What is time?

We refer to time constantly. What time is it? It's time to go. Time flies. I don't have time for that. These are sayings that prove that our lives are inextricably linked to time. We live and move in spacetime, the combination of space and time proposed by Einstein. In fact, he called time the fourth dimension.

But what is time? Is it a real entity or simply a mathematical convenience? Those are fascinating questions.
Time is defined as a means of measuring events that take place in such a fashion as to have a past, present, and future. Time is considered a measure of the duration of events. Humans have created words to define these durations: seconds, minutes, hours, days, weeks, months, years, decades, centuries, millennia, etc. There are 60 seconds in a minute and 60 minutes in an hour, and 24 hours in a day, and 7 days in a week. Thirty days hath September, April, June and November, all the rest have 31, except February, which is 28 unless it's a leap year. A year has 365 days, a century has 100 years and millennia have 1000 years. Everyone is familiar with these time concepts. There are many other terms for time periods like fortnight, jubilee, epoch, etc.

A second is the base unit of time and it's based on a fixed number of cycles of radiation inherent in the Cesium atom. This is the so-called atomic clock. It proves that time is very important, and that we need to have time determined very accurately.

However, Einstein muddled that pot by making time relative. It's the speed of light that's constant. Time depends upon how fast one is moving relative to a fixed observer. As one approaches the speed of light, time comes to a crawl relative to the fixed observer. This is called time dilation and Einstein quantified it. It's referred to as the Lorentz factor λ = 1 / √ 1 - v2/c2. The square root symbol is supposed to extend over the rest of the symbols and v2 is the velocity squared and c2 is the speed of light squared. Astronauts on the ISS (International Space Station) suffer this time dilation effect, but it's too insignificant to be a concern.

Time as a variable is found in many physics equations and is designated as a lower case t. This means that it is considered a real entity, at least in physics. Philosophers and theoretical physicists treat time in a more subjective manner.

Some have declared time to be unreal, meaning that it's an illusion. Einstein made it a dimension. This is a wide disparity. Is time a real entity or just a convenient idea?

Personally, I think it's both. Time has a transcendental nature that is engrained into our brains. We sense time, feel time and have time-related dreams. Time is necessary for our mental health. If it weren't, we would be out of sorts, so to speak. We are immersed in time as a part of our reality. We see motion that occurs in a time period and our brains accept time to be essential to our perception of reality.

Actually, time is very important for how we see and hear things. In the case of sight, the speed of light is paramount to our perceiving what exists in our immediate environment. Light is involved in refraction, the effect that allows us to focus scenes on our retinas, and this depends on the speed of light being a constant. Most people think of light as being instantaneous, but if it were we would not see anything. This concept is the same with hearing. Time is an integral part of audio waves, the means by which we hear sounds. In other words, time is an essential part of the universe. It's linked to space in Einstein's idea of spacetime. Together space and time constitute a continuum, a measurement or physical entity. In other words, physics treats time as a real entity. It has a dimension and a direction. It's a quantity, but at the same time it's relativistic. It can be stretched and compressed. This is almost like the quantum physics' duality of the photon.

In order for time to be a real entity, it must exist as a true entity. In other words, we exist in time, and it affects everything that we do. If you consider time to be an illusion then reality is an illusion. I don't buy that. Time is a reality and it's necessary for everything that we do. We are immersed in time and it constantly drives our lives forward. We age and grow old. This is how time affects us. Time always moves forward. It's the one thing about time that's a constant. However, we can move into the future by traveling at speeds that approach that of light. No one has discovered a way to move back in time. The only proposed ways of time traveling to the past is to find or create a wormhole, or figure out a way to travel faster than light, or create a Tipler cylinder, a dense, infinite length spinning cylinder that's spinning so fast that no material known can withstand the forces required. Currently, no one is able to do any of these things.

So, we're stuck in time that always goes forward.

Thanks for reading.