# What could an average modern human achieve in medieval times?

Let's imagine that on one fateful day, John Doe, the absolutely average citizen, wakes up just outside of a small village during the Middle Ages, somewhere in Europe, maybe France or England. Let's assume for simplicity that he knows the modern language of the specific region. Would he be able to survive? What could he achieve using his modern-day knowledge and skills? Could he "invent" or prove something significal?

To elaborate more, he does not know much about farming or working with wood or metals, besides being a hobbyist DIY-er, but even there, his skills usually depend on a Home Depot and power tools being available. He does know his high school maths, physics, chemistry and biology, but of course relies on calculators or computers for more convoluted operations (e.g. looking up results of trigonometric functions). He also knows everything that is considered trivially known as of todays standards, e.g. the basic principles of heavier-than-air flight, matter being composed of atoms, the crude anatomy of the human body, the existence of microorganisms, etc.

• A book is already written about that: crusade in jeans – ratchet freak Mar 26 '15 at 13:32
• As your 1st sentence of the 2nd paragraph alludes to, the challenge is applying his knowledge without the support of a modern-day infrastructure. Even if you know things that don't necessarily require a lot of support, like say contour plowing, nobody is gonna give a shit until the problem presents itself like post dust-bowl. – coburne Mar 26 '15 at 13:44
• Not exactly a match, but the Tales of Paul Twister stories are based on a very similar premise: a guy from modern-day earth gets somehow stranded in a medieval-fantasy world (with magic) and has to make do somehow because none of his modern skills are relevant. He tries to introduce concepts based on modern technology, but he has to get local scholars and craftsmen to do the actual science and engineering because he only has a vague idea of the principles involved. – Mason Wheeler Mar 26 '15 at 14:20
• As you may know, this is heavily explored in fiction: Examples include Mark Twain's A Connecticut Yankee in King Arthur's Court, L Sprague De Camp's Lest Darkness Fall, and Leo Frankowski's "Crosstime Engineer" novels. The non-fiction book A Time Traveller's Guide to Medieval England is also highly relevant. – Royal Canadian Bandit Mar 26 '15 at 16:39
• @Kreiri I have asked about an average modern human, and put the constraints that it would be a male and be able to speak the modern variant of the region's language in order to skip the quite boring answers about being accused of witchcraft, branded as a fool, sold away as a slave or killed on sight due to mistaking for an invader or a spy. Nonetheless, if you have any ideas that would lead to an interesting scenario at the cost of a constraint, I am interested in that too. – zovits Mar 26 '15 at 17:13

## Depressing, realistic version:

John Doe has major problems:

• His modern skills are of little use in a medieval English village. The peasants don't care about numeracy or crazy ideas, they want somebody who can slaughter a pig or plough a field.
• He has great difficulty communicating with the locals. Have a look at Shakespeare or Chaucer's English, and compare it to the modern version. Remember that pronunciation has changed as well as vocabulary and grammar. He is completely ignorant of local customs and manners, and likely to offend people by accident. (He can probably learn the basic language and customs in a few months, if he lives that long.)
• He hasn't memorised the formula for gunpowder, and vague memories of high school chemistry sound like nonsense to the locals. Biology is equally useless. How many of us can identify penicillin mold in the wild, and distinguish it from the hundreds of other molds which will just give you a nasty fungal infection?
• He doesn't have the connections to become Royal Military Engineer or Chief Treasurer. This is not a society with a strong interest in scientific and technological progress. Technological change over the span of a human lifetime is almost undetectable; new ideas are suspicious at best, heresy at worst.
• He is vulnerable to diseases of the past which have no vaccines (bubonic plague), or against which modern people are not commonly vaccinated (smallpox). One of them may kill him rather quickly.

John's best bet is to find a monastery and stay there. The monks have some degree of charity towards wandering halfwits who can barely communicate -- and make no mistake, this is how John will come across at first. Once the monks get to know him, they may value his more unusual skills, especially his ability to read and write.

