In general, time could be multidimensional. The reason we work with time being a positive real number (1D) is that we can easily observe (measure) changes of the "magnitude of time" (elapsed time). However, there are a many nuances to be considered:
1. By itself in isolation, time is just a characteristic of events, e.g., order of occurrence, duration, etc. The concept of "time" can certainly be defined, tracked and interpreted in many different (mathematical, philosophical) ways. For instance, "time" can be mathematically defined in multiple dimensions, formulated as spanning the smallest complete field containing the real line where all polynomial equations of order "n" have precisely "n" solutions, i.e., the complex plane (complex time is referred to as "kime"). This is all mathematically well-posed, however, it may draw some criticism from experimental physics, as physical “reality” demands concrete “observable” evidence in support of the (higher dimensional time) math model.
2. The utility, value, and universal relevance of time come from its tight integration with the spatial dimensions into "<PERSON> spacetime", a continuous universal model coupling 3D space and 1D time dimensions. The longitudinal order of events in the flat (Euclidean) 4D <PERSON> spacetime universe is represented by a continuous positive real number, we refer to as "time".
3. One can of course, entangle the first two scenarios and consider the universe as a higher-dimensional (5D+) space with multi-dimensional time. The easiest approach for that is to introduce complex time (kime) that effectively and completely unifies the spatial and temporal dimensions, i.e., traversal, measurements, trajectory paths, etc. in space are naturally extended in their space-kime counterparts. Below are 3 examples that illustrate specific higher dimensional universal models that agree with the 4D <PERSON> spacetime observable universe. There are interesting ramifications of such dimensionality lifts of the classical 4D spacetime to higher-dimensional manifolds using multi-dimensional time.
4. Spacekime theory proposed by University of Michigan researchers defined Spacekime as a 5D universe with 3 spatial and 2 complex-time (kime) dimensions. In this framework, longitudinal measurements (e.g., time-series) are represented as kime-surfaces where time is encoded as the magnitude of the radial displacement, and the second degree of freedom, kime-phase, represents the orientation of the event (cf. 298
mathematical parameterization of the complex time plane via polar coordinates).
5. <PERSON> at the University of Southern California proposed a 2T theory, which utilizes an additional time dimension.
6. Another Multi-institutional consortium proposed the 5D space-time-matter (5DSTM) theory to model the universe.
Lifting the dimensions of time results in some profound and about the universe and our interpretation of reality, truth, observations, space travel, and event causality. For instance:
1. Ordered events like classical time-series curves morph into complex kimeseries surfaces where order is relative to parametric descriptions of simple paths/curves, see this animation. There are interesting applications of this generalization to scientific inference or process prediction, and longitudinal data analytics.
2. Increasing the dimensional of time resolves many of the problems of time, like the “arrows of time paradoxes”. Time is actually not just uniformly and automatically marching forward. Our human frame of reference is inertially moving through the 5D+ universe. Time passage is observed as an incremental (time-dimensional) change in this motion. Time traversal is identical to spatial traversal from one location to another (on specific curves/paths). While it's practically impossible, having infinite energy and infinite information allows the theoretical reversal of this spacetime motion (e.g., travel exactly back in time) by applying the inertial motion/transformation in reverse.
3. In higher time-dimensions, and under certain conditions, <PERSON> uncertainty principle does not apply. In other words, in 5D spacekime, one may observe simultaneously and with perfect accuracy both the position and momentum of a particle. The manifestation of the uncertainty principle in 4D spacetime is just due to the presence of a 1 degree of freedom when we project 5D spacekime down to the 4D <PERSON> spacetime. In other words, the observer reflection of uncertainty arises by the natural projection of 5D onto the 4D spacetime and is due to the unobserved complex-time (kime) phase direction.
4. Theoretically, complex-time (kime) permits the existence of simple closed 2D kime curves (CKC). 562