The only reason for time is so that everything doesn’t happen at once – Albert Einstein
There are those who believe that time is a man made construct, conceived as a way of making sense out of the universe. After all, without time, how could anyone accurately describe events, make plans, and so forth? Those who ascribe to this philosophy are in good company: Gottfried Leibniz and Immanuel Kant, among others, believed that time is little more than an illusion.
There are others, such as Martin Heidegger, who argue that time is constantly in flux, and that there is no such thing as “now.” In Being and Time, Heidegger discusses this at length; to summarize, he theorizes that as soon as something is considered to have happened “now,” it is already in the past, therefore making time as we know it illusory at best.
However, there are others who view time as a fundamental element of the universe, a 4th dimension that joins past to present to future, and works together with dimensions one (length), two (width) and three (depth) to create life as we know it. Sir Isaac Newton was a proponent of this theory, thus earning it the name, “Newtonian time.”
If one agrees with Leibniz and Kant, then time becomes irrelevant at best. Concepts such as eternity and infinity as taught in Bible lessons and theorized in physics classes become possible, and the belief of time as being cyclical in nature are bolstered. Finally, the theory of an oscillating universe, once considered by Einstein and others, becomes plausible.
Heidegger’s conclusions on time are abstract, and therefore more difficult to clearly define. However, his point about the elusive nature of “now” are interesting. What I am writing now, at this moment, has already been written in the past. What I am planning to write in the future is currently being typed, and immediately slipping into the past, as well.
Whereas both of these theories are philosophic in nature and unable to be quantified, the same cannot be said for Newtonian time. A 4th dimension is often illustrated as a hypercube, the dimensions of which can be shown in this equation: (2x+1)^4. Furthermore, high school calculus students are taught the equation ds^2=dx1^2 + dx2^2 + dx3^2 + dx4^2 to determine a point in 4D space.
These equations may seem like so much gobbledygook to the average person; after all, most do not understand time as a dimension, much less one that can have various computable points. Allow me to apply what has been hypothesized about time into a more easily-understood scenario:
Imagine you are a recent college graduate. This You is a point in time, as it were. Now imagine you receive a job offer in another state. You call the movers, pack your belongings and hit the road. Upon arriving at your destination, you settle into your new apartment and begin your life in a new state, no longer a student, and working; this is a second You point in time. Theoretically, you can apply the equations listed above to describe what has just happened.
Newtonian time is linear in nature, having a distinct beginning and ending, but with the capability of continuing ad infinitum. In this way, infinity is possible, but quantifiable. With this theory comes the idea of time as tangential. Some take this to the extreme, arguing that, if there are distinct points in 4D space that can be calculated with accuracy, time travel is possible. It is important to note, however, that time is the only dimension that can’t be changed or manipulated, and most discount or dismiss the possibility of time travel.