At worst, John may end up as an unskilled labourer on a farm. At least his good general health gives him a head start, unless he catches some unpleasant disease or bandits burn the village.

## Entertaining version:

Through some combination of luck and natural talent, John acquires a wealthy patron or some resources of his own. He becomes a famous inventor and kicks off the Renaissance and/or Industrial Revolution a few centuries early, as explored in Mark Twain's A Connecticut Yankee in King Arthur's Court and subsequent works of fiction.

• There is a 'sequel' to HG Wells' The Time Machine where the time traveller goes back to medieval England and catches the plague and dies. – Oldcat Mar 26 '15 at 18:37
• Even his reading and writing will not come across as great "skill" - can you (fluently) read a medieval text? Or write those funny letters? - But maybe he can help the copist monks by "inventing" printing? Something that can easily be modded into a press may indeed be available – Hagen von Eitzen Mar 26 '15 at 19:58
• +1 for finding the monastery and staying there for a few months, it's the best strategy. It allows him to learn the dialect, script, and the local customs while in relative safety. It also allows him to slowly gain the reputation and trust of important people. If a priest of higher rank gets to like him, he will have an easier connection to the royal court as a respected scholar. Don't forget, that contrary to popular belief, the biggest scientific curiosity was among the clergy, and most scientific discoveries of the era were made either by the clergy or sponsored by them. – vsz Mar 26 '15 at 21:46
• @Jay: Not really. In 14th-century England, John is a lot more foreign than a visitor from France. He has no idea how a medieval agrarian society operates. He has lots of crazy ideas about hygiene, scientific progress and social equality. Religion is absolutely central to peoples' lives, in a way John is likely to find profoundly shocking. All in all, John will be lucky if he is taken to be a halfwit, rather than a witch or heretic. :-) – Royal Canadian Bandit Mar 27 '15 at 22:53
• @raxacoricofallapatorius While you might be right, I for one can't really imagine a scenario in which logarithms, linear algebra or calculus would prove useful enough for a medieval society to warrant sustenance at all, not to mention fame and reverence. Could you please elaborate on this? – zovits Mar 28 '15 at 19:14

This really should be a comment to Pavel's excellent answer, but I'm afraid I don't have the reputation to add a comment.

Given the sad story of Ignaz Semmelweis, it's pretty unlikely anybody would even listen to your newfangled ideas about the importance of hygiene.

His flash of insight was quite literally that it would be advisable for doctors to wash their hands after touching a dead body before attending to new mothers in the maternity ward.

Despite having dramatic, incontrovertible evidence that was, in fact, a good idea, he was drummed out of Vienna as a quack.

Keep in mind this was mid-19th century Vienna and hardly the dark ages.

Depends on how he plays his cards. The medieval world was disgusting, diseased and woefully violent. Being used to the egalitarian principles of modern times, he would treat the nobles as equals, which might result in beheading or in the nobles assuming they're dealing with a fellow noble.

If he can't speak the (for him) archaic local language well (might take him months to learn properly) short term survival might be a serious issue. Given that he towers about half a foot over the locals, probably some military job might become available if he's up for it.

Even basic high-school mathematics are insanely advanced by medieval standards, his knowledge of chemistry and biology would top the most advanced theoretical skills up until about the 1600 without even trying. The problem would be one of access and persuasion rather than of actually having useful skills.

The medieval world is not known for its meritocracy, but for promoting incompetents of noble birth over skilled commoners. So his best bet would be to finagle his way into becoming the assistant of one of the less atrocious nobles. This would be a mutually beneficial deal: his skillset would allow the noble to rise meteorically, while the noble would 'open doors' for our time-stranded traveler. If that happens, the sky's the limit:

Royal Doctor (with earth-shattering advice such as "wash your hands with soap before eating, and especially after using the ba... going off into the woods" and using certain kinds of mold to treat the royal children when they're sick.)

