In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: Where is everybody?
This became the basis of the Fermi Paradox, which refers to the high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. But despite seventy years of looking, we still havent been able to answer Fermis question, leading to multiple proposals as to why this is. Today, we look at the Aestivation Hypothesis, which argues that aliens are not dead (or non-existent), theyre just resting!
This theory takes its cue from nature, where certain organisms enter a state of prolonged torpor during particularly hot or dry periods. Similar to hibernation in the winter, these organisms will remain in this state until conditions become cooler and wetter. Applied to the Fermi Paradox, the Aestivation Hypothesis asserts that alien civilizations are largely dormant because they are awaiting better conditions.
At the heart of Fermis famous question was a discrepancy that was undeniable in his time, and hasnt changed despite seventy years of research. On the one hand, there is the assumed likelihood that extraterrestrial intelligence (ETI) is plentiful throughout the Universe. On the other, theres the lack of hard evidence attesting to their existence.
Assuming that ETIs are likely is not at all farfetched. Based on the sheer size and age of the observable Universe 93 billion light-years in diameter and 13.8 billion years scientists have typically treated the existence of extraterrestrial intelligence (ETI) as a foregone conclusion. Statistically speaking, the odds are very much in favor of their being millions of civilizations out there.
Dr. Frank Drake illustrated as much in 1961 during a meeting at the Green Bank Observatory. While addressing fellow astrophysicists and SETI researchers, he presented his famous equation for estimating the number of ETIs in our galaxy that we can communicate with at any given time. The Drake Equation, as it came to be known, was expressed mathematically as:
While most of these parameters are subject to varying degrees of uncertainty, the point of the equation is clear. Even when figured for conservatively, the results always indicate that there should be at least a few extraterrestrial intelligences (ETIs) in our galaxy that we should be able to communicate with. Unfortunately, despite decades of research and multiple dedicated SETI surveys, Fermis Paradox still holds.
As a result, multiple attempts have been made to resolve the Paradox theoretically. The first and perhaps best known is the Hart-Tipler Conjecture, named jointly for astrophysicist Michael Hart and mathematician/cosmologist Frank Tipler. This theory argues that there is no evidence of intelligent life out there because none exists.
Another is the Great Filter Hypothesis, theorized by Oxford economist Robin Hanson, who argued that while simple life may be very common, advanced life was not. In other words, there exists in the Universe some type of filter that prevents simple life from reaching the advanced stage and become an ETI that we would be capable of communicating with.
The built-in assumption in both of these cases is that ETIs do not exist, hence why we see no evidence of them. But as Carl Sagan famously remarked when addressing the possible existence of alien intelligence, the absence of evidence is not the evidence of absence. As such, many theorists have proposed alternate explanations of how ETIs can exist, but remain undetected by us.
This raises another issue, which is the notion that advanced species will be able to harness increasingly large amounts of energy over time. In his 1964 essay, titled Transmission of Information by Extraterrestrial Civilizations, Soviet/Russian astrophysicist Nikolai Kardashev proposed a three-tiered scheme for classifying extraterrestrial civilizations based on the amount of energy they could harness.
This scheme came to be known as the Kardashev Scale and consisted of the following:
Civilizations that fit these Types would be detectable by looking for signs of technological activity (aka. technosignatures). For example, a Type I Civilizations could be detectable through Direct Imaging, where astronomers would look for light reflected by massive clouds of satellites (aka. Clarke Belts) around the planet. A Type II civilization, meanwhile, would be capable of building a megastructure around its home star.
These civilizations would be capable of building what Freedom Dyson described in 1960 (what has since come to be known as a Dyson Sphere). This would allow a civilization to harness all of the energy of its sun while multiplying the amount of habitable space in their system exponentially. A Type III Civilization, meanwhile, could be easily detected by looking for signs of megastructures that encompass an entire galaxy (or parts thereof).
So it possible that the Universe if filled with civilizations ranging from Type I to Type III levels of development, but are not currently engaged in any technological activity? Thats where the concept of aestivation comes into play.
The theory was first suggested by research associates Anders Sandberg and Stuart Armstrong as well as famed astronomer, astrophysicist, and philosopher Milan Cirkovic from the Future of Humanity Institute (FHI) at the University of Oxford. In their 2017 study titled, That is Not Dead Which Can Eternal Lie: the Aestivation Hypothesis for Resolving Fermis Paradox, they proposed this as a possible resolution to the Fermi Paradox.
The study was partly based on previous research conducted by Sandberg and Armstrong in a 2013 study where they extended the Fermi Paradox beyond the Milky Way. Titled Eternity in Six Hours: Intergalactic Spreading of Intelligent Life and Sharpening the Fermi Paradox, Sandberg and Armstrong argued that an advanced civilization would be able to colonize a galaxy and even travel between galaxies with relative ease.
