If life is common in our Universe, and we have every reason to suspect it is, why do we not see evidence of it everywhere? This is the essence of the Fermi Paradox, a question that has plagued astronomers and cosmologists almost since the birth of modern astronomy.
It is also the reasoning behind the Hart-Tipler Conjecture, one of the many (many!) proposed resolutions, which asserts that if advanced life had emerged in our galaxy sometime in the past, we would see signs of their activity everywhere we looked. Possible indications include self-replicating probes, megastructures, and other Type III-like activity.
On the other hand, several proposed resolutions challenge the notion that advanced life would operate on such massive scales. Others suggest that advanced extraterrestrial civilizations would be engaged in activities and locales that would make them less noticeable.
This makes sense from a computing standpoint and offers an explanation for the apparent lack of activity we see when we look at the cosmos.
The research was conducted by Gia Dvali, a theoretical physicist with the Max Planck Institute for Physics and the physics chair at Ludwig-Maximilians-University in Munich, and Zaza Osmanov, a professor of physics at the Free University of Tbilisi, and a researcher with the Kharadze Georgian National Astrophysical Observatory and the SETI Institute.
The paper that describes their findings recently appeared online and is being reviewed for publication in the International Journal of Astrobiology.
The first SETI survey (Project Ozma) was conducted in 1960 and was led by famed astrophysicist Dr. Frank Drake (who proposed the Drake Equation). This survey relied on the Green Bank Observatory's 26-meter (85-foot) radio telescope to listen for radio transmissions from the nearby star systems of Tau Ceti and Epsilon Eridani.
Since then, the vast majority of SETI projects have been geared towards the search for radio technosignatures, owing to the ability of radio waves to propagate through interstellar space. As Dvali and Osmanov explained to Universe Today via email:
"Currently, we are mainly looking for radio messages, and there have been several attempts to study the sky for finding the so-called Dyson sphere candidates – megastructures built around stars. On the other hand, the problem of SETI is so complex that one should test all possible channels.
"A whole "spectrum" of technosignatures might be much wider: for instance, the infrared or optical emission from megastructures also built around pulsars, white dwarfs, and black holes. A completely new "direction" must be the search for an anomalous spectral variability of these technosignatures, which might distinguish them from normal astrophysical objects."
For many researchers, this limited focus is one of the main reasons SETI has failed to find any evidence of technosignatures. In recent years, astronomers and astrophysicists have recommended extending the search by looking for other technosignatures and methods – such as Messaging Extraterrestrial Intelligence (METI).
These include directed energy (lasers), neutrino emissions, quantum communications, and gravitational waves, many of which are spelled out in the NASA Technosignature Report (released in 2018) and at the TechnoClimes 2020 workshop.
For their study, Dvali and Osmanov suggest looking for something altogether different: evidence of large-scale quantum computing. The benefits of quantum computing are well-documented, which include the ability to process information exponentially faster than digital computing and being immune to decryption.
Given the rate at which quantum computing is advancing today, it is entirely logical to assume that an advanced civilization could adapt this technology to a much grander scale. Said Dvali and Osmanov:
"No matter how advanced is a civilization or how different is their particle composition and chemistry from ours, we are unified by laws of quantum physics and gravity. These laws tell us that the most efficient storers of quantum information are black holes.
"Although our recent studies show that theoretically, there may exist devices created by non-gravitational interactions that also saturate the capacity of information storage (so-called "saturons"), the black holes are the clear champions. Correspondingly, any sufficiently advanced ETI is expected to use them for information storage and processing."
This idea builds on the work of Nobel-prize winner Roger Penrose, who famously proposed that limitless energy could be extracted from a black hole by tapping into the ergosphere. This space lies just outside the event horizon, where infalling matter forms a disk that is accelerated to near the speed of light and emits tremendous amounts of radiation.
Several researchers have suggested that this may be the ultimate power source for advanced ETIs, either by feeding matter onto an SMBH (and harnessing the resulting radiation) or simply harnessing the energy they already put out.
