What is Time?

Time is interesting. How would you define time? Time is complicated. There is no exact definition. Not all scientists agree on definitions of time. However, there are many different definitions out there. Let’s look at some interesting interpretations on time.

Right now, you are reading this sentence, but what is “right now” to you might not be the “right now” to others. A moment is as you perceive it. However, what you perceive is the light that is hitting your eyes. Light takes time to reach your eyes, so are you actually seeing the past? On a more cosmic scale, the sun we see is from 8 minutes ago. Its light is just reaching us now. Some of the stars we see are actually from the past. Time should universally be what happened rather than what is perceived.

To make ourselves a little more comfortable with this concept, say we have an alien spaceship 100 light years away. This means it would see Earth as it looked in 1924, since the light from 1924 Earth would have just reached it. However, if this alien spaceship were moving away from Earth, then the light from Earth would take longer to reach the spaceship. In effect, time would slow down. If the alien spaceship moves at the speed of light away from earth, then it would forever see 1924 Earth, since no light from after 1924 would ever reach the alien spaceship. A beam of light from 1925 just keeps chasing the spaceship; both are going at the same speed, but the spaceship got a head start. Clearly, there’s no way for the light to catch up to the spaceship. If the alien spaceship were moving towards Earth, then, you guessed it: time would move faster. The light would reach the alien spaceship sooner than if the spaceship were to be stationary.

Great, so now that we are all confused and know what time is, we’re done! (We’re not.) Relativity comes in, and now everything is more perplexing. According to relativity, time and space can’t exist without one another. For example, at 1 p.m., you’re at the supermarket. At 9:00 p.m., you’re doing some homework you forgot to do earlier. At each time, you must be in some place. When you are at a place, you must be in some time. Space and time are one big spacetime. Since space is already three-dimensional, the combination of space and time gives us a big, four-dimensional block of spacetime. Each point in 3D space is a point at a specific time, all of which can be described using a coordinate system. 

Now, since this is just one big block, why should we favor the present over the other possible times? In a 2D Cartesian plane, all points are equal (sounds like the U.S. Constitution!) and can be represented in the same way. In our block universe, the same idea is present (pun not intended): the past, present and future have no reason to be treated differently. In other words, all the points exist simultaneously. The point at the “supermarket at 1:00” exists in the same block of spacetime as the point at “9:00 in your bed.” The future, past, and present are all the same. 

I offer my condolences for your confusion. However, for the readers who continue to seek a headache, there is a thing called time dilation. In 1971, there was an experiment; it was called the Hafele–Keating experiment. Search it up when you have time. 

Time has many definitions. If the past, present, and future are really the same, does that mean that the future, just like the present and past, is already determined? Can we not change our destinies? Are our lives already decided for us? Others think that this block of spacetime grows as time moves along. The future is building itself as we approach. Some people even believe that time is an illusion. Time doesn’t really exist. After reading this article, what do you think?