The Seven Dimensions (7次元, nana-jigen?), also known by the technical name Seven Axis (7軸, nana-jiku?), mistranslated as Seventh Dimension in the localization of Ar nosurge: Ode to an Unborn Star; are the different planes that form reality in the Universe of EXA_PICO. Therefore, unlike what the localization might lead to believe, it doesn't refer to a physical place.
While the Seven Dimensions were never mentioned in the Ar tonelico Series, aside of a few brief mentions to the Time Axis and the Possibility Axis in technical explanations about the nature of Song Magic, they play a central role in the storyline of the Surge Concerto series games, particularly in Ciel nosurge: Ushinawareta Hoshi e Sasagu Uta, and moving through them is known as an Axis Movement or Axis Shift, which is the main characteristic of the power known as Oversight.
The existence of the Seven Dimensions, particularly the Sixth Dimension that contains all the possible versions of the Qualia for every single living being inhabiting a universe, is the base precept for the most accepted dimensional theory established by Ra Ciela's science, which is called the Qualia Dimension Theory.
Zero Axis - Dot World
While this dimension isn't really counted among the main Seven and it doesn't even have an actual Axis, it still is worth mentioning due to the fact that it serves as the basis for the three dimensions forming space. In this dimension, all higher Axis seem to be moving at specific directions and speeds, yet nothing in the Zero Dimension is capable of actually moving.
First Axis - Line World
Also called the X-Axis, beings existing in this dimension can only move through a specific direction, but the concepts of orthogonal Axis and parallels are completely foreign to them.
Second Axis - Surface World
Known by the secondary name of Y-Axis, this dimension combines with the First Dimension to form what we call in Earth the Cartesian plane, which is the X,Y coordinate system. This world can be described as a flat surface like the ones we would see in a sheet of paper. Therefore, beings living in this dimension can move up and down, but the concept of depth is unknown to them. Similarly, while tridimensional objects could pass through the Second Dimension, their inhabitants would only be able to see it appearing and disappearing in strange ways, but would never be able to witness that object's full form.
Third Axis - Tridimensional World
The world we live in, which also receives the name of Z-Axis. In combination with the first two Dimensions, it forms the tridimensional space as we know it, and known by the word wa-fen (wa-fen) in Emotional Song Pact, it serves as the place where all waveforms existing in the universe flow and clash with each other.
Fourth Axis - Time World
The T-Axis, known by the word tes (tes) in Emotional Song Pact, comprises the entirety of the timeline for any given version of the universe from its very beginning to its end, and it can be measured in scales that go from the Planck time units to the cosmological decades.
However, the concept of time is only the meaning we ascribe to the Fourth Dimension due to the fact it moves in a linear way and we're forced to continuously move forward through it, as to inhabitants of the Fourth-Dimensional space, it is just another plane in space through which they can move, which allows them to carry out what we know as time travel. Similarly, it's possible that other universes might have a Fourth Axis that moves either in a cyclic or Brownian way, making time flow in a different way for them.
Fifth Axis - Possibilities World
Called ye-ra jec (ye-ra jec) in Emotional Song Pact, and having the I-Axis (If) to its name, the Fifth Dimension is the group of possibilities each single individual could have for their respective lives. In other words, the I-Axis contains all the events and consequences resulting from every single choice we could have taken at any point in our lives, with different outcomes being said to exist in separate Fifth Axis, and that when something happens to someone, it's said that person has moved to a Fifth Axis containing a specific possibility. And since we're forced to move through the T-Axis, this in turn also forces us to keep moving forward through the I-Axis.
Beings living in this dimensional plane can see the entirety of their lives laid out as a tree diagram showing all possible branches and directions they could take for it. However, while they can see what would happen to themselves, this wouldn't allow them to see what would happen to others or how said branches could be affected by actions taken by other beings aside of themselves.
Sixth Axis - Collectivity World
Called aru-yan (aru-yan) in Emotional Song Pact and existing as the C-Axis (Collective Consciousness), this is the Dimension where all the possible stages for the Qualia of every single living exist. In other words, this is the Axis where the agglomerations of Static H-Waves (souls, Soulspace Address or Genometrics) that give an identity to all living beings are located, containing infinite to the infinite power of possible versions of each Qualia being interfered by other Qualia.
However, this characteristic of containing all the possible viewpoints, life experiences and interactions of every single being within any possible possibility that could have existed in the universe is what makes it so hard to comprehend to humans: as we are permanently locked within our own Qualia and look at the world with our own subjective viewpoints, we have a hard time coping with the viewpoints of others or try to see the world in a way that doesn't conform with our views and understanding.
Therefore, there is no way in which we could control movement through the Sixth Axis if it were possible to us due to the fact that it moves in a completely unpredictable way. In fact, the only way to become able to control the Sixth Axis would be to get out of the shell of our own Qualia and become a being that could be able to observe it and all other Qualia as if we were an outside observer, as is the case for the Seventh-Dimensional beings that have the Oversight ability.
Seventh Axis - World
The seventh and final dimension established by the Qualia Dimension Theory is the W-Axis, called gin-wa-fen (gin-wa-fen) in Emotional Song Pact, and it corresponds to the World itself. To put it simply, it comprises everything that gives form to an entire world: its space, time, and all versions of their possibilities and Qualia interactions are all contained within a point in the Seventh Axis, while the other points correspond to entirely different worlds unrelated to the Universe of EXA_PICO itself, of which there is no knowledge available. This of course means our universe is a point in the Seventh Axis separate from EXA_PICO's.
This also means that all universes are constantly interacting with each other, like the Big Bang Universe (Earth) and the EXA_PICO Universe (Ar Ciel and Ra Ciela), but given the magnitude of their interactions is so large in scale, we have no way of comprehending them with our Third-Dimensional viewpoint. Likewise, while theoretically there is an infinite number of higher dimensions existing over the Seventh one due to the fact that the universe is fractal-shaped, the Qualia Dimension Theory doesn't consider them due to our lack of understanding on the matter.
- The idea of seven or more dimensions comprising the observable reality is taken from the quantum mechanic postulates known as the M-Theory: the theory that is supposed to unify the main five versions of Superstring Theory, and which states that reality is composed by eleven dimensions.
- Despite the importance of the Fifth Axis, it is the only Dimension whose purpose got mistranslated in Ar nosurge: Ode to an Unborn Star's localization, and in two separate instances: the first is that at a point Ion is said to not be aware of a possibility involving Nay, when the original text said she lost awareness of the Possibility Axis where she witnessed that event. The second is when she compares her Earth to that of the player, in which she says it is shifted five axis away from the player's, when the actual case is that both Earths exist in separate Fifth Axis.