Head of the Royal Mint (using negative numbers in book-keeping, and, actually, proper book-keeping)

Apprentice or Head Weapons Engineer at the Imperial Court (Depending on how much chemistry and physics he remembers)

But, most likely, he'd get a digestive tract infection during the first few weeks and die of cholera or some-such.

• Why would he be a foot and a half taller than the locals? – DickieBoy Mar 26 '15 at 14:33
• @SBoss knowing how a steam engine works is not enough to build one, and even having complete technical designs of early steam engines wouldn't help. For accelerating the industrial revolution, the designs are the easy part (they would come out of local inventors), the hard part is accelerating the surrounding metallury and tools industry. Building a railroad line from tons of cheap iron or steel is relatively simple compared to building an industry that can make tons of cheap iron or steel.The same thing for military gunpowder - the hard part is ensuring reliable consistent mass production. – Peteris Mar 26 '15 at 17:39
• @DickieBoy. Modern Westerners ARE a foot and a half taller on average than medieval people. Mostly thanks to epigenetics and better diets for generations. – Serban Tanasa Mar 26 '15 at 18:40
• BTW Medieval people weren't that much shorter than modern people. See, e.g. historymedren.about.com/b/2004/09/15/tall-medieval-men.htm. Apparently if you look at skeletons of people from the 9th to 11th centuries, the average height of a man was ... 5 foot 8 inches. I understand the average American man is 5 foot 10, so our traveler wouldn't tower over Medieval people. He'd have about 2 inches on them. – Jay Mar 27 '15 at 22:16
• @Jay, I stand corrected. – Serban Tanasa Mar 27 '15 at 22:28

He would bring bacterias and viruses, that haven't evolved yet with him and after people around him start getting sick and die, they would realize he is the devil and would burn him at a stake.

• On the other hand, if he would be living with a fatal, transmissable disease unknown in the middle ages with a long dormant period and no treatment options, he could be the patient zero of a possibly world-altering epidemic. A HIV epidemic in the middle ages could have eradicated the human race perhaps? By the time anyone realises the existence of the illness, it has already spread far away, steadily infecting basically everyone except nuns, hermits and a few others. If there were any survivors to make a link between the disease and sex, they might never try to reproduce again. – zovits Mar 26 '15 at 16:14
• HIV wouldn't be as much of a problem, despite modern propaganda people actually were more prude (is prude the right word?) in those times. And -1 for this answer, because this would (as Zovits is stating) far more likely happen the other way round. Of course him dying and him people around him dying would be possible. (Though his chances of dying are far greater than of those around him) – David Mulder Mar 26 '15 at 20:14
• @zovits: "I'd think an average citizen today mostly relies on medicine to keep healthy by keeping viruses and bacteria out of his system" -- might depend where you live, but certainly I don't routinely take any medicine to keep viruses or bacteria out of my system. I get sick from time to time, and might use antibiotics then, but most of the time I'm not infected with anything I can't deal with. If he happens to have the 'flu on the day he goes back, though, then there's certainly a chance he could create an epidemic in the week or so he's infectious. – Steve Jessop Mar 27 '15 at 14:11
• @Michael: I don't think it's true that humans are routinely carrying diseases fatal to other humans without the necessary immunities. If it were, then the idea of "smallpox blankets" wouldn't be remarkable, since most native Americans would have dropped dead anyway just from meeting Europeans. In fact, while there were fatal diseases communicated, it's not like most Europeans were fatal to most Americans or vice versa. – Steve Jessop Mar 27 '15 at 14:18
• @zovits There would be a few nuns infected, too. How many depends on who you ask, but definitely some. – KSmarts Mar 27 '15 at 21:15

Many answers here seem to me excessively pessimistic. Rather than commenting on them individually, let me make some general points:

Yes, language has changed since Medieval times, so knowledge of the modern version of the language would be of only limited value. But it's absurd to say that this would mean that the people of the time would think him insane or a drooling idiot because he can't communicate. Medieval people were well aware of the existence of other countries where people spoke different languages. There would be nothing surprising about such a person at all.