Having concluded that in a Universe of about 2 trillion galaxies (according to recent estimates) that has existed for 13.8 billion years, there should be many Type III Civilizations out there (based on the Kardashev Scale). Not only would these species have been able to colonize their respective galaxies in a relatively short amount of time, but have been able to reach the Milky Way by now.
The reason why this is not evidence to us, argued Sandberg and Armstrong, has to do with the Landauers Principle, which is considered by man to be the basic principle of the thermodynamics of information processing. This rule holds that any logically irreversible manipulation of information (aka. computation) must be accompanied by a corresponding entropy increase (loss of heat) for the information-processing apparatus.
Applied to megastructures like Dyson Spheres, Matrioshka Brains, etc., the level of heat energy and entropy involved would be enormous. Meanwhile, astronomy and cosmology teach us that the Universe is getting steadily cooler over time as star formation slowly dies. At the same time, cosmic expansion causes the wavelength of light to stretch, which causes momentum and energy to be lost.
Eventually, its believed that this will result in the Big Chill (or Big Freeze) scenario, where even the background radiation will cool and the Universe will experience heat death. But from a computational point of view, long before that happens, advanced species could be waiting for the Universe to cool so their megastructures are able to function more efficiently.
According to Sandberg and Armstrong, an advanced civilization could (in principle) perform exponentially more irreversible logical operations by transferring entropy to the cosmological background in the future. In fact, by waiting until the background temperature is significantly lower, they estimate that an additional ten nonillion (1030), or ten quadrillion quadrillion, more computations could be performed.
It is also possible that aestivation is a means for early arrivals to our Universe to skip the long waiting period for other intelligent species to evolve so that when they wake up, theyll have plenty of people to talk to! Considering that life capable of communicating with the cosmos took 4.5 billion years to evolve here on Earth, this makes a fair degree of sense.
Of course, the Aestivation Hypothesis (much like the Fermi Paradox and the Drake Equation) is based on some assumptions about how ETIs would behave. These include:
In short, the hypothesis assumes that given the age of the Universe enough time has passed for civilizations to emerge that are more advanced than humanity. It is also assumed that they would have become space-faring civilizations, actively colonizing neighboring star systems and possibly even neighboring galaxies.
Lastly, it is assumed that this process would be visible by looking for evidence of megastructures and massive construction processes. This would include smashing up planets for building materials, relocating stars or galaxies, or even consuming gas giants, stars, or (again) entire galaxies to create fuel.
Of course, there are drawbacks and some issues with this hypothesis that have drawn criticism from the astronomical and computational community. For starters, the theory assumes that intelligent civilizations should be plentiful and that not all civilizations will aestivate. If this is the case, then there should be at least a few civilizations that would be still detectable through their technosignatures.
Second, Charles Bennett a physicist, information theorist and Fellow at the IBM Watson Research Center along with Hanson and C. Jess Reidel (of the Perimeter Institute for Theoretical Physics) produced a rebuttal paper to the Aestivation Hypothesis in 2019. In it, they argued that Sandberg et al. implicitly assume that computer-generated entropy could only be disposed of by transferring it to the cosmological background.
According to Bennett, Hanson, and Reidel, this is based on a misunderstanding of astrophysics and the physics of computing. While such an argument might apply in the distant future, they argue, it does not apply in the present and renders the aestivation model inaccurate. As they state:
[O]ur universe today contains vast reservoirs and other physical systems in non-maximal entropy states, and computer-generated entropy can be transferred to them at the adiabatic conversion rate of one bit of negentropy to erase one bit of error. This can be done at any time, and is not improved by waiting for a low cosmic background temperature. Thus aliens need not wait to be active.
In the end, the Aestivation Hypothesis is like all other attempts to resolve the Fermi Paradox (and the Drake Equation, for that matter). Far from being a concrete answer, this theory is a thought experiment designed to bring Fermis famous question into focus and perhaps provide some testable assertions. In the end, the ultimate goal is to help refine the search for extraterrestrial intelligence (SETI).
We have written many interesting articles about the Fermi Paradox, the Drake Equation, and the Search for Extraterrestrial Intelligence (SETI) here at Universe Today.
Heres Where Are The Aliens? How The Great Filter Could Affect Tech Advances In Space, Why Finding Alien Life Would Be Bad. The Great Filter, How Could We Find Aliens? The Search for Extraterrestrial Intelligence (SETI), and Fraser and John Michael Godier Debate the Fermi Paradox.
And be sure to check out the rest of our Beyond Fermis Paradox series:
Astronomy Cast has some interesting episodes on the subject. Heres Episode 24: The Fermi Paradox: Where Are All the Aliens?, Episode 110: The Search for Extraterrestrial Intelligence, Episode 168: Enrico Fermi, Episode 273: Solutions to the Fermi Paradox.
