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By Zeeya Merali
Time off from Time
Even though Ellis had reservations about time and the block universe, he still admired Einstein, and his respect deepened when he moved to Cambridge in 1960 to pursue a doctorate degree with world-renowned cosmologist Dennis Sciama. During his early years as a researcher, Ellis earned a reputation as a world-class cosmologist for his ability to tackle the tricky mathematics needed to fully solve some of Einstein’s space-time equations.
Ellis respected Einstein’s mathematical ingenuity, but he later balked at the philosophical implications of the block universe, in which the future stands on the same footing as the past. “If we are just machines living out a future that has already been set, then Adolf Hitler had no choice to do other than what he did; Hendrik Verwoerd, the architect of apartheid, had no choice,” Ellis says. It would be meaningless to tell them they were doing something wrong, he adds. “To me, that’s an untenable view of the world that will lead to great evil because people will just stand by as evil takes place.”
At Cambridge, Ellis soon worked with the young Stephen Hawking, a fellow student of Sciama’s. But while Hawking went on to gain international fame for his work on the origins of the universe and the nature of black holes, Ellis did not share in those glories. In 1973, at age 33, he left Cambridge, breaking off his close research relationship with Hawking, and returned to South Africa to set up his own team within the mathematics department at the University of Cape Town. It may have been a backward step for his cosmology research, but the area’s draw was irresistible — partly because he missed friends and family, but mainly because he felt a duty to try to help remedy the injustices in his homeland. “I wanted to see if I could make a difference,” he says softly.
There was, of course, no easy fix for South Africa’s ills, but Ellis turned his skills to providing help where he could. Placing his cosmology research on hold, he developed mathematical models to help tackle the housing problems that had left millions of non-whites squatting in wretched conditions. His research culminated in two books, which he co-authored, severely criticizing the government’s policies. His writing was brought before the South African Senate, where the minister of housing denounced Ellis and his aims as “pernicious.” But within the decade, the government accepted the policy changes that Ellis had proposed. Apartheid eventually ended in 1994, a year that also saw the election of Nelson Mandela as president.
Convincing policymakers that his housing project was necessary reinforced Ellis’ view that mathematics and science should be harnessed to make the world a better place. “I got involved in these various projects on the ground, where we were actually trying to make a difference,” he says. Unlike his early work on esoteric physics, he adds with a laugh, “it gave me a feeling for how mathematical modeling relates to the real world.”
During these years, Ellis also worked on cosmology, though not as vigorously as he would have liked because of the more immediate needs in his country. Now he had a chance to return to it, but his work in the “real world” inspired him to tackle the structure of the universe from a more philosophical angle.
Chopping the Block Universe
With the twilight of his career approaching, Ellis switched his focus in 2005 back to the more esoteric gripes with fundamental physics that vexed him as a student: how to deal with the absence of personal accountability in a conception of reality without time. To this end, he revisited Einstein’s block universe with an eye toward developing a new model that keeps the best features — including experimentally confirmed predictions about how time is relative — while reinstating the notion that the present is fundamentally distinct from the past and the future.
Ellis’ new model is a modification, rather than a radical upheaval, of the block universe. In his framework, set out in a series of highly regarded papers published from 2006 onward, Ellis retains four-dimensional space-time, in line with relativity’s predictions. However, he argues that Einstein took that concept too far. There’s no need to assume that the fourth dimension must already exist out into infinity. Thus Ellis’ model has one crucial difference from Einstein’s: The future boundary does not encompass all that will ever happen.
Instead, the leading edge of space-time marks the “present” crawling outward, moment by moment, transforming tomorrow’s maybes into yesterday’s fixed happenings. “Tomorrow there will be one more day in the universe than there was today,” says Ellis. “The past is real and can have had an effect on us today, but the future cannot influence us because it does not yet exist.”
Ellis’ calculations show that the evolving block universe does not contradict relativity’s prediction that two people can disagree on the order of two events. In both Einstein’s and Ellis’ pictures, the time at which each person perceives both events to have occurred is based on the discrepancies between how long it takes light from each event to reach them. In Einstein’s view, these events — and all future events — coexist. But in Ellis’ picture, both events must lie in the portion of the evolving block that houses the past; they are fixed into reality before information about them reaches anyone. Similarly, in Ellis’ view, two observers can disagree on the duration of an event, but only if that event has already crystallized into the past. Thus, Ellis’ model of time retains enough of the block universe to match with relativity’s predictions, but without needing to take Einstein’s drastic last step of assuming that the fourth dimension is solidified into the infinite future.