The fact that he is an "outsider" would not result him in instantly being killed or thought to be a witch or any such thing. While travel was limited in Medieval times, there certainly were people who travelled great distances. Ever hear of Marco Polo? Travelers were usually welcomed because they brought news from the outside world and entertaining stories. A traveler could usually get a few free meals or at least some drinks by telling a few stories.

Yes, health and sanitation back then were poor, so the risk of an early death was greater. But it's not like everyone was condemned to instant death. Obviously many millions of people managed to live to adulthood. Maybe you could make a case that there would be diseases circulating then that are not common now, and so he wouldn't have any resistance.

At the other extreme:

It is very unlikely that he would be able to bring much if any modern science and technology to this place. Sure, he'd be familiar with computers and cell phones and airplanes and all sorts of modern things that these people never heard of. But could he teach them how to make these things? I doubt it. I like to think I'm a smart guy -- Mensa-level IQ, work as a software developer, and all that -- and I'm hard pressed to think what technology I could introduce if suddenly dropped in Medieval times.

Yes, I can use a cell phone. But I haven't the vaguest idea how to build one.

I know a lot about computers. But build one from scratch? Let's see, microchips are made using silicon and germanium. I know silicon comes from sand. Exactly how do you extract it? Where do you get germanium? I presume that lithium batteries are made with lithium. Duh. Where does lithium come from? What does it even look like? I don't even know what color it is. Even if I had a pile of lithium, how do you make a battery from that? Etc.

Okay, maybe that's too ambitious. How about something simpler. Maybe a steam engine. I know it has something to do with boiling water, having a small opening for the steam to come out, and running that steam into a piston to make it move along a shaft. But how to make any of those things? Maybe given the time and resources to experiment, I could figure it out. Or maybe I'd just kill myself when my first experimental boiler exploded.

Thomas Edison once said that genius is 1% inspiration and 99% perspiration. Even if you know the basic idea behind some invention, there are many, many details to be worked out to take it from a "basic idea" to a working model, and many more to get from a working model to something that is actually practical. Unless you are an engineer whose job it is to design models of this particular machine, the odds are that you have no idea what the details are.

I suspect about 90% of the people in the world have no idea how any of the modern inventions they use every day actually work, and most of the rest have only vague, general ideas. The number of people who know how to actually build a jet plane or a cell phone or how to make plastic, etc, is tiny.

And even at that, inventions build on earlier inventions. Before you can make a radio, you need electricity. To produce electricity, you need things like wires and magnets. To make wire you have to smelt metal. To smelt metal you have to mine raw ores. To mine raw ores you have to know what the ore looks like and where you find it. Etc. Even someone who knows how to design and build cell phones probably starts with wire and plastic and semiconductors. He knows how to use copper wire, but ask him what raw copper ore looks like, or where you go to find it, and how to smelt it into usable metal ... Odds are he has no idea.

