Knowledge arks – CONSTRAINT N°3: LONGEVITY (8/9)

SUMMARY:

There are all kinds of external and internal constraints that can limit the sustainability of a knowledge ark; these constraints are therefore the most critical factors in the design of such a project

These constraints may, however, conflict with the requirement for accessibility, particularly due to the issue of a knowledge ark’s isolation; different design philosophies are therefore possible

The choice of the ark’s location is critical to ensuring that it is not destroyed during a natural disaster or armed conflict, while the choice of storage medium can be critical in the face of natural wear and tear, while also serving as a means to minimize active and ongoing maintenance as much as possible

Ultimately, there is a wide variety of conceivable knowledge arks, each with different design philosophies. These philosophies can be summarized into seven categories: anarchic, digital, heritage, thematic, universal, encapsulated, or hybrid

Knowledge arcs designed for exceptional longevity are nothing more than highly advanced time capsules, which would exist more for symbolic reasons (to create humanity’s ultimate legacy in the cosmos) than for pragmatic ones (to help future generations (re)build an ever-more-advanced civilization)

Time capsules—whether or not they were designed to be retrieved on a specific date—have historically contained relatively little information, but have recently become much more ambitious and are gaining unprecedented significance.

A time capsule designed to also serve as an ark of knowledge would be the best possible legacy humanity could leave to posterity—a way to encapsulate, at a single point in space, a condensed version of the universe as understood by its most astute observers.

When faced with natural hazards, the choice of storage environment is essential

In creating a knowledge ark, there remains one last major challenge to overcome: longevity. We have discussed all kinds of techniques and storage method to overcome various constraints such as technological obsolescence, language barriers, the quantity of information, and centralization. The avenues explored so far range from traditional digital media to oral transmission, emerging molecular storage technologies, and engraved tablets. But ultimately, all these constraints are subordinate to another, arguably the most important one: longevity. For a large-scale epistemic memory project to be relevant, it is not only necessary to be able to safeguard as much of our heritage as possible and make it available to our descendants, but also to ensure that this accessibility is not limited to our direct descendants and that our knowledge benefits generations that will arrive long after the potential decline of our civilization. The knowledge preservation strategies we have discussed so far have focused mainly on knowledge articulation (accumulation, sorting, transmission, selection, etc.), and less on preservation itself, although it is the core of the project. Preservation is the collection of methods and procedures aimed at keeping the preserved heritage in good condition, and even in good working order if this heritage includes machines. Three main areas of preservation can be identified: preservation against natural damage, preservation against anthropological damage, and preservation against internal wear and tear. In the first two cases, it is mainly the environment surrounding the preservation location that can be configured, while in the last case, it is essentially the nature of the medium itself that determines whether or not it will last.

Firstly, in order for our knowledge to withstand the passage of time, it must be kept in a controlled environment, sheltered from natural disasters. In our section on natural hazards, we saw that there are all kinds of major phenomena that can destroy our heritage: we mentioned floods and fires, which have been responsible for the loss of many priceless structures over time, but we could also mention earthquakes, cyclones, volcanic eruptions, landslides, tornadoes, and other violent winds. The first step in preservation is therefore to choose a geographical location that is relatively spared from this type of violent disaster: avoid geologically active regions, avoid the coast or any waterways, avoid floodplains, and avoid forest areas vulnerable to fire. But there is more: the effects of entropy are not only manifested in violent events, they also leave their mark through common physical phenomena such as temperature, magnetism, humidity, light, etc. There is therefore a second major step to take in preservation, which is to create a healthy preservation environment in which these kinds of external aggression are curbed. Many modern institutions such as museums, libraries, and archives already implement environmental control measures: the temperature must be kept at a relatively constant level to slow down deterioration caused by mold, insects, or microorganisms; while books are not piled up haphazardly to prevent the rapid spread of fire. Artifacts are not exposed to daylight; they are stored in special rooms or even sheltered boxes that allow little or no moisture and contaminants (acid, ozone, dust, fungi, etc.) to pass through; and in the meantime, building foundations must be designed to withstand high-magnitude earthquakes or powerful explosions.

Finally, if a disaster does still occur, numerous procedures must be in place to limit the damage. These procedures may consist of protective installations (fire extinguishers, sprinklers, thermostats, etc.) and detection devices (hygrometers, thermometers, etc.), safety measures, special partitioned rooms that are off-limits to the public, staff training, identification of actors who can help fight disasters (firefighters, police, etc.), the creation of documentation to provide feedback on previous disasters, or restoration plans to repair damaged but not destroyed objects. These measures can have a major drawback: they require significant facilities and personnel, which is fine for contemporary institutions such as libraries and museums, but more problematic for preserving heritage over the very long term: it is best not to assume that the necessary resources will always be available to protect and restore items throughout the duration of a knowledge ark project, which can span several thousand years. In other words, “active” preservation—which relies on agents to ensure everything remains in good condition—is much riskier than “passive” preservation, which would not require the continuous allocation of significant resources. Ideally, an “ark of knowledge” might simply consist of storing our knowledge in a secure, sealed facility, completely isolated from the outside world and never visited by any human being other than those for whom the knowledge is intended. We can therefore understand the value of centralizing knowledge (to limit the number of epistemic memory centers requiring active monitoring), digitization (some digital media are easier to preserve than traditional media such as books, microfilm, etc.), and above all, physical media of sufficient quality to withstand the ravages of time without maintenance.