Two possibilities for this latter scenario involve harnessing the angular momentum of their accretions disks (the "Penrose Process") or capturing the heat and energy generated by their hypervelocity jets (perhaps in the form of a Dyson Sphere).
In their later paper, Dvali and Osamov suggest that black holes could be the ultimate source of computation. This is based on the notions that: a) a civilization's advancement is directly correlated to its level of computational performance, and b) that there exist certain universal markers of computational advancement which can be used as potential technosignatures
Using the principles of quantum mechanics, Dvali and Osomanov explained how black holes would be the most efficient capacitors for quantum information. These black holes would likely be artificial in nature and micro-sized rather than large and naturally occurring (for the sake of computing efficiency).
As a result, they argue, these black holes would be more energetic than naturally-occurring ones:
"By analyzing the simple scaling properties of information retrieval time, we showed that the optimization of the information volume and processing time suggests that it is maximally beneficial for ETI to invest energy in the creation of many microscopic black holes as opposed to a few large ones.
"First, the micro-black holes radiate with much higher intensity and in the higher energy spectrum of Hawking radiation. Secondly, such black holes must be manufactured by means of high-energy particle collisions in accelerators. This manufacturing necessarily provides an accompanying high-energy radiation signature."
Hawking radiation, named in honor of the late and great Stephen Hawking, is theorized to be released just outside the event horizon of a black hole due to relativistic quantum effects. The emission of this radiation reduces the mass and rotational energy of black holes, theoretically resulting in their eventual evaporation.
The resulting Hawking radiation, said Dvali and Osomanov, would be "democratic" in nature, meaning that it would produce many different species of subatomic particles that are detectable by modern instruments:
"The great thing about Hawking radiation is that it is universal in all the existing particle species. Thereby, ETI quantum computers must radiate "ordinary" particles such as neutrinos and photons. Neutrinos, in particular, are excellent messengers due to their extraordinary penetration ability, which avoids the possibility of screening.
"This, in particular, offers novel fingerprints of ETI in the form of a flux of very high energy neutrinos coming both from Hawking radiation of information storing micro black holes as well as from the collision 'factories' that manufacture them. The Hawking component of radiation is expected to be a superposition of black body spectra of very high energies.
"In the paper, we have shown that the IceCube observatory can potentially observe such technosignatures. However, this is just one potential example of a very exciting new direction for SETI."
In many respects, this theory echoes the logic of the Barrow Scale, proposed by astrophysicist and mathematician John D. Barrow in 1998. A revision of the Kardashev Scale, the Barrow Scale suggests that civilizations should be characterized not by their physical mastery of outer space (i.e., planet, solar system, galaxy, etc.) but of inner space – i.e., the molecular, atomic, and quantum realms.
This Scale is central to the Transcension Hypothesis, a proposed resolution to Fermi's Paradox that suggests that ETIs would have "transcended" beyond anything we would recognize.
Herein lies another exciting aspect of this theory, which is how it offers another possible resolution to the Fermi Paradox. As they explained:
"Up until now, we have completely overlooked a natural direction for SETI in form of high energy neutrinos and other particles produced by the Hawking radiation of artificial black holes. Thereby, various experimental searches for such high energy particles can potentially shed an extremely important light on the presence of advanced ETI within the observable part of the Universe."
In short, it could be that we see a "Great Silence" when we look into the cosmos because we've been looking for the wrong technosignatures.
After all, if extraterrestrial life has had a jump on humanity (which seems reasonable given the age of the Universe), it stands to reason they would have outgrown radio communications and digital computing a long time ago. Another advantage to this theory is that it need not apply to all ETIs to explain why we haven't heard from any civilizations to date.
Given the exponential rate at which computing progresses (using humanity as a template), advanced civilizations might have a short window in which they broadcast in radio wavelengths. This is a key part of the Drake Equation: the L parameter, which refers to the length of time civilizations have to release detectable signals into space.
In the meantime, this study offers another potential technosignature for SETI surveys to look for in the coming years. The Paradox persists, but we need only find one indication of advanced life to resolve it.