• @BrendanLong Yes, others had comments about math and geography. I would think that would be his best chance of introducing new ideas. Someone who knows some calculus could teach it to anyone who understands algebra and is reasonably bright. You could point to a map and say "there's a big island here that my people call Greenland" and that would be enough to be at least potentially useful information. – Jay Mar 29 '15 at 21:30
• Another BTW: Several people have said that if he introduces modern science or technology he might be burned as a witch. Probably not. There were many great scientists in the Middle Ages who introduced radical new ideas: Tyco Brahe, Kepler, Roger Bacon, William Harvey, etc. None were accused of being witches or anything like that. Yes, yes, they persecuted Galileo, but the part most people leave out is that Galileo didn't get into trouble until he wrote a book in which he had a character named "Simplico", which means "fool", and he put the words of the pope in Simplico's mouth. ... – Jay Mar 29 '15 at 21:34
• ... Calling one of the most powerful and respected people in the world a fool, in print, has never been a recipe for success. Similarly, he made rude and nasty remarks about other powerful people who disagreed with him. It's one thing to say, "You know, sir, I really have to disagree with you there ..." in a private conversation. Galileo in fact did this and the pope continued to support him. It's another to publicly call him a fool for disagreeing with you. Of course I'm not condoning shutting down free scientific inquiry just because the scientist is rude and arrogant. But the real ... – Jay Mar 29 '15 at 21:38
• ... story is not, "he was persecuted because he disagreed with popular beliefs of the time". The real story is more like, "he was persecuted because he insulted too many powerful people". Oh, and btw, many of Galileo's scientific arguments were seriously flawed and have long since been abandoned. He was still groping toward the truth himself. So people of the time could and did prevent very sound scientific rebuttals of many of his arguments. – Jay Mar 29 '15 at 21:40
• That was supposed to be "did PRESENT very sound scientific rebuttals", not "prevent" them. But apparently I waited too long to edit ... – Jay Mar 29 '15 at 21:47

Sad, but realistic story is: Not much: Let's put aside that most probably he would be burned as witch for appearing out of nowhere. Let's also put aside the fact, that most probably he would die of Dysentery, plague or any other disease caused by poor hygiene standards (Fun fact, both toilet paper and flush toilet were invented in 19th century)

Let's even handwave the fact, that he would be probably considered as idiot, because medieval language did differ a lot from our modern language and go for happily-ever-after scenario.

(English speakers, do read Shakespeare in original edition. How much do you understand?)

People were not allowed to travel in medieval ages. You were property of your king. So most probably he would stay in such village. (Or got explained, that he has to stay inside the village).

If he were really skillful DYI-man, he would probably become blacksmith of such village. If not, he would become "common peasant" of that era.

Because his general well being, he would be "perfect match" for women at that time. So he could pick up a woman he desires most.

He would have 5 to six children. Maybe more, maybe less.

As I told you. Sad, boring and average story it is. But he wasn't killed or died out of any plague

• Thats problem of language :) Since English is not my first language, I understood it as "he knows modern English, but not English of such era"... So, now I am the Joe having language problem ;) – Pavel Janicek Mar 26 '15 at 12:28
• A lot. I am totally convinced that he could survive only as "local idiot" – Pavel Janicek Mar 26 '15 at 12:35
• @zovits: For diseases and hygiene, he would still have the benefits of being vaccinated against many serious diseases... Maybe, but are you vaccinated against the Plague? How about smallpox? I'm not... – Mason Wheeler Mar 26 '15 at 15:21
• Flush toilets were invented in 1596, the modern form with a S-trap in 1775. N=Just not widely manufactured until the mid-nineteenth century, kinda like most things. Toilet paper has been documented as far back 589 AD. – Samuel Mar 26 '15 at 22:52
• Another thing that you probably don't know, since English is not your first language: Shakespeare's works are written in Modern English. That is, it is considered the same language as the one we use (but maybe a different dialect). For a better (and more difficult) example, try reading Chaucer in the original Middle English. – KSmarts Mar 27 '15 at 21:25

An even more depressing take is Poul Anderson's The Man Who Came Early.

A plot summary from Wikipedia:

The story is presented in the first person, related by a Saga-Age Icelander named Ospak Ulfsson. During a violent thunderstorm, an unexplained phenomenon transports the titular 20th-century American GI back in time to Ospak's homestead. The American, who becomes known as Gerald "Samsson", is an engineering student drafted to serve at Keflavik during the Cold War between the U.S. and the Soviet Union.