When faced with human risks, the right balance in terms of accessibility must be found

Secondly, still with a view to ensuring that our knowledge survives the passage of time, we must take anthropological risks into account. On political risks, we discussed conflicts and censorship (in a broad sense: censorship itself, but also selection bias, propaganda, discrimination, etc.), which can damage at least part of our heritage. On industrial risks, we discussed the plausibility of our industrial civilization eventually collapsing due to poor macroeconomic choices (overexploitation of resources, unlimited greenhouse gas emissions, uncontrolled technological developments, etc.), which could also be combined with political risks (an increase in wars and forms of authoritarianism) and even natural risks (increase in natural disasters linked to global warming). To this we can add more trivial risks: theft and vandalism, which in the past have often prevented the scientific community from benefiting from certain archaeological treasures that had survived the passage of time. Consequently, the conservation strategies discussed earlier—namely, selecting locations away from disaster zones, environmental management, and conservation policies—must also take into account all these anthropogenic factors. When choosing a location, the knowledge ark should be far from any conflict areas or even any areas of significant population, these being more vulnerable to bombing than uninhabited areas. On the issue of a controlled environment, intrusion detection and prevention of deliberate damage must be added to the preservation measures. Finally, the preservation center must be as resilient as possible to a military attack.

However, one question remains: if we want to preserve our intellectual heritage as much as possible, isn’t it in our best interest to isolate it as much as possible? If human beings are a potential source of destruction and censorship, how can we balance environmental integrity with resource availability for future generations? It may indeed seem paradoxical to talk about deliberately making our knowledge inaccessible in order to ensure its longevity, even though the measures we might implement would run counter to the need for our knowledge to be accessible to our distant descendants. Doesn’t the issue of longevity conflict with that of accessibility? In this regard, one might refer to the many time capsules left in space in the past—that is, the place par excellence that is inaccessible to humans. For example; we can refer to the objects left behind by the Apollo missions, the plaques onboard Pioneer 10 and 11 probes, the “Golden Record” from the Voyager 1 and 2 probes, and the already mentioned lunar library aboard the Odyssey probe. The advantage of space, apart from the fact that natural hazards are much more limited than on Earth (no wind, no fire, no humidity, etc.), is that it is a rather inaccessible and gigantic area, where humans cannot easily wage war, steal, or censor archives. But precisely because a space memory project is by nature virtually inaccessible, it will be more difficult for our descendants to retrieve the contents of a hypothetical space knowledge ark, especially if they do not master space technologies. Space is clearly the best way to ensure the longevity of knowledge, but this comes at the expense of passing it on to our distant descendants.

In light of this dilemma, there are therefore two strategies: if we prioritize longevity over availability, in which case space is the best place for a knowledge ark project. But in this case, it must either be stored in a fixed location (on the Moon, for example), or be able to return automatically to Earth after a certain amount of time (on board satellites orbiting Earth for instance; even those in distant orbits eventually fall back to Earth after several hundred thousand years). Otherwise, if we prioritize availability over longevity, in which case the knowledge ark project has to be located on Earth, it must still be in a sufficiently isolated location so that our descendants have a chance of finding the contents of the ark intact. In any case, this points to a “passive” rather than active preservation strategy, which is easier to implement far from civilization. Incidentally, the issue of isolation raises two other subsidiary questions: that of secrecy and that of consultation. Should we favor a secret location (to limit the risk of theft or deliberate destruction) or not (to make it easier for our descendants to find our knowledge)? Should the contents of an epistemic memory be accessible in our time or not? These issues must be considered when designing a knowledge arch.

When faced with wear and tear, the choice of physical medium is crucial

Finally, to ensure that our knowledge repository endures over time, we must take into account the natural degradation of information storage media. It is primarily for this reason that the choice of storage medium will be a decisive factor. This choice has already been discussed earlier, since depending on the form a knowledge repository takes, certain technologies are more suitable in some situations than in others. For example, the latest advances in information storage are better suited for a comprehensive knowledge ark. Conversely, more traditional media are better suited for a more selective knowledge ark, as well as for any appendices intended to make our knowledge more accessible to our distant descendants. The choice between a digital or analog medium will also depend on the design of the knowledge repository, depending on whether one wishes to create a “library,” focused primarily on written materials, or a “universal archive,” which would then be multimedia.

