Time travel

This page uses terminology that it might not explain. It is highly recommended that you read and understand this section of the Cosmology of Yata.

Time travel refers to the concept and practice of travelling through time. Usually, this refers to moving a thing, object, or people backwards or forwards through 1-time. When it comes to 2-time however, time travel is described in a "sideways" motion as there is no left-right distinction on the time manifold. The "concept" of time travel usually means travelling back in time whereas the "practice" refers to forward time travel, and this distinction is key. Whereas forward time travel is an observed phenomenon, there is intense debate as to the possibility of travelling backwards in 1-time.

What is time?

The following section refers to 1-time where "time" is used.

The standard unit of time is the second, equal to the time it takes the caesium-133 atom to undergo hyperfine transition 9,192,631,770 times. Time is not constant however, as it "changes speed" for external observers. That is to say, time will always appear to pass the same from Observer A, but Observer B may see Observer A pass through time differently. Time is inversely proportional to velocity with a hyperbolic relationship. This means that where velocity increases, the "speed" of time from a local observer slows down, an effect that becomes much more profound as the velocity approaches c, the speed of light. For the same reason, it is also inversely proportional to gravity, as both gravity and velocity are related factors that affect how a thing passes through spacetime. If an Observer A were to reach a velocity of 0.9c, they would experience time roughly twice as slow from an Observer B's perspective. Likewise, if an Observer A was in the vacuum of space infinitely far from Yata's gravity, an Observer B on Yata would appear to see Observer A moving through time faster. Realistically, this effect is nearly unobservable due to the hyperbolic relationship of time and velocity/gravity. For every 50 years Observer A spends "unaffected" by gravity, the apparent time experienced back on Yata would pass 1 second slower.

Forward time travel

The following section refers to 1-time where "time" is used.

The interaction between time and velocity/gravity to produce differences in perceived time is called time dilation - the primary force underpinning forward time travel. What is key is that forward time travel is not a hypothetical concept, but a legitimised and proven mechanism. By passing a person around an object with intense gravity, such as a black hole, and returning them to where they originated, the apparent time perceived by the observer will be significantly less than the actual time that has passed at the origin point. A practical way of looking at this mechanism is through age - because the apparent time of the person passing around the black hole remains constant, it allows said person to arrive back at the origin in the "future". Say that such a journey was used to transport a person fifty years into the future, the person may only experience 3 days worth of travel but in reality 50 years have still passed where the person was passing around the black hole from an external observer. As a result, it can only be considered "forward time travel" from the perspective of the person who passed around the black hole, when all that happened was that the person passed through an area where time was significantly slower. For all intensive purposes however, it still counts as the person travelling into the future.

Backward time travel

Whereas forward time travel is legitimised, backward 1-time travel is not. 1-Time ultimately drives causality, or cause and effect, and the constant forward-motion of 1-time is what defines anything's past, present and future. In other words, it provides the foundation for allowing anything to happen as a result of some action. The issue with backward 1-time travel is how it interacts with the nature of causality. 1-Time has only one direction, which is forward; it "moves" slower or faster in some places, or zero when velocity is c, however it cannot have a negative value. A good conceptualisation of this is a vase on a shelf: if it is pushed off (cause) it falls to the floor and shatters (effect). By allowing backward motion of 1-time, we could observe the effects preceding the causes, which violates causality and entropy (the idea that systems will always tend to chaos). Therefore, backwards travel through 1-time is not possible.

Apparent backward time travel

However, there have been confirmed instances of phenomena involving "apparent" backwards travel in 1-time, such as the portal clock and Guinevere. The destruction of the Flavros Project apparently caused the portal clock to appear in the past by shattering Guinevere's being across spacetime. In other words, it would appear as if the portal clock spontaneously emerged out of nothing - the effect preceding the cause. However, what had actually happened was that it emerged through timeline collision according to temporal anomaly theory. This meant that Guinevere's shattering meant that these fragments travelled sideways in 2-time and made an apparent "backward" motion in 1-time as well from the perspective of the POV timeline. These fragments would then re-emerge in the POV timeline at an earlier point in actual 1-time. Although it may look like that the effects precede the cause, the cause of their reappearance in the POV timeline was timeline collision. Likewise, timeline collision was the cause in which the fragments "spontaneously" emerged in another dimension across 2-time.

As a result, passing an object through 2-time in this manner "erases" its history, and effectively ascribes it a new cause. What is important in this specific scenario is that the fragments returned to the same timeline that they "came" from, and since the past had already been written before their actual cause, the causing event is still guaranteed to happen. This is called a 2-time secure event. Not only does this not violate causality, it reinforces it for 1-time by emphasising that the 1-time past cannot be altered. The fragments of Guinevere have a defined, linear beginning and end in 1-time, but have a cyclical lifespan in 2-time. This also confirms that causality can only exist for 1-time, not 2-time.

The grandfather paradox does not have the same logic because it assumes that the past of 1-time could be altered. If by some mechanism you exploited 2-time censorship to appear at an earlier point in 1-time to kill your grandfather, you are not actually preventing your own birth because it moves yourself into a new timeline by your own volition, in other words, moving you sideways in 2-time if you tried to do so because the past of 1-time cannot be altered. Situations like these are referred to as "2-time divergent" events, and cannot have a cyclical lifespan when traced on the time manifold. So while from your perspective you could hypothetically go "back in time" and kill your own grandfather, you would end up in a new timeline where you were never meant to have existed, purely because of your actions, meaning that there is no effect preceding the cause.

In summary, instances of apparent backward time travel exist, but this is because they were always meant to happen from the 1-time perspective, even if their true, undisputed cause came after the effect.

Implications

This affects the notion of agency however. Since the past cannot be changed in 1-time but can be "set up" by causes in the future, this implies that time is inherently deterministic, which undermines the idea of free will. Scientists are largely unaware about the existence of the Loom of Fate though - the actual reason that free will cannot exist.