Une conférence de physique fondamentale à Paris

By Louise Mayor

A visit to the Louvre before heading off to Paris Diderot University for the conference

This week I was in Paris at the Eleventh International Symposium on the Frontiers of Fundamental Physics.

It was an intimate affair with only 145 participants, 20 of whom were invited speakers from the forefront of such research areas as dark energy, dark matter, supersymmetry and the LHC.

I was the only member of press, and several high-profile physicists were kind enough to explain their research fields to me over a coffee and mini pain au chocolat.

On Wednesday, I learned about inflationary models of the universe over lunch with Paul Steinhardt, Albert Einstein Professor of Science at Princeton University and co-author of the popular science book Endless Universe: Beyond the Big Bang. I was soon brought up to speed with the basics: inflation is the idea that shortly after the Big Bang the universe underwent rapid expansion over a very short space of time.

As an experimental physicist, I was interested to hear Steinhardt comment about how the roles of theory and experiment in cosmology have reversed: while cosmology used to be theory driven, technology has evolved to such a degree that, just using data from the last 10 years, we can test all the theories conceived over the course of human history to this point, and eliminate nearly all of them. “There are only two survivors capable of describing the current data in full detail – the inflationary model and the cyclic theory,” explained Steinhardt.

He also noted that it’s important to think of cosmology as a very new experimental science – all we really know comes from less than a century of measurements. For example, we only discovered the existence of galaxies and the expansion of the universe in the early 1920s.

Steinhardt also remarked that the rate at which we’re acquiring data about cosmology has now outpaced that of particle physics. (See my schoolgirl representation of this, right.)

There’s a phrase floating around that people use to describe this burgeoning area of physics: “precision cosmology”. I asked Steinhardt what he thinks of it. He said that he doesn’t use the phrase himself, because it implies that we have settled on the underlying theory and we’re down to measuring the detailed values of the underlying parameters. However, there is a real chance that the underlying theory is incorrect. “We might be precise – but precisely wrong,” he stressed.

Steinhardt explained that while we do know a few things reasonably precisely, such as the matter density, there are still deep questions about the underlying theory – both the inflationary and cyclic models are better described as “scenarios” with some details, but many parts that are sketchy and questionable. “For example, the more we have learned about the inflationary theory over the last 30 years, the more we have to question whether it really makes the predictions that it is credited to make,” he said.

Steinhardt went on to describe the inflationary model of the universe and its problems to me in more detail, and while I followed it to some extent, if you want to hear a good explanation then I would direct you to his book!