During the 1940s, Hungarian-American scientist John von Neumann developed a mathematical theory for how machines could endlessly reproduce themselves. This work gave rise to the idea of “von Neumann probes“, a class of self-replicating interstellar probes (SRPs) that could be used to do everything from exploring the Universe to seeding it with life and intervening in species evolution.
Some have naturally suggested that this be a focus SETI research, which would entail looking for signs of self-replicating spacecraft in our galaxy. But as is always the case with proposals like these, the Fermi Paradox eventually reasserts itself by asking the age-old question – “Where is everybody?” If there are alien civilizations out there, why haven’t we found any evidence of their SRPs?
The Fermi Paradox remains a stumbling block when it comes to the search for extra-terrestrial intelligence (SETI). Named in honor of the famed physicist Enrico Fermi who first proposed it, this paradox addresses the apparent disparity between the expected probability that intelligent life is plentiful in the Universe, and the apparent lack of evidence of extra-terrestrial intelligence (ETI).
In the decades since Enrico Fermi first posed the question that encapsulates this paradox (“Where is everybody?”), scientists have attempted to explain this disparity one way or another. But in a new study conducted by three famed scholars from the Future of Humanity Institute (FHI) at Oxford University, the paradox is reevaluated in such a way that it makes it seem likely that humanity is alone in the observable Universe.
The study, titled “Dissolving the Fermi Paradox“, recently appeared online. The study was jointly-conducted by Anders Sandberg, a Research Fellow at the Future of Humanity Institute and a Martin Senior Fellow at Oxford University; Eric Drexler, the famed engineer who popularized the concept of nanotechnology; and Tod Ord, the famous Australian moral philosopher at Oxford University.
For the sake of their study, the team took a fresh look at the Drake Equation, the famous equation proposed by astronomer Dr. Frank Drake in the 1960s. Based on hypothetical values for a number of factors, this equation has traditionally been used to demonstrate that – even if the amount of life developing at any given site is small – the sheer multitude of possible sites should yield a large number of potentially observable civilizations.
This equation states that the number of civilizations (N) in our galaxy that we might able to communicate can be determined by multiplying the average rate of star formation in our galaxy (R*), the fraction of those stars which have planets (fp), the number of planets that can actually support life (ne), the number of planets that will develop life (fl), the number of planets that will develop intelligent life (fi), the number civilizations that would develop transmission technologies (fc), and the length of time that these civilizations would have to transmit their signals into space (L). Mathematically, this is expressed as:
In a study conducted back in 2013, Sandberg and Stuart Armstrong (also a research associate with the FHI and one of the co-authors on this study) extended the Fermi Paradox to look beyond our own galaxy, addressing how more advanced civilizations would feasibly be able to launch colonization projects with relative ease (and even travel between galaxies without difficulty).
As Dr. Sandberg told Universe Today via email:
“One can answer [the Fermi Paradox] by saying intelligence is very rare, but then it needs to be tremendously rare. Another possibility is that intelligence doesn’t last very long, but it is enough that one civilization survives for it to become visible. Attempts at explaining it by having all intelligences acting in the same way (staying quiet, avoiding contact with us, transcending) fail since they require every individual belonging to every society in every civilization to behave in the same way, the strongest sociological claim ever. Claiming long-range settlement or communication are impossible requires assuming a surprisingly low technology ceiling. Whatever the answer is, it more or less has to be strange.”
In this latest study, Sandberg, Drexler and Ord reconsider the parameters of the Drake Equation by incorporating models of chemical and genetic transitions on paths to the origin of life. From this, they show that there is a considerable amount of scientific uncertainties that span multiple orders of magnitude. Or as Dr. Sandberg explained it:
“Many parameters are very uncertain given current knowledge. While we have learned a lot more about the astrophysical ones since Drake and Sagan in the 1960s, we are still very uncertain about the probability of life and intelligence. When people discuss the equation it is not uncommon to hear them say something like: “this parameter is uncertain, but let’s make a guess and remember that it is a guess”, finally reaching a result that they admit is based on guesses. But this result will be stated as single number, and that anchors us to an *apparently* exact estimate – when it should have a proper uncertainty range. This often leads to overconfidence, and worse, the Drake equation is very sensitive to bias: if you are hopeful a small nudge upwards in several uncertain estimates will give a hopeful result, and if you are a pessimist you can easily get a low result.”
As such, Sandberg, Drexler and Ord looked at the equation’s parameters as uncertainty ranges. Instead of focusing on what value they might have, they looked at what the largest and smallest values they could have based on current knowledge. Whereas some values have become well constrained – such as the number of planets in our galaxy based on exoplanet studies and the number that exist within a star’s habitable zone – others remain far more uncertain.
When they combined these uncertainties, rather than the guesswork that often go into the Fermi Paradox, the team got a distribution as a result. Naturally, this resulted in a broad spread due to the number of uncertainties involved. But as Dr. Sandberg explained, it did provide them with an estimate of the likelihood that humanity (given what we know) is alone in the galaxy:
“We found that even using the guesstimates in the literature (we took them and randomly combined the parameter estimates) one can have a situation where the mean number of civilizations in the galaxy might be fairly high – say a hundred – and yet the probability that we are alone in the galaxy is 30%! The reason is that there is a very skew distribution of likelihood.
“If we instead try to review the scientific knowledge, things get even more extreme. This is because the probability of getting life and intelligence on a planet has an *extreme* uncertainty given what we know – we cannot rule out that it happens nearly everywhere there is the right conditions, but we cannot rule out that it is astronomically rare. This leads to an even stronger uncertainty about the number of civilizations, drawing us to conclude that there is a fairly high likelihood that we are alone. However, we *also* conclude that we shouldn’t be too surprised if we find intelligence!”
In the end, the team’s conclusions do not mean that humanity is alone in the Universe, or that the odds of finding evidence of extra-terrestrial civilizations (both past and present) is unlikely. Instead, it simply means that we can say with greater confidence – based on what we know – that humanity is most likely the only intelligent species in the Milky Way Galaxy at present.
And of course, this all comes down to the uncertainties we currently have to contend with when it comes to SETI and the Drake Equation. In that respect, the study conducted by Sandberg, Drexler and Ord is an indication that much more needs to be learned before we can attempt to determine just how likely ETI is out there.
“What we are not showing is that SETI is pointless – quite the opposite!” said Dr. Sandberg. “There is a tremendous level of uncertainty to reduce. The paper shows that astrobiology and SETI can play a big role in reducing the uncertainty about some of the parameters. Even terrestrial biology may give us important information about the probability of life emerging and the conditions leading to intelligence. Finally, one important conclusion we find is that lack of observed intelligence does not strongly make us conclude that intelligence doesn’t last long: the stars are not foretelling our doom!”