Gerald is taken in by Ospak's family who assume him to be a shipwreck survivor. Although his engineering background gives him many ideas of how to improve life for the Icelanders (such as advanced sailing vessels), his lack of practical know-how, and his oversophisticated ideas when set against the nature of 10th-century life, lead to none of his suggestions being implemented. Knowledge of 20th-century metallurgy does not endow him with the highly specialised skill needed to work in a 10th-century smithy, and his attempt to do so ends with a costly fiasco. Also, knowing the theory of how to design a large metal bridge is not a sufficient base for constructing a small wooden bridge over a rivulet with medieval carpentry tools.

There is also a whole series of misunderstandings caused by social and cultural differences. Gerald tries to tell the Icelanders that in his country there are no blood feuds because the government takes care of punishing all wrong-doers. However, his listeners have no concept of a vast impersonal government and its law-enforcement agencies; Gerald's words, when translated into concepts familiar to his listeners, are taken to mean that all law-enforcement is done by the King in person - whereupon the amused Icelanders remark that such a King would be too busy to beget an heir... And conversely, when Gerald tells that he had been a military policeman and describes the task of one, they are astonished at what they see as his foolhardy courage of "offending all the men in the war host" - since Vikings would absolutely not have tolerated the petty regulation of their dress and personal life which is common for soldiers in a 20th-century army.

Then, Gerald guilelessly mentions that his family owns no land and lives in one apartment of a big house where many other families live - not realising that he has just plunged his social status sharply down, as in this rural society a landless man is far down the scale. And when he boasts that the United States is a free society, but admits that US citizens may be called up for military service even at harvest time, his shocked hosts conclude that the US is the worst and most monstrous of tyrannies - since in their economy, calling up the farmers in harvest time would doom their families to starvation.

Meanwhile, Gerald and his host's daughter fall in love with each other. A rival suitor from a neighboring clan, annoyed at her preference for the "useless" foreigner, insults Gerald, who then challenges him to "fight it out" - not realising that in this society, duels between free people are fought with weapons and often to the death, and that fighting bare-handed "is for slaves". Trapped in a holmgang and about to be cut down, he uses his gun and kills his opponent.

In order to avert his host becoming entangled in a blood feud, Gerald departs on his own - which leads to his being outlawed and hunted down. When making his last stand, his ammunition runs out ("his magical weapon failed him" as the locals see it) but he gives a good account of himself with a sword seized from a fallen opponent before being finally killed.

The ending of the story suggests that, in time, Gerald's burial barrow would come to be regarded as the tomb of "an ancient hero" and that he would in death find the place in Icelandic society which he did not gain in life.

# If he knows some medieval theology

Royal Canadian Bandit's answer mentioned him going to a monastery where they would end up valuing his skill to read and write. Now, it just occurred to me that if he's a christian and followed higher level secondary education with Latin (this is still the norm in a lot of developed countries) and at some point he read up on some medieval theology he would definitely be taken seriously by everybody. His knowledge wouldn't even have to be extremely in-depth. Like having spend a couple of afternoon reading Wikipedia articles or the excellent Internet Encyclopedia of Philosophy would probably been enough.

The interesting thing to understand is that the sciences were traditionally seen as sub-categories of theology (which sounds totally ridiculous to us nowadays, but the natural being sub categorized to the supernatural actually makes a lot of sense in such a society). So if he can establish some basic authority as a good theologian (claiming he's a wandering monk or what not, something that is technically true as he just wandered from the present to the past), he can next start thinking about the other sciences. And depending on what he still remembers work from there.

# If he does not know anything about medieval theology

On the other hand, if he doesn't know the above stuff (quite likely) he won't be destined for any greatness. If he accepts being a normal peasant he will probably do just fine, if however he tries to become self important and introduce modern technologies and stuff that will soon be the end of him (nothing dramatic like being burned on the stake, just nobody willing to trade with him or help him*). And yeah, if he's a christian (or is capable to act like one), but not all that learned then just going to a monastery would be the wisest choice.