Added to all this is longevity an ideal medium must certainly have a large capacity, be versatile, and be accurate, but above all, it must be reliable over the very long term. For these reasons, most traditional media are not truly suited for preservation. For example, although paper can theoretically last for several centuries under good preservation conditions, in reality, it is vulnerable to water and fire. As a result, most documents produced by humans have not survived to the present day, due to fires, shredding, or floods—not to mention the many books lost to mold or biological organisms. In addition, the industrial paper used for most contemporary publications is of poor quality, and can deteriorate fairly quickly compared to more traditional paper. When it comes to electronic media, the situation is not much better. Not only do most media (vinyl records, optical discs, memory cards, USB drives, etc.) only last a few decades at most, but they quickly become obsolete as new information technologies emerge. Magnetic tapes and microfilms for instance, which were historically used as substitutes for books, have a lifespan of 10 to 20 years and are no longer widely used today because of the digital revolution.

Of the many information storage techniques we know of, relatively few are actually capable of lasting long enough. But the good news is that these techniques do exist, and some may even be just as suitable in terms of durability, storage capacity, and ease of use. Among the most relevant technologies for a knowledge ark are the following:

*The writing tablet: this is literally the oldest form of writing medium known to us, and paradoxically, it is also one of the most durable. Wooden tablets dating back 5,000 years (Egypt, etc.), clay tablets dating back 6,000 to 7,500 years (Mesopotamia, Europe, etc.), and stone tablets with a similar lifespan have been found. The choice of materials is decisive in terms of lifespan. Organic materials (bone, wood, ivory, wax, etc.) have the disadvantage of being « biodegradable « , even though they can last for thousands of years, whereas metals (silver, gold, etc.) and minerals (slate, basalt, clay, etc.) can withstand exposure to light, living organisms, and even fire to a certain extent. Among these, gold and stainless steel are the metals most resistant to the ravages of time, as they are the least prone to corrosion, while among minerals, basalt, ceramics, and marble are among the rocks most resistant to erosion. The real disadvantage of tablets (and by extension, steles, bas-reliefs, etc.) is their very limited storage capacity and the difficulty of transcribing anything other than text. However, it is undoubtedly the most universally accessible medium, as it does not require a reading device. And if one writes with very small characters, a writing tablet can hold much more information than a book and can even rival certain types of hard drives.

*Molecular storage (including DNA storage): this is a very recent medium, which has not yet been used on a large scale due to limitations in read and write speeds, but which has already been used for knowledge “ark” prototypes. We have discussed this before, but the major advantage of DNA (or molecular storage in general) is its immeasurable storage capacity: DNA strands that are nanometers wide but several meters long could theoretically contain more information than all the libraries on the planet, or even all the data centers and computer servers on the planet. This type of storage is therefore essential for this reason, and also has the advantage of very good longevity, since DNA, under the right preservation conditions, can last for thousands of years. It is estimated that strands of DNA stored in stainless steel capsules could last 50,000 years (on Earth). Traces of DNA from animal species that have been extinct for millions of years can be found in nature, and logically, attempts are being made to reconstruct their genomes. DNA storage could be a much more advanced form of digital storage than traditional media for these reasons, while retaining the advantages of digital technology (variety of information formats stored—video, text, images, etc.—and accuracy). Furthermore, although it is not exactly a universal medium, since a computer language is still needed to encode the information in the DNA, as well as tools capable of reading the DNA (microscopes), the risk of obsolescence remains lower than for conventional electronic media.

*5D optical data storage: this involves the use of crystals with certain light polarization properties, which, depending on the angle at which the content is read, allow several levels of information to be “superimposed” on the same volume. This is also a recent technology, which has been used mainly for long-term storage. The storage capacity of disks using this technology is high (360 terabytes), although lower than that of molecular storage. However, it may be a good compromise between the latter and writing tablets, and, as with DNA, it is a more universal medium than conventional electronic media, since any microscope equipped with a polarizer can theoretically read the contents of the disc. But above all, there is another huge advantage: it is currently the medium with the longest lifespan ever designed. It is estimated that a 5D optical disc could theoretically remain readable for at least billions of years. Thus, to create an archive of knowledge that would remain intact for hundreds of thousands of years or more—and not just for the millennia following the end of our civilization—5D optical storage appears to be the most suitable medium at the time of this writing.