So take heart, SETI enthusiasts! While the Drake Equation may not be something we can produce accurate values for anytime soon, the more we learn, the more refined the values will be. And remember, we only need to find intelligent life once in order for the Fermi Paradox to be resolved!
In 1961, famed astrophysics Frank Drake proposed a formula that came to be known as the Drake Equation. Based a series of factors, this equation sought to estimate the number of extra-terrestrial intelligences (ETIs) that would exist within our galaxy at any given time. Since that time, multiple efforts have been launched to find evidence of alien civilizations, which are collectively known as the search for extra-terrestial intelligence (SETI).
The most well-known of these is the SETI Institute, which has spent the past few decades searching the cosmos for signs of extra-terrestrial radio communications. But according to a new study that seeks to update the Drake Equation, a team of international astronomers indicate that even if we did find signals of alien origin, those who sent them would be long dead.
To recap, the Drake Equation states that the number of civilizations in our galaxy can be calculated by multiplying the average rate of star formation in our galaxy (R*), the fraction of stars that have planets ( fp), the number of planets that can support life (ne), the number of planets that will develop life (fl), the number of planets that will develop intelligent life (fl), the number that will develop transmissions technologies (fc), and the length of time that these civilizations will have to transmit signals into space (L).
This can be expressed mathematically as: N = R* x fp x ne x fl x fi x fc x L. For the sake of their study, the team began by making assumptions about two key parameters of the Drake Equation. In short, they assume that civilizations emerge in our galaxy (N) at a constant rate, and that they will not emit electromagnetic radiation (i.e. radio transmissions) indefinitely, but will experience some type of limiting event over time (L).
As Dr. Grimaldi explained to Universe Today via email:
“We assume that hypothetical communicating civilizations (the emitters) send isotropic electromagnetic signals for a certain duration of time L, and that the birthrate of the emissions is constant. Each emission process gives rise to a spherical shell of thickness cL (where c is the speed of light) filled by electromagnetic waves. The outer radii of the spherical shells grow at the speed of light.”
In short, they assumed that technologically-advanced civilizations are born and die in our galaxy at a constant rate. However, these civilizations do not produce communications at an indefinite rate, but their communications will still be traveling outwards at the speed of light, where they will be detectable within a certain volume of space. The team then developed a model of our galaxy to determine whether humanity would have any change at detecting these signals.
This model treated alien communications as a donut-shaped (annulus) shell that gradually passes through our galaxy. As Dr. Grimaldi explained:
“We model the Galaxy as a disk. The emitters occupy random positions in the disk. Each spherical shell intersects the disk in annuli. The probability that an annulus crosses any given point of the disk (e.g. the Earth) is just the ratio between the area of the annuli and the area of the galactic disk. The total area of the annuli over the area of the galactic disk gives the mean number (N) of electromagnetic signals that intersect any given point (e.g. the Earth). This mean number is a key quantity, because SETI can detect signals only if these cross the Earth at the time of measurement.”
As they determined from their calculations, two cases emerge from this model based on whether the radiation shells are (1) thinner than the size of the Milky Way or (2) thicker. These correspond to the lifetimes of technologically-advanced civilizations (L), which could be less than or greater than the time it takes for light to cross our Milky Way (i.e. ~100,000 years). As Dr. Grimaldi explained:
“The mean number (N) of signals crossing Earth depends on the signal longevity (L) and their birthrate. We find that N is just L times the birthrate, which coincides with Drake’s N (that is, the mean number of currently emitting civilizations). This result (mean number of signals crossing Earth = Drake’s N) arises naturally from our assumption that the birthrate of signals is constant.”
In the first case, each shell wall would have a thickness smaller than the size of our galaxy and would fill only a fraction of the galaxy’s volume (thus inhibiting SETI detection). However, if there is a high enough birthrate of detectable civilizations, these shell walls may fill our galaxy and even overlap. In the second case, each radiation shell would be thicker than the size of our galaxy, making SETI detection more likely.
From all this, the team also calculated that the average number of E.T. signals crossing Earth at any given time would equal the number of civilizations currently transmitting. Unfortunately, they also determined that the civilizations we would be hearing from would have long since gone extinct. So basically, the civilizations we would be hearing from would not be the same ones that were presently broadcasting.
As Dr. Grimaldi explained, this raises a rather interesting implication when it comes to SETI research:
“Instead of viewing the Drake’s N as a product of probability factors for the development of communicating civilizations, our results imply that Drake’s N is a directly measurable quantity (at least in principle) because it coincides with the mean number of signals crossing Earth.”
For those hoping to find evidence of extra-terrestrial intelligence in our lifetime, this is likely to be a bit discouraging. On the one hand (and depending on the number of alien civilizations that exist in our galaxy), we may have a hard time picking up extra-terrestrial transmissions. On the other, those that we do find may be coming from a civilization that has long since gone extinct.
It also means that if any civilization should pick up our radio wave transmissions someday, we won’t be around to meet them. However, it does not rule out the possibility that we will find evidence that intelligent life has existed within our galaxy in the past. In fact, over the course of own our civilization’s lifetime, humanity may find evidence of multiple ETIs that existed at one time.
In addition, none of this negates the possibility of finding evidence of an existing civilization. It’s just not likely we’ll be able to sample their music, entertainment or messages first!
Decades after Enrico Fermi’s uttered his famous words – “Where is everybody?” – the Paradox that bears his name still haunts us. Despite repeated attempts to locate radio signals coming from space and our ongoing efforts to find visible indications of alien civilizations in distant star systems, the search extra-terrestrial intelligence (SETI) has yet to produce anything substantive.
But as history has taught us, failure has a way of stimulated new and interesting ideas. For example, in a recently-published paper, Dr. Duncan H. Forgan of St. Andrews University proposed that extra-terrestrial civilizations could be communicating with each other by creating artificial transits of their respective stars. This sort of “galactic internet” could be how advanced species are attempting to signal us right now.
The paper begins by addressing the two fundamental problems associated with interstellar communication – timing and energy consumption. When it comes to things like radio transmissions, the amount of energy that would be needed to transmit a coherent message over interstellar distances is prohibitive. Optical communications (i.e. lasers) need less energy, but spotting them would require incredibly precise timing.
As such, neither method would be particularly reliable for establishing an interstellar communications system. Taking a cue from humanity’s recent exoplanet-hunting efforts, Forgan argues that a method where transits in front of a stars are a basis of communication would solve both problems. The reason for this is largely due to the fact that the Transit Method is currently one of the most popular and reliable ways of detecting exoplanets.
By monitoring a star for periodic dips in brightness, which are caused by a planet or object passing between the observer and the star, astronomers are able to determine if the star has a system of planets. The method is also useful for determining the presence and composition of atmospheres around exoplanet. As Forgan indicates in the paper, this method could therefore be used as a means of signalling other civilizations:
“An ETI ’A’ can communicate with ETI ’B’ if B is observing transiting planets in A’s star system, either by building structures to produce artificial transits observable by B, or by emitting signals at B during transit, at significantly lower energy consumption than typical electromagnetic transmission schemes.”
