There is this to ask first, "Is time universal?" In other words, if there are beings on a planet orbiting the nearest star to us, Proxima Centauri, only 5.9 trillion miles away, will they perceive a second, a minute, or an hour as "flowing" or "running" at the same rate that it does on earth?"
The quick answer is: No, they will not. In fact, neither will anyone on Jupiter, Venus or Saturn, or anywhere else in the entire cosmos. On a neutron star, where a teaspoon of its material weighs 5.5 billion tons (about 900 Egyptian Giza-size pyramids, according to one calculation by someone with too much "time" on his hands), time may not even "move" a second, the way we perceive a second "to move" here on earth. This gives new meaning to the term "local time", doesn't it? More on this in a bit.
The long answer is that earth time - seconds, minutes, hours, days, years - were established arbitrarily. A day, for example, is how long it takes for earth to rotate on its axis, allowing for equal but alternating exposure of its one side facing the sun (daylight), and the other side facing away (night time). Then early "timekeepers" subdivided one rotation into 24 segments, giving us the standard 24-hour cycle. It could easily have been, say, 20 hours or 10! {Actually, many hundred million years ago earth was spinning much faster than it does presently, a day would have been indeed 20 hours long - hours as we "measure" them today}. Each hour was then subdivided further into 60 minutes, then 60 seconds. That's all it was. Arbitrarily. Local to earth and nowhere else.
{And get this: Recently, like a two weeks ago, scientists just found out that earth is spinning faster than previously "clocked" by 1.59 milliseconds. If this keeps up we may someday need a leap second to compensate for the speeding rotation!}. Like, anyone really cares.
Now, the ancients also figured out that it took earth approximately 365 days to make one complete revolution around the sun. Although at first people then believed that the sun revolved around the earth.
With the exception of the Chinese, Jewish and the Mayan calendar, the entire world uses the Gregorian calendar today. It was in October 1582 that Pope Gregory XIII made a small modification on the then widely used Julian Calendar. As was then determined by the astronomers of that time, the year was not exactly 365 days. It was 365.25. Pope Gregory XIII reduced the year to its present period of exactly 365.2425 days. There was and continues to this day approximately one quarter of a day each year that must be accounted for; otherwise, the accumulated "error" will build up to a ridiculous calendar "drift" that will render the calendar useless. So, every four years that amounts to, again approximately, an entire extra day. Hence, we have a leap year to account for it. And for anyone born on February 29 .. well, it's complicated.
Okay, we got that out of the way, so, are the present, the past and the future just illusions?
The present technically, in the shortest interval of "time" possible, is that moment when the past ends and the future begins, instantaneously, as we perceive them as being different one from the other. But, literally and instantaneously, that shift happens in less than a blink of an eye, or using an atomic clock, from microsecond to microsecond (as in a millionth of a second to the next millionth second). By the time we say, "Give me a second", it's over! The present moment is ephemerally fleeting, at best.
Here's something to think about first.
The past is established as something we can never go back to while the future is beyond reach until it happens! So yesterday, we can remember and everything significant that happened then can be read in yesterday's papers or on the internet. Unless you are the fabled Merlin, of King Arthur lore, who can remember the future, tomorrow is nothing more than a gazillion probabilities, if we try to anticipate what potentially awaits everyone from around the globe of over 7 billion people and every conceivable possibility one field mouse escapes its predator, or what and how many flowers in a meadow one particular butterfly will land on. Until it "happens", nothing is ever certain.
Using the reel of film analogy, the past is a series of exposed frames, the present is as it is being presently filmed (though quickly at perhaps 24 frames per the arbitrary second), the future are blank frames yet to be exposed. Time is merely an accessory to the events being filmed.
Time that we think we are able to measure is something we cannot store, save and spend later. Unless we associate it with observable physical changes, like a ball rolling down an incline or an egg breaking into a bowl, time by itself has no meaning, it is without physical form, body, color and texture.
