Seeking our cosmic origins on the far side of the Moon
Amazon CEO Jeff Bezos shared his vision in late May of creating permanent colonies on the Moon. He isn’t alone: a new space race is taking shape as diverse companies and governments, including our own, have set their sights on putting boots on the Moon for the first time in 40 years.
What has been missing in these discussions is how the Moon may serve as a jumping off point to explore one of the most profound questions ever posed by humanity: how did the universe begin?
We have proposed a lunar radio array that would do just that. It would be made up of thousands of simple radio antennas deployed over tens of kilometers of lunar terrain. This sprawling observatory on the far side of the Moon, built and operated by humans in tandem with robots, would transmit data to orbiting satellites to correlate and send back to Earth.
Why the Moon? The Earth is a noisy environment, and human-produced interfer- ence, in the form of radio waves and other signals, leaks through into space. The far side of the Moon, in contrast, is the most radio-quiet environment in the inner solar system. Telescopes built there could have a clear view to probe the dark ages of the universe, long before the birth of stars.
When we first proposed this idea more than 30 years ago, such an observatory would have been impossible. Not now.
That is because in December 2017, President Donald Trump directed NASA to return to the Moon. The European Space Agency is currently designing a “Moon village” featuring business, tourism and some scientific research, with work to possibly begin in the 2030s. Private entrepreneurs are eagerly awaiting the chance to mine rare minerals from the Moon.
The potential for commerce and tourism is vast. But for a small fraction, perhaps only a few percent, of the cost of developing a permanent base on the Moon, we argue that NASA should take the high road: aim to explore the universe via building telescopes on the Moon.
And there’s a lot to see. The scientific consensus is that all we see in the visible universe emerged from “inflation,” a phase of rapid expansion that occurred some trillionth of a trillionth of a second after the Big Bang. But this hypothesis lacks compelling observational evidence.
Within the fossil glow of the universe’s background radiation is a pattern of scattered light that scientists have detected and mapped as tiny ripples. These ripples are the seeds of all large-scale structure in the universe. By examining them, we may finally find that elusive evidence of the Big Bang, and also gain valuable clues about how stars and galaxies formed.
That is no easy task, requiring that scientists find trillions of relic ripples. Our only recourse is to seek out the ripples emanating from the vast numbers of cold hydrogen clouds that are the precursors of galaxies. These dim shadows are the holy grail of cosmology.
The signals from such dark age clouds, which formed when the universe was 50 times smaller than now, are detectable at highly stretched-out wavelengths of tens of meters, longer than the radio waves that reach your car stereo. Environments on Earth or in space are simply too noisy with natural and human-made radiation for us to pick out such long wavelengths. We have no choice but to look to the moon.
The Moon is a unique environment where such an exciting future of discovery awaits us, if we can only persuade the space agencies to take the high road, to give due weight to the cosmic challenge of observing our cosmic origins.
Joseph Silk is a cosmologist, author of many books (including The Big Bang) and Homewood Professor of Physics at the Johns Hopkins University. Jack Burns is a professor of astrophysics and radio astronomer at the University of Colorado. He was recently a member of the Presidential NASA Transition Team.