In short, Forgan argued that within the Galactic Habitable Zone (GHZ) – the region of the Milky Way in which life is most likely develop – species may find that the best way to communicate with each other is by creating artificial megastructures to transit their star. These transits, which other civilizations will be looking for (looking for exoplanets, like us!) will lead them to conclude that an advanced civilization exists in another star system.
He even offers estimates on how often such transmissions could be made. As he put it:
“A message with a path of 20 kpc (the diameter of the GHZ) has a total travel time at lightspeed of just under 0.06 Myr. If we assume a relatively short timescale on which both ETIs remain in the transit zone of 100,000 years (which is approaching the timescale on which both secular evolution of planetary orbits and the star’s orbit become important), then a total of 30 exchanges can be made. This of course does not forbid a continuing conversation by other means.”
If this is starting to sound familiar, that’s probably because this is precisely what some theorists say is happening around KIC 8462852 (aka. Tabby’s Star). Back in May of 2015, astronomers noticed that the star had been undergoing considerable drops in brightness in the past few years. This behavior confounded natural explanations, which led some to argue that it could be the result of an alien megastructure passing in front of the star.
According to Forgan, such a possibility is hardly far-fetched, and would actually be a relatively economical means of communicating with other advanced species. Using graph theory, he estimated that civilizations within the GHZ could establish a fully connected network within a million years, where all civilizations are in communication with each other (either directly or via intermediate civilizations).
Not only would this network require far less energy to transmit data, but the range of any signal would be limited only by the extent of these civilizations themselves. Beyond saving energy and having greater range (assuming intermediate civilizations are able to pass messages along), this method presents other advantages. For one, a high level of technological sophistication would be required to pick up the transit of exoplanets.
In other words, civilizations would need to reach a certain level of development before they could hope to join the network. This would prevent any unfortunate “cultural contamination”, where less-advanced civilizations learned about the existence of aliens before they were ready. Second, once acquired, the transit network signals would be extremely predictable, with each transmission corresponding to a known orbital period.
That being said, there are some downsides that Forgan was sure to acknowledge. For starters, the periodicity of these signals would be a double edged sword, as signals could only be sent if and when the receiver begins to see the transit. And while a megastructure could be moved to alter the transit period, this poses problems in terms of synchronizing transmission and reception.
Addressing the limitations of the analysis, Forgan also acknowledges that the study relies on fixed stellar orbits. The orbits of stars are known to change over time, with stars passing in and out of the GHZ regularly on cosmic timescales. In addition, there is also the issue of how such a network would differ between denser regions in the galaxy – i.e. globular clusters – and areas populated by field stars. Binary stars are also not considered in the analysis.
In addition, planetary orbits are known to change over time, due to perturbations caused by neighboring planets, companion stars, or close encounters with passing stars. As a result, the visibility of transiting planets can vary even more over cosmic timescales. Last, but not least, the study assumes that civilizations have a natural lifespan of about a billion years, which is not based in any concrete knowledge.
However, these considerations do not alter the overall conclusions reached by Forgan. Making allowances for the dynamic nature of stars and planets, and assuming that civilizations exist for only 1 million years, Forgan maintains that the creation of an interstellar network of this kind is still mathematically feasible. On top of that, an artificial object could continue to signal other species long after a civilization has gone extinct.
Addressing the Fermi Paradox, Forgan concludes that this sort of communication would take a long time to detect.As he summarizes in the paper (bold added for emphasis):
“I find that at any instant, only a few civilizations are correctly aligned to communicate via transits. However, we should expect the true network to be cumulative, where a “handshake” connection at any time guarantees connection in the future via e.g. electromagnetic signals. In all our simulations, the cumulative network connects all civilizations together in a complete network. If civilizations share knowledge of their network connections, the network can be fully complete on timescales of order a hundred thousand years. Once established, this network can connect any two civilizations either directly, or via intermediate civilizations, with a path much less than the dimensions of the GHZ.”
In short, the reason we haven’t heard from or found evidence of ETI could be an issue of timing. Or, it could be that we simply didn’t realize we were being communicated with. While such an analysis is subject to guess-work and perhaps a few anthropocentric assumptions, it is certainly fascinating because of the possibilities it presents. It also offers us a potential tool in the search for extra-terrestrial intelligence (SETI), one which we are already engaged in.
And last, but not least, it offers a potential resolution to the Fermi Paradox, one which we may have already stumbled upon and are simply not yet aware of. For all we know, the observed drops in brightness coming from Tabby’s Star are evidence of an alien civilization (possibly an extinct one). Of course, the key word here is “perhaps”, as no evidence exists that could confirm this.
The possibilities raised by this paper are also exciting given that exoplanet-hunting is expected to ramp up in the coming years. With the deployment of next-generations missions like the James Webb Space Telescope and the Transiting Exoplanet Survey Satellite (TESS), we expect to be learning a great deal more about star systems both near and far.
Will we find more examples of unexplained drops in brightness? Who knows? The point is, if we do (and can’t find a natural cause for them) we have a possible explanation. Maybe its neighbors inviting us to “log on”!
Is there life out there in the Universe? That is a question that has plagued humanity long before we knew just how vast the Universe was – i.e. before the advent of modern astronomy. Within the 20th century – thanks to the development of modern telescopes, radio astronomy, and space observatories – multiple efforts have been made in the hopes of finding extra-terrestrial intelligence (ETI).
And yet, humanity is still only aware of one intelligent civilization in the Universe – our own. And until we actually discover an alien civilization, the best we can do is conjecture about the likelihood of their existence. That’s where the famous Drake Equation – named after astronomer Dr. Frank Drake – comes into play. Developed in the 1960s, this equation estimates the number of possible civilizations out there based on a number of factors.
During the 1950s, the concept of using radio astronomy to search for signals that were extra-terrestrial in origin was becoming widely-accepted within the scientific community. The idea of listening for extra-terrestrial radio communications had been suggested as far back as the late 19th century (by Nikolai Tesla), but these efforts were concerned with looking for signs of life on Mars.
Then, in September of 1959, Giuseppe Cocconi and Philip Morrison (who were both physics professors at Cornell University at the time) published an article in the journal Nature with the title “Searching for Interstellar Communications.” In it, they argued that radio telescopes had become sensitive enough that they could pick up transmissions being broadcast from other star systems.
Specifically, they argued that these messages might be transmitted at a wavelength of 21 cm (1420.4 MHz), the same wavelength of radio emissions by neutral hydrogen. As the most common element in the universe, they argued that extra-terrestrial civilizations would see this as a logical frequency at which to make radio broadcasts that could be picked up by other civilizations.
