Scientists have spent years hunting for alien life by listening in on the radio signals that bombard our planet from outer space to see if they can detect transmissions beamed using extraterrestrial technology.
But this search method has a flaw: It relies on what we can easily spot, in other words, radio signals. What if a highly developed alien civilization has figured out a way to communicate instead in encrypted code using particles of light?
This question is not the stuff of sci-fi. In fact, it is at the heart of a recent preprint study that makes the case for expanding our search for extraterrestrial life to include quantum communication.
Quantum communication uses the properties of quantum physics to relay encrypted messages from point A to point B.
This is a technology that aliens may have already conquered.
Ravi Kopparapu, a researcher at NASA’s Goddard Spaceflight Center, explains to Inverse that scientists typically look for signs of alien technology based on what we have right now on Earth. As quantum communication becomes increasingly sophisticated here on Earth, it would be a good one to add to the arsenal, he says.
“I would say it’s a good way to communicate and send a lot of information to another civilization,” Kopparapu says. “So it’s an interesting idea to propose.”
What’s new — The idea is essentially to create a new focus for a so-called “quantum SETI.”
For more than 60 years, the modern search for extraterrestrial life has focused on detecting technosignatures from foreign worlds. SETI (Search for ExtraTerrestrial Intelligence) is a series of interrelated programs looking for intelligent life beyond our solar system.
“Future searches should also target quantum communications.”
As scientists look for alien life today, they may want to add signals of quantum communication to their list of so-called “technosignatures” — the signals that reveal technology must be at play.
The recent study suggests that since quantum communication is developing on Earth, then scientists should soon add it to the list of signals to look out for from alien civilizations.
“I argue that future searches should also target quantum communications,” Michael Hippke, a researcher at Sonneberg Observatory and lead scientist of the new research, writes in the preprint.
“They are preferred over classical communications with regards to security and information efficiency, and they would have escaped detection in all previous searches.”
Here’s the background — SETI’s focus has been on radio signals. But now that humans have established quantum communication between cities on Earth, it may be worth looking for these encrypted signals beyond our planet, too.
In 2017 China inaugurated the first long-distance quantum communication landline in the world, connecting the capital city of China with the coastal city of Shanghai.
In quantum systems, data is transferred through photons — units of light known as quantum bits or qubits.
The quantum properties of qubits are linked in pairs, and those pairs are generated in random order. The pairs that are shared between the two parties spell out a secret phrase, which is then used to encrypt a follow-up data transmission.
Quantum communication systems use single photons that are encoded in a quantum superposition state, where particles can be thought of as waves. These encoded photons are then sent to distant locations.
Through this mechanism of encoding and decoding, two distant parties share a string of random bits called “secret keys” which are used to encrypt and decrypt these confidential messages.
Can aliens use quantum communication?
Although quantum communication hasn’t really taken root on Earth, a distant alien civilization that is slightly more advanced than humans may have developed the technology to send encrypted messages through photons by now.
Quantum communications, via photons, can travel large distances across the universe, transcending from one star system to another, the same way that interstellar dust and grains can reach different planets.
“We can’t hide.”
In order to detect these signals, the paper suggests that existing telescopes can be used to detect photons. The author also suggests using a femtosecond photon counter that would reveal the time stamps at which the photons are sent out — but that device, unfortunately, is yet to be invented.
Why it matters — Some may be wary that by intercepting an encoded message, humans are exposing themselves on Earth.
This alien civilization, according to Kopparapu, may have already developed a space telescope similar to the James Webb Telescope, launching in October, which would be able to detect life on distant worlds far in the universe.
“There are also other kinds of civilization activities we might be looking at where they might be building big huge structures that can go in front of a star and block the star’s light, which would give us some clue about the structure and what kind of objects they would be constructing,” he says.
Kopparapu suggests that if humans are able to intercept a quantum communication signal, then it is likely that the civilization responsible for it already knows of our own existence.
“If someone is communicating with quantum technology, I think they may already know we are here,” Kopparapu says.
The risk of exposing humanity by intercepting an encrypted code, whereby the sender would know that the signal was intercepted, does not really make a difference at this point, he says.
“It's like a kid closing their eyes and trying to hide,” he says. “We can’t hide.”
Abstract: The modern search for extraterrestrial intelligence (SETI) began with the seminal publications of Cocconi & Morrison (1959) and Schwartz & Townes (1961), who proposed to search for narrow-band signals in the radio spectrum, and for optical laser pulses. Over the last six decades, more than one hundred dedicated search programs have targeted these wavelengths; all with null results. All of these campaigns searched for classical communications, that is, for a significant number of photons above a noise threshold; with the assumption of a pattern encoded in time and/or frequency space. I argue that future searches should also target quantum communications. They are preferred over classical communications with regards to security and information efficiency, and they would have escaped detection in all previous searches. The measurement of Fock state photons or squeezed light would indicate the artificiality of a signal. I show that quantum coherence is feasible over interstellar distances, and explain for the first time how astronomers can search for quantum transmissions sent by ETI to Earth, using commercially available telescopes and receiver equipment.