Physicists reflect on gravity wave discovery

Sky maps from the BICEP-2 telescope reveal evidence of gravity waves.

Sky maps from the BICEP-2 telescope reveal evidence of gravitational waves.

Contributed by Lloyd Knox, Department of Physics

On March 17, the scientific world was shaken by a dramatic announcement: Astronomers reported what many consider to be the “smoking gun” of a theorized stage in the very early evolution of the universe called inflation, revealed in data they gathered using the BICEP-2 telescope at the South Pole.

While many believed this signal was out there, it was unclear if it would be strong enough to be seen in our lifetimes, or even ever. This announcement was a very exciting one for cosmologists around the world, and of particular significance to Professor Andreas Albrecht, chair of the UC Davis physics department.

In 1982 Albrecht and Paul Steinhardt of Princeton University invented “slow-roll inflation,” a mechanism operating in the earliest fractions of a second of the Big Bang that appeared to explain key features of our universe: principally, why the universe is big and smooth and old.

That the universe might have gone through a period of inflation (accelerated expansion) had been realized a few years earlier, but the variety proposed by Albrecht and Steinhardt, and separately by Andrei Linde, was the first one that actually worked. Based on the BICEP-2 data, it now appears slow-roll inflation is actually what nature has chosen to do!

Albrecht was thrilled with the announcement and said his head has been “spinning all week.”

“Back in the 80’s, it was thrilling to work with such adventurous new ideas, but the ideas were so new and exotic it seemed a stretch to think that nature might have actually chosen to work that way. A few decades later, it is even more thrilling to contemplate the huge amount of evidence that nature really does seem to have chosen to inflate!” Albrecht wrote. (Read more of Albrecht’s thoughts on the discovery here.)

Albrecht noted that although inflationists long believed the gravity wave signal would be there, they had no way of knowing how strong the signal would be, or if they would be able to detect it even with future technology.

“It is amazing to learn that nature has been incredibly generous with us, and chosen a path where the gravitational wave signal is about as strong as it could be,” he said. The strength of the signal opens up a whole new field of gravitational wave astronomy, he said.

UC Davis physics professor Nemanja Kaloper has been another leading thinker about many aspects of inflation and he commented on a number of aspects of the discovery.

Regarding our quest for the fundamental laws of nature: “The fact that the [energy] scale of inflation is so close to the so called unification scale, where the observed matter forces may be united into the so called Grand Unified Theory (or GUT), is uncanny. Does it mean that such a GUT really exists? Is it an accident? Or are all hints of such dynamics in actual fact really indications of something else, pointing to some special corners of quantum gravity, string theory or some yet undiscovered grander scheme? We don’t know yet, but the promise of discovery is real.”

Regarding implications for models of inflation: “[This result] cuts like a hot knife through the proverbial butter of hundreds, if not thousands, of different scenarios, and tweaks of scenarios, of inflationary dynamics (and non-inflationary alternatives). The non-inflationary alternatives are now de facto ruled out. Perhaps we will still see some claims of tweaks to them, attempting to salvage what’s left, but they will be ugly, complicated and unappealing. Furthermore, most of the many inflationary models are also ruled out, being relegated to the dustbins of history of cosmology.”

Professor Lloyd Knox is an expert on the observational signatures of inflation working with data from the South Pole Telescope (SPT) and from the Planck satellite. Just last July we wrote about a step towards discovering gravitational waves, using data from the SPT. Knox praised the BICEP-2 team saying, “This measurement requires sensitivity to temperature differences on the sky of about 10 billionths of a Celsius degree, which means controlling all sources of spurious signal at this level. It’s a beautiful experiment.”

Even so, Knox said he is particularly concerned about contamination from interstellar dust.

“Fortunately we should be able to get a definitive answer on this question with the Planck data we will be releasing later this year,” he said.

“If this holds up, I just can’t believe how lucky I am to be alive now and to be a cosmologist,” Knox said. “The next 10 to 20 years will be VERY interesting! Cosmologists 100 years from now may very well be filled with envy.”

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