What Is Time?

Original post date: July 21, 2018

Is it the clocks you see around every day? Is it an infinite tick-tock across the universe? How to define something that is so vast and long and has no evidence of birth? I've been collecting my own thoughts and answers from everybody around me to understand more about this so-called fourth dimension. I'm nowhere near a definite answer. Each time, I end up with a unique idea about time.

Time is constructed by our brain. This is what some of them said. When we are in a very pleasant situation, we feel like we spent less time in it. When the situation is unpleasant, we tend to feel that the bad time never ends. Some also had the opinion that when we're bored, time moves slow, and when we're busy doing something fun, time moves fast. Is this true?

Time is like a river. For a practical world, time is always unidirectional. There is a past which can't be touched, a present which can't be changed, and a future which can't be seen. Time is something which has existed since the beginning of the universe (if there is any!) and will exist till the very end (if there is any!). This, however, leads to many controversial thoughts. If time has existed ever since two singularities bombarded to give us the universe we live in, what was before that? Negative time? No time at all? We use time to keep record of events, but who kept the record of time itself?

So how do we measure time? The clocks we use are just one of many methods. Ancient astronomers depended entirely on the cosmos. They constructed simple devices like sundials and sandglasses. Even a straight pole on the ground served as an instrument to measure time using its shadow. As civilizations developed, measuring time became more and more accurate. We now have atomic clocks, the most accurate ones ever made. In fact, "one second" is defined through atomic clocks: one second is the time that elapses during 9,192,631,770 cycles of the radiation produced by the transition between two levels of the caesium-133 atom. So is this what time really is? We have measured it with extraordinary precision, and yet this is nowhere close to what horologists say. Time is relative.

Being the most accepted idea in the science community, relativity was first introduced by Albert Einstein. According to him, time dilation is a difference in elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field. In other words, time need not be the same for everyone, literally.

Consider a hypothetical situation: a clock on a spaceship travelling at a speed almost equal to that of light, and a similar clock with you on Earth. Both are switched on simultaneously as the spaceship takes off. After an hour on Earth, you contact the person on the spaceship. Surprisingly, the clock there reads less than an hour. Time slows down for objects in motion. This phenomenon has actually been proven with atomic clocks. The one carried on a plane ticked slower than the one on the ground.

One more theory holds that our universe is stitched with a fabric called space-time, joining the concepts of space and time into a single continuum. Wherever matter exists, this continuum is bent due to mass. The heavier the object, the larger the bend. A black hole is so massive that it rips apart the space-time continuum, leading to a singularity known as a tesseract (hypothetical). If you have watched the sci-fi film Interstellar, you may recall that the protagonist enters a tesseract where he sees his past. What most scientists presume is that a black hole is a place where space-time is bent so much that the universal assumption of irreversible time may break down. Can time be reversed?

Our human mind is limited to a three-dimensional world, making it very difficult to even assume higher dimensions. Theories like String Theory require dimensions well beyond what we can intuitively picture. Is time a vast ocean? Can it be slowed down? We get more questions than answers.

Take a step back. Did we define time? No. Every concept about time holds true in its own way. No single theory is perfect and complete. But what we can say is that our brain is capable of generating remarkably different answers to the same question. We might not have defined time, but we certainly have questions worth pondering. Are we stitched with the fabric called time? Can we reverse it?

What is time?
Or does time even exist?

Originally posted on thedopplerdude.blogspot.com.