There are many knowledge arch strategies, and not all of them are designed for long periods of time

In summary, we have so far considered three main constraints for the creation of a knowledge ark: comprehensiveness, accessibility, and longevity. Each of these constraints involves all sorts of problems, for which there are all sorts of strategies and technical solutions. This means that the concept of a knowledge ark—and thus also the concept of epistemic memory—are not easy to define, but rather encompass a wide variety of very different projects. Knowledge arks can thus be classified into different categories based on the motivations they primarily seek to address: an ark can be comprehensive or selective, even specialized; hierarchical or non-hierarchical; centralized or decentralized; object-oriented or information-oriented; analog or digital; physical or digital; designed for very long-term preservation or not. Those categories can be summarized the following way:

*Anarchic memory: knowledge is preserved in the form of collections of items scattered across the globe. The primary objective is the preservation of artifacts and literature. This is a decentralized, object-oriented mass memory: it is the main way knowledge is currently preserved within heritage institutions and various private archives scattered across the globe.

*Digital memory: knowledge is preserved in digital storage arrays, which today is done through computer servers and data centers using electronic media. The primary objective is the preservation of information. This is a mass memory system, still decentralized but information-oriented.

*Heritage memory: knowledge is preserved with minimal use of storage and is transmitted from person to person through education, the media, and simple oral transmission. The primary objective is the continuous development of humanity despite crises. This is a selective, decentralized, and information-oriented memory.

*Thematic memory: knowledge is preserved in a kind of library, each one packed with information, as they are able to centralize a large portion of our knowledge within as limited a storage space as possible. The main objective is the preservation of a specific type of heritage (from an academic discipline, a particular country, a major institution, an encyclopedia, etc.). This is a selective, centralized, and information-oriented memory. This form of memory is ideal for serving as a “backup” for anarchic memory.

*Universal memory: knowledge is again preserved in libraries packed with information, but this time, EACH of these libraries must be exhaustive or nearly exhaustive. The main objective here is the centralization of the entire cultural heritage. This time, it is a mass, centralized memory, still information-oriented. This form of memory does not yet exist because current technology and legal frameworks do not permit it, but this could change.

*Encapsulated memory: knowledge is preserved in the form of a few objects and messages inside time capsules. The main objective is the duration of preservation of the “encapsulated” item. This is a form of selective, centralized, and object-oriented memory.

*Hybrid memory: the various forms of knowledge arcs mentioned above complement one another (for example, thematic memory can serve as a “backup” for anarchic memory, heritage memory can facilitate navigation within digital memory…) and some may even merge (anarchic memory may be gradually transforming into digital memory, and when technology allows it, a time capsule could very well serve as a suitable container for thematic memory or even universal memory).

Each type of knowledge repository has its merits, and none is truly more relevant than another. It’s especially important to keep in mind that certain design constraints are difficult to reconcile. Accessibility and longevity, in particular, can be conflicting constraints, since to ensure that an ark survives as long as possible, the best solution is often to place it as far away as possible from any human beings; while this certainly helps avoid many risks of external threats, it limits the value of a knowledge ark, which is ultimately intended for future generations. To put it another way, all the forms of knowledge arks we have discussed and will discuss are complementary, and all these forms deserve to be realized, without this entailing truly astronomical costs.

But since we are discussing the typology of knowledge arcs, let us now turn our attention to a specific case that will be of particular interest to us going forward: namely, knowledge arcs designed exclusively for a long and specific duration (encapsulated memory). In fact, this is the only category of arks we haven’t discussed so far, even though it is the one for which the requirement of durability is most critical. This is also an opportunity to revisit the concept of a time capsule: a time capsule consists of creating a “box” into which any object or information medium chosen by the creator of the box can be inserted. This box is then stored or even buried in a relatively isolated location and is only intended to be opened after a very long period of time, or even not to be opened at all. The time capsule is therefore designed either for maximum longevity or for programmed longevity. In any case, the idea of time capsules is based entirely on a desire for preservation for preservation’s sake, and by extension, on a desire that nothing and no one should open the contents of the capsule, at least for a certain period of time. The main virtue of time capsules is therefore that they largely escape the accessibility paradox, since in theory, for a well-designed time capsule project, no one can access the contents of a capsule before a certain date, and in some cases, the contents and/or location of the capsule may even be kept secret. A knowledge ark is ultimately a specific type of time capsule, designed to serve as a repository of knowledge and even of humanity’s entire cultural heritage; but in essence, nothing fundamentally distinguishes arks from other forms of time capsules, beyond the amount of information they preserve. But so far, we have assumed that a knowledge ark must absolutely be comprehensive, accessible, and durable all at once, whereas if we look at other forms of time capsules, not all of them are designed with these three objectives in mind, and more often than not, it is longevity that takes precedence, with the capsule’s contents serving merely as a symbolical pretext to leave behind something capable of defying the immensity and apparent eternity of the cosmos.