If Ellis is correct, how does he explain the mechanism that causes the front edge of the universe to push forward? “The surface is where the uncertainty of the future changes to the certainty of the past,” says Ellis. He found hope in another branch of physics, well known to physicists, where a transformation from uncertain possibilities observably becomes a fixed reality. It’s in the realm of quantum mechanics — a weird theory that governs the behavior of subatomic particles.
At the quantum level, chance and probability rule. For instance, it is impossible to predict the precise state of a particle — its position and energy — until you measure it. Before that moment, the particle comprises myriad possibilities, a “superposition” of all possible locations, speeds and energies at once. Upon being observed, however, this bubble bursts, and the particle collapses into a single, randomly determined identity. This is a strictly one-way process: Once collapsed, the particle can’t spontaneously revert to its multiple personalities. And there is no way to predict which state the particle will settle into; this final outcome is not predetermined.
This apparent contradiction of Einstein’s block universe has been demonstrated many times in the lab. Physicists have known for decades that quantum mechanics and general relativity are incompatible. Their contrasting notions of the nature of time — in one case as a real flowing entity and in the other as an apparent illusion — is one of the major hurdles in uniting the two frameworks into a single theory of quantum gravity that explains the motions of all objects, from atoms to planets.
Quantum experiments give Ellis the heart to believe that time is real and Einstein’s simple block universe is wrong. “Some physicists say that the future is already written into today, but I think that they are not taking quantum uncertainty seriously,” says Ellis. “Quantum uncertainty, to me, says the future is not determined until it’s happened.”
He contends that at the front edge of his evolving block universe, the uncertain future crystallizes into the past through a sequence of microscopic quantum events. At each event, particles are forced to transform from their original uncertain quantum state — where they juggle multiple conflicting identities — and settle into one rigid identity. As adjacent particles go through this process, a wave of certainty converts the open future to the closed past.
Not So Fast
Ellis may have worked out a framework that puts time back into physics, but he’s still a long way from convincing his peers. Julian Barbour, a visiting professor at the University of Oxford, respects Ellis, but he has long held the view that time is “excess ontological baggage” that should be thrown out of physics entirely. Just because something feels natural, he notes, it does not necessarily mean that it is the correct description of reality.
“This reminds me of Galileo trying to persuade the Aristotelians that the Earth moves around the sun,” says Barbour. Although this belied the everyday experience of a solid and stationary planet beneath our feet, it was ultimately right. The notion that we move through time, Barbour believes, will one day be recognized as archaic a concept as the belief that the sun revolves around the Earth.
Craig Callender, a philosopher of physics at the University of California, San Diego, sympathizes more with Ellis’ frustration: “Physicists often pooh-pooh our experiences of time, saying that it’s just an illusion, that it’s rubbish. But if it is an illusion, then it’s a very persuasive one.” The evolving block universe may be correct, Callender says, but before Ellis can convince most of his peers, he will need to give a more rigorous explanation of how quantum processes, which usually affect only subatomic objects in experiments, cascade upward to create an effect across the cosmos.
Another objection is that vast swaths of the universe are devoid of people to observe quantum processes, which physicists traditionally say is what triggers particles to transform from their uncertain superpositions into defined states. So who or what is observing these quantum particles and forcing them to change their nature? Ellis counters that quantum collapse can occur without a conscious observer, whenever particles collide with each other, knocking each other out of their uncertain states. This idea, called decoherence, is already gaining popularity (independently) among physicists.
“In my opinion, quantum collapse is happening all the time, everywhere,” Ellis says. Pointing to a sun-drenched tree, he adds: “Every time a particle of light hits a leaf, quantum uncertainty about that particle changes to certainty.”
Still, Ellis concedes that his ideas are speculative. “I wouldn’t say I think it’s all tied together yet,” he admits. “But I think that I’ve got a framework in which everything makes sense.”
And he scoffs that the burden of proof should lie not with him, but with those who claim that time is a mirage of our own making. After all, Ellis says, not only does his model gel with quantum experiments that appear to show that time is real, it also encapsulates our common sensations, “which is tested every day, by everyone, whenever anything happens.” Life itself is an experiment that backs his view.
With this in mind, he quotes from the ancient Persian poet Omar Khayyam’s musings on the visceral difference between what has gone and what is yet to come: “The moving finger writes; and having writ, moves on: Nor all thy piety nor wit shall lure it back to cancel half a line, nor all thy tears wash out a word of it.” Then, with a guttural laugh, Ellis throws down a challenge to his critics: “If you don’t believe that, then you go back and change the past!”
This article first appeared in print as “Tomorrow Never Was.” It was then published in the June 2015 Discover Magazine and on their web site