Seven months later, Frank Drake made the first systematic SETI survey at the National Radio Astronomy Observatory in Green Bank, West Virginia. Known as Project Ozma, this survey relied on the observatory’s 25-meter dish to monitor Epsilon Eridani and Tau Ceti – two nearby Sun-like stars – at frequencies close to 21 cm for six hours a day, between April and July of 1960.
Though unsuccessful, the survey piqued the interest of the scientific and SETI communities. It was followed shortly thereafter by a meeting at the Green Bank facility in 1961, where the subjects of SETI and searching for radio signals of extra-terrestrial origin were discussed. In preparation for this meeting, Drake prepared the equation that would come to bear his name. As he said of the equation’s creation:
“As I planned the meeting, I realized a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extraterrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms.”
The meeting, which included such luminaries as Carl Sagan, was commemorated with a commemorative plaque that is still in the hall of the Green Bank Observatory today.
The formula for the Drake Equation is as follows:
N = R* x fp x ne x fl x fi x fc x L
Whereas N is the number of civilizations in our galaxy that we might able to communicate with, R* is the average rate of star formation in our galaxy, fp is the fraction of those stars which have planets, neis the number of planets that can actually support life, fl is the number of planets that will develop life, fiis the number of planets that will develop intelligent life, fc is the number civilizations that would develop transmission technologies, and L is the length of time that these civilizations would have to transmit their signals into space.
Limits and Criticism:
Naturally, the Drake Equation has been subject to some criticism over the years, largely because a lot of the values it contains are assumed. Granted, some of the values it takes into account are easy enough to calculate, like the rate of star formation in the Milky Way. There are an estimated 200 – 400 billion stars within our Milky Way, and modern estimates say that there between 1.65 ± 0.19 and 3 new star form every year.
Assuming that our galaxy represents the average, and given that that there are as many as 2 trillion galaxies in the observable Universe (current estimates based on Hubble data), that means that there are as many as 1.5 to 6 trillion new stars being added to the Universe with every passing year! However, some of the other values are subject to a great deal of guess work.
For example, estimates on how many stars will have a system of planets has changed over time. Currently, it is estimated that the Milky Way contains 100 billion planets, which works out to about 50% of its stars having a planet of their own. Furthermore, those stars that have multiple planets will likely have one or two that lies within their habitable zone (aka. “Goldilocks Zone”) – where liquid water can exist on their surfaces.
Now let’s assume that 100% of planets located within a habitable zone will be able develop life in some form, that at least 1% of those life-supporting planets will be able to give rise to intelligent species, that 1% of these will be able to communicate, and that they will able to do so for a period of about 10,000 years. If we run those numbers through the Drake Equation, we end up with a value of 10.
In other words, there are possibly 10 civilizations in the Milky Way at any time capable of sending out signals that we could detect. But of course, the values used for four parameters there – fl, fi, fcand L – were entirely assumed. Without any real data to go by, there’s no real way to know how many alien civilizations could really be out there. There could just be 1 in the entire Universe (us), or millions in every galaxy!
The Fermi Paradox:
Beyond the issue of assumed values, the most pointed criticism of the Drake Equation tend to emphasize the argument put forth by physicist Enrico Fermi, known as the Fermi Paradox. This argument arose in 1950 as a result of conversation between Fermi and some colleagues while he was working at the Los Alamos National Laboratory. When the subject of UFOs and ETI came up, Fermi famously asked, “Where is everybody?”
This simple question summarized the conflict that existed between arguments that emphasized scale and the high probability of life emerging in the Universe with the complete lack of evidence that any such life exists. While Fermi was not the first scientists to ask the question, his name came to be associated with it due to his many writings on the subject.
In short, the Fermi Paradox states that, given the sheer number of stars in the Universe (many of which are billions of years older than our own), the high-probability that even a small fraction would have planets capable of giving rise to intelligent species, the likelihood that some of them would develop interstellar travel, and the time it would take to travel from one side of our galaxy to other (even allowing for sub-luminous speeds), humanity should have found some evidence of intelligent civilizations by now.
But perhaps the best known explanation for why no signs of intelligence life have been found yet is the “Great Filter” hypothesis. This states that since that no extraterrestrial civilizations have been so far, despite the vast number of stars, then some step in the process – between life emerging and becomes technologically advanced – must be acting as a filter to reduce the final value.
According to this view, either it is very hard for intelligent life to arise, the lifetime of such civilizations is short, or the time they have to reveal their existence is short. Here too, various explanations have been offered to explain what the form the filter could take, which include Extinction Level Events (ELEs), the inability of life to create a stable environment in time, environmental destruction. and/or technology running amok (some of which we fear might happen to us!)
Alas, the Drake Equation has endured for decades for the very same reason that if often comes under fire. Until such time that humanity can find evidence of intelligent life in the Universe, or has ruled out the possibility based on countless surveys that actually inspect other star systems up close, we won’t be able to answer the question, “Where is everybody?”
As with many other cosmological mysteries, we’ll be forced to guess about what we don’t know based on what we do (or think we do). As astronomers study stars and planets with newer instruments, they might eventually be able to work out just how accurate the Drake Equation really is. And if our recent cosmological and exoplanet-hunting efforts have shown us anything, it is that we are just beginning to scratch the surface of the Universe at large!
In the coming years and decades, our efforts to learn more about extra-solar planets will expand to include research of their atmospheres – which will rely on next-generation instruments like the James Webb Space Telescope and the European Extremely-Large Telescope array. These will go a long way towards refining our estimates on how common potentially habitable worlds are.
In the meantime, all we can do is look, listen, wait and see…
When you consider that age of the Universe – 13.8 billion years by our most recent counts – and that which is “observable” to us measures about 93 billion light years in diameter, you begin to wonder why we haven’t found signs of extra-terrestrial intelligence (ETI) beyond our Solar System. To paraphrase Enrico Fermi, the 20th century physicists who advanced the famous Fermi Paradox – “where the heck are all the aliens?”
Essentially, aestivation is a prolonged state of torpor that organisms enter into during a particularly hot or dry period. Similar to what hibernating animals do during the winter, this state is designed to keep creatures alive until more favorable conditions emerge. And when applied to the cosmos, this concept could explain why one of the key things astronomers have been looking for – i.e. activity – has been lacking.
This is not the first time Sandberg has addressed questions arising out of the Fermi Paradox. In a previous study, he and Stuart Armstrong (also a research associate with the FHI and one of the co-authors on this study) extended the Fermi Paradox to look beyond our own galaxy, addressing how more advanced civilizations would feasibly be able to launch colonization projects with relative ease (and even travel between galaxies without difficulty).
In the end, they concluded that civilizations from millions of galaxies should have been able to reach us by now, which only serves to bring the Fermi Paradox into greater focus. If these early civilizations are around, why are they not visible to us? The reason for this, they claim in this new study, has to do with the thermodynamics of computation.