Let us now turn our attention to the specific case of knowledge archives that set aside the constraints of comprehensiveness and—above all—accessibility in favor of extreme longevity. It is worth noting in passing that with the storage technologies we mentioned earlier, the constraint of exhaustiveness is much easier to reconcile with longevity than is the constraint of accessibility: media that are both durable and have high storage capacity do exist. If this form of “ark” is of particular interest to us, it is notably because it allows us to bypass many obstacles (particularly those of active preservation and transmission) and because such a project can have a much stronger symbolic significance. The goal of preserving our knowledge intact for our distant descendants becomes secondary to that of creating a sort of ultimate library of human knowledge, one capable of surviving even the extinction of humanity. By chance, these arks might even be discovered by “someone” who has no idea of the existence of our civilization, and would then hold in their hands a veritable black box of the knowledge of an entire vanished world.

Knowledge arcs are the ultimate form of the most ambitious time capsules

Time capsules are not a recent invention, since, technically speaking, most of the archaeological traces left by our ancestors can be considered unintentional time capsules. Every archaeological discovery, in fact, contains its share of objects, human traces, and sometimes even texts and other artistic representations. The Lascaux caves, the ruins of Çatalhöyük, and the Rosetta Stone are all examples of time capsules. But what interests us most are intentional time capsules—those that specific individuals decided to leave for future generations, or even for no one in particular. The oldest known example is that of the tablets recounting the Epic of Gilgamesh, carved in Iraq during the Mesopotamian era (around 3000 BCE), since these tablets mention the existence of a metal box buried underground near the city of Uruk, containing a copy of the said epic, but carved from lapis lazuli. Letters and books have also been found buried by various individuals, whose names are sometimes unknown to us, but who nevertheless managed to leave a trace of their passage, a part of themselves, long after their death.

Over time, these individual initiatives became increasingly ambitious and even began to involve far more people: this was the case with the Crypt of Civilizations at Oglethorpe University in Atlanta (in 1936), the time capsules from the 1939 and 1965 World’s Fairs in New York (Westinghouse Time Capsule I and II), the one from Expo ’70 in Osaka, and the Millennium Vault in England, created for the turn of the millennium. While most time capsules are generally simple sealed boxes or chambers containing various objects and documents, some can be of a much more unusual nature. For example, the Zeitpyramid in Germany consists of a pyramid made of 120 concrete blocks, with one block to be added every 10 years, meaning the pyramid will not be completed until the year 3183, as the project began in 1993. There is also a film titled “100 Years” intended to be viewed only in the year 2115. We can also mention the Long Now Foundation’s 10,000-Year Clock project, which has not yet been realized, or the numerous initiatives to warn our distant descendants of the presence of nuclear waste disposal sites. But above all, many ambitious time capsules are also “spacetime” capsules—that is, projects carried aboard spacecraft launched by humankind. Ever since the Apollo missions to the Moon, humans have left behind small works of art and messages of goodwill. After that, the Pioneer and Voyager probes became famous, among other things, for carrying on board, respectively, a plaque and a vinyl record, each containing basic information about Earth and humanity. Human DNA can also be found aboard the International Space Station (Immortality Drive), depictions of continental drift aboard the LAGEOS-1 probe, a DVD aboard the Phoenix Mars lander, and there are now even proto-space libraries on the Moon and around the Sun, thanks to an initiative by the Arch Mission Foundation.

Indeed, as the concept of the time capsule gains popularity, technology advances, and the impending end of civilization seems increasingly likely to many, numerous organizations have emerged around the world, whose goal is no longer merely to encapsulate a few scattered objects or overly selective information, but to go much further and ensure that as much of our heritage and knowledge as possible survives for as long as possible. In other words, the first knowledge ark initiatives began to emerge fairly recently, at the start of the 21st century. The Arch Mission Foundation’s lunar and solar libraries date back only to 2018 and 2017, respectively, while this organization is also behind a “Global Knowledge Vault” in Switzerland, which was established as recently as 2024. These projects are no longer mere messages but small libraries containing the contents of Wikipedia, linguistic archives, DNA samples, and copies of books engraved on discs designed for long-term preservation. This closely aligns with the spirit of the knowledge arks and epistemic memory we have been discussing from the start. But the Arch Mission Foundation isn’t the only organization seeking to preserve our civilization’s knowledge; we can also mention the “Memory of Mankind” project (a collection of ceramic tablets with eclectic content, stored in the Hallstatt salt mines in Austria), the “Arctic World Archive” project (a collection of digitized works and guides in five languages housed in a room dedicated to the Svalbard Islands—not to be confused with the Global Seed Vault on those same islands), or the “Human Document Project” (an initiative by the University of Twente in the Netherlands to preserve documents for up to one million years). At the same time, the digitization of documents and the preservation of internet content—which is not always archived properly—are becoming major concerns for many people, as illustrated by initiatives such as the Internet Archive, Wolfram Alpha, the Universal Digital Library, and Project Gutenberg, to name just a few. With the proliferation of time capsules, the growing number of players in this field, and the increasing ambitions of these players, the world has never been closer to creating repositories of knowledge worthy of the name. And it is the time capsules that are leading the way.

