As David Gerrold puts it, when it comes to interstellar empires Control depends upon communication.
If you are keeping your novel constrained to realistic physics, it is not fair to exceed the speed of light. No FTL starships and no Ansibles. Which will more or less limit your empire to the bounds of the Solar System because of timelag. Travel and communication with with other stars will take years to decades to hundreds of thousands of years to arrive. Communication within the orbit of Neptune will be at a maximum travel time of about 8 hours (though that can increase to up to two years if you decide to include the Oort cloud).
No way around it: a galactic empire is going to need FTL starships and/or FTL communication.
As a vague general rule, figure that the maximum time allowed to send a message from the central capital to a colony on the rim of the empire should be no more than about 15 weeks. This is about the lag-time of the old Mongol Empire. So the radius of the empire and the speed of the courier starships or superluminal radio should be adjusted so the results is 15 weeks or less.
The three main ways communication methods used in various science fiction universes are:
- Communication by faster-than-light radio
- Communication by faster-than-light courier starships
- Faster-than-light radar detection of hostile star fleets
If the science fiction author is postulating the existence of either FTL travel and/or FTL communications things get more complicated. Does FTL travel exist yes/no? Does FTL communication exist yes/no? And if both FTL travel and FTL communication exists, which if either is faster? And faster by how many orders of magnitude?
The answer to these questions will have major implications to your science fiction universe in general and your galactic empire in specific.
If you have both and both have the same speed, which one you will use will depend upon whether you want to move matter or move information.
As I mentioned before, the maximum speed of starships and the maximum speed of communications limits the maximum size of the empire. If the travel time of the intel and the travel time of the armed response is too high a total, the Empire will not be able to prevent a rebellious planet on the rim from leaving the empire. This is assuming that the travel time increases with the distance, all bets are off if you have something weird like instantaneous communication.
Bandwidth is important as well. The Capital will have the data to make a reasoned policy if you can transmit to them several terabytes of situational reports, not so much if all you can send is a 140 character tweet.
If ansibles are much faster that starships, the situation will be much like modern-day Navy vessels talking to home port by radio. You will be not be required to send the ship's engines along with the message. Note that "much faster" does not necessarily mean "instantaneous." In classic Star Trek, when the Starship Enterprise was in deep space, a Subspace Radio message might take a couple of weeks to travel to Starfleet Command. But the Enterprise would take months to make the same trip. Subspace radio was only "real time" if you were closer than a few tens of light-years or so.
If there are ansibles but no FTL starships, you will have a lively interstellar Internet, but the massive overhead of slower-than-light starships will restrict interstellar travel to only such people and material objects that absolutely positively must be transported.
And it is possible to have ansibles that provide instantaneous communication, regardless of distance.
Naturally below the level of imperial government, ansibles are vital for the civilian/commercial news media. Without ansibles the news is only as recent as the latest starship arrival.
Having a private encoded ansible means commercial organizations can sell information. For science-fiction authors I will mention in passing the association between shipping news and the Lloyd's coffee house.
In Charles Stross' IRON SUNRISE, the most valuable things are packages of entangled quantum dots (called a "causal channel"), used for FTL communication via Bell's Inequality (yes, I know that is impossible, it's science-fiction OK?). Each dot can instantaneously transmit one bit of information, and then is worthless.
They also have the fascinating twist that the dots must be transported slower than light or they are ruined. They are shipped by Starwisp, taking years to transport between stars.
In the Renegade Legion universe, the Terran Overlord Government (TOG) alone has the technology for "Very Large Communication Relays" (VLCA). These are titanic FTL communication installations (meaning they will not fit inside a standard starship, you need one that is outrageously huge) that have a range of pretty much anywhere inside the entire Milky Way galaxy.
Their rivals the Renegades have to make do with pathetic P-Comm FTL communication. P-Comms are lucky if it can reach a neighboring star system. VLCAs have a range that is about 100,000 times greater.
Such is the overwhelming advantage of TOG having VLCAs, that for the Renegades such installations are pretty much automatically the primary military target in a given star system. If the Renegades can destroy the VLCA, the TOG loses its unfair communication advantage and the military odds become more equal. As long as the VLCA exists the TOG has it all their own way.
Also note that since the VLCAs are such a powerful strategic asset, they are more or less a government monopoly not a private corporation.
In the BattleTech universe, ansibles are a monopoly of a private corporation called ComStar. The corporation arose out of the ashes of the Star League Department of Communications, when the Star League died in the Successor wars. ComStar is transnational, beholden to none of the Successor States. They jealously guard their monopoly and the independence of their FTL relay stations. States that threaten ComStar could have their ansible links cut off, no longer able to engage in FTL communication or trade. ComStar also has their own military. Don't piss off ComStar.
So it appears that the Renagade Legion Terran Overlord Government has an ansible monopoly because TOG is close to being a galactic empire, while the BattleTech ComStar independent corporation has an ansible monopoly because there is no galactic empire.
But whether government or private monopoly, anybody stupid enough to deliberately attack an ansible relay station had better be prepared for the prompt arrival of a monopoly battle fleet who will hunt you down like an animal. The monopoly takes such attacks very personally, since you are more or less threatening their very existence. Especially so if the relay is in a remote area, since in such places there is little or no redundancy.
And if the ansible relay station belongs to a government, the battle fleet responding will be worse by an order of magnitude. Remember that for a government, control depends upon communication. So the attackers are not threating the quarterly profits of an ansible corporation, they are threatening the existence of an interstellar empire. As far as the empire is concerned, the attack is either an act of high treason or an act of war. The only difference is if the attackers are citizens of the empire or not.
If there are starships but no ansibles, or if the starships are much faster than ansibles, you will see the creation of ultra-fast manned message-courier FTL starships or unmanned FTL message drones. Much like the Express Boat Network in the Traveller role playing game or the unmanned Courier Drones from Starfire.
No ansibles means the current news is only as fresh as the most recent arrival of a news-bearing starship. Couriers are intended to make the arrivals as fast as possible. They pop into the solar system wherever is quickest, and send the message by radio for the last few astronomical units.
Remember that historically the postal service and telegraph coexisted. The telegraph was much faster but the mail was much cheaper (with telegraph the cost was per word of message). Physical mail didn't start to die until telegraph messages basically became free, when the telegraph morphed into Internet email.
For some ideas about how a planetary and interstellar postal service can help a fallen civilization bootstrap its way out of a dark ages, read David Brin's novel The Postman.
As with most other science fiction predictions, many ideas about future mail were full of zeerust. Many of them focused on the writing of a letter using a pen or pencil, not realizing that future email would be more like a telegram written with a typewriter.
Understand, there are actually three types of security involved in message sending:
- LETTERS CLOSED (litterae clausae): so that the message sender could ensure that a letter could only be read by the intended recipient.
- LETTERS PATENT: so that the message recipient had some proof that the letter actually came from the sender name written on the letter. This can also be used to securely sign a legal document or contract, remotely.
- IMMUTABLE MESSAGE : so that once the sender composes and transmits the message, the message cannot be subsequently edited or rewritten.
All three types of messages are created by using Seals.
The current state-of-the-art for seals is by using public-key encryption. The writer can encrypt a message with their private key, which gives Letters Patent. They can then encrypt the encrypted message with the recipient's public key, which gives Letters Closed as a digital or electronic signature. And if a man-in-the-middle alters the doubly encrypted message, it will decrypt into random garbage, which give proof of a failure of Immutability (though a data hash can also be used). To help combat evil people repudiating their own signatures, a Trusted third party is useful.
Back in medieval levels of technology, an ornately carved seal was used with sealing wax for Letters Closed and Letters Patent. The "Seal" or "Matrix" is the metal stamp used to impress the image on the hot sealing wax. The "Wax Seal" is the blob of wax imbossed with the image from the matrix.
A matrix for an entire nation is called a Great Seal, used to sign official treaties between nations and other national documents. The Keeper of the Seals are the individual(s) entitled to keep and authorize use of the Great Seal of a given country. A Privy Seal is the personal matrix for an individual who just so happens to be a reigning monarch of a nation. Privy seals are used to sign personal documents.Sometimes the matrix was incorporated into a finger ring, these were called signet rings.
If the letter arrived with the applied wax seal intact, this was a crude form of Immutability. Sadly once the wax seal is broken it can no longer be used as proof of either Letters Closed or Immutability. Letters Patent used pendant wax seals, which are designed not to be broken in normal usage.
The Byzantine Emperors decided that sealing wax was too plebeian for them, instead ostentatiously using gold, or at the least gold-plated lead.
Such seals date back to the bronze age. The skill to carve (or copy) such seals was only possible for a handfull of people, who were mostly employed by nobles or royalty. Thus counterfeit or forged seals was almost unheard of. The operating word being "almost", this is perilously close to the security through obscurity fallacy.
A physical wax-like seal seems so quaint and medieval nowadays. Except there are a few places they are still being used to this day. This is not technically an item of mail, but it is a seal.
Tamper-Evident Seals are a way to detect unauthorized access. Most of you young scamps reading this had no idea that most over-the-counter medications have tamper-evident plastic bands over the screw cap lids due to the 1982 Chicago Tylenol murders. Before then, you could go to a drug store, open a bottle of a medication from the shelf, drop in something awful, and put it back on the shelf. 1982 also brought the advent of foil innerseals on bottles and jars with metal lids containing pop up safety buttons.
Going a bit further, there exists Security Tape. Close a box of groceries with security tape, and you will know if somebody secretly opened the box and stole something from it. The tape suddenly says VOID! and there is no way to fix it. This is also found on outside fuel dispenser, to reveal if somebody unauthorized has opened the dispenser and put a credit card skimmer inside or something.
But the most dramatic use of middle-ages sealing technology is by the International Atomic Energy Agency (IAEA).
If a nuclear nation signs a treaty limiting the manufacture and use of nuclear weapons, the IAEA will monitor compliance. How? By using tamper evident seals of course.
The IAEA will place these seals on vault doors, storage cabinets, reactor lids, and other access routes. If any of the seals are broken, the nation has violated their treaty.
The seal consists of a fabric coated wire, a brass colored disk, and a copper colored cap. The wire is placed such that the door or whatever cannot be opened or operated as long as the wire is intact. If the wire is cut, the seal is considered broken. The two ends of the wire enter two holes in the brass disk. The wire is knotted with three or four square knots. The copper cap is snapped on the brass disk. The knots cannot be undone without removing the copper cap, unfortunately it is pretty much impossible to remove the cap without destroying it. And the interior of each copper cap has a unique hand-drawn signature, which makes the copper cap more or less unduplicatable.
Periodically the seals are replaced with new seals by the IAEA. If they see that a wire has been cut, that is an instant violation. The same goes if the copper cap has been mangled or missing. Otherwise the inspectors cut the wire, attach a new seal, and take the old seals to headquarters for inspection. All the old seals are cut open to have their signatures scanned and compared the signature on file for that seal, to ensure it is not counterfeit. If it is counterfeit, that is a violation.
Remember that Letters Closed (litterae clausae): function is so the message sender could ensure that a letter could only be read by the intended recipient. Or at least alert the recipient that somebody read it first. Example: put your letter inside an sealed envelope.
Using public-key encryption, the contents of the email are public, but since the contents are encrypted in theory only the intended recipient can decrypt and read the message.
Sometimes the old inconvenient ways are more secure. A courier can deliver a physical message, sometimes inside a briefcase handcuffed to the wrist (though a sufficiently determined enemy can circumvent that). The message container can be rigged to destroy the message if tampered with, or to also destroy the tamperer as well with a booby-trap if the message sender is not playing around. In some science fiction stories intelligence agencies and governments keep top secret information stored only in the form of written paper, since there is no such thing as an unhackable computer.
Sometimes the message is gimmicked to self-destruct after reading. Venerable people may remember the TV show Mission: Impossible where the IMF leader would covertly receive an audio tape from a faceless voice giving the mission briefing, ending with "This message will self-destruct in five seconds" followed by the tape turning into ash. This was a running gag in the cartoon Inspector Gadget. In Isaac Asimov's FOUNDATION series, the message enclosed in a Personal Capsule was written on paper that would vaporize ninety seconds after it was exposed to air (occasionally something more durable is desired. In Asimov's THE END ETERNITY they write messages on metal foil instead of paper. Paper wears out too soon, when you have to store it for millennia.).
In medieval times to ensure that a letter could only be read by the intended recipient, an applied wax seal was used. The letter was enclosed in an envelope so nobody could read it, and held shut by the wax seal. The idea was that the wax seal had to be broken (or the envelope cut open) in order to read the letter. This may not totally ensure that only the recipient reads the letter, but at least it does makes obvious the fact that some evil person has read it prior to delivery. In other words they were tamper-evident technology or a security seal. This also prevented the evil person from altering the message, for instance adding a couple of sentences to alter the letter's meaning.
However, evil persons figured out that if you used a thin heated knife at the base of the wax seal you could separate the seal base from the paper, open the letter, read the contents, then use the same heated knife to re-seal the letter. This defeats the very purpose of the wax seal.
This turned into an arms race between secretive people and evil persons. Increasingly elaborate systems of folds, slits, and wax seals were devised to secure the missives. These are called "letterlocking". It had become a lost art but Jana Dambrogio (the Thomas F. Peterson conservator at MIT Libraries) and her research team have been reverse engineering examples from all the way back to the 16th century. She has been studying this for more than a decade and so far has found the secret to hundreds of them. Indeed, she coined the term "letterlocking" in the first place, which was adopted by other researchers beginning in 2009.
Typically the letters are locked by a still-attached slice of the letter paper stabbed through a slit, and closed with a wax seal. This was done in such a manner that the letter could not be opened without ripping the slice. The end of the slice was embedded into the seal, because the seal was placed right over the slit where the slice emerged. So an evil person using the heated knife method would either rip the slice or mutilate the embossed image on the seal. The heated knife could only separate half the seal from the paper until it ran right into the slice. You could separate the other half but since the seal is too large to fit through the slit you can either cut the slice or melt the wax seal until the slice can be released. Either event would reveal the evil person's eavesdropping. The slice was acting like security tape.
Some had multiple layers of security. The "dagger-trap" letterlock was disguised as a common less secure letterlock. But if the evil person used the heated knife method and opened the letter, they would run afoul of an internal booby trap. There was a hidden internal slice with a second seal that would rip or break when the letter was unfolded.
Nowadays letters are sealed in envelopes, but even those can be steamed open and resealed. In the old Soviet Union people would sometimes scribble with a pen along the sealed edge. This made it very difficult to reseal the letter and get the scribbled lines to align.
Remember that Letters Patent function is so that the message recipient had some proof that the letter actually came from the sender name written on the letter. A secure signature in other words. Example: if the "letter" is actually a contract or other legal document, the "sender" signs the contract with their signature. This proves that the message originated with a specific person AND ensures Non-repudiation (i.e., the sender lying and claiming that's not their signature, so they are not bound by the legal document).
Letters Patent is also known as Authentication. These are usually open letters that anyone can read, or at least more than just the recipient. These are less a letter and more like a binding legal contract (where both parties have to sign the document). Or a certification like a pilot's license or something along those lines (where just the accrediting authority signs the document).
In medieval times, to authenticate (sign) a document or contract a pendant wax seal was used. The document is not closed or enclosed: anybody can read it. But a loop of ribbon is attached, with the ends joined with a blob of sealing wax embossed with the matrix. This proves that the sealer has signed the document. These were generally embossed with a special two-sided matrix, which a pattern on both sides of the wax blob (sometimes the two matrix sides were held by two different people, sort of a medieval two-man rule).
The pendant wax seals are permanent signatures on the document, they are not intentionally broken as are applied wax seals. Since the wax seals were made of fragile wax, they were often protected by being put in little pouches of leather or fabric. A broken pendant wax seal can no longer be proof of a signature.
The ribbon is to prevent re-use of the pendant wax seal as a type of forgery (i.e., removing it from a legitimately signed document and fraudulently attaching it to another document in order to forge a signature). Presumably the cut in the ribbon or the cut in the original document would be a dead giveaway.
To prevent abuse, it was traditional for a matrix to be destroyed or defaced after the death of the owner (since dead people have little need to sign documents). Needless to say, being caught in possession of a signet ring or other matrix that didn't belong to you was indisputable physical evidence of a crime. It was even worse if the signet ring was a forgery.
The symbol on the matrix was usually the coat of arms of the owner. This is because [A] heraldic coats of arms are intentionally designed to be easily visually distinguishable, and [B] non-nobles generally couldn't read but can recognize icons (think modern-day corporate logos designed so simple-minded consumers in the grocery store will know which product to buy).
By the Nineteenth century instead of wax it was common to glue on a colored paper wafer and imprint upon it an impression of a seal using an embossing machine or press. These are still used by notaries public.
In the 1900s England, the used of seals declined into a curious practice of signing legal documents by affixing a postage stamp and writing one's signature across it.
In the western world a handwritten signature has taken the place of a seal. Even though signature forgery is an easily acquired skill. And it is even easier to forge a signature using a cell phone camera along with an ink-jet printer and 30 seconds of work with Adobe Photoshop.
In Japan, there are at least four kinds of seals. Only one (jitsuin 実印) is registered with the government to certify ownership and it is only used for legally binding events. Since the jitsuin is far too valuable to just carry around in your pocket, Japanese citizen use the cheaper type of seals for things like bank transactions and taking deliveries. Jitsuin are typically stored in a bank safety deposit box. The seals are usually hand carved, and will cost roughly $100 US to have one made.
Ginkō-in (銀行印) seals are for bank transations. So they are custom-made by professionals or citizens make their own by hand. They are generally only carried if you are planning to visit the bank on that day.
Mitome-in (認印) seals are for low-security signatures, such as postal deliveries, signing utility bill payments, signing internal company memos, etc. These are generic seals, plastic seals with the more common Japanese names can be found at stationary stores for about $10 US. These seals can be stored in desk drawers and other unsecured places.
Gagō-in (雅号印) seals are generally for artists to sign their artwork. Instead of their name, the seal can have the artist's pen name or nickname.
Japan is worried that modern technology is making it progressively easier to forge seals. In Jennifer Lindsky's science fiction novel Flowers of Luna the seals incorporate a near-field chip containing a digital signature to verify the stamp.
Remember that Immutable Message function is so that once the sender composes and transmits the message, the message cannot be subsequently edited or rewritten. For example, after you've mailed a cheque to pay a bill, you would be furious if somebody altered the cheque and added a couple of zeroes to the amount.
As mentioned above, public-key encryption will ensure the message is immutable. If an evil man-in-the-middle alters the encrypted message in any way, it will decrypt into gobbledegook. Unless the evil person has the sender's private encryption key, in which case the sender has bigger problems.
The low-tech alternative is to not transmit the message over the public internet, but instead use secure lines or have it hand-delivered by courier.
There is another "communication-like" consideration. If you have FTL starships, and you want your universe to contain FTL starship battles and also have interstellar empires, you need Strategic FTL Sensors. This means the communication-esque function known as "detection" must be capable of spotting hostile incoming starships early enough for the defenders to muster their defenses. Otherwise FTL starship battles will only occur by mutual agreement. And there will be no interstellar empires because enemy FTL starships will be able to drop a planet-buster on all the empire's planets before the empire knows what is happening. Meanwhile the empire's FTL starships will be returning the favor.
As discussed in the Strategic Sensor link, the two traditional methods are Jump Points "choke points" at some distance from habitable planets and FTL "radar" that can detect enemy ships in time to send your interceptors.
Science fiction writers back in the middle of last century thought that speech-to-text technology would happen any day now. While there are some example of such software nowadays, none of them is quite ready for prime time yet.
For a while with early PDAs there was some experimenting with using a stylus and special written alphabet for text entry. But currently most people use conventional keyboards for their desktop computers, and cramped touch sensitive virtual keyboard on smartphones that are almost but not quite totally impossible to use if you have fat fingers.
Gather around and listen, children. Way back at the dawn of history in days of yore when dinosaurs roamed the earth (about 1996) there was a type of gadget called a "Personal digital assistant" (PDA). These were sort of like a smart phone with no phone in it, no internet connection, and a low-res monochrome screen. Apps typically included an appointment calendar, a to-do list, an address book for contacts, a calculator, and some sort of memo (or "note") program.
After smart phones came out PDAs died off, since there really wasn't anything they could do that a smart phone couldn't do better. Plus smart phones could be used as phones.
Manually entering data into a PDA tended to be clumsy. Most of them had touch screens, but they were so tiny that one would commonly tap on the screen with a stylus instead of one's fingers. Text entry was by:
- An array of buttons forming a tiny computer alphanumeric keyboard
- A separate physical keyboard connected to the PDA by a cable, infrared signal, or Blue Tooth. Most had physical keys, one drew a virtual keyboard on the tabletop using laser beams.
- A virtual alphanumeric keyboard appearing on the touch screen, that you'd tap with the stylus
- A stroke recognition system, with a stroke area on the touch screeen that you'd draw in with the stylus
A button array keyboard tended to have tiny buttons, which wasn't easily used by fat-fingered people. A separate keybord was easy to use, but inconvenient to carry along (even if some did fold up, the laser keyboard wasn't bad but it still was an extra bit to carry). The virtual keyboard with stylus was a bit fiddly to use and it made it difficult to rapidly enter text data.
The stroke system is not fiddly, does not require extra equipment, is easily used by the fat-fingered, and allows quite rapid text input.
The main drawback is that a user has to learn the stroke alphabet.
Back around 1998 I had one of the first Handspring Visors. These used Palm OS, and a stroke system called Graffiti. Personally I managed to learn Graffiti in about two days, and found I could enter text pretty darn quickly. Most of the strokes are fairly close in shape to the character they encode, making them easy to memorize.
When I am struggling with text entry on my current smartphone, I often find that I miss Graffiti.
Stroke recognition is done on an area on the touch screen about the size of a postage stamp. Since each letter had to be drawn one on top of the other, there has to be a way for the PDA to know when one letter ends and another starts. In Graffiti each letter is one single stroke, lifting the stylus off the touchscreen is the signal that the current letter has ended. This means no dotting the "i" or crossing the "t".
Well, they did make an exception. A "prefix" stroke of going from upper left to lower right means you are writing one of the "extended mode" or "two-stroke" characters. What this means is they ran out of easy-to-write-strokes before they ran out of characters. So the extended mode is a way to re-use some of the strokes on some of the more lesser-used characters (such as ©, €, and ¢).
Propagating data via physical books (perhaps printed on bamboo paper), USB flash drives containing eBooks, or other material non-cloud non-broadcasty item is much slower than distribution by the local equivalent of the internet.
But it has advantages:
- It does not require the existence of an FTL internet (in case the science fiction author does not want their empire having that high a tech level, or FTL Wifi is forbidden by the laws of physics)
- It does not require the local infrastructure of the unindustrialized newly colonized planet to be high enough to support an FTL internet. A tech level equivalent to 2000s USA will do for USB flash Drives. Or a tech level of 1400s Europe for printed books.
- It can be (slowly) propagating by unorganized random starships carrying the books, after the galactic empire declines and falls
In the Dark Ages scenario, isolated planets will have their local languages drift and change over the centuries. The language used on the books may become sort of a Lingua franca, much like the Roman Empire language Latin did during the medieval era after Rome fell.
On the one hand, a physical printed book can be used by anybody who has normal vision and the knowledge of how to read the language the book is printed in. Usability is high.
The disadvantage is the relatively large space a book takes up (as compared to an eBook), and the difficulty in reproducing a given example of a book. You have to optically scan the book then use up all the ink cartridges in your printer. Or typeset each page to use in a printing press. Or even write it manually, like a monk in a scriptorium. Let's hear it for manuscript culture!
On the other hand, an eBook reader the size of a tablet can hold a small library's worth of books. Data density is high. If the eBooks are not protected by DRM, making an electronic copy takes a fraction of a second and can be as easy as connecting two eBook readers with a cable and pressing a button. Or connected over the internet.
The disadvantage is that without an eBook reader or without the reader's battery being charged, the eBooks are unreadable. Especially during the Long Night, when potential scholars probably don't know what electricity is.
And then there is the digital preservation problem, or why you cannot read all the eBooks that are on floppy disks in obsolete formats. The US Library of Congress is having a real problem with digital data becoming unaccessible for this very reason, and is finding that migrating the data from obsolete formats to new formats is almost impossible to perform successfully. And this will have to be a constant effort since data formats change so rapidly. Zip discs were hot stuff as recently as 1994, a mere ten years later the format was pretty much dead and Zip drives became hard to find.
Be that as it may, the motivation to further miniaturize book storage only grows. Currently the hot new method is femtosecond laser etched nanostructured glass, for which Andrew Doull coined the name FLENG. Yes, you need special equipment to read it and drivers to decode the format, but the it can cram 360 TB into a single disc and the data's lifespan is about 13.8 billion years at 190°C
Libraries communicate messages that travel through time more than through distance, but it is still communication. Meaning instead of getting a message from a star 400 light-years away, a library can give you a message from 400 years in the past written by William Shakespeare.
A related concept is a knowledge clearing house. In a multi-world interstellar association, many of the planets are producing new science and technology. It would be real nice if all of this new knowledge was made available to to all the other worlds. The logical method is to forward all the knowledge to a central clearing house for it to be accumulated and distributed to all the member worlds. Or at least sold to all the member worlds.
Technological information can sometimes be found in libraries. Which can make libraries prime sources of information. Especially if it is a library on a planet of a galactic empire that has fallen, and people living in the Long Night are desperate to bootstrap themselves back into civilization.
- THE SHADOW OUT OF TIME by H. P. Lovecraft (1936): About a billion years ago on Terra, The Great Race of Yith stole the bodies of cone shaped monsters who were native back then. The Yithians would telepathically swap bodies with beings living on Terra through eons of time. Such captives would be forced to write books about their native geological epoch. These books would be added to the Yithian's great library city (currently buried in Australia's Great Sandy Desert at 22°3′14″S 125°0′39″E for the last 250 million years).
- NOVICE by James Schmitz (1962): Telzey Amberdon has a pocket law library which contains most of the important legal reference works of the civilized galaxy
- FAHRENHEIT 451 by Ray Bradbury (1953): In the future, since all books have been outlawed for dystopian reasons, the underground resistance preserves books by their members memorizing works of classic literature.
- THE FINAL ENCYCLOPEDIA by Gordon Dickson (1984): The eponymous encyclopedia is a huge memory bank orbiting Terra doing its darnedest to store all human knowledge in hope that sheer volume will lead to some kind of qualitative breakthrough.
- STAR TREK TOS: The Starships of Starfleet each are equipped with a "library computer" containing much of human knowledge. In addtion the Federation established the huge electronic library Memory Alpha on a select planetoid.
- FOUNDATION'S EDGE by Isaac Asimov (1982): Professor Janov Pelorat is forced to accompany Golan Trevize in what is a virtual exile from their homeworld. But Pelorat doesn't care. He has his entire research library with him, on a super-dense futuristic CD-ROM.
- SECOND FOUNDATION by Isaac Asimov (1953): The Library of Trantor is the primary library of the galactic empire, even after the empire fell. There also exists the Encyclopedia Galactica, which contains most of the empire's knowledge in encyclopedia digest form.
- A CANTICLE FOR LEIBOWITZ by Walter Miller, Jr. (1959): After the nuclear war, a monastery collects and copies books of science and engineering, much like medieval monasteries copied classical manuscripts. Neither really understood what the books were about.
- THE CEREBRAL LIBRARY by David Keller (1931): In this gruesome little story people are forced to read a book a day. After five years they are killed, and their brains stored in jars to provide instant access to everything they have read.
- HOBBYIST by Eric Frank Russell (1947): Deep space explorers discover a titanic libary on a distant planet, stretching for mile. The librarian is a cosmically powerful alien, who makes copies of the explorers for his library then lets the orginals go.
An interesting example of a cosmic library was in Jerry Pournelle's KING DAVID'S SPACESHIP. There was the First Galactic Empire. It was highly advanced, and it established sub-section libraries at strategic planets. Unfortunately the secession wars caused the empire to fall into pre-starflight barbarism. After about 260 years of the Long Night, the Second galactic empire rises.
The second empire incorporates human planets as they are discovered. If the planet has managed to raise its technology level to the point where is has spaceships, the planet enters the empire as a sovereign state. If the tech level is below that, it becomes a peon planet and galactic empire aristocrats are imported to run the place.
In the novel, the second empire has discovered Prince Samual's World, which unfortunately is below spaceship tech level. So it is peon state for them. The head of the planetary secret police doesn't want that to happen. Using a network of spies he discovers the facts of life. The wild-card is that a short starship trip away is the planet Macassar. It is a very primitive planet, about medieval knights-in-armor level. But it has a sub-section of the First Empire library, hidden away in a castle. If the secret police can somehow get a team of agents to Macassar, they might be able to access the library and figure out how to make a spaceship. Then Prince Samual's World can try to quickly make a spaceship, and enter the Second Empire as a sovereign state.
Spoiler: they manage, but the "spaceship" will make your jaw drop!
The internet is so ubiquitous and vital that today most people cannot imagine life without it. At least those of us who are young enough to be born after the September That Never Ended. So it is assumed that galactic empires will have a galactic version of the net.
Keeping in mind that things connected to the net will be subject to the dread spectre of computer hackers. Just ask anybody who has been a victim of ransomware. Or the director of the Iranian nuclear program. For science fiction authors, here is a list of computer hacking incidents you can use for inspiration for your next novel.