According to this basic rule, the cost of a certain amount of computation is proportional to the temperature it generates. For some time, astronomers and cosmologists have been aware that the Universe is steadily cooling down over the time. Not only is star formation in galaxies slowly dying out over the course of billions of years, but even the cosmic background radiation is becoming colder.
As such, it makes sense that ancient and advanced civilizations would want to wait for cooler conditions to prevail. Sandberg explained to Universe Today via email:
“The core idea is that if advanced civilizations mainly or solely care about computation, then it is rational for them to wait until the Universe is much older than now. The reason is that the energy cost (which will eventually limit how much computation you can do) is proportional to temperature, and this means that the far future is vastly more hospitable than the hot present. If this were true, we have a nice explanation for the apparent absence of big old civilizations. It would also lead to observable consequences: a reduction in processes that waste resources they would want in the late eras.”
Timing is a key feature to this hypothesis. Much like the theory that humanity may have arrived early to the Universe, this theory states that the lack of detection has to do with species being in different places in their biological/technological evolution. In this case, the aestivation period of early civilizations has coincided with the subsequent rise of humanity as an space-faring and technologically-adept species.
Herein lies another reason why ancient civilizations might want to take a cosmic nap. Given how long life needs in order to emerge – humanity took roughly 4.5 billion years to get to where it is today – then it stands to reason that ancient civilizations might want to skip ahead a few eons in order to let new races emerge.
“There is an entropy cost to irreversible logical operations, including error correction,” said Sanders. “So unless there is some magical energy source or entropy sink, if you want to do as much computation as possible you should wait until the cosmic background radiation levels off. In addition, civilizations may want to go to the future if they want to meet other, independently evolved civilizations. If intelligence is rare in time and space but aestivates to the far future, then it will meet there.”
Of course, the aestiation hypothesis (much like the Drake Equation and the Fermi Paradox) is based on a few assumptions about what ETI would be capable of. These include:
There are civilizations that mature much earlier than humanity.
These civilizations can expand over sizeable volumes, gaining power over their contents.
These civilizations have solved their coordination problems.
A civilization can retain control over its volume against other civilizations.
The fraction of mature civilizations that aestivate is non-zero
Aestivation is largely invisible.
In other words, the hypothesis assumes the existence of civilizations that are more advanced than humanity which is based on the notion that they have had billions of years to develop elsewhere in the Universe. These civilizations would be higher on the Kardashev Scale (between Level II and III) by now, meaning that they had evolved to the point where they could harness the energy of entire star systems and perhaps even galaxies.
Also, it assumes that these civilizations would have become space-faring races that had expanded to occupy parts of the cosmos that lie well beyond their own star systems. Ultimately, those civilizations that have chosen to become dormant would therefore be invisible to us since they are not currently traveling between stars and galaxies, smashing up planets to create megastructures, or consuming entire stars for fuel.
You know, the kind of stuff we think mega-civilizations would do. Which naturally raises the question, how might we be able to detect such civilizations at rest? To this, Sandberg has a few possible suggestions, ones which ETI-hunters may want to heed:
“Look for galaxies that either move out of the way of galaxy collisions or towards big clusters by ejecting mass or energy in one direction, or have an unusually low number of heavy blue-white stars, or otherwise avoid losing gas to interstellar space. Or, try launching a self-replicating space probe to pave the universe and see if somebody stops you.”
As with all things having to do with aliens and ETI, a measure of guess-work is required here. And some would naturally argue that it is also possible that advanced civilizations are not subject to the same limitations we humans are, which would limit our ability to speculate here. In the end, we humans are required to theorize about what we don’t know based on what we do – aka. the “low-hanging fruit” approach.
The findings reported in the study were also the subject of a talk that took place at the second annual meeting of the UK SETI Research Network (UKSRN), which took place on September 11th and 12th, 2014, at Birkbeck College in London.
During the 1960s, Freeman Dyson and Nikolai Kardashev captured the imaginations of people everywhere by making some radical proposals. Whereas Dyson proposed that intelligent species could eventually create megastructures to harness the energy of their stars, Kardashev offered a three-tiered classification system for intelligent species based on their ability to harness the energy of their planet, solar system and galaxy, respectively.
With missions that are now capable of locating extra-solar planets (i.e. the Kepler Space Observatory) scientists have been on the lookout for signs of possible alien megastructures. Unfortunately, aside from some very arguable results, no concrete evidence has yet come to light. Lucky for us, in a study from the Free University of Tbilisi, Professor Zaza Osmanov offers some new insight on why megastructures may have eluded us so far.
While fascinating, the idea of alien megastructures invariably suffers from the same problem as all other attempts to find signs of intelligent life in our Universe. Basically, if intelligent life exists, why have we consistently failed to find any evidence of it? This conundrum, which was summed up by Enrico Fermi in the 1950s (thereafter known as the Fermi Paradox), has hung like a shadow over all our efforts.
For example, in the summer of 2015, a team of astronomers announced that they found what might be an indication of an alien megastructure around Tabby’s Star (KIC 8462852). However, they were quick to point out that any number of possibilities could explain the strange dimming pattern coming from the star, and subsequent studies offered even more plausible explanations – such as the star having consumed a planet at some point in its past.
To this, Osmanov has argued that the problem is that we are looking in the wrong places. Last year, he wrote a research paper in which he ventured that an alien super civilization – i.e. one that was consistent with a Level II Kardashev civilization – would likely use ring-like megastructures to harness the power of their stars. This is in contrast to the traditional concept of a “Dyson’s Sphere”, which would consist of a spherical shell.
Furthermore, he argued that these Dyson Rings would likely be built around pulsars rather than stars, and offered estimates on their dimensions which were dependent on the rotational speed of the pulsar. According to Osmanov’s latest study, titled “Are the Dyson rings around pulsars detectable?“, Osmanov extends the problem of spotting alien megastructures to the observational realm.
Specifically, he addressed how alien megastructures could be spotted by identifying their infrared energy signatures, and at what kinds of distances. By examining how such structures would vary in terms of the amount of IR radiation they would emit, he believes that they could be spotted within our local Universe using existing instruments.
Once again, it comes down to the diameter of the structures, which would in turn depend on the type of pulsar they orbit. As he states in the paper:
“A couple of years earlier before publishing the paper of Kardashev, the prominent physicist Freeman Dyson has suggested that if such superadvanced (in the terminology of Kardashev, Level-II) extraterrestrials exist, for increasing efficiency of energy consumption they can construct a thin spherical shell with radius ?1AU surrounding a host star (Dyson 1960).It has been argued that for such distances the sphere will be in the so-called habitable zone (HZ) and therefore the sphere will have the temperature of the order of (200 – 300 K), making this object visible in the infrared spectrum.”
