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 of 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?
Rather than resolving the dispute, additional observations only deepened the mystery, even giving rise to suggestions that it might be an extra-terrestrial solar sail. For this reason, scientists are very interested in finding other examples of ‘Oumuamua-like objects. According to a recent study by a team of Harvard astrophysicists, it is possible that interstellar objects enter our system and end up falling into in our Sun somewhat regularly.
On October 19th, 2017, the first interstellar object – named 1I/2017 U1 (aka. ‘Oumuamua) – to be observed in our Solar System was detected. In the months that followed, multiple follow-up observations were conducted to gather more data on its composition, shape, and possible origins. Rather than dispel the mystery surrounding the true nature of ‘Oumuamua – is a comet or an asteroid? – these efforts have only managed to deepen it.
In a recent study, Harvard Professor Abraham Loeb and Shmuel Bialy – a postdoctoral researcher from the Smithsonian Center for Astrophysics (CfA) – addressed this mystery by suggesting that ‘Oumuamua may be an extra-terrestrial solar sail. Building on this, Loeb and Amir Siraj (a Harvard undergraduate student) conducted a new study that indicated that hundreds of “‘Oumuamua-like” objects could be detectable in our Solar System.
Interestingly enough, there has also been some speculation that based on its shape, ‘Oumuamua might actually be an interstellar spacecraft (Breakthrough Listen even monitored it for signs of radio signals!). A new study by a pair of astronomers from the Harvard Smithsonian Center for Astrophysics (CfA) has taken it a step further, suggesting that ‘Oumuamua may actually be a light sail of extra-terrestrial origin.
One of the more interesting and rewarding aspects of astronomy and space exploration is seeing science fiction become science fact. While we are still many years away from colonizing the Solar System or reaching the nearest stars (if we ever do), there are still many rewarding discoveries being made that are fulfilling the fevered dreams of science fiction fans.
For instance, using the Dharma Planet Survey, an international team of scientists recently discovered a super-Earth orbiting a star just 16 light-years away. This super-Earth is not only the closest planet of its kind to the Solar System, it also happens to be located in the same star system as the fictional planet Vulcan from the Star Trek universe.
Since the 1990s, astrophysicists have known that for the past few billion years, the Universe has been experiencing an accelerated rate of expansion. This gave rise to the theory that the Universe is permeated by a mysterious invisible energy known as “dark energy”, which acts against gravity and is pushing the cosmos apart. In time, this energy will become the dominant force in the Universe, causing all stars and galaxies to spread beyond the cosmic horizon.
At this point, all stars and galaxies in the Universe will no longer be visible or accessible from any other. The question remains, what will intelligent civilizations (such as our own) do for resources and energy at this point? This question was addressed in a recent paper by Dr. Abraham Loeb – the Frank B. Baird, Jr., Professor of Science at Harvard University and the Chair of the Harvard Astronomy Department.
The paper, “Securing Fuel for our Frigid Cosmic Future“, recently appeared online. As he indicates in his study, when the Universe is ten times its current age (roughly 138 billion years old), all stars outside the Local Group of galaxies will no be accessible to us since they will be receding away faster than the speed of light. For this reason, he recommends that humanity follow the lesson from Aesop’s fable, “The Ants and the Grasshopper”.
This classic tale tells the story of ants who spent the summer collecting food for the winter while the grasshopper chose to enjoy himself. While different versions of the story exist that offer different takes on the importance of hard work, charity, and compassion, the lesson is simple: always be prepared. In this respect, Loeb recommends that advanced species migrate to rich clusters of galaxies.
These clusters represent the largest reservoirs of matter bound by gravity and would therefore be better able to resist the accelerated expansion of the Universe. As Dr. Loeb told Universe Today via email:
“In my essay I point out that mother Nature was kind to us as it spontaneously gave birth to the same massive reservoir of fuel that we would have aspired to collect by artificial means. Primordial density perturbations from the early universe led to the gravitational collapse of regions as large as tens of millions of light years, assembling all the matter in them into clusters of galaxies – each containing the equivalent of a thousand Milky Way galaxies.”
