The idea of finding extraterrestrial life has grown into a whole field of scientific study. Of course, ideas and stories of “aliens” have existed (depending on your interpretation of the word) since the dawn of civilization. However, it has become “scientific” only recently because of advances in quantum physics and the technology and understanding of the universe it has provided. And while that technology largely belongs to the digital age, newer quantum technologies might be just the thing to finally answer the question, “Are we alone?”
Where is everybody?
Putting aside mystical nonsense, it may seem surprising that quantum physics has much to do with the search for life in the cosmos. Amusingly, though, it was a pioneering quantum physicist who is often credited with the genesis of the modern scientific search. Enrico Fermi, during a casual lunch chat at the Los Alamos National Laboratory back in 1950, asked, “Where is everybody?” He was musing about where all the aliens might be, given the vastness of the universe stretching out in both space and time. This question has since shaped what we now call the Fermi Paradox. In a nutshell, given the billions of stars and planets out there, it seems almost impossible that we haven’t found any signs of alien life yet. Despite the age of our universe and the countless chances for life to evolve and maybe hop across stars, we’ve come up empty-handed, neither hearing anything on the cosmic radio nor bumping into aliens in space.
Fast forward to 1961. Astronomer Frank Drake devised a formula known as the Drake Equation to guesstimate the number of advanced civilizations we might potentially communicate with in our galaxy. (It is perhaps a coincidence that this type of “back of the envelope” guesswork is also called Fermi Estimation.) Drake broke down the big question of alien existence into smaller, more manageable bits, like the rate of star births, the odds of those stars having planets, the chance of life sprouting on those planets, and so on. Although there’s a lot of guessing involved in filling in the details of this equation, it gives us a way to play with numbers and get an idea of what we might expect. Drake himself threw out a ballpark figure of about 10,000 civilizations in our galaxy.
The Drake Equation gives us a hopeful picture of a galaxy buzzing with communication, while the Fermi Paradox throws cold water on that, pointing out our lonely reality. Both the equation and the paradox stir up much discussion, while in scientific circles, we focus on what can be measured and tested. Roughly speaking, two kinds of measurements are attempted, which can be categorized by what they seek to measure: biosignatures and technosignatures. While the former relates to signs of life as we know it, the latter delves into the traces of technologically advanced civilizations. Let’s dive into how quantum physics propels our search in these two domains.
Biosignatures is the technical term for “signs of life.” It encompasses a range of features we hope to detect on extraterrestrial surfaces and atmospheres. The basic idea is to detect biological things, like organic compounds or their byproducts, which might not be “alive” themselves. As you might imagine, this becomes nuanced very quickly. For example, life on Earth produces a lot of simple molecules like oxygen, carbon dioxide, methane, and so on. But these are also common on other planets we are quite certain contain no life. Venus has an atmosphere of almost entirely carbon dioxide, for example.
For now, then, we have settled on searching for abundant and highly complex molecules. They must be sufficiently so to exhibit life’s universal propensity for complexity while at the same time be highly improbable to have arisen from directionless non-biological processes — “by chance,” as it were. Basically, we seemed to have won the cosmic jackpot, so that’s what we are looking for.
The Moon and Mars are the only places we’ve been to, with at least part of the mission devoted to biosignatures. There are currently three active rovers on Mars from the US and China. The Perseverance rover is currently caching Martian rock samples for a future return mission a decade from now. But what do you do with rocks and other samples once you have your hands, or robot claws, on them? Quantum physics, again, to the rescue!
The primary way to identify a substance is through spectroscopy. In broad strokes, it works by shining light on something and seeing what colors (frequencies) it absorbs and emits. Each substance has a unique absorption and emission spectrum, like a fingerprint, dictated by the quantum energy level structure it has. For some simple elements and compounds, we can isolate them on Earth and catalog the fingerprints. Ideally, though, we should be able to use the theory of quantum physics to derive what the fingerprint should look like because not all compounds can be easily isolated, nor could we perform exhaustive cataloging if they could.
