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October 10, 2002 Astrophysicist Hubert Reeves on our surprising, stardust past



Hubert Reeves

Hubert Reeves

by Sophie Pelland

“You were there at the Big Bang, but at that time, each of your particles was living its independent life.” Hubert Reeves, a nuclear astrophysicist best known to the public for his popularization of cosmology, gave about 60 fascinated listeners a short course in the history of the universe on Oct. 7.

His presentation, called “The Universe Has a History,” was the first of this year’s Montreal Inter-University Seminars on the History and Philosophy of Science, organized by Concordia’s Science College. For about an hour, Reeves discussed what he considers the most important scientific discovery of the 20th century: that our universe is not static, but has a varied history.

Before this discovery, scientists from Aristotle to Einstein considered the cosmos to be an essentially changeless backdrop disconnected from the bustle of life on Earth. Questions about how stellar objects formed were considered meaningless or beyond the scope of science.

Starting in the 1920s, evidence to the contrary began to accumulate. In 1929, Edwin Hubble’s observations of galaxies revealed that the universe is expanding.

Viewed in reverse, this expansion becomes a contraction. Extrapolating the contraction back in time provides the framework of the Big Bang theory: an early universe that was extremely dense, hot and bright expanding over time to become progressively darker, cooler and less dense.

Although the Big Bang model had been derived independently by Friedmann (1922) and Lemaître (1927) by the time of Hubble’s discovery, the model was not accepted until decades later. As Reeves emphasized, observational evidence was crucial in overcoming opposition and indifference to the model.

Penzias and Wilson provided a key piece of evidence in its favour in 1965, when they accidentally discovered a relic of the Big Bang predicted by Gamow (1948) and Alpher and Herman (1949): microwave radiation at a temperature of 2.7 degrees Kelvin (or –270.5 degrees Celsius) pervading all of space.

With the discovery of the so-called cosmic background radiation, the community of physicists and astronomers truly began what Reeves describes as “the exploration of time,” or the systematic mapping of the history of our universe.

The current standard model of cosmology, based on the Big Bang scenario, provides a coherent account of how structure gradually emerged from collisions between the individual elementary particles that made up the early universe.

As Reeves explained, the universe is structured like language, with elementary particles playing the role of letters. As the universe cooled, the elementary particles were able to form stable structures ranging from nuclei and atoms to stars and galaxies, much like letters organizing into words and sentences. Reeves smiled as he told his audience, “You are made of stardust.”

When Reeves had finished his presentation, the question period threatened to go on indefinitely, as members of the audience clamoured for clarifications and opinions. Typically, Reeves answered the questions with the simplicity and clarity that has won his popular science books and television programs public acclaim.

An expert on the production of light elements in the early universe, Montreal-born Hubert Reeves is the retired director of the prestigious Centre National de la Recherche Scientifique in Paris, and the recipient of numerous prizes and awards, including the Order of Merit of the French government and the 2001 Einstein Prize.

Although he is 70 and retired, Reeves is still active as a teacher, researcher and public lecturer. Not content to study the universe’s past, he is also deeply interested and concerned about its future, and is well-known for his involvement in environmental protection.

In fact, he delivered a talk on Global Environmental Governance (the importance of the Kyoto protocol) on Oct. 15 at Montréal’s Palais des Congrès as part of an international conference on Civil Society—Global Governance.

The next Interuniversity Seminar on the History and Philosophy of Science will take place on Nov. 11 at 4:15 p.m. in Room H-609 of the Henry F. Hall Building.