Dr. Loeb also indicated where humanity (or other advanced civilizations) should consider relocating to when the expansion of the Universe causes the stars of the Local Group to expand beyond the cosmic horizon. Within 50 million light years, he indicates, likes the Virgo Cluster, which contains about a thousands times more matter than the Milky Way Galaxy. The second closest is the Coma Cluster, a collection of over 1000 galaxies located about 336 million light years away.
In addition to offering a solution to the accelerating expansion of the Universe, Dr. Loeb’s study also presents some interesting possibilities when it comes to the search for extra-terrestrial intelligence (SETI). If, in fact, there are already advanced civilizations migrating to prepare for the inevitable expansion of the Universe, they may be detectable by various means. As Dr. Loeb explained:
“If traveling civilizations transmit powerful signals then we might be able to see evidence for their migration towards clusters of galaxies. Moreover, we would expected a larger concentration of advanced civilization in clusters than would be expected simply by counting the number of galaxies there. Those that settle there could establish more prosperous communities, in analogy to civilizations near rivers or lakes on Earth.”
This paper is similar to a study Dr. Loeb conducted back in 2011, which appeared in the Journal of Cosmology and Astroparticle Physics under the title “Cosmology with Hypervelocity Stars“. At the time, Dr. Loeb was addressing what would happen in the distant future when all extragalactic light sources will cease to be visible or accessible due to the accelerating expansion of the Universe.
This study was a follow-up to a 2001 paper in which Dr. Loeb addressed what would become of the Universe in billions of years – which appeared in the journal Physical Review Letters under the title “The Long–Term Future of Extragalactic Astronomy“. Shortly thereafter, Dr. Loeb and Freeman Dyson himself began to correspond about what could be done to address this problem.
Their correspondence was the subject of an article by Nathan Sanders (a writer for Astrobites) who recounted what Dr. Loeb and Dr. Dyson had to say on the matter. As Dr. Loeb recalls:
“A decade ago I wrote a few papers on the long-term future of the Universe, trillions of years from now. Since the cosmic expansion is accelerating, I showed that once the universe will age by a factor of ten (about a hundred billion years from now), all matter outside our Local Group of galaxies (which includes the Milky Way and the Andromeda galaxy, along with their satellites) will be receding away from us faster than light. After one of my papers was posted in 2011, Freeman Dyson wrote to me and suggested to a vast “cosmic engineering project” in which we will concentrate matter from a large-scale region around us to a small enough volume such that it will stay bound by its own gravity and not expand with the rest of the Universe.”
At the time, Dr. Loeb indicated that data gathered by the Sloan Digital Sky Survey (SDSS) indicated that attempts at “super-engineering” did not appear to be taking place. This was based on the fact that the galaxy clusters observed by the SDSS were not overdense, nor did they exhibit particularly high velocities (as would be expected). To this, Dr. Dyson wrote: “That is disappointing. On the other hand, if our colleagues have been too lazy to do the job, we have plenty of time to start doing it ourselves.”
A similar idea was presented in a recent paper by Dr. Dan Hooper, an astrophysicist from the Fermi National Accelerator Laboratory (FNAL) and the University of Chicago. In his study, Dr. Hooper suggested that advanced species could survive all stars in the Local Group expanding beyond the cosmic horizon (100 billion years from now), by harvesting stars across tens of millions of light years.
This harvesting would consist of building unconventional Dyson Spheres that would use the energy they collected from stars to propel them towards the center of the species’ civilization. However, only stars that range in mass of 0.2 to 1 Solar Masses would be usable, as high-mass stars would evolve beyond their main sequence before reaching the destination and low-mass stars would not generate enough energy for acceleration to make it in time.
But as Dr. Loeb indicates, there are additional limitations to this approach, which makes migrating more attractive than harvesting.
“First, we do not know of any technology that enables moving stars around, and moreover Sun-like stars only shine for about ten billion years (of order the current age of the Universe) and cannot serve as nuclear furnaces that would keep us warm into the very distant future. Therefore, an advanced civilization does not need to embark on a giant construction project as suggested by Dyson and Hooper, but only needs to propel itself towards the nearest galaxy cluster and take advantage of the cluster resources as fuel for its future prosperity.”
While this may seem like a truly far-off concern, it does raise some interesting questions about the long-term evolution of the Universe and how intelligent civilizations may be forced to adapt. In the meantime, if it offers some additional possibilities for searching for extra-terrestrial intelligences (ETIs), then so much the better.