The problem is that solving the equations of quantum physics on a digital computer is practically impossible. That’s where quantum computers could be helpful, as they naturally obey the laws of quantum physics. In other words, one sufficiently rich quantum system should be able to mimic the behavior of another. Quantum computers are essentially an engineer’s formalization of this idea.
This is also where quantum sensing might play a role in future missions. Quantum sensing could be called a quantum computing “spin-off” technology. A quantum sensor is essentially a small, special-purpose quantum computer that can detect and analyze signals (do spectroscopy, in some sense) with more sensitivity than conventional technology. The intuition is in using the fragility of quantum systems to our advantage. Quantum sensors could be used to detect much smaller signals or traces of the fingerprints we are looking for.
Technosignatures, in contrast to biosignatures, refer to the technological footprints left behind by advanced civilizations. They encompass a range of indicators that might hint at the existence of intelligent, technologically proficient extraterrestrial life. While biosignatures focus on detecting signs of biological activity, technosignatures trace technological activities. The underlying idea is to identify anomalies or artifacts in space that cannot be explained by natural processes alone. These would presumably be more obvious and longer-lived than mere biological signals.
Technosignature research is often far more speculative than biosignature research. While it often arises from legitimate questions like, “How could a technologically advanced civilization extract energy from a star with maximum efficiency?” it often quickly devolves into science fiction. Take, for example, Dyson spheres.
Dyson Spheres, now an example of so-called alien megastructures, emerged from a thought experiment by physicist Freeman Dyson. Their ideal form is some encapsulation of a star entirely to harvest most, if not all, of its energy output. While Dyson himself saw it more as a way to illustrate the potential energy needs of advanced civilizations, rather than a practical blueprint, the idea has since taken on a life of its own, presenting a tantalizing yet speculative target for technosignature searches.
The hunt for Dyson Spheres and other megastructures primarily involves scanning the cosmos for signals heavy in the infrared spectrum. The idea here is that an efficient construction would extract all of the high-energy light from the star and be forced to give off lower energy as heat radiation. It’s a curious blend of real science — in terms of physics calculations — and science fiction not too dissimilar from a Hollywood script.
Interestingly, this type of research seems to be dominated by people outside of academia, including former academics, amateur astronomers, and citizen scientists. While there is nothing wrong with this per se, private funding is often viewed more suspiciously than publicly funded science. Of course, many professional astronomers implicitly work in this field since they are looking for all cosmic signals.
Interest and funding in the search for technosignatures have fluctuated over time in perfect cadence with Earthly technological innovations. New telescopes, missions, and proposals always stir up optimism. Yet, the ghost of Fermi inevitably echoes with silence, and what was once excitement worthy of press releases becomes just another archived project folder on some institutional OneDrive. Today, the recently launched James Webb Space Telescope — with its ability to image planets in other solar systems — is meant to be the bearer of comic tidings.
Quantum technologies might be in the next iteration of technosignature-hunting. Quantum imaging, for instance, might allow us to detect faint or distant signals with precision limited only by the laws of physics.
Ideas from quantum technologies might also teach us that we are looking in the wrong places. For example, it’s been suggested that, since black holes are the most efficient storers of information, advanced civilizations will be using them as quantum computers. In fact, so the proposal goes, we should be searching for signals from black hole manufacturing.
Similar ideas have been suggested around quantum communication, which seems to require atypical states of light. All the “natural” light in the universe is thermal, radiating from hot things like stars. However, since the invention of the laser, at least some of the light in the universe is coherent rather than thermal, and quantum states of light can be even more exotic than that.
If you’ve ever put on night vision goggles or looked down the lens of a UV camera, you’ll have realized that what you see depends on how you look. Quantum physics provides valuable tools to build new goggles and shows us which goggles we ought to build, continuing to advance the search for life in the cosmos. Where is everybody? Perhaps they’ve always been there, using quantum physics much more effectively than we are.
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Dr. Chris Ferrie