The universe is constantly beaming its history to us. For instance: Information about what happened long, long ago, contained in the long-length radio waves that are ubiquitous throughout the universe, likely hold the details about how the first stars and black holes were formed. There’s a problem, though. Because of our atmosphere and noisy radio signals generated by modern society, we can’t read them from Earth.
That’s why NASA is in the early stages of planning what it would take to build an automated research telescope on the far side of the moon. One of the most ambitious proposals would build the Lunar Crater Radio Telescope, the largest (by a lot) filled-aperture radio telescope dish in the universe. Another duo of projects, called FarSide and FarView, would connect a vast array of antennas—eventually over 100,000, many built on the moon itself and made out of its surface material—to pick up the signals. The projects are all part of NASA’s Institute for Advanced Concepts (NIAC) program, which awards innovators and entrepreneurs with funding to advance radical ideas in hopes of creating breakthrough aerospace concepts. While they are still hypothetical, and years away from reality, the findings from these projects could reshape our cosmological model of the universe.
“With our telescopes on the moon, we can reverse-engineer the radio spectra that we record, and infer for the first time the properties of the very first stars,” said Jack Burns, a cosmologist at the University of Colorado Boulder and the co-investigator and science lead for both FarSide and FarView. “We care about those first stars because we care about our own origins—I mean, where did we come from? Where did the Sun come from? Where did the Earth come from? The Milky Way?”
The answers to those questions come from a dim moment in the universe about 13.7 billion years ago.
When the universe cooled about 400,000 years after the Big Bang, the first atoms, neutral hydrogen, released their photons in a burst of electromagnetic radiation that scientists can still see today. This cosmic microwave background, or CMB, was first detected in 1964. Today scientists use complex tools like the European Space Agency’s Planck probe to detect its minute fluctuations, which create a snapshot view of the distribution of matter and energy in the young universe. Scientists can also fast-forward about a hundred million years to study much of the roughly 13 billion years since the formation of the first stars, or “Cosmic Dawn,” thanks to visual data gleaned from starlight by telescopes like the Hubble (and soon, the upgraded James Webb). They allow us to see so far that we are literally looking into the past.
After the initial fireball from the Big Bang faded into the CMB, but before the first stars started burning, there was a period when almost no light was being emitted in the universe. Scientists refer to this period without visible or infrared light as the “Cosmic Dark Ages.” During this epoch, it seems likely that the universe was very simple, consisting mostly of neutral hydrogen, photons, and dark matter. Evidence about what happened during this period might help us understand how dark matter and dark energy—which by our best guesses make up about 95 percent of the mass of the universe, yet are largely invisible to us and which we still don’t really understand—shaped its formation.
There are clues about what happened during the Cosmic Dark Ages whizzing around, hidden in hydrogen, which still makes up the majority of the known matter in the universe. Each time the spin of a hydrogen’s atom’s electrons flips, it gives off a radio wave at a specific wavelength: 21 centimeters. But those wavelengths released during the Cosmic Dark Ages are not actually 21 centimeters long by the time they reach Earth. Because the universe is rapidly expanding, hydrogen wavelengths also expand, or “red-shift,” stretching out when they travel across vast distances. This means each wave’s length functions like a timestamp: The longer the wave, the older it is. By the time they reach Earth, they are more like ten or even 100 meters long, with frequencies below the FM band.