- Reflection Telescope Market Statistics, Facts, Key Players and Forecast by 2026 | Celestron, Meade, Vixen Optics, TAKAHASHI, ASTRO-PHYSICS KSU | The... - February 10th, 2021
- Comments on: Puzzling Astrophysics of Quasars in the Early Universe - SciTechDaily - February 10th, 2021
- Student astronomer finds galactic missing matter - News - The University of Sydney - February 10th, 2021
- Program Director, Moore Experimental Physics Investigator Initiative in Palo Alto , CA for Gordon and Betty Moore Foundation - Physics - February 10th, 2021
- The Woman Who Knew The Stars - ZME Science - February 10th, 2021
- Cosmos mapping project tied to YSU | News, Sports, Jobs - Youngstown Vindicator - February 10th, 2021
- Op-ed | Space weather bill will fizzle without funding - SpaceNews - February 10th, 2021
- How Andrei Linde Redefined the Universe - The Atlantic - February 10th, 2021
- 207's Best In Academic Achievement Named For February - Journal & Topics Newspapers Online - February 10th, 2021
- Life on Venus? The Picture Gets Cloudier - The New York Times - February 10th, 2021
- St. Mary's College Board of Trustees Approves Academic Program Changes for Fall 2021 - The Southern Maryland Chronicle - February 10th, 2021
- Widespread Report on the Global Refracting Telescope Market 2020-2028 with the Leading Players Celestron, Vixen Optics, ASTRO-PHYSICS, ORION, Barska,... - September 8th, 2020
- UK Part of New NSF Physics Frontier Center Focused on Neutron Star Modeling in 'Gravitational Wave Era' - UKNow - September 8th, 2020
- University subject profile: physics - The Guardian - September 8th, 2020
- This triple star system warped the protoplanetary discs around it, new research says - CTV News - September 8th, 2020
- Scientists discover first 'intermediate-mass' black hole in massive merger - Big Think - September 8th, 2020
- Looking skin deep at the growth of neutron stars - Washington University in St. Louis Newsroom - September 8th, 2020
- Scientists detect massive galactic collision between black holes that "aren't supposed to exist" - Boing Boing - September 8th, 2020
- China's secretive 'space plane' makes successful return to Earth - CNET - September 8th, 2020
- New High-Res Images of The Sun Show How Creepy Sunspots Look in Closeup - ScienceAlert - September 6th, 2020
- The End of the Universe Will Probably Be Fairly Disappointing - WIRED - September 6th, 2020
- Zooming In Tight on Dark Matter Equivalent of Being Able to See a Flea on the Surface of the Moon - SciTechDaily - September 6th, 2020
- Indian astronomers discover one of the farthest star galaxies in universe - Livemint - September 6th, 2020
- Astronomers Spot a Black Hole so Massive They Werent Sure it Could Exist - Gizmodo Australia - September 6th, 2020
- Space discoveries that will blow your mind | News | helenair.com - Helena Independent Record - September 6th, 2020
- How neutrons and protons arrange themselves in the nucleus? - Tech Explorist - September 6th, 2020
- Warped gas disc torn apart by three stars directly observed for the first time - ZME Science - September 6th, 2020
- Kentucky by Heart: Many Kentuckians have made their mark in fields of science and technology - User-generated content - September 6th, 2020
- Q&A with Astrophysics Professor, Viktor Ambartsumian International Science Prize winner Adam Burrows - The Daily Princetonian - August 17th, 2020
- Astro Bob: Hubble helps solve the mystery of why Betelgeuse faded - Duluth News Tribune - August 17th, 2020
- The Alternative to Dark Matter May be General Relativity Itself - Astrobites - August 17th, 2020
- This is the way the universe ends: not with a whimper, but a bang - Science Magazine - August 17th, 2020
- The Week of August 17, 2020 - FYI: Science Policy News - August 17th, 2020
- Nearly $13 million in federal funding awarded to University of Rochester for Physics Frontier Center - WWTI - InformNNY.com - August 17th, 2020
- The Last Supernovae - Universe Today - August 17th, 2020
- Astronomers find Milky Way look-alike galaxy 12 billion light-years away - BusinessLine - August 17th, 2020
- Dark Matter Breakthrough Allows Probing Three of the Most Popular Theories, All at the Same Time - SciTechDaily - August 17th, 2020
- Exploding Black Dwarfs Could Be the 'Last Interesting Thing to Happen in the Universe' - Gizmodo UK - August 17th, 2020
- Security Inspection Equipment Market is slated to grow rapidly in the coming years Astrophysics, Smiths Detection, Garrett, C.E.I.A., Rapiscan Systems... - August 17th, 2020