And as Dr. Dyson said, if there are currently no ETIs preparing for the coming “cosmic winter” with cosmic engineering projects, perhaps it is something humanity can plan to tackle someday!
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.
During the 1930s, astronomers came to realize that the Universe is in a state of expansion. By the 1990s, they realized that the rate at which it is expansion is accelerating, giving rise to the theory of “Dark Energy”. Because of this, it is estimated that in the next 100 billion years, all stars within the Local Group – the part of the Universe that includes a total of 54 galaxies, including the Milky Way – will expand beyond the cosmic horizon.
At this point, these stars will no longer be observable, but inaccessible – meaning that no advanced civilization will be able to harness their energy. Addressing this, Dr. Dan Hooper – an astrophysicist from the Fermi National Accelerator Laboratory (FNAL) and the University of Chicago – recently conducted a study that indicated how a sufficiently advanced civilization might be able to harvest these stars and prevent them from expanding outward.
When it comes to the search for extra-terrestrial intelligence (SETI) in the Universe, there is the complicated matter of what to be on the lookout for. Beyond the age-old question of whether or not intelligent life exists elsewhere in the Universe (statistically speaking, it is very likely that it does), there’s also the question of whether or not we would be able to recognize it if and when we saw it.
Given that humanity is only familiar with one form of civilization (our own), we tend to look for indications of technologies we know or which seem feasible. In a recent study, a researcher from the Instituto de Astrofísica de Canarias (IAC) proposed looking for large bands of satellites in distant star systems – a concept that was proposed by the late and great Arthur C. Clarke (known as a Clarke Belt).
This proposal is based in part on a paper written by Arthur C. Clarke in 1945 (titled “Peacetime Uses for V2“), in which he proposed sending “artificial satellites” into geostationary orbit around Earth to create a global communications network. At present, there are about 400 such satellites in the “Clarke Belt” – a region named in honor of him that is located 36,000 km above the Earth.
This network forms the backbone of modern telecommunications and in the future, many more satellites are expected to be deployed – which will form the backbone of the global internet. Given the practicality of satellites and the fact that humanity has come to rely on them so much, Socas-Navarro considers that a belt of artificial satellites could naturally be considered “technomarkers” (the analogues of “biomarkers”, which indicate the presence of life).
As Socas-Navarro explained to Universe Today via email:
“Essentially, a technomarker is anything that we could potentially observe which would reveal the presence of technology elsewhere in the Universe. It’s the ultimate clue to find intelligent life out there. Unfortunately, interstellar distances are so great that, with our current technology, we can only hope to detect very large objects or structures, something comparable to the size of a planet.”
In this respect, a Clarke Exobelt is not dissimilar from a Dyson Sphere or other forms of megastructures that have been proposed by scientists in the past. But unlike these theoretical structures, a Clarke Exobelt is entirely feasible using present-day technology.
“Other existing technomarkers are based on science fiction technology of which we know very little,” said Socas-Navarro. “We don’t know if such technologies are possible or if other alien species might be using them. The Clarke Exobelt, on the other hand, is a technomarker based on real, currently existing technology. We know we can make satellites and, if we make them, it’s reasonable to assume that other civilizations will make them too.”
According to Socas-Navarro, there is some “science fiction” when it comes to Clarke Exobelts that would actually be detectable using these instruments. As noted, humanity has about 400 operational satellites occupying Earth’s “Clarke Belt”. This is about one-third of the Earth’s existing satellites, whereas the rest are at an altitude of 2000 km (1200 mi) or less from the surface – the region known as Low Earth Orbit (LEO).
This essentially means that aliens would need to have billions more satellites within their Clarke Belt – accounting for roughly 0.01% of the belt area – in order for it to be detectable. As for humanity, we are not yet to the point where our own Belt would be detectable by an extra-terrestrial intelligence (ETI). However, this should not take long given that the number of satellites in orbit has been growing exponentially over the past 15 years.
