no longer immutable, the present is no longer a reality and the future becomes undefined. One can meet one's future or past self, or meet fellow time-travellers from the past of future. Time streams crossing is chaos, and the TARDIS will normally prevent this from happening. Coordinates which would force time streams to cross are rejected outright. Time-streams which cross and collide instantly are safe, as for a while time-streams will run together, before parting and going their separate ways.
Time loops are caused when time-streams fold back on themselves, the result being that a certain event will cause a certain event , the result of which will cause the original event . For example, a time traveller, distressed at the death-toll of a certain battle, goes back in time to try and change the outcome. However, he will inevitably become part of history, and will probably inadvertently contribute to many deaths, or will perhaps become the mysterious observer mentioned in the history books.
2.3.2 Blinovitch Limitation Effect
The Blinovitch limitation effect is a physical, real limitation which prevents time travellers from interfering with their own history. It has two manifestations, one which prevents time travellers from changing their own past, and one which prevents a time traveller from meeting themself.
In its first form, the effect is simply a time loop. A time traveller attempting to change their own history, for better or worse, will simply just create a time-loop, where his or her actions in the past are pre-destined and in fact have already happened. Time loops are paradoxical in nature, and to occur time travel across time-streams must have happened. Of course, visiting your own personal past is only possible by crossing your own time-stream.
The Blinovitch limitation effect also has a second form, in this scenario it manifests itself as a force which prevents time travellers from interfering directly with their own past selves. The force which intervenes may take any known form, manipulating chaotic and quantum variables in a weak manifestation, and manipulating explosive energies in a more violent manifestation.
It may be surprising to learn that both forms of the Blinovitch limitation effect can be circumnavigated. To cancel out the time-loop in the first instance, it is necessary for an external time-traveller not previously connected with the time-loop to interfere with the creation of the time-loop. This may sound like interfering with a past-event, but there is a subtle difference here. A time-loop is not a real event. Once a time-loop is destroyed, the energy it had consumed to create its alternative reality is released back into the real universe. Note this time that the destruction of a time-loop is a real event, and any attempts to change this will prevented by the second form of the Blinovitch limitation effect.
However, the second Blinovitch limitation effect can itself be avoided. The trick is simple: cross time-streams. The Blinovitch limitation effect only occurs as a result of a time-traveller meeting himself in his own time-stream. By meeting oneself in another time-stream, the effect does not take place.
At this stage it is necessary to expand our understanding of time-streams. Recall the analogy of the wave running down the infinitely long stream, which is in reality our event wave running along its time-stream.
Yet another analogy to explain the illusion of time and the higher-order mathematics which governs it. Time tracks separate time-streams, and generally provide some level of causality whilst time-travelling.
A technique used in flight, time-track cross-jumping effectively moves the TARDIS into its past or future time-stream. Yes, it is an ontological absurdity. Normally, an event wave always travels in its present, after all, this is the definition of the present. Whilst travelling through the space-time vortex, it is possible to replace the inhabitants event waves into their own past or future. In theory this would enable them to re-write their past or create their own destiny. They would replace their former existence in the real universe with a new version. In practice, this is not possible, and if one cross-jumps a time track during flight, the maneuver must be reversed before landing. Otherwise, time friction may occur.
A very rare phenomenon, technically known as an accidental track jump. This can occur either because of a technical fault during flight, an emergency forced rematerialisation, or as extremely poor piloting. In theory, one should be either existing in one's own past or future. In practice, one co-exists with one's past or future. The combined reality is a less than the sum of its parts. The first indication of a time track jump is a loss of present. Literally, some present has passed by, which the victims will not be aware of. The interior of the TARDIS is not immune to the effects of the track jump, as it not isolated from the exterior world. Some objects inside the TARDIS, apparently from random, will appear to be from the future. This is quickly observable as they either will not be able to be touched, or will not be able to be interacted with (i.e. you can touch a glass but can't leave fingerprints on it). The same applies for the world outside the TARDIS. Here none of the world can be interacted with, and as before, some objects can only be seen but not touched. Worse still, the world is the personal future/past of the TARDIS's time travellers. One may see oneself going about one's life from a ``third-person'' perspective.
The situation will not revert itself until the event-waves which are the time travellers are back within the correct time track. The operation of the time dimension tracker circuit should perform this. When this happens everything that the time travellers interacted with will suddenly happen. The glass which had no fingerprints after a touch will seemingly suddenly change, the fingerprints appearing. Worse still, although one's positions remain the same, the future which was before one's eyes has gone to be replaced with the ``present''. There is an element of fate here, as nothing has changed. One's other self may still be observing the situation. If before one saw oneself die, this may happen now. However, as one has foreknowledge, this can actually be avoided.
The past is immutable. What has happened has happened. Everything one does in the present is recorded in the past. So what happens when someone tries to change history? Various phenomena occur as one battles with time. If one attempts to change the past of their own time-stream, the Blinovitch limitation effect comes into play. If one attempts to change the past of someone else's time-stream, they will find this immutable. For an individual, the future has yet to happen. As such, it is an blank page, awaiting ink. For another, this future is her present. For another, his past. The TARDIS allows its inhabitants to visit their future, but there are a few caveats. As time-travellers enter their future, it becomes present, and is immediately recorded as their past in their time-streams. Hence, the future becomes immutable. The future is not different from the past in the eyes of a time-traveller. Both the known future and known past are immutable. The unknown past, the unknown present, the unknown future, this is always subject to change. In a sense returning to the present is paradoxical, as wherever a time-traveller is situated is their own ``present''. However, there is a notion of true present. The true present is informally defined to be a space-time within the time-traveller's original causal horizon such that there is only one instance of the traveller observable to all within the causal event horizon. The TARDIS travels through a dimension called the space-time vortex to make its journeys. There are, however, many different ways of achieving time travel. Exact methods vary; the following are some common and not so common examples: simple static electro-flux field distortion, devices which can warp and distort space-time; vastly complex event wave creators which in theory can shape space-time and artificially create events; and illegal and dangerous methods such as time corridors, bi-directional passageways in space-time.The space-time vortex is a merge of time and space, and exists where time and space intersect. There are no limbo barriers in the space-time vortex, neither is there any atmosphere. Within the vortex there is no sense of time, size or scale. All seems relative. The dimension is not empty, though. Great gushes of energy, known as time winds, play havoc in the vortex. Thought to be primarily made up of high energy delta particles, these winds can be deadly to both humanoid life-forms and organic/inorganic matter.
The space-time vortex can be compared to an ocean of water, stretching out infinitely in all directions. As in craft that cross the ocean, craft that travel through the space-time vortex can have different levels of submersion. Most aquatic-based craft have only a small part of the base under the water, other larger craft have a greater part of their body submerged under the water. Some craft, such as submarines, travel entirely underwater whereas others float above the surface such as hover-craft. This principle can equally applied to ships travelling in the space-time vortex. The Type 40 TARDIS has a low submersion factor, and as such the tunnel-like vortex pattern normally associated with the vortex is very hard to discern. Craft which travel deeply though the vortex are further removed from the real-world than crafts which only skim the surface. Transduction of external forces is kept to a minimum for fully submerged craft.
When craft enter or leave the vortex, they must rise to the surface, which is the point where the vortex `meets' the real-world. Whilst craft are close to the surface, normally just after dematerialisation or just prior to rematerialisation, it is common for the craft to experience energy transduction -- the conduction of energies from the real-world into the vortex. At this point, the TARDIS is more vulnerable to outside attack; for example, a device may be built which could pull TARDIS off-course just prior to rematerialisation.
Generally, the higher the gelocity of a TARDIS, the greater the submersion. Any loss of gelocity results in the TARDIS feeling the effects of temporal buoyancy, i.e. if the TARDIS stops moving through the space-time vortex, it will generally automatically dematerialise, as the TARDIS emerges from the surface of the space-time vortex. However, due to a combination of poor piloting and a turbulent vortex, it is possible to briefly have a very low submersion and a very high speed. This is very dangerous, and could cause an unstable dematerialisation.
A TARDIS can also be pulled out of the space-time vortex if it happens to be travelling close to the surface. The energy needed to snare a TARDIS from the real-world rises exponentially with level of submersion for that TARDIS. Generally, unless a TARDIS has just dematerialised or is about to immanently rematerialise, there is little chance of a TARDIS being pulled out of the space-time vortex.
Just as oceans are composed of more than just water, the space-time vortex has
its various constituent components. The space-time vortex is subjected to dense delta-particle streams, which cause temporal friction, and are also the cause of space-time trails. Apart from delta-particles, there is also cosmic debris which litters the vortex, material dumped from travelling craft. In addition to the other craft which navigate the vortex, indigenous creatures known as Kronavores are thought to have their home here. Little is known of these powerful entities, who apparently feed directly upon time itself.Sometimes, due to powerful energy sources in real-space, phenomenon known as time-eddys may appear. These are violent whirlpool section of the vortex, which may snare time-travelling craft, and prevent further travel. Time-eddys normally prevent rematerialisation from the vortex, and have been known to break-up timeships. However, TARDISes are programmed to detect the signs of an approaching time-eddy and alter their flight-path accordingly.
Another phenomenon found in the vortex are nexus particles. These are massive particles formed by the combination of many delta particles. Nexus particles, because of their large mass, are often stationary, although are more commonly found adrift. The nexus particles can be used as anchors, if required. Note that all the phrases mentioned in this section are analogous terms to describe what are essentially very complicated mathematical models and equations. There is no physical anchor as such, but from the way the mathematical model behaves, the name has been given. The space-time vortex does not exist in the reality of the our world, and is governed mostly by mathematical equations. There exists the potential for crafts, in the future, to exploit this fact and henceforth manipulate these equations directly using block-transfer computations. This is beyond the scope of present-day science, and TARDISes interact indirectly with these equations in the unreal world of the space-time vortex.
As mentioned briefly earlier, when craft travel through the vortex, they leave behind a space-time trail. Composed of a concentrated but random scattering of delta particles, held together by an artron field, the space-time trail can show where a TARDIS has been recently, as can also be used to find out where a TARDIS is currently. Using advanced computations, and by appealing to the circular theory of time, a TARDIS's current time-track can be calculated. Now, by statistical analysis, it is also possible to predict the time-path a TARDIS is travelling on, and henceforth predict the destination of a TARDIS in flight. With a fast enough ship equipped with such sensors, one could in principle intercept a renegade in a stolen timeship by arriving at its destination before it did, even if the pursuing craft had a later departure! However, most attempts at this manoeuvre would result in a coordinate error. (See: 4.6.4.)
Often a timeship can be subjected to what is known as temporal turbulence. Normally only occurring in `deeper' section of the vortex, it can occur anywhere. The disturbance is caused by high-energy delta particles which has a gelocity given to them by active artron fields. The turbulence can cause an uneasy journey at best, and can sometimes even force rematerialisation.
Time Lords can survive without protection in the space-time vortex, although this is very dangerous and is not recommended. The Rassilon Imprimature reduces the risk of molecular destabilisation considerably; however, a risk remains. The main danger is that one may find oneself unable to get back to their TARDIS once out in the vortex. In addition, it is very dangerous for the ship's doors to open during flight; dimensional instability inside or outside the ship may occur, with wide-ranging consequences.
The space-time vortex has five degrees of freedom (the three dimensions of space, the dimension of time and the depth of the vortex), in addition to the extensive warping of `space-time' which occurs throughout the vortex. Tremendous sources of energy can leek into the vortex from the real-world; a good example of this are black holes, which can create havoc for time-travellers.
The four laws of time, also known as Time Laws, are simple rules which are the only constraints on time travel. Although only a regulation, it is a pseudo-physical barrier as well, because the very concept of the laws of time is built into the heart of the TARDIS. It is impossible to remove these circuits without destroying the TARDIS. To prevent abuse of the laws of time, the TARDIS can utilise built-in controls that will ensure that the laws of time are complied with.There are four central laws of time which are the pillars upon which modern time travel stands. Each individual law is given a mention below.
The laws provide pseudo-physical constraints on the limit of variation of time travel and are implemented via the central computer and the navigational computer systems, and are enforced by coordinate modification, the process of altering user-set coordinates which would force the TARDIS to break a Time Law. This, though, does not mean that you can whiz around the universe as you please. In addition to the laws of time, a section of Gallifreyian law, Article 214, has been laid down to regulate time travel and related matters. For reference purposes, a summary of this law has been included in the Appendix.