There is a wide variety of time capsules

There are at least two main categories of deliberate time capsules (which include arks of knowledge). On the one hand, there are capsules with a scheduled retrieval date, i.e., capsules designed to remain sealed for a fixed period of time, usually intended to be opened on a date chosen by the capsule’s designer. These capsules are generally designed to be made accessible to future generations after a long period of hibernation, in decades, centuries, or even millennia for the most ambitious ones. In any case, they are primarily intended for other human beings. On the other hand, there are capsules with unscheduled recovery, which are intended to be opened at an indeterminate time. Although this isn’t always the case, these capsules often have an exceptionally long lifespan, and given that longevity, they aren’t necessarily designed for humans, but sometimes even for potential extraterrestrials or for post-human civilizations on Earth. Sometimes, these capsules serve only a symbolic purpose and aren’t even intended for any specific recipients. To put it simply, programmable time capsules are designed primarily for practical reasons (to convey knowledge), whereas non-programmable time capsules tend to be designed for artistic reasons (to leave a lasting testament to our civilization).

The first category we will focus on here is that of programmable time capsules—that is, those with a set opening date. We see that their designers usually have a clear desire to communicate with other people, to pass on a legacy from one human being to another. Most of the time, these capsules are designed during important cultural events. such as the turn of the millennium for the Millennium Vault, international exhibitions such as those in New York in 1939 and Osaka in 1970, or anniversaries such as the independence of a country or the founding of a city. Also, the opening dates of the capsules are often scheduled to coincide with an anniversary date, i.e., such that the interval between the burial of the capsule and its scheduled opening is 100 years, 1,000 years, or a multiple of these numbers (for example, the Westinghouse capsule buried during the 1939 World’s Fair is scheduled to be opened in 6939, 5,000 years later). There is no shortage of important anniversaries for the rest of the 21st century: the centenary of the end of World War II in 2045, the centenary of Indian independence in 2047, the centenary of the founding of the People’s Republic of China in 2049, 1000 years of the Kingdom of England in 2066, the 300th anniversary of the French Revolution in 2089, etc. There are also many approaches and subcategories of time capsules with scheduled retrieval:

*Underground capsules: Most traditional time capsules are literally capsules, small hollow but sealed metal objects containing various types of items. These capsules are usually buried in the ground, sometimes under a commemorative plaque or monument, warning passersby not to open the capsule before a certain date. These are the most common types of time capsules, as well as the most criticized, since the amount of information they contain is very limited. A typical example of an underground capsule is the British Columbia Time Capsule, buried in Victoria, Canada, in 1967, scheduled to be opened in 2067.

*Time rooms: a step above traditional capsules, entire rooms inside buildings or underground galleries are sometimes specially designed to store a large quantity of objects as part of a time capsule project. One example is the “Crypt of Civilizations,” a room at Oglethorpe University in Atlanta (United States) that was set up in 1936 and intended for the inhabitants of the year 8113.

*Digital capsules: In the past, time capsules occasionally contained manuscripts, photographs, books, or even microfilms to hold a lot of information in a small space. Nowadays, capsules can contain electronic and digital storage media, capable of storing much more information. There are many spontaneous initiatives to bury or protect hard drives and other digital media in small capsules placed underground.

*Architectural projects: These are not strictly speaking “capsules,” but rather human constructions specially designed to last a very long time, or even to be built over a very long period of time. Examples include the Great Wall of China, certain cathedrals, necropolises, and nuclear waste disposal sites. The Zeitpyramide is another contemporary example of a time capsule of this type, which is scheduled to remain in place until 3183. By extension, this can also include certain types of street furniture (plaques, statues, or commemorative steles, for example).

*Orbital capsules: some capsules are attached to satellites orbiting the Earth, meaning they can fall back to Earth after a certain amount of time. For example, DVDs are to be placed in the KEO satellite (the launch of which has not yet been announced) to fall back to Earth in around 50,000 years and thus be available to any humans living on Earth at that time. Of course, capsules sent to the surface of other celestial bodies or into interstellar space are not considered programmable recovery time capsules.

It should be noted that in all cases, to ensure that time capsules are not opened before their scheduled date, it is crucial to first list all time capsules that exist around the world, along with their scheduled opening dates. Secondly, it is obviously also necessary to find ways to ensure that the existence and location of these capsules are not forgotten by future generations, which can be achieved through all kinds of techniques: commemorative plaques, public education, Rosetta stones scattered around the globe, etc. One of the biggest risks associated with these capsules is that forgetting about them could lead to their accidental destruction (during renovation work, for example).