Time has no effect on what will occur because events happen whether there is a clock, timer or any other "time" measuring instrument. Instead, "time", if we are to give it a character role - a literary extravagance, in a manner of speaking - is a bystander, just like we are if we were just watching what is happening around us. We can choose to ignore it but events will continue to occur. Time and you and I, who are expecting for a sunrise or a sunset, are all bystanders! There is nothing we can do but wait. Well, not if instead we elect to be doing something, which "time" has no ability to do at all.
Wait, isn't the act of waiting an acknowledgement of "time running"? No. One is waiting for an event to occur, not for time to "pass" to cause an event to happen. The brain, in an effort to sift through or to make sense of what it is witnessing, is forced to process the sequence of events, the cause and effect phenomenon; that is, putting the cause ahead of the effect. But "time" is not the reason for events happening, except as a marker of the order and sequences by which events occur. Blunter still would be that "time" as a bystander is not an observer, such as we are. We have consciousness, which time doesn't. That's the difference. So, time is not real? Physically, no; but perceptively, yes. Bear with me a little bit longer.
Notice that when one is busy doing something, as in something really interesting or engrossing, time "runs" much too fast versus sitting idly, not doing anything. It is exacerbated when one is waiting for someone to arrive, who is already running late. Time seems to "run" at one particular pace when we are painting the room but excruciatingly a lot slower when we're waiting and watching for it to dry.
Furthermore, when we were children, summer seemed to last a lot longer than the summer we experienced as adults. As children our mind was not quite as heavily laden with lots of so many things to worry about, plan for and sort through, as adults do. Children's perception of a slower passage of time than how adults perceive time is best explained by another film analogy. A thick spool of film about to unwind is that of the child's. As the film unwinds from the wider diameter of the spool it would seem to move slowly. By the time it gets closest to the inner diameter of the spool, closer to its center, the film will now seem to be moving faster, as one perceives that there is not very much left to unwind.
That is the film of life. The thinning of that spool is what seems to give people much grief. Why? How about if we think of it this way? If we allow ourselves to be just mere bystanders, such as "time" is, then yes we see the spool getting smaller.
Ready for the "method to the madness" I referred to in the fourth paragraph above?
The film of life consists of two spools and the lens in between. The forward spool where developed frames are wound is the written part of our story - that scroll of life already lived and experienced. We look to those as we have lived and experienced. They are not to be repositories of regret or guilt. We should be grateful to have had that much film accumulated in that spool. There is no reverse motor that drives the spool, so forget the do over.
The lens in between is where the film gets developed in the present tense. That is also where we are allowed to change directions. But, most importantly, that is where we get to enjoy our experiences. However, there is no such thing as a free lunch, so the lens will also develop our aches and pains, our moments of anguish and grimaces that are best and soon reposited to the forward spool.
Whatever we do, it should not be to look at the other spool of film. We do not need to see how thick or thin the remaining film is in that spool. Instead, we focus on what is running across that lens. That is because today is all there is where we get to do what we like to do. It is no longer possible to do anything at the forward spool. The other spool is all about what could probably happen.
So yesterday, today and tomorrow are each a frame in the film of life. But today is all there is. There is nothing we can do about yesterday, we cannot touch tomorrow, so we are left with today - the only place where we can do anything, including where we dream, plan and prepare. So, we make the most of it before it becomes yesterday because soon tomorrow is here. Therefore, we cannot just be bystanders today. That is the job for "time"!
Below is just elective reading for anyone willing to over stimulate his or her brain cells, but definitely not required to make any more sense of Yesterday Today Tomorrow. But Michael Jordan and Shaquille O'Neal will help.
That is one thing for time to be perceived differently by different people or observers. But what if time, as we've come to understand it, really moves at really different rate - slower for some, faster for others, in real terms.
And so it was that one clever fellow, named Albert, postulated that time is relative! He's been in the news lately because the James Webb Space Telescope (JWST) has proven once again another theory or two of his.
“Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That's relativity.”
It is widely accepted that Einstein said the above - a tongue in cheek commentary on relativity - but I don't know if he really was the one who said it.
