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In the late 1970′s the French philosopher and sociologist Bruno Latour spent two years at the Salk Institute observing molecular biologists the way an anthropologist might observe a tribe of hunter-gatherers. By the end, Latour had formed the opinion that scientific facts are not simply discovered but rather constructed through a social process that depends partly on the status and prestige of the people involved.

The work launched a heated academic debate about the practice of science that has gained new relevance in an era when scientific facts guide our responses to pandemics, climate change and other pressing challenges.

For James Peebles, a Manitoba-born cosmologist and co-winner of the 2019 Nobel Prize in physics, Latour’s study of scientists in situ was “charming” but its conclusions were coloured by the complexity of the problem the scientists were tackling: elucidating the structure and biological function of a protein.

Canadian cosmologist James Peebles.Handout

In his new book, The Whole Truth: A Cosmologist’s Reflections on the Search for Objective Reality, Peebles suggests there is more to be learned from scientists who are working on the comparatively simpler problem of understanding the nature of the universe at large.

At face value, such a characterization seems absurd. After all, what could be more complicated than the universe itself, which contains everything complicated we know, including galaxies, proteins and manuals for assembling inexpensive Swedish furniture?

Images from the newly commissioned James Webb Space Telescope have lately served to underscore, in rich detail, just how far from simple the universe looks when viewed through the most powerful astronomical instrument ever built.

But Peebles’s point is that the laws that govern the universe are surprisingly straightforward and testable by observation. Unlike philosophers of the ancient world, cosmologists are not just trying to out-argue one another with their theories. They are measuring, sometimes with breathtaking precision, the concrete physical parameters on which our understanding of the universe is based. As a result, Peebles argues, the development of cosmology over the past 60-odd years makes for a good “worked example” of how science uncovers objective reality – something that is independent of human belief systems and political rhetoric.

This is a story in which Peebles, now 87, has played a formidable role – albeit with an understated style that reflects his Canadian roots. As a theorist, his work has helped to reveal how matter was forged in the fiery aftermath of the Big Bang, how a still-unidentified substance called “dark matter” shaped the cosmos as we see it today, and how a ubiquitous sea of “fossil” radiation that can be detected all around us carries information about the universe’s fundamental properties.

For Peebles, the passion for decoding the secrets of the cosmos was not the product of a boyhood romance with the heavens. Growing up in and around Winnipeg in the 1930s and 40s, Peebles says he admired the stars but didn’t pay much attention to them.

“My interest was more in how things work,” he said in an interview with the Globe and Mail. “I am kind of a practical person. I like to see things up close. I’m uncomfortable with theories that are not based on any evidence, even though I’ve contributed my share of them.”

Yet, in spite of this inner pragmatism, Peebles would go on to make his mark in a field of science that is arguably the least up-close and practical of them all.

His introduction to cosmology came courtesy of Robert (Bob) Dicke, a charismatic and observation-oriented astrophysicist at Princeton University, where Peebles arrived in 1958, after graduating from the University of Manitoba. Peebles became part of a circle of young researchers in Dicke’s orbit who were busy applying the scientific harvest of wartime research and development to deeper questions about the nature of gravity and the cosmos. It was at Dicke’s suggestion that Peebles began looking into the theory of an expanding universe after earning his PhD in 1962.


“I was uneasy about that because at the time there was precious little evidence that the universe is expanding,” Peebles said. “But I stayed in it for two reasons. First, practically no one else was working on this field. And second, there were these open questions that I could investigate on my own as a post doc and write papers.”

One paper led to the next. Soon, Peebles, who until then had imagined himself returning to Canada, had found both a professional focus and a permanent home at Princeton. His scientific output was prodigious, aided by proximity to colleagues who were hardware-oriented and working at the leading edge of a technological revolution in astronomy.

The outcome is evident in Peebles’s Nobel Prize citation, which recognizes recognizes multiple contributions rather than a single breakthrough. It has also provided him with a front row seat to a field of research as it evolved from a collection of loose speculations to a data-rich and highly quantitative enterprise. Based on this experience, Peebles makes his case that cosmologists are onto something bigger than humans and their social networks.

Peebles says that scientists, lacking any guarantee that nature is made to be intelligible, can draw on experience and count on two key features of reality. One is that experiments conducted in repeatable circumstances produce repeatable results. Let go of an apple and it drops to the ground. Try it again tomorrow and you can expect the same. The other is that good theories about the physical world tend to predict far more than the phenomena used to develop those theories. It was Isaac Newton who showed that the same mathematical equations that describe the falling apple also predict the moon’s motion around the Earth. Einstein took it further, developing a theory of gravity that describes with exceptional accuracy the overall appearance and basic properties of the expanding universe.

But that hardly satisfies cosmologists’ curiosity to understand why the universe has those particular properties instead of others. The situation recalls a Hindu myth that imagines Earth as resting on the backs of four elephants, which, in turn, stand atop the shell of a giant turtle. But what is the turtle standing on? A droll answer, sometime framed as the punchline to a fictitious encounter between an academic and a wise elder is that “it’s turtles all the way down.” In Peebles’s view, science is doing something similar. Newton stands on Einstein who in turn stands on the work of some future theorist. Each offers a closer approximation to a core reality, but not necessarily the “whole truth.”

The whole enterprise would be doomed without a set of assumptions that Peebles says scientists must make in order to perform their work. They include the expectations that reality abides by rules of logic and that theories can be improved based on how well their predictions fit with observations. A more subtle assumption is that scientists, whatever their initial starting points, are converging on a singular truth. In other words, the evidence we draw from the natural world should ultimately be pointing us toward the same description of reality, says Peebles. The corollary – which Peebles calls an expression of hope – is that it will never be demonstrated that there is no theory that fits all the available evidence.

Over the course of the book, Peebles shows how well those assumptions have served cosmologists and, in turn, what that says about the fundamental soundness of the scientific enterprise. It has also yielded a well-verified but incomplete picture of our universe as the product of a tug of war between the gravitational pull of dark matter (whose identity has yet to be discovered) and the accelerating push of dark energy (whose nature remains undetermined).

Where current theories are frustratingly silent relates to the small fraction of the universe – about 5 per cent in term of energy density – that is made up of what cosmologists call “ordinary matter.” This is the part of the universe that we see with our own eyes, unaided or un-augmented by devices such as the James Webb Space Telescope. It is the universe of galaxies, stars, penguins and people. It is also the only piece of reality seemingly capable of producing life, including creatures with the capacity to wonder what reality is all about.

Is life just a chance byproduct of nature’s laws or necessary aspect of them? Peebles doesn’t know and so far there is no indication in cosmological theory. For some, this is the point where religion takes over with ready-made answers of a different sort. Peebles says he is not interested.

“Although my mother did drag me periodically to St. Mark’s Anglican Church in Winnipeg, I never ‘got it’ as a kid. I couldn’t wait to get out of there,” he said.

The dissatisfaction with science is that it offers theories that get us closer to reality but that never seem to fully capture its essence. Perhaps the point is that this is a feature rather than a bug. While science may be unable to tell us everything, it has repeatedly shown itself capable of telling us more than we expected, often to scientists’ profound surprise.

If that seems unsatisfying, Peebles adds, “don’t forget the satisfaction of making improvements in what we know – discovering a new insect, a new star, the nature of dark matter. There are discoveries large and small to be made all through the world. Although we can never have final answers, that doesn’t bother me. We can have satisfaction in increasing our understanding of what is, after all, a remarkable place.”

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