Humanity has done it - the first time-machine was built! However, the machine's capabilities are very limited as it is very costly and fragile, which means we only have one shot. Building another one is out of the question, additionally it cannot transport living beings through time. It was therefore decided to get the most out of it by transporting a book back in time to speed up the development of human civilization. It was decided to pick the european medieval age as target as it was a long-lasting bottleneck for scientific progress. Now the question arises:

What should this book contain?

Some considerations:

  • It can be any existing book or a newly written compendium about some kind of knowledge.
  • It can be the size of a large textbook you would need for university, but it can only contain knowledge of one specific branch.
  • Language barrier shall not be a problem as the book can be translated by specialists. This does not account for scientific and technological terms, however.
  • The book can be delivered directly to an open-minded scholar who will try his best to disseminate the knowledge, but he may do so at his own peril, because:
  • To be of any use, the contained knowledge must be comprehensible and accepted by the people and it's leaders, most notably the church. So anything that would be considered heresy would diminish the chances of success (but it could still work).

Remember, the man doing the convincing is also just from the medieval age.

Some possible topics I've come up with (but feel free to add something else):

  • Chemistry: How to identify and isolate elements to create new materials and substances
  • Agriculture: Modern techniques to help grow more food
  • Mathematics: Probably stuff we learn in school today but I'm really no expert there
  • Theology/Philosophy: Some tractate that would aim to break the church or transform it into something science-friendly (very risky!)
  • Metallurgy: Everything you could know about steel and how to make it

Please explain why you think your pick has the best chance of success. As for the exact destination year I have not fully decided one, but I think the chances are best when cities with artisans and maybe even a university have already been established.

This question is a bit similar but it is about sending a person who would be able to explain stuff, the book would need to self-sufficient:

How could an engineer advance human civilization by time traveling to the past?


closed as primarily opinion-based by We are Monica., Mołot, Renan, Halfthawed, Cyn says make Monica whole Jul 29 at 0:02

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ "a book" is a rather odd unit of measure. That aside, I think this is opinion based. $\endgroup$ – L.Dutch - Reinstate Monica Jul 28 at 18:59
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    $\begingroup$ There's a book written specifically for this purpose, titled How To Invent Everything howtoinventeverything.com $\endgroup$ – Dotan Jul 28 at 19:08
  • $\begingroup$ (1) So you are an expert in chemistry, agriculture, and metallurgy, but you are ignorant of calculus and algebra? How does this work? (2) "Termini" is a Latin word; it means "boundaries". You probably want the English word "terms". (Yes, in Italian the word does have a meaning suitable for the context. But the question does not seem to be written in Italian.) (3) A modern text-book would be by and large incomprehensible before the end of the 18th century. It has the wrong structure, speaks in the wrong tone, uses unknown mathematical notation, and presupposes concepts not yet known. $\endgroup$ – AlexP Jul 28 at 19:14
  • $\begingroup$ @L.Dutch Well it is more about the type of content than an actual page count $\endgroup$ – And Jul 28 at 19:18
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    $\begingroup$ It was decided to pick the european medieval age as target as it was a long-lasting bottleneck for scientific progress This is an oft-repeated statement but does not bare up to examination. The period saw a lot of development in science, not least the development of universities as formal institutes. $\endgroup$ – StephenG Jul 28 at 19:31

There is already a book which would suit your needs quite well, although it might need a revision for this specific purpose.

The Knowledge: How to Rebuild Our World from Scratch by Lewis Dartnell

This book might seem somewhat ill-suited, as it is just a general pop-Sci paperback, but the beauty of this particular solution lies in the details, or more importantly lack thereof.

This book will provide a general avenue of research and not throw a zillion ready made blueprints at an unprepared civilization, so it would accelerate progress in areas where the understanding was lacking but the technological know-how was there, while providing stable foundations for organic development. This would have two important effects:

  • the researchers would be more motivated, as they are not given a solution but rather a hint, so their work would still matter, ensuring that the progress would be much more stable

  • the society is allowed to develop at their own (albeit accelerated) pace, so there would be no pairing of magical or feudal mentality with starships.


General observations

  1. The European Middle Ages span almost a full millennium, from the 5th to the 15th century CE. There is very little commonality between the wretched barbarian chiefdoms of the 7th century and the large-ish well-established states of the 14th.

  2. The Middle Ages in Europe are indeed characterized by rather slow progress in science and technology. But please remember that (a) the slowdown started in the 2nd or 3rd century, hundreds of years before the conventional beginning of the Middle Ages; (b) Europe is not the whole world -- the Arabs and Persians were very busy operating as a bridge between the west and the east, with very happy consequences for the eventual flourishing of science and technology; and finally, (c) slow progress does not mean stagnation -- science and technology continued to progress, only at a slower pace than in the first three or four centuries of the Hellenistic civilization.

  3. If the question is serious that "[the book] can only contain knowledge of one specific branch", then that branch must be mathematics. You cannot teach modern (where modern means "mid-19th century") physics, or chemistry, or metallurgy without a solid mathematical base. So if you want to teach physics at the level of William Thomson, 1st baron Kelvin, or chemistry at the level of Pierre Eugène Marcellin Berthelot, or metallurgy at the level of Carl Wilhelm Siemens and Pierre-Émile Martin, then you have no choice but to teach mathematics at least at the level of Johann Carl Friedrich Gauss; which means that the book would contain knowledge of two branches.

Common misconceptions

First, science and technology are fundamentally based on three pillars:

  • The constant accumulation of knowledge over time, with inherent correction, reformulation and discarding of old knowledge which is no longer valid.

  • The capacity of the world to sustain and use the corresponding level of knowledge. Knowledge which cannot actually be sustained and used becomes stale and is lost in a short time.

  • The permanent search for new knowledge and new formulations for old knowledge.

A book sent back in time to the 11th century may well present the current (or, preferably, not current but still modern-ish) state of knowlegde in mathematics (or in mathematics and one additional field, if this is allowed). But it cannot magically make that knowledge useful, it cannot magically transform the society so that it can sustain that knowledge, and it cannot magic into existence the vast number of scientists and engineers needed to apply, perpetuate and enhance the transmitted knowledge.

Second, what is to be understood by medieval Europe? Does Constantinople count? Do the Italian possessions which the (Eastern) Roman Empire count? Do Spain and Portugal count? The Iberian peninsula was Arabic-speaking and Muslim from the 8th to the 13th century, and its southern provinces remained Arab-speaking and Muslim to the end of the Middle Ages...

In-depth analysis: chemistry

Let's say that the book tries to teach mid-19th century level chemistry. How does one teach mid-19th century chemistry to 11th century people?

  • To introduce fundamental laws, such as, for example, the law of multiple proportions the book must by necessity describe quite a large set of simple chemical experiments. Did I say "simple" experiments? Oh sorry, I meant that the book must describe a vast swath of 18th century technology:

    • How make glass laboratory vessels. (What is a "retort"? You mean one can actually grind glass? What do you mean that my test tubes should all be exactly the same? How do I even go about making clear glass?)

    • How to make accurate balances and accurate weights. (Do you mean to tell me that "thirty-two grains of wheat, taken from the middle of the ear" is not an acceptable level of accuracy? Why, the most learned counsellors of the king say that it is!)

    • How to make accurate measurements. (Units of measurement and how they can be reproduced accurately, including for stuff like temperature and pressure which 11th century people didn't even know about.)

    • How to process those measurements. (Mathematics mathematics.)

    • How to obtain and purify the reactants. (Oxygen? What's that? What do you mean that my sal ammoniac is impure? It is the best sal ammoniac in the whole of Christendom!)

    Teaching chemistry to 11th century people is very difficult. They did not have a concept of a chemical substance; in fact, for them the word "substance" had another meaning entirely, being the Latin equivalent (coined by Cicero, no less!) of Greek ousía, namely that which gives individuality to an object, as distinct both from accidental changes and from the general properties of that class of objects. ("Transsubstantiation" is the only remnant of this meaning still in common use, and even this last remnant is rarely understood correctly.) They did not know that in any chemical reaction the mass of the products of reaction must equal the mass of the reactants. They did not know about, and had no access to, common reactants which we take for granted. They didn't even have words for "gas", "temperature", "acid" or "base".

And what about mathematics? It is the 11th century: a very large part of very early modern mathematics is useless and/or utterly inapplicable. Logarithms? What for, when they did not have printing, and thus simply could not make and distribute tables of logarithms in any significant numbers? Arabic numerals? What for, when they simply did not ever calculate in writing? Calculus? What for, when they did not have Newtonian mechanics? Statistics? To be applied where?

The most severe misconception

The entire premiss of the question is "to speed up the development of human civilization".

  • But why would anybody think that anybody in the 11th century was interested in speeding up the development of the human civilization? The bright, shiny and holy goal of the Middle Ages was stability, not progress. Their ideal was order, not change. (Which is perfectly understandable -- they had change aplenty, and it was seldom, if ever, a good thing.)

  • Even more, why would anybody in the 11th century belive that the humans civilization was developing at all? They all knew that the good times and the great knowledge were in the past, and the human race was falling. They knew it. They saw the ruins before their very eyes, they were all scrambling to get translations of translations of ancient texts, they watched the last remnants of the Roman roads and aqueducts and basilicas fall down.

  • And the most important thing of all, why would anybody even think that an 11th century man of learning would consider physics and chemistry and metallurgy respectable subjects? Men of learning studied grammar, and logic, and geometry, and law, and theology, and music, and rhetoric. Calculations were for clerks. Chemists and metallurgists were tradesmen. One can never overestimate the revolution started by Paracelsus when he invited barber-surgeons, alchemists, and apothecaries to speak at the University of Basel and openly declared that only those who practiced an art actually knew it; a medieval scholar willing to get his hands dirty is a very rare thing to find.

  • $\begingroup$ As for "great knowledge was in the past" and why is " metallurgy [a] respectable subject"? Have a textbook on metallurgy disguised as a roman manuscript on better weapons, and it will be very very well received $\endgroup$ – Bald Bear Jul 29 at 19:39
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    $\begingroup$ @BaldBear: Oh, they had Roman technical books, including one specifically on "better weapons", better military organization and better tactics and strategy -- Vegetius's De re militari. It was quite popular with military men and very influential. We have hundreds of manuscript copies, and it was one of the first books to be printed (1473). Now tell me one medieval scholar who quotes it or stops to think how the principles of organization and planning described in the book could be applied more widely. $\endgroup$ – AlexP Jul 29 at 21:35

I would think that Sir Isaac Newton's Principia Mathematica would be a very good choice. It was written in latin, so should be perfectly comprehensible to scholars in the middle ages, and is considered to be one of the underpinning works of the scientific and industrial revolutions beginning in the mid the 1700s.


I think to change the world you shouldn't be sending back hard science books, but books on philosophy or the soft sciences that focus on human behavior and interaction. If you put the knowledge of gunpowder or metallurgy or chemistry in the hands of a xenophobic empire builder (and the Church certainly was) all you're going to wind up with is an imbalance of technological power leading to an enslaved population and a world in peril, if not actively conquered. Grant the church better weapons or the ability to discover new forms of chemical warfare (which has been used since ancient times and was not unknown to them) and they will put it in the hands of a soldier and send him off to kill "in the name of god."

You would have a changed world, but not much of an improved one.

The things that held back knowledge for so long was serfdom and the death grip of the church, which was only loosened by the Black Plague causing enough mayhemto upend and destroy the power structures. But certain philosophies can do so, as well, especially if you can integrate them into thinkers in the church.

But I don't think you can pick a modern book off the shelf and schlep it back in time and call it good. Everything about it will be wrong, from the way it's made to how the words are spelled and even the definitions--language drift is real, and surprising. For instance, did you know some of the words for color we now use used to refer to different colors or didn't even exist at all? Or that "villain" just meant "poor person?" In the meantime, words that sound like endearing nonsense to us (hey nonny-nonny anyone?) had real meaning back then, and it may not have been the most...genteel one.

And that's just a few common, simple examples. Any book sent would have to be recreated carefully to fit into whatever actual century you were sending it to, including having language experts piece together the proper language of the time so the meaning couldn't be misinterpreted or misunderstood.

Also, I'm surprised you didn't mention medicine in your world-changing books, because good medical practice was sorely needed. You want to change the world, send back a book emphasizing one thing--to not kill your patients, wash your hands with soap before treating them. Oh yeah, and sterilize your gear. For the leech happy era, you might send a primitive treatise on how blood actually works; nothing as complex as we have now, but something they could have observed with their own eyes, like how much blood a man can lose in battle before becoming woozy or weak, and comparing it to blood loss through bloodletting, and setting up viable alternatives.

For philosophy, you'd want to build on the beliefs they already have. For instance, how powerful could it have been had they had the belief that the vows of marriage should be held sacrosanct to both parties, and that if the man broke his, it freed the woman from hers. (Or visa-versa.) That would put a wrinkle on everything from warfare (is wartime rape adultery?) to law. It could reshape the entire culture.

For instance, what are the legal rights of a woman who proved her husband broke his vows? Can she demand restitution through money or lands? Can she go back home to mom and remarry without stigma? What about children, can his name (and therefore his lineage) be taken away from them? Would they then be given the name of the mother's family as traced through her father? What are the social consequences on him for failing in his sacred oath to her? Will he fall in society's eyes with all the consequences that implies (no promotions, people less willing to support his business, and other stigma)? Will he be required to pay money in the form of a fine or some sort of "penance" fee to the Church? Will he be considered as a marriage partner in the future or is he now effectively "off the market?"

That's within the purview of the Church, under their direct control, doesn't threaten their power (in fact, can actually help solidify it and bring in extra wealth), and yet could have had us making great strides for women's equality in society centuries ahead of schedule. And as history marched on, that would snowball to giving us more scientists, mathematicians, business people, and so on, changing the face of history forever.

Heck, even encouraging the Church to classify women as "like children" would have been better than "more like animals than people, possibly without any souls at all."

You could choose less women-centric ideas as well, I'm just personally always a fan of any idea that gets all hands on deck working towards solutions rather than marginalizing a large segment of people and taking away from our resource pool.

Agriculture would have been handy too, though the problem is it'd have to be one heck of an agriculture book. Again, it'd have to be rewritten for the period, since many of the machines and chemicals we now rely on they wouldn't have access to, or even the means to create. It would have to focus on natural methods of agriculture, and frankly, you'd have to drop a lot of those books (or one huge-ass tome), because what would be needed to make crops flourish near the Vatican would bomb in rainy Britain. In the case of anywhere with micro-climates, the advice could fail just by traveling for about an hour to a different location.

But hey, you really want to shake up the population, send back numerous copies of the Bible written in the common language of the time. Have whoever your hero is handing them out, and teaching people to read them. For a long time the only people who could translate the word of God was the Church itself, leading to terrible abuses of power. You want to subvert that, beat them at their own game and with a book they can't possibly reject. Then sit back and enjoy the fireworks.


I think a solid compendium of human history from the big bang to the mastery of time, including detailed explanations of people behind major political movements, scientific discoveries, space travel and their impacts on human society would be the most powerful source of knowledge to advance human society faster

We, humans, have a wonderful capacity to learn from others mistakes. And, admittedly history would change, that is kind of the goal. The Great Book would clearly illustrate what was true and possible, and what was foolish thought, cruel social structure, and feeble thinking. There would be tremendous pressure for social and cultural reform to embrace democratic and free societies with effective balances between individual, state and economic power.

They’d have solid proof of how Socialism and Fascism sound seductive to the uninitiated but in truth bankrupt philosophies the only benefit the few at the top — just like the political structures of the medieval times.

Once humans know a thing is possible, whether its steelmaking, electricity, or living with dignity, freedom, free of disease and famine, then we are effective in creating and then optimizing solutions.


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