Based on simulations conducted by Socas-Navarro, humanity will reach the threshold where its satellite band will be detectable by ETIs by 2200. Knowing that humanity will reach this threshold in the not-too-distant future makes the Clarke Belt a viable option for SETI. As Socas-Navarro explained:
“In this sense, the Clarke Exobelt is interesting because it’s the first technomarker that looks for currently existing technology. And it goes both ways too. Humanity’s Clarke Belt is probably too sparsely populated to be detectable from other stars right now (at least with technology like ours). But in the last decades we have been populating it at an exponential rate. If this trend were to continue, our Clarke Belt would be detectable from other stars by the year 2200. Do we want to be detectable? This is an interesting debate that humanity will have to resolve soon.
As for how these belts would be detected, that would come down to the most popular and effective means for finding exoplanets to date – the Transit Method (aka. Transit Photometry). For this method, astronomers monitor distant stars for periodic dips in brightness, which are indications of an exoplanet passing in front of the star. Using next-generation telescopes, astronomers may also be able to detect reflected light from a dense band of satellites in orbit.
“However, before we point our supertelescopes to a planet we need to identify good candidates,” said Socas-Navarro. “There are too many stars to check and we can’t go one by one. We need to rely on exoplanet search projects, such as the recently launched satellite TESS, to spot interesting candidates. Then we can do follow-up observations with supertelescopes to confirm or refute those candidates.”
While these space-telescopes would search for rocky planets that are located within the habitable zones of thousands of stars, next-generation telescopes could search for signs of Clarke Exobelts and other technomarkers that would be otherwise hard to spot. However, as Socas-Navarro indicated, astronomers could also find evidence of Exobands by sifting through existing data as well.
“In doing SETI, we have no idea what we are looking for because we don’t know what the aliens are doing,” he said. “So we have to investigate all the possibilities that we can think of. Looking for Clarke Exobelts is a new way of searching, it seems at least reasonably plausible and, most importantly, it’s free. We can look for signatures of Clarke Exobelts in currently existing missions that search for exoplanets, exorings or exomoons. We don’t need to build costly new telescopes or satellites. We simply need to keep our eyes open to see if we can spot the signatures presented in the simulation in the flow of data from all of those projects.”
Humanity has been actively searching for signs of extra-terrestrial intelligence for decades. To know that our technology and methods are becoming more refined, and that more sophisticated searches could begin within a decade, is certainly encouraging. Knowing that we won’t be visible to any ETIs that are out there for another two centuries, that’s also encouraging!
And be sure to check out this cool video by our friend, Jean Michael Godier, where he explains the concept of a Clarke Exobelt:
In the 1950s, famed physicist Enrico Fermi posed the question that encapsulated one of the toughest questions in the Search for Extra-Terrestrial Intelligence (SETI): “Where the heck is everybody?” What he meant was, given the age of the Universe (13.8 billion years), the sheer number of galaxies (between 1 and 2 trillion), and the overall number of planets, why has humanity still not found evidence of extra-terrestrial intelligence?
This question, which has come to be known as the “Fermi Paradox”, is something scientists continue to ponder. In a new study, a team from the University of Rochester considered that perhaps Climate Change is the reason. Using a mathematical model based on the Anthropocene, they considered how civilizations and planet systems co-evolve and whether or not intelligent species are capable of living sustainability with their environment.
Today, Climate Change is one of the most pressing issues facing humanity. Thanks to changes that have taken place in the past few centuries – i.e. the industrial revolution, population growth, the growth of urban centers and reliance on fossil fuels – humans have had a significant impact on the planet. In fact, many geologists refer to the current era as the “Anthropocene” because humanity has become the single greatest factor affecting planetary evolution.
In the future, populations are expected to grow even further, reaching about 10 billion by mid-century and over 11 billion by 2100. In that time, the number of people who live within urban centers will also increase dramatically, increasing from 54% to 66% by mid-century. As such, the quesiton of how billions of people can live sustainably has become an increasingly important one.
“Astrobiology is the study of life and its possibilities in a planetary context. That includes ‘exo-civilizations’ or what we usually call aliens. If we’re not the universe’s first civilization, that means there are likely to be rules for how the fate of a young civilization like our own progresses.”
Using the Anthropocene as an example, one can see how civilization-planet systems co-evolve, and how a civilization can endanger itself through growth and expansion – in what is known as a “progress trap“. Basically, as civilizations grow, they consume more of the planet’s resources, which causes changes in the planet’s conditions. In this sense, the fate of a civilization comes down to how they use their planet’s resources.
