Wait!

Am I the only one who thought of these first lines from the Big Bang Theory opening song as cosmologists were announcing their big find about gravitational waves as evidence of the inflationary period of early cosmic history today?

“Our whole universe was in a hot dense state,
Then nearly fourteen billion years ago expansion started… Wait”

                                                Barenaked Ladies

Wait, indeed. Because, in that pause after “expansion started” and “Wait” an important thing happened. The universe, which had been this incredibly hot, dense point-source object, suddenly expanded 100 trillion trillion times in a fraction of a second. We commonly refer to that opening event of our universe as “The Big Bang” and the incredibly fast expansion of the universe that followed as “inflation”. The period of inflation occurred between 10^-36  to around 10^-32 seconds after the Big Bang started. (I’ve read that at 10^-32 seconds after the Big Bang, the universe had expanded to nearly a millimeter in diameter.) The creation of the universe left behind a fingerprint of itself called the cosmic microwave background radiation (CMBR), which has been detected and confirmed across the skies.

At this early point in cosmic time, quivers in the light, called quantum fluctuations, were amplified by the inflation (expansion) of the newborn universe. At the same time, density waves rocked the “stuff” of the expanding cosmos. Astronomers have long wondered if gravitational waves were also created by the activity of the newly formed cosmos. If so, they would be proof of inflation, and THAT would provide another link in our chain of understanding about the earliest moments of the universe. Today’s announcement of the discovery of the fingerprints of gravitational waves from the Big Bang provides evidence for inflation and that is big news in cosmological circles.

Gravitational Waves?

To understand gravitational waves and why they’re important to this discovery, you need to get a mental picture of what gravity does. Masses have gravity. Earth has mass, and that mass deforms or curves nearby space.The deformation can travel through the universe (a type of travel called propagation), through empty space, in the form of gravitational waves. Think of how earthquakes kick up seismic waves on our planet and send them through Earth’s crust. It turns out that gravitational waves travel at the speed of light. As it travels through space, a gravitational wave alternately stretches space in a left-right direction and compresses it in an up and down motion. It does this at the speed of light through empty space.

So, the gravitational waves were generated by inflation in the infant universe. They traveled across space and left an imprint in the cosmic microwave background as they passed. To detect that imprint, scientists needed a very sensitive detector and a cold, dry place to measure them from that doesn’t have interference from radio frequency pollution. This is because the CMBR is measured using radio telescopes. The only place on the planet to do that these days is Antarctica, and that’s where a group of scientists from Harvard, NASA-JPL, and other institutions, built a special detector called BICEP2. ( It’s essentially an instrument sensitive to microwave light that is polarized. Light (including microwaves) are polarized by scattering off surfaces. In the case of the cosmic microwave background, light scattered off particles in the early universe and became slightly polarized

So, the gravitational waves spread out from the moment of the universe’s “birth” and rushed through the early universe, leaving behind polarized “ripples”— in a characteristic swirly pattern that astronomers call “B-mode” polarization. The BICEP2 instrument detected those ripples, thus giving our first “look” at gravitational waves heralding the birth of the universe.

This is very big news, and like all scientific findings, it will be discussed and tested. But, the data look very strong and point to a clear “signal” from the beginning of the universe. It’s one more step in understanding what happened in that gap between “expansion started” and “wait” in the Barenaked Ladies song. There’s surely more to come from this research, in particular implications about other universes beside our own.

If you’d like to read more about this amazing finding, check out this article called “Echoes from the Big Bang”  and a nice background article from Nature about gravitational waves.

A B-mode polarization (the swirls) map of light coming the first fraction of a second after the birth of the Universe itself. Think of this as the fingerprint of the Big Bang, which occurred some 13.8 billion years ago. Courtesy BICEP2 Collective.