One thing Einstein did postulate that was counterintuitive but later was proven true is that time "moves" at a different rate between two observers who are moving at different speeds relative to one another. This phenomenon is real because if we don't account for the difference, navigation via GPS, how emergency and police locate where accident or crime victims are with pinpoint accuracy would be impossible (assuming, of course, their cell phones are on). These devices (including our car GPS) emit and receive signals to and from satellites circling the globe. However, the clock on the satellite and our phones move at different rates, so somewhere in Colorado Springs, a "correction" is constantly being done to synchronize the two clocks at regular intervals. Otherwise, in just a short period of "time" without the correction, your GPS navigation will be useless.
If you thought clocks "running" at different rates are such a complicated concept, it is not! Old Albert used trains and flashes of lightning for his mental analogy/thought experiments but I can't find any locomotive graphics so I used the ones below. No rocket ships yet in 1903-05.
Imagine Michael Jordan (MJ) dribbling a basketball down and up the ceiling inside a rocket ship (top drawing) that is speeding through space at half the speed of light, say. {The drawing shows a mirror and detector as a photon of light bounces from the mirror above to a detector below, so just imagine it to be a basketball}. Shaquille O'Neal (Shaq) was watching him wheeze by from another ship (bottom) that was either slower or stationary relative to or in the opposite direction to MJ's ship. MJ sees the basketball going vertically up and down as he dribbles it, hitting the ceiling and down to the floor and back endlessly (possible in zero-gravity). Nothing unusual and no different from you tossing a coin while sitting on a plane going at 400 mph. The coin drops back to your hand straight down. That's because MJ and the basketball, you and the coin are going at the same speed in your respective flying machines.
Shaq, however, sees the basketball taking a much longer path as it goes up and down because relative to him the rocket ship is wheezing by, so the ball traces an inclined path as it goes up the ceiling, and an inclined path the other way as it comes down the floor, as shown by the middle drawings.
So, what gives? Both are observing the same thing but they perceive it differently. To Shaq, the basketball takes a longer path than how MJ sees it. Yet, it is the same event!
Reason: From MJ's perspective, watching the ball go up and down vertically, time "runs normally" as if he were on the ground; however, where Shaq is concerned, "time" must be running slower for MJ since the ball is taking a longer path.
Actual experiments using identical atomic clocks - one on the ground and another on board a flight on a 747 jet around the globe - had shown that the one on the plane had slowed down, albeit very minutely, but slower nevertheless. But if it were possible for an astronaut to travel at, say, even just half the speed of light, he will come back to find his twin brother an old man, perhaps even bed ridden, while he had aged only a year based on the clock/calendar on board his space ship. If the astronaut took a longer trip, say five years at an even faster speed, he may come back to find his brother and an entire one or two future generations of his family all gone. It is as if he had leaped-frog to the future. That phenomenon is, of course, fondly labeled by scientists as the "twin paradox".
A photon of light that reaches our telescopes after leaving its source, be it a star, another galaxy, etc. some millions or even billions of years ago, is still the same photon. Unaged. Not by a nanosecond.
Now, if you were a photon of light, streaming through the cosmos, you too will not age, you will not grow old, become literally eternal, for sure. It will take another musing to explain why it is impossible for you or I to travel, at the speed of light, so let's get that fantasy out of our mind. For now, anyway.
So, what is time then? We've established that time is arbitrary. It is also local. But as arbitrarily as we've made it, relative motions of observers perceive it differently, and then gravity also affects it. Those living at sea level will age a bit slower than those up in the Himalayas. Twins Peter and Paul work at the Sears tower. Peter works at the top floor. Paul works at the basement parking garage. Peter will age sooner (will be older than Paul) after a certain time. That is the other weird part about the flow of time. Gravity affects the passage of time. A massive gravitational field like inside or at the black hole, will cause time to not only slow down but perhaps to not move at all. This is what complicates the correction that the navigation system must do. The satellite is moving fast but it is also farther away from earth where gravitational field is stronger so the correction algorithm must account for it.
This is exhausting. So, enough for now.
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