- Lovely Professional Universitys Aerospace Engineering student wins international award - The Tribune India - August 17th, 2020
- Minecraft, Bollywood Dance, and Astrophysics Help College Students Connect With Kids Online - NBC Bay Area - August 10th, 2020
- UR #26: Improved Methods for Ground-Based Follow-Up of Young Stars and Planets from the ZEIT Survey - Astrobites - August 10th, 2020
- Investigating the far-flung reaches of the universe - Times Higher Education (THE) - August 10th, 2020
- Alien life bombshell: Scientist says we will find intelligent life 'within our lifetimes' - Daily Express - August 10th, 2020
- Space roar: NASA detected the loudest sound in the universe, but what is it? - Space.com - August 10th, 2020
- From exploring immigrant identities to treating cancer: U of T awarded 29 Canada Research Chairs - News@UofT - August 10th, 2020
- A deep, giant cloud disruption found on Venus - EarthSky - August 10th, 2020
- Astronomers Sink Their Teeth Into Special Supernova Exploding Stars Produce the Calcium in Our Bones and Teeth - SciTechDaily - August 10th, 2020
- Mysterious 'fast radio burst' detected closer to Earth than ever before - Live Science - August 10th, 2020
- Half of All the Calcium in the Universe: Unprecedented Observations Shine Light on a Dying Stars Final Moments - SciTechDaily - August 10th, 2020
- Rapid Changes Detected in a Black Hole May Explain Origin of the Most Energetic Radiation in the Universe - SciTechDaily - August 10th, 2020
- What is Astrophysics? | Space - August 10th, 2020
- Astrophysics - Wikipedia - August 10th, 2020
- NASA Astrophysics | Science Mission Directorate - August 10th, 2020
- Astro-Physics - Buy Telescopes - August 10th, 2020
- An Epic, Planet-Scale Wave Has Been Hiding in The Toxic Clouds of Venus For Decades - ScienceAlert - August 10th, 2020
- 'Roaming reactions' study to shed new light on atmospheric molecules - UNSW Newsroom - August 10th, 2020
- From the Italian Renaissance to the stars: an exciting approach to fulfilling GEs > News > USC Dornsife - USC Dornsife College of Letters, Arts... - August 8th, 2020
- This Is How It All Ends - The New York Times - August 8th, 2020
- Ben Collins The Stig Top Gear | Surrey - Surrey Life - August 8th, 2020
- Mega Science On The Cover: Class XI Maharashtra Physics Text Shows Gravitational-Wave Detection By LIGO - Swarajya - August 8th, 2020
- Scientists May Have Just Found The Youngest Neutron Star Ever - Forbes - August 8th, 2020
- 'Roaming reactions' study to shed new light on atmospheric molecules - Science Codex - August 8th, 2020
- 'A space race of sorts': Stanford Space Initiative hopes to cross into space with a 'rockoon' - The Stanford Daily - August 8th, 2020
- From the Manhattan Project, a legacy of discovery and a national burden - Stars and Stripes - August 8th, 2020
- Beyond: Dilhan Eryurt and the Formation of the Sun - Astrobites - August 7th, 2020
- Whats The Loudest Sound In The Universe? - Gizmodo Australia - August 7th, 2020
- Airport Automated Security Screening Systems Market Manufacturers Overview 2020-2027 over the Worldwide Regional Analysis of Industry Trends and... - August 7th, 2020
- From the Manhattan Project, a legacy of discovery and a national burden - Stripes Korea - August 7th, 2020
- Security Inspection Equipment Market 2020 Analysis by Geographical Regions, Type and Application Till 2025 with Top Key Players:Astrophysics, Smiths... - August 7th, 2020
- 7 safe and socially distant things to do in Denver this weekend - The Denver Channel - August 5th, 2020
- Mystery radio signal sent to Earth from closest ever point within Milky Way - New York Post - August 5th, 2020
- Dark Energy Survey census of the smallest galaxies hones the search for dark matter - Stanford University News - August 5th, 2020
- MLB Has Made No Changes To The Baseball And Doesnt Plan To For 2020 - Forbes - August 5th, 2020
- 'The Umbrella Academy 2': Who Plays Lila on the Netflix Series and What Else Has She Been In? - Showbiz Cheat Sheet - August 5th, 2020
- Christopher Keane to serve as chair of the APLU Council on Research - WSU News - August 5th, 2020
- Physicists Measured The Central Engine That Powers Solar Flares For The First Time - ScienceAlert - August 5th, 2020
- Cosmic tango between the very small and the very large - ScienceBlog.com - August 3rd, 2020
- Telescope Market Report 2020: Acute Analysis of Global Demand and Supply 2025 with Major Key Player: Celestron, Meade, Vixen Optics, TAKAHASHI,... - August 3rd, 2020
- NASA Is Blasting Just the Biggest Balloon Into the Stratosphere - Popular Mechanics - August 3rd, 2020