Today’s time capsules have enormous potential but are still too limited

At present, the contents of most programmed capsules are relatively limited: everyday objects, small devices, sound recordings, messages of goodwill, samples of materials or seeds, a few copies of documents, sometimes converted into film or digital media, etc. However, for a time capsule to be of real interest to future generations, it must not be a simple “sample” of objects from the era in which it was created, even if this sample is representative. In fact, the opening of some time capsules buried in the early 20th or 19th centuries has often led to disappointment, particularly for historians and archivists, as the contents of the capsules are often too sparse to provide information about the era in which they were created. This, for a time capsule to be a relevant project, i.e., an “ark” of knowledge, it should ideally contain as much information as possible, including encyclopedias, languages, scientific works, images, representations, videos, music, sound recordings, artistic or historical works, and many other elements of heritage. Consequently, a “2.0” time capsule project is much more useful to future historians if it contains information that is not only representative of our civilization (our knowledge in the strict sense, our traditions, our art, our lifestyles and ways of thinking, etc.), but also very comprehensive. As mentioned above, there are now media that can store large amounts of data, and with digitization, it is possible to save immovable or fragile heritage items that cannot be “encapsulated” in other ways. Projects such as “Memory Of Mankind” in Austria and the “Global Knowledge Vault” in Switzerland are moving in the right direction by proposing to archive the contents of several encyclopedias on ceramic tablets or on the famous 5D optical discs that we constantly refer to.

A further step would be achieved by also preserving the contents of entire libraries and national or private archives, as well as to massively digitize the contents of museums and important cultural sites, so that future generations will have much more usable knowledge at their disposal. This would enable time capsules to truly fulfill their role as “arks” of knowledge, thereby effectively countering the risk of mass social amnesia in the event of the collapse and/or totalitarian takeover of civilization. Moreover, it should be remembered that an epistemic memory can also be seen as a “black box” that can warn our descendants of the dangers facing our civilization (conflicts, economic management, global warming, ethnocides, etc.) or even, in extreme cases, warn our descendants of a potential future catastrophe. Examples include the markers planned for nuclear waste disposal sites (Waste Isolation Pilot Plant in New Mexico, Bure site in France, etc.) or in areas of high radioactive contamination around Chernobyl and Fukushima. The creation of time capsules with a scheduled retrieval date is therefore part of a long-term approach, i.e., an ethical approach that focuses on the perspectives of future generations.

Time capsules may not have a specific recipient

The other major category of time capsules includes all those that were not originally designed for retrieval at a specific date. Here again, as with capsules designed for retrieval, there are a wide variety of approaches:

*Terrestrial capsules: many voluntary time capsules do not necessarily have an opening date and are designed to last a long time without being intended for a specific era. One example is the Arctic World Archive on the island of Svalbard, which contains thousands of digital archives (offline) converted into films, as well as guides in five languages. Earth capsules can be traditional capsules, digital capsules, or architectural projects, similar to the scheduled recovery capsules seen above. By extension, this subcategory can also include “bottles in the sea,” bottles emptied of their liquid contents and filled with handwritten letters, which are then literally thrown into the sea in the hope that someone will recover them “one day.” Earth-based capsules have the disadvantage of being vulnerable to wear and tear (particularly erosion and corrosion) as well as to destruction, whether intentional or accidental. On the other hand, they are the most accessible of all subcategories of unprogrammed capsules, since they are located on Earth.

*Immaterial capsules: this category of capsules mainly includes radio messages and, by extension, any form of electromagnetic signal sent in a particular direction in space. Since humanity invented radio signals powerful enough to penetrate the atmosphere, the content of radio broadcasts, television programs, and even the Internet has been dispersing into space, in a radio bubble that extends at the speed of light around the Earth. It should be noted that these unintentional radio signals become weaker as the distance traveled increases. However, there are also radio signals sent intentionally into space, toward specific solar systems, in the hope that a response will one day be sent by a possible extraterrestrial civilization toward Earth. One example is the Arecibo message, a short binary-coded radio message sent to the Messier 13 nebula (25,000 light-years from our solar system) in 1974. While most experts agree that there is a very low probability that an extraterrestrial civilization will ever actually receive a message sent by humanity, we can nevertheless consider that these “messages” have a much more symbolic purpose and are created on behalf of our own civilization rather than for potential extraterrestrials.

*Space-time capsules: this type of capsule consists of non-recoverable objects or information carriers that are scattered throughout space, where preservation conditions are much more favorable (provided there is no collision with a celestial body, the probability of which remains negligible given the immensity of the vacuum of space), since many terrestrial hazards (humidity, wind, conflicts, censorship, etc.) are absent there. For this reason, space capsules are designed to have a considerably longer lifespan, in the order of millions or billions of years. Furthermore, when recipients are designated for these capsules, they are not necessarily our distant descendants, but potentially also other intelligent species, possibly even extraterrestrial. There are several possible strategies for this subcategory of time capsules: deposit the capsule on or below the surface of a body in the solar system (think of the “lunar museum” deposited on the Moon by the Apollo 12 astronauts), send the capsule into distant orbit around the Sun (think of the Arc Mission Foundation’s solar library aboard a car sent into space), or send a probe into deep space (think of the Pioneer 10 and 11 probes and the Voyager probes, which carry a plaque and a gold vinyl disc, respectively). In the very distant future, some even envision the possibility of creating interstellar probes capable of leaving the galaxy or even capable of self-replication, but for now, this remains the realm of science fiction.

