In his new book, Nobel laureate and cosmologist James Peebles suggests the universe is simpler than it seems

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

The work has launched a heated academic debate about the practice of science that has gained new relevance at a time when scientific evidence guides 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 in situ scientists was “charming,” but his findings were colored by the complexity of the problem the scientists wrestled with. attacked: elucidating the structure and biological function of a protein.

In his new book, The Whole Truth: A Cosmologist’s Thoughts on the Search for Objective RealityPeebles suggests there’s more to learn from scientists working on the comparatively simpler problem of understanding the nature of the universe as a whole.

At first glance, 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 cheap Swedish furniture?

Images from the recently commissioned James Webb Space Telescope recently served to highlight, in great detail, how far from simple the universe is when viewed through the most powerful astronomical instrument ever built. .

But Peebles’ point is that the laws that govern the universe are surprisingly simple and verifiable by observation. Unlike the philosophers of the ancient world, cosmologists don’t just try to contradict themselves with their theories. They measure, sometimes with breathtaking precision, the concrete physical parameters on which our understanding of the universe is based. As a result, argues Peebles, the development of cosmology over the past 60 or so years provides a good “concrete example” of how science discovers objective reality – something that is independent of human belief systems and rhetoric. Politics.

It’s 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 revealed how matter was forged in the fiery aftermath of the Big Bang, how an as yet unidentified substance called “dark matter” shaped the cosmos as we see it today, and how an ubiquitous sea of ​​”cosme radiation” that can be detected all around us contains information about the fundamental properties of the universe.

For Peebles, the passion for decoding the secrets of the cosmos was not the product of a childhood romance with the sky. Growing up in and around Winnipeg in the 1930s and 1940s, Peebles says he admired the stars, but didn’t pay much attention to them.

“I was more interested in how things work,” he said in an interview with The Globe and Mail. “I’m a pretty practical person. I like to see things up close. I am uncomfortable with theories that are not based on any evidence, even if I have contributed my part.

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

His introduction to cosmology came from Robert (Bob) Dicke, a charismatic and observationally-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 expanding universe theory after earning his doctorate in 1962.

“I was uncomfortable about it because at the time there was little evidence that the universe is expansion,” Peebles said. “But I stayed there for two reasons. First of all, hardly anyone else was working in this area. And second, there were these open questions that I could investigate on my own as a postdoc and write papers.

One paper led to the next. Soon Peebles, who until then had imagined himself returning to Canada, had found both career guidance and a permanent home in Princeton. His scientific output has been prodigious, aided by proximity to material-oriented colleagues working at the forefront of a technological revolution in astronomy.

The result is evident in Peebles’ Nobel Prize citation, which recognizes several contributions rather than a single breakthrough. It also provided it with a front row seat in a field of research as it evolved from a collection of loose speculation into a data-rich and highly quantitative enterprise. Based on this experience, Peebles argues that cosmologists are onto something bigger than humans and their social networks.

Peebles says scientists, having no guarantee that nature is made to be intelligible, can rely on experience and rely on two key features of reality. The first is that experiments conducted under reproducible circumstances produce reproducible results. Drop an apple and it falls to the ground. Try again tomorrow and you can expect the same. The other is that good theories about the physical world tend to predict much more than the phenomena used to develop those theories. It was Isaac Newton who showed that the same mathematical equations that describe the fall of the apple also predict the movement of the moon around the Earth. Einstein went further, developing a theory of gravity that describes with exceptional accuracy the general appearance and basic properties of the expanding universe.

But this hardly satisfies the curiosity of cosmologists to understand why the universe has these particular properties rather than others. The situation is reminiscent of a Hindu myth that imagines the Earth resting on the backs of four elephants, who, in turn, stand atop the shell of a giant tortoise. But what is the turtle standing on? An amusing answer, sometimes presented as the downfall of a fictional encounter between an academic and an ancient sage, is that “they’re turtles all the way”. According to Peebles, science is doing something similar. Newton stands on Einstein who in turn stands on the work of a future theorist. Each offers a closer approximation to a fundamental reality, but not necessarily the “whole truth”.

The whole enterprise would be doomed without a set of assumptions that Peebles says scientists must make to do their job. They include expectations that reality obeys the rules of logic and that theories can be improved based on the agreement of their predictions with observations. A more subtle assumption is that scientists, regardless of their initial starting points, converge on a singular truth. In other words, the evidence we derive from the natural world should ultimately point us to 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 matches all the available evidence.

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

Where current theories are frustratingly silent, they concern the small fraction of the universe – about 5% in terms of energy density – that is made up of what cosmologists call “ordinary matter”. It’s the part of the universe that we see with our own eyes, unaided or unaugmented by devices such as the James Webb Space Telescope. This is the universe of galaxies, stars, penguins and people. It’s also the only piece of reality apparently capable of producing life, including creatures capable of wondering what reality is.

Is life just a chance by-product of the laws of nature or a necessary aspect of them? Peebles does not 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 another kind. Peebles says he’s not interested.

“Although my mother periodically dragged me to St. Mark’s Anglican Church in Winnipeg, I never understood when I was a kid. I was looking forward to getting out of there,” he said.

The dissatisfaction with science is that it offers theories that bring us closer to reality but never seem to fully capture its essence. Maybe the point is that it’s a feature rather than a bug. Although science cannot tell us everything, it has repeatedly shown itself capable of telling us more than we expected, often to the deep surprise of scientists.

If that sounds unsatisfying, adds Peebles, “don’t forget the satisfaction of making improvements to what we know – discovering a new insect, a new star, the nature of dark matter. There are discoveries big and small to be made all over the world. Although we may never have definitive answers, I don’t mind. We can have the satisfaction of increasing our understanding of what is, after all, a remarkable place.

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