One year ends and another begins… But what really is time and how true is the belief that only the present exists?

But have you ever wondered what time really is beyond what clocks and almanacs show?

Think about it for a moment. In our experience as human beings we perceive time as a sequence of events. That is to say: a future that becomes the present and a present that becomes the past.

We feel that the present is the only thing that exists, but it is ephemeral, it disappears every second.

We consider that the past is what has ceased to be and moves away from us towards oblivion, although part of it remains in our memories.

And we believe that the future is something potential that has not yet happened and promises various alternative paths.

But what is true in all this? Is time real or a mere illusion? Or a mix of both?

Get ready, because what classical and current physics says about it may cause you a mixture of amazement and perplexity, since it questions some of the most widespread beliefs about our future.

“Physicists do not agree when it comes to answering the general question of what time is,” Dr. Chamkaur Ghag, renowned astrophysicist at University College London (UCL), tells BBC Mundo.

“But there is consensus in accepting what Albert Einstein’s theory of relativity says, which presents a universe where space and time are inseparable and influence each other, and where phenomena are experienced in different ways depending on the state of movement of the observers.”

In this cosmos, time is relative, Ghag explains: it dilates as one body moves faster relative to others. Thus, the closer an object (or an individual) approaches the speed of light, the more noticeable the slowdown of the clock is.

According to Einstein, time also passes more slowly when a body experiences a greater gravitational force.

in the movie Interstellar (2014), by Christopher Nolan, there is a scene that explains it well: the protagonist descends to a planet subjected to intense gravity because it is near a black hole. When he returns to the main ship after what for him has been little more than an hour, he meets a crew member for whom it has been… 23 years.

Time dilation has been proven experimentally in recent decades using ultra-precise atomic clocks and modern particle accelerators. To which has been added the detection of gravitational waves generated by distortions in space-time.

Several triumphs for Einstein’s ideas.

“Another principle accepted by physicists is that time goes forward and never backwards,” says Ghag.

However, a new – and controversial – current in physics that bears the name of post-quantum theory of classical gravity it adds even more complexity to the notion of time, by imbuing it with a degree of chance.

According to her, the way time passes can oscillate randomly in certain parts of the universe, like the ebb and flow of a stream, Jonathan Oppenheim, researcher at the UCL Institute of Quantum Science and Technology and proponent of the revolutionary theory, explains to BBC Mundo.

“These fluctuations occur due to the interaction between the quantum world, which has strange and unpredictable behavior, and the fabric of space-time, which is dominated by predictable rules,” says Oppenheim.

Which would explain curiosities of our cosmos such as, for example, that a particle can be in two places at the same time or be connected to another particle millions of light years away.

But is there anything more than relative time with hints of chance? In your bestseller In “A Brief History of Time,” the famous British physicist Stephen Hawking mentions the existence of “psychological time.”

According to Chamkaur Ghag of University College London, it’s about the way our brain processes temporal relativity.

“For some reason that neurological science has not yet been able to explain, a part of our psyche interprets the future in terms of past, present and future.”

“We are trapped in a limited brain that understands something as complex as time… What are we going to do! This is a fascinating field of study in which there is much left to investigate,” says the British particle physicist.

The question then is: how do the categories that we know as past, present and future function in the universe?

One of the notions that can leave us most bewildered is that, in theory, our past still exists somewhere in the universe.

“As space and time are inseparable and interact, each and every event in our lives occurs in a different space-time, even if they happen in what we believe to be the same place,” clarifies Dr. Ghag.

“It is as if our existence were a succession of snapshots,” he says.

So that you understand it, reader, think for example about what you are doing right now: reading this article perhaps on your cell phone. But your current “I” no longer occupies the same space-time as the one a second ago. The one you left behind continues to exist on another plane even if you can’t see it. And so every second that passes.

Ghag explains that if we knew the exact coordinates of the episodes from our past and it were possible to travel to those points – something very unlikely – we could meet our past “selves”.

Fascinating, isn’t it? The terrifying one?

Regarding the present, current physics maintains that what we call “now” is the set of events that, in our human perception, occur simultaneously at a given moment.

However, since time can dilate, pass at different rates for different observers, and even have random comings and goings, it is also feasible that the present is a “duration” rather than a moment.

That would make it a little less fleeting than we thought.

And what about the future, now that a new year begins. Is it worth making a list of resolutions for the next 12 months if we consider that the future depends on our freedom?

Or is the future predetermined, which would invalidate free will but also make it easier to predict what is to come?

This is where physicists feel most disoriented when talking about time.

“Some say we can influence the future by choosing between different pathways,” says Dr. Ghag.

“But suppose free will were also subject to relativity. Theoretically, if you knew all the possible trajectories of minds and phenomena, you could predict the future,” he speculates.

Of course, that would create a paradox, as the UCL physicist explains: “Knowledge of what is going to happen ends up altering what will happen.”

“The truth is that physics still doesn’t have a clear answer about what the future is,” Ghag admits.

Meanwhile, the scientist points out, human beings’ hope and desire for change continues to be nourished by the idea that tomorrow can be forged, even the year that is about to begin.