A Day Without Yesterday

When Georges LeMaitre first proposed the Big Bang theory in 1927, everyone thought he was crazy. Few other scientists at the time conceived of the universe as changing at all, let alone beginning as a single point in space-time. It was nearly impossible for them to believe that something as big as the universe started out as something smaller than an atom. Even the term “Big Bang” was coined as a sarcastic jab at the theory’s ridiculousness.

But in the 80 years since, evidence confirming the Big Bang has kept piling up. In 1929, Edwin Hubble observed that galaxies and other visible matter in the universe seemed to be rushing away from Earth, supporting LeMaitre’s idea of an expanding universe powered by the explosion of a “primeval atom” that brought the universe into being on what he called “a day without yesterday.”

Hubble’s observations helped the Big Bang gain traction, but the best evidence for the theory was discovered 40 years later. In 1964, Robert Wilson and Arno Penzias stumbled upon the cosmic microwave background (CMB), or light that is left over from the Big Bang. When the universe started to cool down and charged particles started to combine to create nuclei and atoms, photons were left out. These photons continue to permeate space, and the CMB can be observed from everywhere in the universe with the same intensity.

One scientist currently exploring the cosmic microwave background is Columbia physics professor Amber Miller. She is an experimental cosmologist, focusing on the early universe—which is unlike anything we know today. One of the reasons the early universe presents a quandary is its density—all the matter in the universe expanded out from a single point. The problem is that we usually use one set of rules to describe the very big (relativity) and another set to describe the very small (quantum mechanics). In the early universe, the very big and the very small were one and the same. But the Big Bang theory doesn’t tell us how that happened in the first place.

“We’re trying to go back even further than what the Big Bang theory says,” Miller explained. “The Big Bang doesn’t really give you a technical description of what’s happening. It just says it was hot, it was dense. So we know that’s true, but now we want to know how did it get hot and dense, where did that come from?”

In order to examine those questions, Miller and her collaborators at Columbia and other institutions around the world are taking what she calls “baby pictures of the universe.” By studying better and better maps of the cosmic microwave background, the teams can search for signatures of gravity waves produced during the Big Bang, which Miller compares to “fossil remnants of what was going on in the universe when it was even younger”—less than a second old.

Gravity waves are ripples in space-time and can be produced by many events, including spinning neutron stars—two black holes orbiting each other—and the Big Bang itself. Many models of the Big Bang suggest that: “in that really, really, really early time, the nature of space-time is so twisted and it is expanding so quickly that you generate gravity waves, and ... we are going to observe the signature of those gravity waves in the CMB. And depending on whether they are there and depending on what they look like, we can learn a lot about what made that period happen in the first place,” Miller explained. The experiments QUIET (Q/U Imagining Experiment) and EBEX (E and B Experiment) are currently working toward detecting the signatures of gravity waves in the CMB.

Cosmology is one of the exciting fields where the very small and the very big come together to attempt to answer some of the most fundamental questions in science. But particle physics and astrophysics intersect more often than their discrepancies suggest. Janet Conrad, another Columbia physics professor, stumbled upon what she calls “the crossroads” of the fields in her research on neutrinos.

Conrad and her team devised a streamlined experiment called the Mini Booster Neutrino Experiment, or MiniBooNE, which would confirm or refute the possible existence of a fourth kind of neutrino, called a sterile neutrino, which the Standard Model does not predict or describe. After several years of running the experiment, the sterile neutrino has been, as Conrad says, “backed into a corner.” It is still possible that the sterile neutrino does exist and that MiniBooNE will find it, but it is growing more and more unlikely.

What MiniBooNE did find, however, was an interaction that could help explain extremely dense neutron stars. MiniBooNE scientists observed neutrinos bouncing off atomic nuclei in their detector and producing photons, or a particle of light. If neutron stars could reverse that process and produce neutrinos from interactions between nuclei and photons, those neutrinos could escape into space unnoticed and take their energy with them. It would be “a way of having energy stream out of a neutron star in a way you don’t expect,” Conrad explains. Neutrinos escaping a supernova may also be the reason the dying star is able to explode, a surprising and beautiful link between a tiny charge-less particle and one of the most dramatic events in the large-scale universe.

Ever since the Big Bang theory tried to bring together the big and the small we’ve had trouble understanding that mysterious unity. It is common and important in nature but nearly impossible to describe in an equation. As we work toward a theory of everything that describes the unity of the largest scales and the smallest scales, we get closer to understanding not only the universe we live in today, but maybe even the Big Bang’s yesterday.

Elizabeth Wade is a Barnard senior majoring in comparative literature.
Fear of Physics runs alternate Mondays.
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