What if i told you that time is note real. That it is fake, a mirage. Would you believe me? Is time a physical or an abstract construct? Would time exist in the absence of humanity? How does time flow? These are some of the questions about the nature of time. I shall, in the simplest of ways, try to answer them.

**Time is both real and abstract.**

Every day we experience the flow of time. The sun rises and it sets indicating the beginning of a new day and the beginning of a new night. From this point, we know that time is real. However would time still be felt if, hypothetically, we lived in a world without the sun moon and stars? What would we measure time with or relative to? Genuinely speaking it would not be possible. So from this point of view time is abstract.

But if we look at most things measured in Classical physics and Special relativity, most of which we take to be real, we realise that they are not real qualities. Examples such as temperature and length come to mind. Temperature is the measurement of the amount of kinetic energy in an object. Kinetic energy is indeed real but temperature is abstract. Distance is real because there will be a physical space between two points of interest but length which is the quantification of this space is abstract.

So if one defines time as the duration of occurrence of an event then duration becomes real but the quantity time assigned to measure that duration becomes abstract. However if one considers the occurrence of a single event such as that moment I held my girlfriend’s hand, then duration can’t be used as definition because the said action is instantaneous. This instantaneous event requires one to have a clock or a watch to give the time that the said event occurred.

The clocks and watches that we use to measure time are agreed upon by convention. It is we who decided that a day should have 24 hours. We could have easily just decided that a day should have 12 hours or even 6 hours. The unit that is used to measure time is not at all important because as all other units of measurement they are just numbers that we assign to physical qualities.

There is currently a huge debate in physics as to whether time is a part of the fabric of the cosmos. Newtonian physics, especially Newton’s equations on motion, rely heavily in the use of time as a physical entity and in this case, duration is what is taken into account. In the same breath, the equations of both special and general relativity suggests that time is real. It is a physical phenomenon. The problem lies in quantum mechanics. In quantum mechanics, time is not really a factor. Without the use of time in its equations, quantum mechanics can make very accurate predictions. So in the quantum world, the current evidence points towards a timeless universe.

So, depending on which side you chose to incline, time can be considered a physical property of our universe or an abstraction used to understand our universe.

**How does time flow?**

Time seems always from the past towards the future. However in theoretical physics, it is possible for time to flow in the opposite direction as well. That is from the present towards the past.

Special relativity as proposed by Einstein holds that we live in a 4 dimension universe; composed of 3 dimensions of space and 1 dimension of time. And this single dimension of time covers all the 3 dimensions of space. Hence, it does not matter which direction you move, the single dimension of time will always be one of your dimensions. Therefore, space and time are not 2 different entities but are one entity called SPACE-TIME. Keep in mind that the assertion here is that time is real and is an integral part of our physical universe.

I know it may be rather difficult to imagine a 4D universe given that we live in a 3D world. Everything that we do see has length, width and height. So how does a 4D structure look like?

A dot has neither length nor width nor height; it is a 0D structure. If you join two 0D structures you get a 1D structure i.e. a line. If you join all the ends of a 1D structure to form a closed loop, you come up with a 2D structure; your figure will have a length and a width. If you continue the process and join several 2D structures to form a closed structure, we get a 3D structure with a length, width and height. To get to a 4D structure, you join all the points of a 3D structure to the points of another 3D structure. Such as a square within a square. Its important to note that this is not a 4D structure but just a way to represent a 4D structure on a 2D surface. Nobody knows how a 4D structure looks like.

The universe that we live in is a 4D universe but we are only able to observe the 3D of space only.

From the representation above it is clear that in any direction of space that one moves, time (the 4^{th} dimension) will always be part of that movement. By space here I mean any direction that one can move; up, down, east, west, left, right etc. both on earth and in outer space.

What everybody did not know before Einstein was that movement through space affected how time flowed. In particular, movement through space slowed down time.

**Time Dilation**

If two people are standing relative to each other, all their motion is now dedicated to the time dimension and their clocks will move in synch. However, if one of them starts to move some of his movement is directed towards the space dimension and some of it to the time dimension. In this effect, some of the momentum is used to cover the space dimension and the other the time dimension.

This is analogous to people that is moving due. If two people are moving northwards at the same speed, they cover the same distance at the same time. But if one of them starts to move north-west, some of the progress to move north is used to move west and he does not cover as much a distance northwards as his partner who maintains the northward movement.

Whenever we are moving, time moves slower to us as compared to somebody that is not moving. This phenomena is called time dilation. It was predicted in the equations of special relativity and confirmed through experimentation.

An example of an experiment was done in the 1970s. in the experiment, an atomic clock was taken aboard an airplane and flown around the world. When the plane finally landed, it was discovered that the clock on the plane was had lost 59 nano seconds while the stationary one had not gained or lost time. It’s cool to know that an atomic clock loses or gains one second in 15 billion years. Therefore to lose 59 nano seconds the clock on the ground would have to run for 885 years!

We however do not feel the effect of time dilation due to the slow relative motion that we move at. It takes only 8 minutes for the space shuttle to live earth and go into orbit a distance of about 200 Km. it takes the same time for light to leave the sun and reach earth, a distance of 150 million Km. if we could travel at the speed of light, then time would slow down such that everything around us would stop moving.

But this only depends on the frame of reference. That is who the observer is. If you were to hitch a ride on a beam of light, time for you would slow down so much it would seem to stop. However an observer observing you as you surf the light beam will see your time move rather quickly. That is why the theory that gave birth to this phenomena is called RELATIVITY. Observations depend on the relative position of the observer.

This slowing down of time does not change the answer that we get when the two observers calculate the speed of light in their own frame of reference. I know calculating the speed of light by the stationary observer is not difficult to understand. The guy on the beam, will not realise that his time is slower so when he computes the speed of the beam he is on, both answers are identical.

I will talk about the flow of time to enable us move to the future and past in another post. Thank you for reading and leave your comments and questions below.

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