The narrative of the beginning of the universe as we currently understand it is pretty interesting. It deals with both energies, distances, and time scales that are beyond our brains’ ability to fully comprehend. For hundreds of thousands of years – far longer, in fact, than Homo sapiens have even been a species – the universe was a rapidly expanding ball of matter and energy. This probably won’t even really register in its massiveness, but for 378,000 years, the universe was too hot for particles to even form basic atoms.
That’s right. A swath of space 378,000 light years in diameter was more than 5,000 degrees Fahrenheit, which is too much energy for electrons and protons to even form a simple hydrogen atom.
Scales too large to comprehend.
But as soon as the universe had cooled enough for protons and electrons to start teaming up, they did so with reckless abandon. And as they were forming the universe’s first atoms, they gave off microwaves of a specific frequency. For decades, theorists speculated that because these energetic microwaves were given off in every corner of that early universe, they should still be traveling along, expanding at the speed of light along with the very edge of the universe. Thus, a faint glow of radiation should be detectible in the vast nothingness of the universe no matter which direction we look.
And indeed, in 1963, that’s precisely what scientists found. It’s the entire reason that we believe the Big Bang theory to be correct today. If the universe were not expanding from an infinitely dense, miniscule beginning, this faint microwave signal would not be out there.
That, my friends, is the Cosmic Microwave Background.
Since it’s detection, science has built more and more sensitive devices to measure this universal background noise. And as our ability to detect it gets better and better, an interesting result starts being very readily apparent – it is by no means completely uniform. There are patterns, warm spots, and cold spots throughout the entire microwave background.
The reason for this can be found in the physics that was happening in that early universe. Waves of energy and eddies of instability created small inconsistencies in the distribution of matter and energy. Not only did this cause the fluctuations we see today in the microwaves from 13.82 billion years ago, it also gave rise to the universe as we know it. Those inconsistencies pushed matter to form clumps and begin the process of forming gas clouds, galaxies, stars, and eventually planets.
The more we can understand about how the universe worked at this early and crucial point in its history, the better we can theorize as to how everything wound up the way it is today. But as you might imagine, studying anything at 5,000 degrees Fahrenheit is no easy matter. Luckily, physics is pretty weird when it comes to scales; many phenomena that occur at huge volumes and massive scales also come into play at the opposite end of the spectrum.
Taking advantage of this, scientists at the University of Chicago are investigating the physics of the universe that produced the Cosmic Microwave Background by going the other direction. They’re chilling a cloud of atoms to a billionth of a degree above absolute zero (-459.67 degrees – so cold that even electrons nearly stop) and probing the physics of the ultracold.
“At this ultracold temperature, atoms get excited collectively. They act as if they are sound waves in air,” said Cheng Chin, a professor of physics at the University of Chicago. The dense package of matter and radiation that existed in the very early universe generated similar sound-wave excitations.
These sound-wave patterns are called Sakharov acoustic oscillations, and were named for the Russian physicist who described them more than five decades ago. To reproduce this phenomenon, Chin and his collaborators chilled a flat, smooth cloud of roughly 10,000 cesium atoms to a billionth of a degree above the coldest temperature allowed by nature, creating an exotic state of matter known as a two-dimensional superfluid.
I won’t pretend to know exactly what the hell that means, but I believe Chin when he says manipulating this cloud of atoms produces phenomena much like what was around in the early universe.
What’s important here is not necessarily the size of the region that creates the waves, but the relative sizes of length scales creating the oscillations. Everything produced in the laboratory is, obviously, much smaller than that of the early universe; but as long as the scales are accurate, much can be learned about the physics that dominated those first few hundred thousand years. The end goal is to better understand the cosmic evolution of the infant universe. Although the “universe” simulated in Chin’s laboratory measures no more than the diameter of a human hair, “It turns out the same kind of physics can happen on vastly different length scales,” Chin explained. “That’s the power of physics.”
The paper, “From Cosmology to Cold Atoms: Observation of Sakharov Oscillations in a Quenched Atomic Superfluid,” was published in the journal Science by Chin along with labmate Chen-Lung Hung and Victor Gurarie from the University of Colorado, Boulder.