Extending this to pulsars, Osmanov estimates that the habitable zone around a relatively slowly-rotating pulsar (with a period of about half a second) would be on the order of 0.1 AU. According to his calculations, a ring-like megastructure that orbited a pulsar at this distance would emit temperatures on the order of 390 K (116.85 °C; 242.33 °F), which means that the megastructure would be visible in the IR band.
From this, Osmanov concludes that modern IR telescopes – such as the Very Large Telescope Interferometer (VLTI) and the Wide-field Infrared Survey Explorer (WISE) – would have the necessary capacity to monitor nearby pulsars for signs of alien megastructures. He further concludes that for this purpose, these telescopes would have an effective range of up to 200 parsecs (~652 light years).
In addition, he goes on to state that within this volume of space, multiple candidates could be found and examined using these same existing instruments:
“We have considered the sensitivity of VLTI and by taking into account its higher possible angular resolution, 0.001 mas, it has been shown that the maximum distance ~0.2 kpc leads to the IR spectral density of the order of 7.4 mJy, which in turn, can be detected by the VLTI. We have argued that by monitoring the nearby zone of the Solar System approximately 64 pulsars are expected to be located inside it.”
Beyond these distances, up to the kiloparsec range (about 3260 light years), the angular resolution of these telescopes would not be enough to detect the structure of any rings. As such, finding megastructures at this distance would require telescopes that can conduct surveys in the UV band – which corresponds to the surface temperatures of neutron stars (7000 K). However, this would have to wait upon the development of more sensitive instruments.
“As we see, the search of infrared rings is quite promising for distances up to -0.2 kpc, where one will be able to monitor potentially 64 ± 21 pulsars by using the IR instruments,” he concluded. “Observation of distant pulsars (up to -1kpc), although will significantly increase the total number of potential objects – to 1600 ± 530, but at this moment the UV instruments cannot provide such a level of sensitivity.”
So while the range would be limited, the opportunities for testing this hypothesis would not. All told, between 43 and 85 candidates exist within the observable volume of space, according to Osmanov’s estimates. And with existing IR telescopes – and next-generation telescopes like the James Webb Space Telescopes – up to the task, some surveys could be conducted that would yield valuable information either way.
The concept of alien megastructures remains a controversial one, and for good reason. For one, the potential evidence for such structures – i.e. the periodic dimming of a star – can easily be explained by other means. Second, there is an undeniable degree of wishful thinking when it comes to the search for extra-terrestrial intelligence, which means that any findings could be subject to bias.
Nevertheless, the search for intelligent life remains a very fascinating field of study, and a necessary one at that. Not only would finding other examples of life in our Universe put to rest one of the most burning existential questions of all time – are we alone? – it would also allow us to learn a great deal about what other forms life could take. Is all life carbon based, are there other possibilities, etc? We would like to know!
In the end, the Fermi Paradox will only be resolved when we find definitive evidence that there is intelligent life out there other than our own. In the meantime, we can expect that we will keep searching until we find something. And anything that make this easier by telling us where we should (and what specifically to look for) is sure to help.
Whenever I do a new livestream on Instagram (hint hint, @universetoday on Instagram), it’s generally with an audience that doesn’t have a lot of experience with my work here on Universe Today or YouTube.
They’re enthusiastic about space, but they haven’t been exposed to a lot of the modern ideas about astrobiology and the search for extraterrestrials. They have, however, seen a lot of TV and movies.
And so, the most common question I get, by a long shot is, “do you believe in aliens?”
That’s actually a more complicated question. On the one hand, the question could be: do I believe that aliens are visiting Earth, creating crop circles, infiltrating our government, and experimenting on human/alien hybrids for the eventual overthrow of human civilization?
The answer to that question, is no.
I believe in UFOs, in that, I believe there are unidentified objects flying in the air, which haven’t gotten a definitive categorization. And when they do get an explanation, it’s weather balloons, or Venus, or airplanes, or fireworks, or drones, or a hoax.
It’s never aliens.
Because if it was aliens, we would have some kind of evidence. There would be something, anything, that gave definitive proof that aliens were here.
What I’m talking about is some kind of monument, or machine, or vehicle, or factory. Something that’s been around here on Earth for as long as human history, and has no explanation for how it could have been created.
UFO researchers point to things like the pyramids, or the statues on Easter Island, or the Nazca lines, when there’s plenty of evidence these things could be created by humans and their tools of the age. Even when the hoaxers who created crop circles with a plank on a rope and a little planning tried to explain how they did it, people didn’t really believe them.
I want to show you a series of amazing visualizations created by Sam Monfort, a data researcher in the Human Factors and Applied Cognition program at George Mason University. Sam pulled in data from the National UFO Reporting Center or NUFORC which has been collecting reports all the way back to 1905.
Since its inception, NUFORC has received almost 105,000 UFO reports. And sighting are at an all time high.
But what’s really fascinating is how the trends of what people see have changed over time. A century ago, the vast majority of UFOs were spheres or cigar shaped. But then saucers showed up in the 20s, and that’s all anyone saw.
Cigars have dropped down to almost nothing, while lights in the sky have grown in prominence to become almost 50% of the UFOs that people see these days.
Clearly spaceship design took a turn away from cigars, to saucers to glowing lights. Oh, fickle aliens spacecraft designers, following the latest fashions.
The timing is interesting too. There’s a rise in sightings around July 4th in the US every year. Fireworks maybe?
The other piece of data that’s pretty interesting is that people in the US are 300 times more likely to report a UFO sighting than any other country in the world. My own Canada is number 2.
Here’s the thing. A huge percentage of the population is now carrying around their own personal tricorder, which will record audio, video and take amazing pictures, even in a dimly lit alien spaceship. And yet, there still hasn’t been any definitive, scientifically proven evidence for aliens.
Google is watching everywhere I go, and reminds me that I visited Home Depot last week, but you think the occasional trip to an orbital research facility would get picked up.
I feel pretty confident when I say, there’s no evidence that aliens are visiting Earth.
But the deeper question is a little more unsettling. Do I believe there are aliens in the Universe?
The Universe is huge. The very edge of the Universe we can see is known as the observable Universe. The first light in the Universe has been traveling through space for 13.8 billion years to reach our eyes. And because of the expansion of the Universe, those regions are now more than 46 billion light years away from us.
That’s just the observable Universe. The actual physical Universe is much larger. Hundreds of billions, trillions, quadrillions or more light years across. Maybe it’s even infinite.
Forever is a long way.
And we know that the Universe is old. It’s been around for 13.8 billion years. Our Milky Way has been around for almost that entire period. The Solar System showed up a relatively recent 4.5 billion years ago. We’re late to a party that’s been raging for almost 10 billion years already.
Fossil evidence tells us that life formed here on Earth pretty much as quickly as it was possible to do so. Just a few hundred million years after the Earth formed, and it wasn’t entirely a ball of molten rock, life popped up and started evolving.
