It’s common to hear time referred to as the fourth dimension, an assumed complement to the three dimensional space we are used to. With length, width, and height must come a unidirectional flow of time. However, this assumption of time as a truly independent companion to space seems to be a fallacy.
Three dimensional space correlates to properties of physical matter in a dependent sense. If one of the three spatial dimensions is removed, matter does not behave in a way our universe permits. Time does not correlate directly to physical matter in this same sense. With time removed from the picture, matter can still behave as it would in the universe we know. Yet, this doesn’t mean time is not valid alongside the spatial dimensions. Time is more of an epiphenomenon of matter and energy interacting in three dimensional space. That is to say, time is embedded within matter-energy movement, which is understood to be in the x,y,z axes of space. This is because time is correlated to changes in matter when a human perceives this change. So, time is a tool of scaling, patterning, and tracking which is useful for humans when comprehending the physical three dimensions we perceive matter and energy flowing in.
As a side note (placed front and center rather than to the side), it is likely there are more spatial dimensions which we are unable to see and comprehend. These non-visible dimensions would explain oddities such as dark matter and dark energy, quantum entanglement, and gravity; the latter two acting at a distance without apparent contact and the former only indirectly inferable. We see with three spatial dimensions but there are physical impossibilities we see (e.g. planets orbiting the sun with no strings attached) that suggest things are doing stuff in hidden spatial dimensions.
So, time is surely a dimension but not surely a reality in the sense that it is really a concept we use as humans but it is not a fundamental component of the universe. This is where I highlight that a dimension is essentially a framework we use to relate, reference, quantify and analyze things we observe; that is it’s a mental tool more so than an objective part of reality. With that, time is as much a dimension as it is useful for that purpose, but at it’s core it is just an intrinsic part of spatial dimensions, all which ultimately are created by our perception rather than the nature of the universe proper. In human terms of dimensions, this means time is a manifestation of actions occurring in our three spatial dimensions and does not have relevance as a dimension on it’s own.
Now, let’s look at some interesting takes on time as a dimension to show how it’s both useful as well as extraneous. The first will show how time is epiphenomenal to spatial matter-energy movement, the second will show how Einstein embeds time into his theory of relativity, and the third will proclaim time exists in the only time machine known to man.
- Entropy is a thermodynamic law that states matter will tend toward a disordered, uniform state over time. Here, it’s not that time is driving matter toward a certain state, but rather that the state of matter is a way of measuring time. Time is not an agent nor is it something created or shaped other than within our perception. Without a human observer watching matter decay into an entropic state, time is non-existent. Once a person uses the decay of matter as a means of measuring something does time – and it’s dimensional reality – come into play.
- Assuming Einstein’s theories of relativity hold true, the photon can serve as an interesting example. A photon is known as a timeless particle because it is fully engrossed in space and dislodged from time. As it travels through space-time it is pure energy going the maximum cosmological speed through space outside the timed realm. The resulting rule is that if something is going the speed of light it experiences no time (judged relative to slower objects), the closer to the speed of light something goes the less time it experiences than something going slower (again, experience of time of an object is relative to another objects’ speed, hence the name of the theory). To continue this rule, something at absolute zero (a temperature of zero degrees, and so without any movement, i.e. no kinetic energy) would experience only time. This can be simplified by imagining a four dimensional graph where there are three spatial dimensions and a fourth one for time. When the spatial dimensions are changing time must flow too, as the spatial dimensions stop changing time is the only thing still going, when the spatial dimensions max out in rate of change the time dimension stops moving. Note: This is all counterintuitive but supposedly has been verified by atomic clocks being synced and compared after one was on Earth and the other in orbit; the orbital clock was at a relatively higher speed and lagged behind as if it was experiencing less time.
- It turns out time machines are possible! They’ve been right behind and above our nose the whole time in our skull. That’s right, the human brain is a time machine. This can be true in two ways. First, the machinery of our brain produces time and time-related events. Second, we can time travel to the past, present, and future with our brain’s machinery. The first explained: time is a construal of our perceptions based on the regularity and patterns we are forced to see in the world. We thus use time in the sense that we have a minimal amount of things we can perceive at a “time” so we chunk our perceptions into regular intervals. Also, it is useful for us to make plans and predictions in set intervals rather than in random interval sizes. The second explained: Because we have memory we can time travel to the past and relive or alter the past purely in our mind (afterall, the past only exists in our minds, it’s otherwise as unreal as the future). Because we have imagination we can time travel to the future and preview possible life paths or future universes. Because we have cognizance and a need to survive in a dynamic world of hazards, we can always return to the present and engage the now, keeping with us what we have learned from our past and future time travels.
To wrap up, time is a dimension per definition but one embedded in or redundant to the spatial dimensions due to it’s basis in change within the spatial dimensions. If space-time is real and consists of four dimensions, that is fair. But nonetheless, if you have matter and energy changing about in space, time is a tool to help analyze that change but it is not a requirement for it to do what it does.