"If you try to keep time in your hands, it always slides through your fingers"

(Julián Barbour)

What is time? Is it just a simple human perception? Or is it really a concrete phenomenon alien to us? In appearance it has accompanied nature from the birth of the Universe, separating our instants, ordering the events of our own history. Until recently, it was believed to represent something absolute, that is, it was the same for everyone who observed it, and also, everyone would agree to classify the same event, as present or past. But later it was discovered that time depended on observers and their movement, and it could happen, for example, that for one of them the future would happen before the other. In this way, time began to be a stranger entity than it seemed to be...

The evocative image in Salvador Dalí's painting of the melting clocks is recognized worldwide. It is believed these clocks are a representation of time in the Theory of Relativity formulated by Albert Einstein. When Dalí was asked about the meaning, he said they were nothing more than a surrealistic perception of soft cheese under the Sun. The ant plague on one of the pocket watches is a symbol that appears in more paintings, and it is generally accepted as a symbol of death and deterioration. Dalí said he painted this to systematize the confusion, and thus, help to completely discredit the appreciation we have about reality itself.

In 1952, the extraordinary Ray Bradbury wrote a story called A sound of thunder, in which a company of time-travel safaris offers dinosaur hunts for its richest clients. The system of this safari apparently is designed so the travelers cannot introduce any modification in the destination, except for the hunted animals, which anyway would have died immediately for other reasons. However, one of the hunters inadvertently steps on a butterfly. When the travelers return, they find a world very different from the one they had abandoned: the slight alteration caused in the past by the hunter, has detonated a cascade of events changing the course of history. There is no doubt that Bradbury's talent was precisely a precursor of the Butterfly Effect in Chaos Theory.

In fact, in almost all science fiction novels it is assumed that modification of the past rewrites the future, (as in the work of Bradbury), and often this is precisely the plot. This is why Skynet sends the Terminator to kill John Connor, or the reason Marty tries to make his parents fall in love. And consequently: all fiction about time travel often meets sooner or later with the problem of temporal paradoxes. The most classic example is the one of the traveler who kills his own grandfather, preventing his own possibility of being born.

But, there is something that we should not confuse with time, and it is its measure. Our current conceptions of time were pre-established mostly by Western ideologies. Of course, all societies have developed concepts about time and space to organize their daily lives and correspond to natural phenomena such as day or night, the position of the stars, or the running of the seasons. But the calculation of time has been monopolized by the "West": we use the sidereal cycle, while other cultures of the "East" use the sequence of lunar periods. In both systems, the beginning of the year is frankly arbitrary and even the division of the months. However, the alignment of the week in seven days is the most impartial of all these measurements. In Africa one can find the equivalent of a week in three, four, five or six days (often associated with dates organized by local markets); in China, as an additional reference, they were ten days previously. The notion of day and night clearly corresponds to our spatial experience, but once again, the subdivision into hours or minutes exists only in our clocks and in our mind.

The different ways of "inventing" time have essentially a religious component, offering as starting points the life of a prophet/ saint, or some miraculous event of importance. These points of reference, ironically, continue to be relevant, even though today's societies boast of being fully secular. The "linear calculation" of time is an intrinsic practice of our own life, which originates from birth to death. However, with the "cosmic calculation", there is a strong tendency to circularity, since the movement of the stars presents a clearly cyclical notion.

Time seems to flow in a continuous evolution of small instants, but then, what is really that instant? Could it be infinitely small? Is there a minimum limit to classify those tiny beats of time? If time passes as it seems to us, where is the past? Just an "instant" before we inhaled air to breathe, we were one step behind, or our hand was in another position, and at that moment we physically lived our present. But "after a moment" that air is no longer the same, we have taken a step forward and our hand is in another position, as real as the previous one. Has that moment evaporated or stayed somewhere forever? If so, each of the moments passed since the Big Bang, could have been fixed in their own space-time dimension as frames of a movie, and the trips to the past might be at least in theory, possible to happen.

In a similar way, the future can be conceived. If we could travel forward in time, it would mean the whole history of the Universe, until its end, has already passed and that we are part of those past instants. Paradoxically, the future would have already happened.

But the attempts to provide those instants, have led us to define a minimum measure in the field of science, called the "Planck Time", and it is, what takes light to travel the smallest space measured in the Universe (or that we can measure at least), and by definition that is, the "Planck Length", a space so small, that underneath it, classical geometry would cease to exist. A photon goes through it in 10 -43 seconds. So to have an idea, in each second there are tens of trillions of quadrillions of Planck Times, an interval so, so tiny, until today, it has not been able to be measured, because the record of the shortest time captured by scientists is in 12 attoseconds, ("only" twelve times the trillionth part of a second).