Multiply the Universe’s age by its size and you get a place that really should be teeming with life, and yet we don’t see any evidence of aliens. Not in cigars nor saucers.
This is of course, the Fermi Paradox, and we’ve talked about this several times in the past. We can’t seem to find evidence of aliens, or their robotic spacecraft which should be busily colonizing the Milky Way turning every planet they reach into more robots.
The Fermi Paradox has been the source of arguments and existential terror for many.
In fact, if the Fermi Paradox doesn’t bother you in an existential way, then I don’t think you’ve thought about the Fermi Paradox enough.
Are there aliens? There might be single-celled, simple organisms across the Universe. But more complex animals like we have here on Earth might be incredibly uncommon.
This is the idea of the Rare Earth hypothesis, which was put forward in the year 2000 in a book by paleontologist Peter Ward and astrobiologist Donald Brownlee. If you have any interest in this subject, I highly recommend you give it a read.
In Rare Earth, Ward and Brownlee argue that Earth was lucky in many factors that we never really thought about before.
The Earth is the right distance from the center of the Milky Way so we’re not bombarded by radiation, but not too far so that we’re in the outskirts, with no heavy elements.
We orbit the right kind of star, and the right configuration of other planets in the Solar System. No big bully super-Jupiters that caused havoc with our planet or kicked us out of the Solar System entirely.
The orbit of the Earth has been stable for a long time, following a roughly circular orbit around the Sun. Our planet is the right size and density for life to survive and thrive. With plate tectonics, which help recycle our rocks and atmospheric gasses, so we don’t become a hellworld like Venus.
With a single large Moon that helped regulate our tides and provided an environment where some lifeforms could have been forced to find a better way.
And then some kind of secret sauce that helped give Earth life the kick it needed to go from simple to complex lifeforms.
Maybe there’s life everywhere, but we’ll never find anything more complex than bacteria. Or maybe we’ll never find anything anywhere. Ever.
I understand why the search for UFOs is so fascinating for people, and why many think that’s a reasonable default answer for seeing glowing lights in the sky. But for me, I want to know for sure that we’re not alone, that there are other aliens lifeforms and maybe even civilizations out there among the stars.
I don’t believe UFOs are aliens, and I’m not entirely convinced there’s anyone else in the entire Universe.
And that’s why I think we should dedicate ourselves to finding out the answer. Listen to stars for signals from extraterrestrial civilizations, search planets for the chemical signatures of alien life. Scour our own Solar System for anything. Under the rocks on Mars or under the oceans of Europa.
If it does turn out that we’re alone? What then? Do we have a greater responsibility to take care of ourselves and our planet, to make sure the candlelight of life and intelligence doesn’t flicker out?
Now you know how I feel about aliens, what about you? Do you think we’re being visited on a regular basis? Do you think there are aliens out there, somewhere, waiting to be discovered? Or do you think we’re all alone in the Universe. I’d like to know your thoughts.
In our next episode, we’re going to talk about one of the biggest current mysteries in astronomy: Fast Radio Bursts. They were only recently discovered, and they’re a total mystery. No answers next time, only questions.
What would we do if aliens actually visited us here on Earth? How prepared are our governments to deal with them? It turns out, there are some specific plans and preparations, and I detail them in this video.
We’ve covered the Fermi Paradox many times over several articles on Universe Today. This is the idea that the Universe is huge, and old, and the ingredients of life are everywhere. Life could and should have have appeared many times across the galaxy, but it’s really strange that we haven’t found any evidence for them yet.
We’ve also talked about how we as a species have gone looking for aliens. How we’re searching the sky for signals from their alien communications. How the next generation of space and ground-based telescopes will let us directly image the atmospheres of extrasolar planets. If we see large quantities of oxygen, or other chemicals that shouldn’t be around, it’s a good indication there’s life on their planet.
We’ve even talked about how aliens could use that technique on us. We’ve been sending our radio and television signals out into space for the last few decades. Who knows what crazy things they think about our “historical documents”? But Earth life itself has been broadcasting our existence for hundreds of millions of years, since the first plankton started filling our atmosphere with oxygen. A distant civilization could be analyzing our atmosphere and know exactly when we entered the industrial age.
But what we haven’t talked about, the space elephant in the room, if you will, is what we’ll do if we actually make contact. What are we going to say to each other? And what will happen if the aliens show up?
Although there’s no official protocol on talking to aliens, scientists and research institutions have been puzzling out the best way we might communicate for quite a while.
Perhaps the best example is the SETI Institute, the US-based research group who have dedicated radio telescopes scanning the skies for messages from space.
Let’s imagine you’re a SETI researcher, and you’re browsing last night’s logs and you see what looks like a message. Maybe it’s instructions to build some kind of dimensional portal, or a recipe book.
Whatever you do, don’t try out the recipes. Instead, you need to make absolutely sure you’re not dealing with some kind of natural phenomenon. Then you need to reach out to other researchers and get them to confirm the signal.
If they agree it’s aliens, then you need to inform the International Astronomical Union and other international groups, like the United Nations, Committee on Space Research, etc.
Unless they’ve got some good reason to stop you, it’s time to announce the discovery to the worldwide media. You made the discovery, you get to break the news to the world.
At this point, of course, the entire world is going to freak right out. Whatever you do, however, you have to resist the urge to send back a message or build that dimensional portal, no matter how much you think you understand the science. Instead, let an international committee mull it over while you stockpile supplies in a secret alien proof bunker in the desert.
What kind of message should we actually craft to our new alien penpals? Will we become fast friends, jump starting our own technological progress, or will we insult them by accident?
In 2000, and international group of SETI researchers including the famous Jill Tarter devised The Rio Scale. It really easy to use, and there’s even a fun online calculator.
Step 1, figure out the class of phenomenon. Is it a message sent directly to Earth, expecting a reply? Or did we merely find some alien artifact or old timey Dyson sphere orbiting a nearby star?
Step 2, how verifiable is the discovery? Are we talking ongoing signals received by SETI researchers, or a hint in some old data that’s impossible to confirm?
Step 3, how far are we talking here? Hovering over Paris? Within our Solar System, or outside the galaxy?
Step 4, how sure are you? 100% certain, and everyone agrees because they can all see that enormous mothership floating above London? Or nobody believes you, and they’ve locked you up because of your insane ramblings and misappropriation of government equipment?
Punch in your numbers and you’ll get a rank on The Rio Scale between 0 and 10. Level 0 is “no importance” or “you’re a crank”, while level 10 is “extraordinary importance”, or “now would be a good time to panic”.
SETI researcher Seth Shostak, calculated the Rio Scale for various sci-fi movies and shows. The first message from aliens in Independence Day would count as a 4. While the obliteration of the White House by a massive floating alien city that everybody could see would count as a 10.
the messages received in Contact, and independently confirmed by researchers around the world would qualify in the 4-8 range, while the monolith discovered on the Moon in 2001 would be a solid 6.
