Why time doesnt exist

Carlo Rovelli is an Italian theoretical physicist who wants to make the uninitiated grasp the excitement of his field. His book Seven Brief Lessons on Physics , with its concise, sparkling essays on subjects such as black holes and quanta, has sold 1. We meet outside the church of San Petronio in Bologna, where Rovelli studied.

A cheery, compact fellow in his early 60s, Rovelli is in nostalgic mood. Before that, he was in the US, at the University of Pittsburgh, for a decade.

He rarely visits Bologna, and he has been catching up with old friends. We wander towards the university area. Piazza Verdi is flocked with a lively crowd of students.

There are flags and graffiti and banners, too — anti-fascist slogans, something in support of the Kurds, a sign enjoining passers-by not to forget Giulio Regeni , the Cambridge PhD student killed in Egypt in He was a passionate student activist, back then. What did he and his pals want? We wanted a world without boundaries, without state, without war, without religion, without family, without school, without private property.

He was, he says now, too radical, and it was hard, trying to share possessions, trying to live without jealousy. And then there was the LSD. He took it a few times. And it turned out to be the seed of his interest in physics generally, and in the question of time specifically. Things were happening in my mind but the clock was not going ahead; the flow of time was not passing any more. It was a total subversion of the structure of reality. Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

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Download PDF. History Caltech confronted its racist past. Close banner Close. Email address Sign up. Get the most important science stories of the day, free in your inbox. So time is subjective? According to the second law of thermodynamics, as time goes by, the amount of disorder — or entropy — in the Universe will always increase. Many physicists now suspect that when gravity forces enough tiny particles to interact with each other, the forward-facing arrow of time emerges, and entropy can increase.

The rules then change to favour a more directionless Universe only once these tiny particles start interacting with much larger things. But for that to work, entropy must have increased, which means the Universe had to have started off more ordered than it is now — something that some physicists have tried to explain by suggesting there are parallel universes where time runs forwards, backwards, sideways, you name it.

In an effort to get to the bottom of one of the biggest conundrums in modern science, a pair of physicists decided to test the assumption that gravity is the force behind all this craziness.

The point at which particles are thought to transition from being governed by the arrow of time to being governed by the directionless laws of the Universe is known as decoherence. Planck time — the smallest unit of time that has any physical meaning — is second, less than a trillionth of a trillionth of an attosecond.

Beyond that? Tempus incognito. At least for now. Efforts to understand time below the Planck scale have led to an exceedingly strange juncture in physics. The problem, in brief, is that time may not exist at the most fundamental level of physical reality. If so, then what is time? And why is it so obviously and tyrannically omnipresent in our own experience? One consequence is that the past, present, and future are not absolutes.

Some four decades ago, the renowned physicist John Wheeler, then at Princeton, and the late Bryce DeWitt, then at the University of North Carolina, developed an extraordinary equation that provides a possible framework for unifying relativity and quantum mechanics. But the Wheeler-DeWitt equation has always been controversial, in part because it adds yet another, even more baffling twist to our understanding of time.

It may be that the best way to think about quantum reality is to give up the notion of time — that the fundamental description of the universe must be timeless. No one has yet succeeded in using the Wheeler-DeWitt equation to integrate quantum theory with general relativity. Nevertheless, a sizable minority of physicists, Rovelli included, believe that any successful merger of the two great masterpieces of 20th-century physics will inevitably describe a universe in which, ultimately, there is no time.

As far as we can tell, though, time is a one-way process; it never reverses, even though no laws restrict it. Are we done? The mother of all initial conditions, Lloyd says, was the Big Bang. Physicists believe that the universe started as a very simple, extremely compact ball of energy.