However, does the reader remember Zeno of Elea's paradoxes about time? For example, that race in which the hero Achilles gave a few meters of advantage to a turtle?

Achilles arrives at the place where the turtle was, when he started to run, but in that interval of time the turtle would have advanced a little more; and when Achilles travels that distance, the turtle would have advanced again. The conclusion is that Achilles never manages to reach the turtle because it has to travel infinite distances, which are divided infinitely:

"The slowest when he runs will never be reached by the fastest, because the one who is pursuing must first reach the point from which the slowest started, so he will always be some distance ahead."

Plato considered Zeno an incorrigible sophist, and it took many centuries until his ideas were recovered by Newton and Leibniz when they created the infinitesimal calculus. In the words of Bertrand Russell:

"In this capricious world, nothing is more capricious than posthumous fame. One of the most notable victims of the lack of judgment of posterity is the Zeno of Eleatic. Having invented four arguments all immeasurably subtle and profound, the rudeness of later philosophers ruled that he was a mere witty conjuror, and his arguments simple sophisms. After two thousand years of continuous refutation, these sophisms were rehabilitated, and produced the foundation of the mathematical renaissance ...".

Well, continuing with this line of subsequent claim, Peter Lynds, a New Zealand theorist, seems to have recovered the amazing ideas of movement and Zeno's time, but not for applying them again to the calculus, but to the Physics and Cosmology, stating that Universe’s clock, has no beginning or end, despite time is "finite."

According to classical Physics as well with modern, an object has a certain position relative to another. In fact, the laws of movement since ancient times and Newton, up today, takes this presumption as established. But probably this is not true.

There is no object completely static in nature, so that moment of “quiet” is something entirely subjective we project to the world surrounding us. In other words, it is a product of brain functions and "consciousness".

That is, no matter how small the interval is used to measure the speed, or how slowly the object moves, in the end we must accept that it doesn’t stop moving. Immobility is an illusory phenomenon, even for objects that we believe are at rest. Therefore, in the midst of such conceptual seditions, there would be no other option but to accept the disintegration of time: absolutely everything is in motion; or nothing is in such a state. The Universe would behave as a single block in which all the events of history are agglomerated in a representation alien to our precarious imagination. In the absence of such a concept of time, ideas typical of quantum mechanics, the principle of causality or the impossibility of being present simultaneously in two events, may begin to be approached from a completely different view than the actual one.

And it becomes more evident with the "mathematical flexibility" time “enjoys” in appearance; from the gravity of Newton, to the relativity of Einstein, there have never been any impediments in the theoretical formulations, so time cannot move in the opposite direction to which it moves (or to which we believe it moves).

Apparently, the only plausible alternative remaining for the moment, is to sink into the "temporary illusion" of the infinitesimal present, knowing the existence of a space in which, what we did is still there, what we do, the same way, and what we will do is not distinguished from the previous. Or as a great physicist quoted to the point of exhaustion would say: "People like us, who believe in Physics, know that, distinction between the past, the present and the future is just an obstinately persistent illusion."

To finish this text I would like to look out at Wonderland, to offer the reader my intimate representation of what I consider the definition of time. A dialogue between Alice and the Hatter, has always shown me clearly:

“Alice sighed wearily.

"I think you might do something better with the time" she said, "than waste it in asking riddles that have no answers."

"If you knew Time as well as I do" said the Hatter, "you wouldn’t talk about wasting IT. It’s HIM."

"I don’t know what you mean," said Alice.

"Of course you don’t!" the Hatter said, tossing his head contemptuously. "I dare say you never even spoke to Time!"

"Perhaps not," Alice cautiously replied: "but I know I have to beat time when I learn music."

"Ah! that accounts for it," said the Hatter. "He won’t stand beating. Now, if you only kept on good terms with him, he’d do almost anything you liked with the clock. For instance, suppose it were nine o’clock in the morning, just time to begin lessons: you’d only have to whisper a hint to Time, and round goes the clock in a twinkling! Half-past one, time for dinner!"

"That would be grand, certainly," said Alice thoughtfully: "but then–I shouldn’t be hungry for it, you know."

"Not at first, perhaps," said the Hatter: "but you could keep it to half-past one as long as you liked...”