For a galaxy that’s supposed to be full of alien radio waves, Space seems awfully quiet. A new study suggests that perhaps this is because the extraterrestrials they can see that we don’t have the right quantum equipment to hear alien signals. Not yet, at least.
Quantum alien signals
Of course, there are plenty of plausible explanations for why years of research have failed to yield even the slightest whisper from a non-human intelligence among the stars.
Maybe they’re all too scared. Maybe they are all long dead. Maybe we’re too boring. Maybe we just need to be patient. Maybe we really are alone.
Or, according to Latham Boyle, a theoretical physicist at the University of Edinburgh, alien signals may be too cool for the old school, having discovered the advantages of using qubits to pack more resources into their bandwidths.
“The possibility of interstellar quantum communication is intriguing because it expands the concept of interstellar communication in fundamental ways,” Boyle explains in his paper, which can be downloaded from the peer-reviewed pre-server arXiv.
If quantum communication of alien signals existed, it could represent a victory for advanced technologies on our planet, but the process would make it impossible to detect without major equipment upgrades.
Classical communication exploits the fundamental characteristics of electromagnetic waves to send a message.
By changing the characteristics of photons, such as their number or frequency, it is possible to transfer information that remains readable across vast expanses of interstellar nothingness, allowing technological species like ours to transmit sounds, images and text at the speed of light.
As humans have discovered over the last century, a light wave is much more than just a ripple and dimension.
Quantum mechanics is the meeting point between classical physics and gambling, combining the mathematics of probability with the laws that govern the functioning of particles.
Based on this strange way of thinking about the Universe, light waves can exist in a confusion of states, intertwining their fates so that the sum of their characteristics can be used to calculate, observe, communicate and even teleport alien signals into ways that individual photons cannot do on their own.
Experiments have shown that the vague state of a photon’s probability remains intact even over quite impressive distances, making the concept of interstellar quantum networks feasible in principle.
To assess how alien signals might exploit the quantum nature of light compared to classical communications technology, Boyle compared the information capacity of each and the different ways errors could ruin classical, quantum and combined transmissions.
Accurately sending a radio signal any distance relies on the receiver capturing at least a small fraction of the light waves. In theory, a single photon could transmit a significant piece of information, allowing ample redundancy for light waves that get lost in the void along the way.
This is not the case for a quantum connection, where multiple photons contribute to a single transmission, most of which must be received in its delicate state for alien signals to be interpreted accurately.
By Boyle’s calculations, any transmitting and receiving dish would have to be more than 100 kilometers wide to ensure that enough alien quantum signals survive the journey.
This is also the best-case scenario, which involves optimistically collecting waves from our nearest galactic neighbor, at the highest frequency that could easily pass through Earth’s atmosphere.
Smaller dishes could collect shorter wavelengths, but to have a chance of collecting enough photons, they would have to be above our atmosphere, like on the Moon.
Or smaller dishes could be used in a two-way circuit in which quantum alien signals are accompanied by classical ones, attenuating the error correction process just enough to allow a few more photons to get lost along the way.
Nonetheless, any alien who wanted to scream at us in quantum would surely have the technology to see our planet in enough detail to conclude that alien signals would fall on deaf ears. So, he wouldn’t even bother trying.
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