Now you know how important the discovery is, what do you say back to those chatty aliens?
This falls under the term CETI, which means Communications with Extraterrestrial Aliens, which shouldn’t be confused with SETI, or the Search for Extraterrestrial Aliens. And it turns out, that horse has already left the stable.
When the Pioneer and Voyager spacecraft were constructed, they were equipped with handy maps to find Earth’s precise location in the Milky Way.
In 1974, Carl Sagan and Frank Drake who composed a message in alienese and broadcast it into space from the Arecibo Observatory.
In 1999 and 2003 a series of signals were transmitted towards various interesting stars. The messages contained images of Earth, as well as various mathematical principles that could be used by aliens as a common language.
We’ll know if that was a good idea in a few decades.
According to Seth Shostak, the best message we can send is the entire internet. Just send it all, they’ll work out what we’re all about.
The science fiction author David Brin thinks that’s a terrible idea, and we should keep our mouths shut.
Personally, I think the aliens already know we’re here. If they wanted to invade and destroy our planet, they would have done it millions of years ago when early life made it obvious this planet was inhabited. The jig is up.
It’s a mind bending concept to imagine what life might be like if we knew with absolutely certainty that there’s an alien civilization right over there, on that world. I’m sure people will freak out for a while, but then we’ll probably just go back to life as normal. Human beings can get bored by the most surprising and amazing things.
If you learned there was definitely an alien civilization out there, how do you think humanity would respond? Let me know your thoughts in the comments.
If you’ve seen at least one other episode of the Guide to Space, you know I’m obsessed about the Fermi Paradox. This idea that the Universe is big and old, and should be teeming with life. And yet, we have no evidence that it exists out there. We wonder, where are all the aliens?
Ah well, maybe we’re in a cosmic zoo, or maybe the Universe is just too big, or the laws of physics prevent any kind of meaningful travel or communications. Fine. I doubt it, but fine.
As we’ve demonstrated here in our own corner of the galaxy, it’s not our weak fleshy bodies that will be doing the hard work of exploring the Solar System, and eventually the galaxy, it’ll be the robots.
So a better question might be, where are all the robots? At the time that I’m writing this video, we’re in October of 2016. If you’re watching this on a video device years in the future, the robot uprising and apocalypse hasn’t happened yet.
The most sophisticated walking robots can barely lurch around and they’re laughably slow, 3D fabrication is an inefficient process, and our artificial intelligence devices are pretty dumb, barely able to understand when I ask for directions.
But even so, our robots have helped us explore the Solar System, and helped us see things with cameras that our fleshy meat eyeballs may never experience. Robots from Earth have orbited asteroids, visited comets, observed Mars from orbit and the ground, and even flown past Pluto.
In the coming decades, many new robotic missions will continue this era of exploration, maybe floating in the cloud tops of Venus, sailing the hydrocarbon seas of Titan, flying in the skies of Mars, or exploring the vast oceans under the ice of Europa.
It makes sense then, for us to eventually get around to sending a robotic spacecraft to another star. Based on our current technology, it’ll be incredibly complicated and expensive, but there’s nothing in the laws of physics that prevents it.
And if we’re going to send a robot to another star system, we might as well make it a factory, capable of creating another version of itself. Find an asteroid with all the raw materials to make more robot factories, and send them off to other stars, where they can make more copies, and so on, and so on.
What I’m describing is the concept of a von Neumann probe, named after the mathematician John von Neumann. He was investigating the implications of self-replicating robots in the 1940s, and imagined non-biological “Universal Assembler”, devices that could make copies of themselves.
Von Neumann didn’t apply the idea to spacecraft, but others like George “Spheres” Dyson understood that out in space, there was a nearly limitless amount of raw materials for spacecraft to build copies of themselves.
Even though the Milky Way measures 120,000 light-years across and contains 100 to 400 billion stars, self-replicating robot factories traveling at just 10% the speed of light could colonize the entire galaxy in about 10 million years. That’s the power of exponential exploration.
Think about it. All it takes is for a single clever alien engineer to craft a single robotic factory. That factory builds copies of itself which fly off to other stars. Once they get there, they build more copies of themselves, and so on and so on.
Seriously, in the 13.8 billion years that the Universe has been around, why didn’t a single alien engineer do this?
The cosmologist Frank Tipler concluded that this was such an obvious thing to do that he wrote a paper in the 1980s called “Extraterrestrial intelligent beings do not exist.” Carl Sagan found the argument troubling, proposed that aliens would be concerned with environmental collapse and would restrict the use of this kind of technology.
Why haven’t we received signals from extraterrestrials yet? Maybe because it’s inefficient. It’s much more efficient to send physical probes to communicate with other civilizations.
Remember 2001? I know it was a pretty complicated movie, but that was the point. The aliens let us know we’re not alone by sending their robotic spacecraft to our Solar System. That’s what those monoliths were for. Well, sort of. They were a message, they were a kind of encyclopedia, an evolutionary accelerator and doomsday device, all rolled up in one.
Still think it’s important to take your fleshy meat body to experience other worlds personally? No problem. Modify your von Neumann probes to be terraforming probes. Instead of merely building factories, they travel to other star systems, identify the planets that could be made habitable for humans, and then get to work.
We’ve written many articles about what could be done to terraform worlds here in the Solar System, and that work would mostly be done with robots anyway. Some robots could redirect asteroids and comets to supply raw materials, robotic shades to cool planets down, ground-based factories could change the atmosphere to something breathable.
You could even imagine robotic nurseries, carrying seeds and genetic material for plants and animals. They could get these planets livable, so that when our descendants arrive, the world is ready to go and fully habitable.
There’s a darker idea too, the concept of Berserker Probes. These were first put forth by the science fiction author Fred Saberhagen. Imagine aliens send an initial scouting robotic spacecraft to a star system to search for life, and any possible competition to the colonization of the galaxy.
If a potential competitor is found, the robotic spacecraft redirect a bunch of asteroids at the habitable planet to scour it free of life.
Then the terraforming robots move in and make the place livable for the aliens. And then the aliens move in, blissfully unaware of who used to live on the planet.
Maybe other aliens anticipating this threat, create their own police von Neumann probes, designed to seek out Berserkers and defend against them.
If you play video games, the best telling of this story is through the Mass Effect series, and their Reapers. Edge of Tomorrow was about defending Earth from terraforming robots.
Although I find the Fermi Paradox puzzling, I get that it’s probably hard for aliens to travel and communicate across the vast distances of space. But shouldn’t we at least see their robots?
Actually, based on what I just said, I’m think I’m okay if we never meet their robots.
Want to learn more about von Neumann probes? PBS Space Time just did a great video on it too. You should check it out.