In order to illustrate this process Frank and his collaborators developed a mathematical model that considers civilizations and planets as a whole. As Prof. Frank explained:
“The point is to recognize that driving climate change may be something generic. The laws of physics demand that any young population, building an energy-intensive civilization like ours, is going to have feedback on its planet. Seeing climate change in this cosmic context may give us better insight into what’s happening to us now and how to deal with it.”
The model was also based on case studies of extinct civilizations, which included the famous example of what became of the inhabitants of Rapa Nui (aka. Easter Island). According to archaeological studies, the people of the South Pacific began colonizing this island between 400 and 700 CE and its population peaked at 10,000 sometime between 1200 and 1500 CE.
By the 18th century, however, the inhabitants had depleted their resources and the population declined to just 2000. This example raises the important concept known as “carrying capacity”, which is the maximum number of species an environment can support. As Frank explained, Climate Change is essentially how the Earth responds to the expansion of our civilization:
“If you go through really strong climate change, then your carrying capacity may drop, because, for example, large-scale agriculture might be strongly disrupted. Imagine if climate change caused rain to stop falling in the Midwest. We wouldn’t be able to grow food, and our population would diminish.”
Using their mathematical model, the team identified four potential scenarios that might occur on a planet. These include the Die-Off scenario, the Sustainability scenario, the Collapse Without Resource Change scenario, and the Collapse With Resource Change scenario. In the Die-Off scenario, the population and the planet’s state (for example, average temperatures) rise very quickly.
This would eventually lead to a population peak and then a rapid decline as changing planetary conditions make it harder for the majority of the population to survive. Eventually, a steady population level would be achieved, but it would only be a fraction of what the peak population was. This scenario occurs when civilizations are unwilling or unable to change from high-impact resources (i.e. oil, coal, clear-cutting) to sustainable ones (renewable energy).
In the Sustainability scenario, the population and planetary conditions both rise, but eventually come to together with steady values, thus avoiding any catastrophic effects. This scenario occurs when civilizations recognize that environmental changes threaten their existence and successfully make the transition from high-impact resources to sustainable ones.
The final two scenarios – Collapse Without Resource Change and Collapse With Resource Change – differ in one key respect. In the former, the population and temperature both rise rapidly until the population reaches a peak and begins to drop rapidly – though it is not clear if the species itself survives. In the latter, the population and temperature rise rapidly, but the populations recognizes the danger and makes the transition. Unfortunately, the change comes too late and the population collapses anyway.
At present, scientists cannot say with any confidence which of these fates will be the one humanity faces. Perhaps we will make the transition before it is too late, perhaps not. But in the meantime, Frank and his colleagues hope to use more detailed models to predict how planets will respond to civilizations and the different ways they consume energy and resources in order to grow.
From this, scientists may be able to refine their predictions of what awaits us in this century and the next. It is during this time that crucial changes will be taking place, which include the aforementioned population growth, and the steady rise in temperatures. For instance, based on two scenarios that measured CO2 increases by the year 2100, NASA indicated that global temperatures could rise by either 2.5 °C (4.5 °F) or 4.4 °C (8 °F).
In the former scenario, where CO2 levels reached 550 ppm by 2100, the changes would be sustainable. But in the latter scenario, where CO2 levels reached 800 ppm, the changes would cause widespread disruption to systems that billions of humans depends upon for their livelihood and survival. Worse than that, life would become untenable in certain areas of the world, leading to massive displacement and humanitarian crises.
In addition to offering a possible resolution for the Fermi Paradox, this study offers some helpful advice for human beings. By thinking of civilizations and planets as a whole – be they Earth or exoplanets – researchers will be able to better predict what changes will be necessary for human civilization to survive. As Frank warned, it is absolutely essential that humanity mobilize now to ensure that the worst-case scenario does not occur here on Earth:
“If you change the earth’s climate enough, you might not be able to change it back. Even if you backed off and started to use solar or other less impactful resources, it could be too late, because the planet has already been changing. These models show we can’t just think about a population evolving on its own. We have to think about our planets and civilizations co-evolving.”
And be sure to enjoy this video that addresses Prof. Frank and his team’s research, courtesy of the University of Rochester: