The time machine allows sending an object to an exact location(Earth only) and time(Medieval or Renaissance as early as possible).

Suppose that only one book can be sent to the past. Book has hard-cover and at maximum 800 color high-res A4 pages. No electronic devices only paper and ink.

The book should contain instructions how electricity works(laws, milestones) plus blueprints of basic generator, (electric motor ?) and light source(maybe light bulb or equivalent). The book should not reveal any future events, only pure technical description.

The questions are:

  1. Is it possible to write such book so the recipient would understand it and use as solid starting point? If not, why?

  2. Where and when should it be sent(maybe some great well-known historical event)?

  3. Who would make the best usage of this book for the humanity(not only one nation/personal gain)?

  • $\begingroup$ I'm not up to answering all three parts of the question, but I will say that a major component of this book would have to focus on metallurgy. $\endgroup$
    – Wingman4l7
    Dec 23, 2015 at 17:42
  • $\begingroup$ @Wingman4l7 Probably yes, and the recipients may need more than one generation to truly benefit from it. The point is to give solid boost and milestones to show what need to be developed to get final reward. $\endgroup$
    – light
    Dec 23, 2015 at 17:44
  • 1
    $\begingroup$ Just for the fun of it, make three versions of the book (and ideally several copies of each): one in Latin, one in Arabic and one in Chinese. Send them to the same time. $\endgroup$
    – Crissov
    Jan 2, 2016 at 12:01

7 Answers 7


Not only is it possible, but it's easy! You won't need more than a few pages to adequately explain how to generate simple light. I'll explain how, later, but first I'll answer your other questions.

My choice of location would be the late 1400s, to Leonardo da Vinci. He was a brilliant scientist and inventor, and would most likely understand the book and be able to carry out the instructions. More importantly, his exact location in both time and space is well known; you could send the book to his bedroom, if you wanted. And perhaps most importantly of all, not only are the materials required available, but he was at the very start of the scientific revolution. If his plans for a "light machine" were spread over the known world in the early 1500s, life would be very different indeed!


The very first wall you're going to hit is communication. Depending on where you send the book, you may have to write in a language that is radically different from today. English in the middle ages, for instance, is almost unreadable today, and vice versa. The smart choice would be to use Latin; most scientists read it fluently, and thus could pass the book around all over Europe. Remember also that a picture is worth a thousand words - use a diagram over a "word picture."

What the heck is this?

If you're sending the book back in time, you don't have the option to actually explain how this book works. Without that, you'll need to write a foreword, a page or two describing what this book is, what it intends to communicate, and how to read it. Explain things like page numbers, how to match the words "figure A" to the drawing, and so on.

Importantly, the cover should be waterproof and very garish; if it ends up under a bed somewhere, we want it to be visible, and if it ends up outside, we don't want it getting soaked and ruined.


Copper, gold, silver, and iron weren't all that hard to come by in the middle ages, or even earlier. Magnetic materials are a little harder to come by, but not unheard of. To make electricity, you need something to carry it. Copper is a good choice because it's flexible and has a low internal resistance, though really any metal will do. Don't bother explaining electricity, unless you have some room in the footnotes; if the person you send this book to can use your plans, they'll figure it out in short order. Just explain how to make wire, how to insulate it with varnish, and how to wrap it, join it, or otherwise work with it.

Motors and generators

A motor in reverse is a generator; wrap some wire in a big loop, stick a magnet on a spindle in the middle, and crank - instant electricity! Make sure to include instructions for finding the north and south poles of a magnet, and the proper direction to align them. A multi-step process with better and better motors may seem like a good way to go, but a better approach is to show the plans for the best motor possible (multiple windings per core, multiple cores on a spindle, etc.).

Finally, tie it all together. Connect the wires from all the windings into a big bundle, with one big wire coming out of the "start" and the "end" wires. At this point, you have a working hand-crank generator. Or, scaled up, a huge water-driven or mule-pulled generator. Either way, you can make some big sparks.

If you'd like, a short note on how to feed this energy back into a motor (with heavier wire) would be a fantastic way to note how practical all this is. Imagine the endless possibilities of water power in the early 1500s!

If there's space afterwards, you can explain the physics, but for now, we just want to build a light. Speaking of...

Light bulb moment

Don't try to create a light bulb - or at least, not one of today's standards. Instead, you'll want to make either a carbon-filament light, or just a simple spark light. The second is easy - inside a big blow-glass ball, have the two ends of the wires really close to each other. When the generator is turned, sparks will jump the gap; the more power from the generator, the brighter the light. This isn't an efficient light bulb; it isn't particularly bright, either. Still, it's a light, right?

A carbon filament bulb will be much, much brighter, but won't last as long. Two carbon tubes next to each other, with current applied, with glow as bright as the sun for a little while. Not long, but enough to really leave an impression. Edison used a carbonized bamboo filament with great success, lasting over 1200 hours in good conditions.


The first vacuum pump wasn't discovered until 1650, 148 years after Leonardo's death. However, with the right help, it wouldn't be too hard for the inventor to come up with his own version. However, technology would not be in place for some time to create enough vacuum to produce modern filament light bulbs. So, devote a few pages to explaining how a vacuum pump works, and how to create an efficient version. With the right carbon filament and enough of a vacuum, a bulb should last over a thousand hours - far more than a candle or a simple oil lamp.

Exotic materials and Other Information

Today, we use tungsten, because it has a high heat tolerance; however, not only would it be almost impossible to find, it would also be hundreds of years before machines were advanced enough to make a filament. LEDs and fluorescent tubes would also require materials that wouldn't be available or produce-able for centuries. Still, writing it down would be useful; even if the first inventor never made it, his successors would surely find a way.

In fact, all these explanations should only be a handful of pages; it's really not that hard to make wire, make the wire into a generator, and make a bulb that the generator powers. So, devote the rest of the pages to the science of electricity: transformers and motors, generators driven by water, wind, steam, or horse-power, AC, DC, voltage, current, resistance, even capacitors, inductors, and various micro-circuits. Include mine locations to dig up any metals or minerals needed to make modern circuitry, and modern maps to guide them. Circuits for telegraphs, radios, even television are simple enough to be included. The sky's the limit! Explain as much about modern machinery as possible; the more information available, the faster scientists and inventors will be able to create it.

  • $\begingroup$ Yes, vacuum and tungsten would be problem then, but as I wrote it can be light bulb and equivalent. Carbon filament bulb would still be better than candle. $\endgroup$
    – light
    Jan 2, 2016 at 7:38
  • $\begingroup$ You also need instructions to create a strong enough magnet to generate enough power for light - natural lodestone won't do. $\endgroup$ Feb 19, 2016 at 22:54

The book would have to be written in a language that the recipient could understand. Not just the words, but the concepts.

It would need a primer, an explanation of the concepts starting with "This is a copper wire, and this is how you connect it to another copper wire."

You wouldn't necessarily have to explain how or why it all works (maybe later in the book), just a dumb diagram with plenty of visual instructions.

Concepts such as magnetism would have to be worked around for the motor/generator, but that is easy enough.

The lightbulb would be more difficult than the motor (electric motor and electric generator are essentially the same thing).

I would guess that an alchemist or a priest would be the best person to hand the book to in medieval times in Europe. The alchemist would be used to working with different minerals and metals, and priests were often the most educated. A blacksmith would be able to help.

The moslem world was flourishing during those times, and they had a highly advanced grasp of mathematics and science at that time.

During the renaissance, your one-stop-shop would have been Leonardo Da Vinci, the original 'renaissance man'. Jack of all trades, and master of them as well.

I think that if the book were written the right way, it would be possible for someone in those times to put it all together.

If WW2 prisoners of war could build functioning radios out of bits of junk found around the camps, and people 2,000 years ago could make a battery (although the usefulness of the Baghdad battery is disputed), then it would be possible to build some simple electrical devices.

As to who would make the best usage for humanity, I couldn't say. After the Roman Empire, Europe was in chaos. Splintered kingdoms who were pretty much all in it for themselves.

But I think Leonardo would be your best bet.

UPDATE: Thomas Edison's carbon coated bamboo filament lightbulb might work. He already did the hard work inventing it. Not sure how available bamboo was in medieval Europe (assuming you're thinking about Europe). But you could do the research in your current timeline before sending it back to the past. There must be an alternative available to your intended audience.

The vacuum inside the bulb could be more or less achieved. A metal box sealed with wax, and emptied of air by a bank of bellows with non return valves. Might be tough to get a complete vacuum, but you'd get a fair way. Maybe oxen turning a geared wheel linked to a cam shaft to keep the bellows going?

Have the bulbs and filaments all set up inside the box. Set leather gloves into the side of the box to work on the bulbs inside. Leather would probably leak air into the box, but keep those oxen moving. Promise them a bonus if they make budget.

Using the gloves (they'd need to be tight but supple gloves to counter the ballooning that would happen from the negative pressure inside the box, maybe banded with wire), assemble the bulbs. All you'd need to do is attach the glass bulbs onto the bases with the filaments already attached.

One problem would be to attach the bulbs and bases together. With the electricity you are already producing, it might be possible to have a soldering iron inside the box. Otherwise some kind of glue, maybe made from boiled sinew, potato starch, whatever.

Edison got around 1200 hours of life out of his bamboo filament bulbs.

  • 2
    $\begingroup$ Good call on the purely visual diagrams -- reminds me of the instruction manual for the Liberator pistol, which was to be dropped to Resistance fighters speaking various European languages. $\endgroup$
    – Wingman4l7
    Dec 23, 2015 at 17:52
  • 1
    $\begingroup$ The Baghdad battery may be up for debate, but the voltaic pile was pretty straightforward, and the Daniell cell wasn't much more complex. $\endgroup$
    – Wingman4l7
    Dec 23, 2015 at 22:40
  • $\begingroup$ I knew there were others, glad your memory is better than mine. I kept thinking about the potato battery too. $\endgroup$
    – Smoj
    Dec 24, 2015 at 2:34
  • 1
    $\begingroup$ @Smoj: The potato battery would have the problem that in medieval Europe, there were no potatoes. $\endgroup$
    – celtschk
    Dec 25, 2015 at 20:41
  • $\begingroup$ @celtschk Umm... Yeah. I'll concede that point. :-) $\endgroup$
    – Smoj
    Dec 26, 2015 at 1:23

Yes it is possible to write such book, there are however a number if issues that need to be addressed.


Since you have exact control over location and time of arrival we can use historical records to drop the book at the proverbial lap of Leonardo da Vinci, Copernicus, Rene Descartes, or any other appropriately bright mind of the time. That's great, it wasn't until 19 century that universal education became a concern at all, and in any prior time, most people wouldn't be able to even read the title.

Language, part 1. Math.

Electricity requires specific language: math. Unfortunately, a lot of math that goes into electromagnetism wasn't even known back then. Integrals, differential equations, even something as obvious as Cartesian coordinates (you remember last of the 3 people I mentioned earlier? Rene Descartes is the one who formulates Cartesian coordinate system) are things yet to be formulated if you are truly aiming at medieval times. Thus, some part of your book would have to be a mathematics handbook. Don't worry, scientists of the time would be excited to stumble upon this part alone, general populace gives too little credit to late medieval and renaissance mathematicians. Book however needs to be properly adapted to time period, taking into account and dealing with quirks like refusal to use negative numbers.

You may argue that they don't need math to build electric lights and you would be right, as I explain in later parts, generator and lamp itself are very simple devices, however by providing blueprints without underlying science you risk your gift being treated like magic. It will be slavishly replicated without any understanding of concepts behind, you even run a sizeable risk that such book becomes hailed as gift of god and changing something as small as number of coils in generator becomes heresy.

Language, part 2. Latin.

Latin, obviously. Use of latin makes it easy to copy and share, and it was THE language of educated men back then. As a bonus, writing it in latin means you can send it without change to many people at the same time, preferably within same year.

Language, part 3. Metric system.

This part is by far THE hardest. You don't believe me? Look up on wikipedia how metre, kilogram and second are defined. Modern definitions have great advantage: they rely on laws of nature, thus they can be replicated anywhere, without any contact with original "ideal" (yes, if we build FTL capable ships and get stranded in another galaxy, we could replicate metric system from literally nothing but pure knowledge, after multiple generations of advancing our tools to high enough precision, that is). Unfortunately you need correct tools for that. Very, very precise tools.

The only way to solve it, that I can think of, is to accept much lower precision and just supply a 10 centimetre ruler with the book. They can easily measure how much is 1m. Distilled water has known density, so after measuring 10cm*10cm*10cm cube they know what 1kg is. Time, seems to be trickier but it's not - pendulum. Measure up a bit of string of proper length, attach ball made of heavy metal and let it swing - period of oscillation depends on gravitational acceleration and length of string. With 1m, 1kg and 1s defined, it's possible to further define 1 newton, 1 joule, 1 watt, 1 ampere, 1 coulomb, 1 volt and any I missed. That way, bit by bit it's possible to reconstruct most of the metric system, introducing final part of mental framework required not just copy, but understand, improve and adapt electrical devices.

Electric generator.

This one's relatively easy. It's copper wire and magnet. Copper was known and used since ancient time. Some cultures knew magnetite since 1000 BC, and compass was used for navigation by Chinese as soon as 10th century, some records suggest it has reached Europe as early as 12th century. Attach generator to water mill and you are done.

Technically speaking, you can just show them diagrams how to make it, completely omitting math, electric generators are very simple at the core, but if you want people at the time to have any chance to improve initial design, or better adapt it to the tools they have, you need to introduce proper math.


This one's right out.

Lightbulbs look simple, but really, they are not. Lightbulb requires glass, inert noble gasses or high vacuum and Wolfram aka Tungsten. First vacuum pump was invented in 1654 and most likely required mechanical precision that may be unfeasible in times before. Tungsten wasn't discovered until late 18 century and even if you explain how to obtain it, it has ~3500 Celsius melting point. If you however manage to cram that much info into one book, you are very close to vacuum tubes and simple computers.

Carbon Electric Arc

Since Lightbulbs are too complicated we need simpler alternative: Carbon Arc Lamp. It's as simple as 2 carbon rods touching together, creating spark which is stretched into electric arc, while evaporating carbon is feeding the plasma conduit. Simple, easy, but short lived. No vacuum or Wolfram required, just carbon. Coal and Graphite are known since prehistory.

  • $\begingroup$ Metric system 👍 $\endgroup$
    – light
    Jan 2, 2016 at 7:27

Is it possible to write such book so the recipient would understand it and use as solid starting point? If not, why?

It is not possible to provide a solid starting point with a book like that. Making efficient use of electricity requires ability to manufacture nearly pure metals at affordable cost and large volumes. Knowledge of electricity itself does not really provide this.

What you need is the proper economics for industrialization, which starts the mass production of metals, which allows use of electricity on a scale that actually makes a difference.

By itself the teachings of a book on electricity will be of great interest, but of little practical value. While a medieval genius might be able to build a battery and a working light bulb, it would be too expensive in both manufacture and maintenance to be anything other than a toy for a king or emperor. Byzantine and Chinese Emperors apparently did have some pretty cool toys, you'd just be adding one more.

Maybe a description of a simple steam engine written as Latin translation of an earlier Greek work by Heron of Alexandria or Archimedes of Syracuse? The name recognition would give it enough credibility that someone might pay for building one. It might be a good idea to include a suggestion of a practical application by including a water pump or a paddle wheel in the design.

If the practical value is good enough the idea will spread and kick-start industrialization. Which will create both access to bulk metals and demand for artificial light. Which didn't really exist before factories...


I think that the correct lead-in technology is the electric telegraph. A crude battery, copper wires mounted on glazed pottery insulators and wooden poles, a coil around a compass as the simplest receiver. Messages at the speed of light rather than the speed of a horse. No difficult materials. Value obvious to merchants and princes and military men.

To get the book accepted it should be handwritten in Latin using mediaeval ink on vellum. Good idea to pass it off as ancient Greek or Roman knowledge ( perhaps with a note giving provenance as having been "liberated" from the saracens by an ancestor and recently copied, from a scholar in a distant war-torn place seeking help in understanding it)

Recipient most likely to catch the ball and run with it: surely Leonardo da Vinci. He'd probably invent the electric motor without further hints although you'd have plenty of space to provide them!

The electric light and generation and distribution of significant amounts of power is probably out of reach for a generation or two after the telegraph demonstrates all the necessary science and makes sure it is not forgotten.

  • $\begingroup$ Working telegraph for merchants/military surely would attract enough people to invest their assets for concepts in books. But probably this would go in some kind of arm race. 👍 for provenance part, book should not be burnt because of fear deamons/magic. $\endgroup$
    – light
    Jan 2, 2016 at 7:43
  • $\begingroup$ Telegraph isn't radio. Pretty useless for offense but priceless for defending the realm against invaders. So should act to damp down wars of aggression and encourage long distance trading which also works against wars of aggression. $\endgroup$
    – nigel222
    Jan 2, 2016 at 11:19

Others have pointed out that there would have to be significant advances to several fields of engineering and science first, metallurgy in particular, so that electric lighting would become possible, desirable and affordable. I think gas lighting could be easier to achieve, even if it is more dangerous and isn’t as practical for in-house illumination.

There is a lot of useful scientific information that can be fit on 800 A4 pages (i.e. 400 sheets, almost a ream, 50 m²), which will definitely help medieval scientists a lot. Highschool math and pre-relativity physics, a periodic table together with anorganic and some organic chemistry would go a long way and shouldn’t require more than half the available space, if not every proof and explanation is included in detail. (It’s a good idea to also introduce a replicable and coherent system of units at the beginning of the physics section.) The other half could be filled by engineering, e.g. how to make steel and glass, and would probably use more drawings and diagrams. Part of this would be work management, e.g. the importance and efficiency of shared specialized labor in factories. If dropped in, say, 1500, this alone could accelerate scientific advance enough to get light bulbs by ca. 1700, maybe sooner. The book shouldn’t be teleological, i.e. it should not try to describe a straight path to electric lighting. It should instead establish and reinforce foundations that are needed to achieve that goal. Non-prominently, I would include a crude map of the world, e.g. as part of where to find relevant mineral resources.

Accessibility and credibility are, of course, important factors that cannot be ignored. Contemporary scholars would welcome the text to be written in Latin or Greek in Christian Europe, Classical Arabic in the Muslim world and Literary Chinese for the Ming dynasty. To be taken seriously, the book would have to draw from what was already known back then. That may include simple debunks of misbeliefs or definite answers to open questions of the time (and future ones, to avoid ether, miasma, phlogiston etc.). It must avoid touching on delicate matters of religion. Astronomy and biology seem to be the riskiest topics – luckily, they’re completely irrelevant for the tasks at hand. Without saying something about that explicitly, there should be a believable source of the book that is neither time travel nor some god or devil. Maybe reference the Great Library of Alexandria or claim to be the translation of writings by scholars from the other end of the world.


Good question, and I know this is not the answer you want, but...

We already had artificial light: Candles

But you don't want them to just use candles, you want to show them how to generate electricity, create a storage ("battery") system, source the metals required, and make the glass bulbs.

My recommendation would be to send it to someone respected, a thinker, and whose language is relatively similar today as it was then (for the bast transmittal).

How about sending it, in Arabic, to Abu Al Farabi.

  1. He is a thinker, philosopher, scientist from the 9th/10th century.
  2. He was respected and known in the Arab-Islamic world, which stretched at some points from modern day Spain to Africa to East Asia.
  3. Arabic as a language has been very strictly kept from deviating much - obviously there will still be some lost in translation, but this is still helpful.

What should it say?

Well I don't know too much Arabic, but it should describe the basics of metal alloys (which he was already familiar with), a pictorial demonstration of how electro-magnetism is generated and stored, and glassworks for a bulb.

In 800 pages, your electrical engineers should be able to present this.

  • 3
    $\begingroup$ 👍 For not sending it to Europe. I also thought about other locations like (China, Japan, South America, India) $\endgroup$
    – light
    Jan 3, 2016 at 12:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .