For centuries, people have pondered the question, "Are we alone in the universe?" To date, however, researchers in the search for extraterrestrial intelligence (SETI) have come up with a resounding "we're not sure." But that hasn't stopped people from wondering.

How would we know if ETs were trying to communicate with us? What language might they use? And how might we communicate back with them?"

Taking a Quantum Leap

Researchers from the University of Edinburgh, United Kingdom, believe that the answers to these questions could lie in a field of study called quantum communication. In a paper published recently in Physical Review D, Professor Arjun Berera and Jaime Calderé³n-Figueroa, both theoretical physicists, suggest that high-fidelity communications at interstellar distances could be achieved by exploiting the quantum nature of light.

SETI at a Glance

In an interview with Now, Seth Shostak, senior astronomer and fellow at the SETI Institute in Mountain View, California, astronomers look for signs of intelligent ET life in three ways:

Conventional search for extraterrestrial intelligence (SETI), which uses large radio telescopes (such as the SETI Institute's Allen Telescope Array, with its 42 antennas, each one six meters in diameter) to scan the heavens looking for narrowband signals.
Optical SETI, which involves watching for flashing laser pulses using instruments such as the SETI Institute's LaserSETI detection devices.
Making careful observations of optical data looking for artifacts of ET societies — such as the infrared signature of a Dyson swarm, a theoretical "cloud" of habitats, satellites and solar energy collectors orbiting a star that would allow an advanced society to harvest and exploit all the energy coming from its home star.

However, Shostak clarifies that SETI involves listening only — primarily in the 1-10 Gigahertz (GHz) frequency band — and no broadcasting.

"SETI scientists often monitor frequencies adjacent to 1420 Megahertz, also known as the hydrogen line, where neutral hydrogen produces radiation," he explains. "Every astronomer on Earth has that frequency marked on their dial, so to speak, so any messages from aliens in that band will be heard by everyone."

What Is Quantum Communication?

According to MIT Technology Review, the basic unit of quantum communication is called a qubit. Qubits are typically subatomic particles such as photons or electrons.

Unlike bits — the electrical or optical "1s" and "0s" that carry your e-mail, podcasts, tweets and TikToks — qubits have some rather unusual properties that allow quantum computers to process information exponentially faster than conventional binary computers.

One of these properties is called superposition, which allows qubits to represent multiple combinations of "1" or "0" at the same time. While classical bits can only access one of 2ⁿ states at a time (e.g., two bits have 2² = 4 possible states, three bits have 2³= 8 possible states, etc.), qubits can access all 2ⁿ possible states at once.

The State of Entanglement

Even more relevant to alien quantum communication is a property of qubits called entanglement, which allows two members of a qubit pair to exist in a single quantum state. Changing the state of one paired qubit instantly changes the state of the other in a very predictable way, even if they are separated by very long distances.

Berera and Calderé³n-Figueroa propose that entanglement could be exploited in a process called quantum teleportation to potentially enable interstellar communications with ET societies. Quantum teleportation instantly transfers the "state" (i.e., information contents) of one quantum particle to a distant one without sending the particle itself.

Contemplating Quantum Teleportation

Quantum teleportation requires a pair of entangled qubits shared between a sender and receiver, plus a third qubit whose contents are to be teleported between those points. The sender initiates an interaction between their entangled qubit and the third qubit, which causes a change in the quantum state of their entangled qubit. When that change is analyzed and relayed to the receiver using a conventional electromagnetic pathway, the receiver can recreate the original message contained in the third qubit, effectively teleporting the information from sender to receiver.

"It's conceivable that a very advanced society could set up entangled particles all over the galaxy and use quantum entanglement to communicate," says Shostak.

However, he emphasizes that quantum communication can never exceed the speed of light, even for aliens, because quantum messaging between senders and receivers still relies on using a conventional electromagnetic signal.

Maintaining Coherence

For Berera and Calderé³n-Figueroa, the real challenge with quantum teleportation is that quantum messaging over interstellar distances needs to retain its coherence and maintain high fidelity, i.e., to maintain the integrity of its message as it travels long distances.

A peculiar aspect of quantum messaging is that if a message is "observed" or interacts with its environment, its waveform collapses, resulting in the loss of its information. This so-called state of decoherence can result from quantum messages interacting with say, gravitational fields, gas, dust and radiation from stars.

The universe is largely empty space, of course, but is it empty/transparent enough to facilitate reliable interstellar messaging? Berera and Calderé³n-Figueroa ran calculations on the movement of photons in different frequency bands across space to gauge the likelihood of decoherence occurring.

They determined that photons, particularly those in the X-ray spectrum, could be beamed across hundreds of thousands of light years, a distance comparable to the width of our own Milky Way galaxy. These conditions could give interstellar communications with aliens a fighting chance.

What Are We Looking For?

As SETI scientists scan the night skies with their ginormous radio telescopes looking for dispatches from ET, how do they even know what to look for?

"A lot of astronomical phenomena — quasars, pulsars, the planets in our solar system, hot and cold gas, black holes — create radio noise," observes Shostak. "But they generally don't make noise that's confined to a particular frequency band."

However, he notes that if astronomers observe a signal centered around a narrow frequency band much like a station on your car's radio, "that would indicate a signal produced by a transmitter, not a natural process."

Still Waiting â€¦

And has the SETI Institute ever received such a signal? Shostak just smiles.

"If we'd found one that was clearly an alien signal, you wouldn't have to call me up," he chuckles. "You would know about it."

Keeping It Real

Even if Shostak and his SETI colleagues thought they had detected signals from ETs, several realities currently shape the nation's ability to conduct such a "conversation."

For one, there is the matter of technology. Quantum communication is still in its infancy. As a nation, we're a long way from being able to extract information in a meaningful way from incoming ET quantum communication.

Shostak acknowledges that there are also practical considerations: time and, by extension, money.

"If the nearest aliens are 100 light years away, it will take 100 years for your response to reach them, and another 100 years for their response to reach you again," he muses." And in those 200 years, your funding has probably gone away as well."

Instead of trying to engage aliens in logistically impossible conversation, Shostak suggests that it might be smarter to just download and send them the entire internet.

"The internet is a rich information source indeed," he says. "They could put their computers on it, take advantage of its repetitive nature and build up a complete vocabulary — everything from cats to cars to humans. It would sure be a lot easier than us trying to decipher hieroglyphics back in the early 19th century."

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