In all cases, it should be noted that many examples of time capsules with unscheduled recovery are potentially not even recoverable in the first place, or are not even designed to be recovered. For example, the Voyager Golden Record, the gold disc aboard the Voyager 1 and 2 probes, is in a way less designed to be recovered by extraterrestrials than to serve as the “ultimate” message in a bottle for humanity. This is where we must remember that time capsules should not be viewed “only” as repositories of knowledge (which is already ambitious in itself), but also as means for humanity to challenge its mortality and the ephemeral nature of the world around us. This act of defiance involves creating an object, ideally a new Library of Alexandria, focusing on longevity and nothing but longevity during its design. Unscheduled recovery capsules, particularly space capsules, are less about preserving our heritage than about the more symbolic goal of leaving something in the universe that transcends us, yet which we can proudly claim as our own creation. Our science and our heritage are our response, as creatures, to creation.

We can go very far in designing the ultimate epistemic memory

The design of time capsules has become increasingly sophisticated over time. While the first-time capsules in history contained relatively little information, technological innovations and the enthusiasm of a growing number of initiators have given rise to increasingly ambitious initiatives. We’ve gone from simple boxes containing a few messages and items to massive storage arrays capable of holding the entire contents of the web, models of entire cities, traditions from around the world, or the genetic code of thousands of living species, and much more besides, etc. With the mastery of new materials, we can hope to store information for very long periods of time, whether using gold, stainless steel, DNA, concrete, nanomaterials, or even certain crystals, such as those used for 5D optical memory, which could survive for up to several thousand billion billion years, which is quite close to the estimated time scale for the end of the stellar era of the Universe. Contemporary industrial society is now capable of digging increasingly long and deep underground networks in increasingly inaccessible places, where a time capsule is much more likely to remain sealed for a very long time.

But it is mainly thanks to space exploration and astronomy that there has been a turning point in reaches of time capsules in recent decades: we can now send radio signals in all directions, we can scatter probes throughout the solar system from Luna 1, and even throughout the galaxy from Pioneer 10. As we have seen, space offers many advantages for the longevity of capsules, if only because of the virtual absence of natural or anthropogenic hazards, but also because our planet Earth is doomed to disappear when the Sun dies, while certain distant bodies in the solar system (gas giants and their natural satellites, comets, and planetoids) will survive well beyond this event. In interstellar space, where the density of celestial objects is even lower than in the solar system, the longevity of a time capsule could be even greater. It is estimated that the Pioneer and Voyager probes are not likely to collide with another star or star remnant for approximately 100 billion billion years. Of course, the more time capsules are sent into space, the greater the probability that one of them will remain intact for longer.

After the era of small sealed boxes buried in the ground, the new “2.0” time capsules are now veritable encyclopedias scattered across the Earth and throughout the cosmos, with the possibility of further developments in the years to come to centralize even more of our knowledge in even more limited space. With nanotechnology, perhaps the maximum lifespan of an information medium could be extended even further, without sacrificing storage capacity. With advances in astronautics, we may be able to create probes capable of navigating intergalactic, rather than interstellar, space, or even equip each probe with a shield strong enough to protect a time capsule from any collision with a relatively small celestial body (comet, asteroid, etc.), even at high speed. With advances in robotics and 3D printing, we may even be able to consider creating probes equipped with relatively autonomous intelligence, possibly capable of self-maintenance or even self-replication, further increasing the lifespan of the knowledge stored inside those probes. Political and legal changes are also conceivable in the near future, facilitating the preservation of artistic works and scientific and other publications by overriding copyright, which is one of the main obstacles to the creation of a modern Library of Alexandria. Come to think of it, it doesn’t really make sense to try to protect the copyright of works contained in a time capsule, where they cannot be viewed or distributed, and where they will be preserved for eternity. One could even consider storing confidential information in time capsules, as these are in any case inaccessible to the entire human race at present.

Finally, one last possible development concerns the organization of the information contained in the time capsule, i.e., the creation of new methods for prioritizing, classifying, or linking all the information together. The “3.0” time capsule would then be not only a knowledge bank, but also a highly structured database, an information network capable of at least partially mimicking the organization of the real world. One could consider integrating a computer program into such a capsule that is capable of performing many kinds of computer simulations of complex phenomenon (celestial movements, climate, human mobility, electromechanical circuits, etc.). In short, the most complete possible version of an “ark of knowledge” would be a comprehensive model of the observable universe, including humanity.