* Most of medieval times weren't half as barbaric as depicted in modern media. Realistically it depends on what he would say though. If he starts proclaiming post modernist notions or even modernist notions the Church would take interest probably and excommunicate him. But besides that he would be more likely treated like an idiot than 'burned on a stake' like some of the other answers suggested.

PS. This is assuming that language is not an issue, as that's how I understood the question. And just for the record, it's not that faith was that much more important in that time, but there are only two theoretical powers where he could flourish: political or theology. The first requires the right bloodline and the second requires knowledge.

• Yes, I defined that he knows the language exactly because if he didn't even speak the same language, his chances would be abysmal for even short term survival. – zovits Mar 26 '15 at 20:47
• I don't get why a cursory knowledge of theology would be an advantage. He could claim to be a lost monk or whatever, but if anybody cares enough about him to look into the matter further, it would become obvious that he wasn't part of any known order and hadn't ever experienced a monastic life. And what advantage would this even give him -- to be considered a wandering, homeless holy man? That's not really going to earn a lot of respect, unless he starts a religious movement or something (the latter would be pretty dangerous though, and I can't think of how being from the future would help). – zeta Mar 29 '15 at 8:31
• @sumelic First of all let me clear up that I meant an average Christian that thus knows most of the modern typical theology, but that on top of that he is also aware 'how stuff worked theologically back then'. Now, depending on where he is wrong it would depend on just how useful it is. In the east wandering 'preachers' (early middle ages) where quite common and he could relatively easily fit in there. (cont.) – David Mulder Mar 29 '15 at 13:22
• In the rest of Europe it would be a bit harder to pass by, but a lot of hermits where not part of any order and 'did their own thing' during medieval times. It was later that that got institutionalized a lot more. – David Mulder Mar 29 '15 at 13:22

The first challenge would be just to survive and for him to establish himself. Many medieval societies did not treat outsiders well. He would have no travel permits and no one to speak for him. Village communities would shun him and cities could deny access.

Language barrier will be hard to overcome and despite being literate he could not utilize this skill to the fullest. Perhaps if he had taken Latin in high school and paid attention he could use that for rudimentary communication.

As others have stated without any specific skills and almost NO actual skills for the time period survival would be hard. Even many simple innovations require a lot of supporting technologies and skills that would not be available to him.

I wouldn't say that he would be completely useless. He would have a lot of information but much of it would be hard to demonstrate or utilize. He would know world geography, stuff about hygiene and biology, even some history what will happen, math etc. but good luck demonstrating your value.

With out any usable skills he would require a benefactor but I think he could prove quite useful in the long rung.

• How could he utilise his history knowledge? Even if he can remember the exact date of a significant event, he'd still need to know some specific details about it. Of course it depends on the concrete event itself, so he might be able to flee from a country that is known to become invaded in his near future, but what other events would be simultaneously considered important enought that it is not only taught in schools but actively remembered years later AND able to benefit from (either personally or on a larger scale) foreknowing? Plagues and major fires come to my mind, do you have any more? – zovits Mar 26 '15 at 16:39
• He would know the outcomes of some major wars and invasions, the significance of Columbus' expedition and maybe a few other things. He would have to be in the right place at the right time, and in a position where the knowledge can be used for benefit. It seems quite unlikely, so at the very least, I feel, it would be inconsequential for his survival. – palako Mar 26 '15 at 17:17

Once properly adjusted to the nuances of Olde English, I think your man (and most others from our time) would have an excellent career as a storyteller. Just imagine:

Gather 'round children, and listen to my tale,

"Geo geara, fram heofonsteorra ealfela feorran..."*

*constructed with this nifty tool: http://hord.ca/projects/eow/

• This is another quite interesting idea. He would if course know many great stories that could be adapted to the age, but the question remains: how much does it contribute to these stories being enjoyable to us the fact that they were written by contemporary authors? – zovits Mar 27 '15 at 6:45

The first problem is: Immediate survival.
People will find him extremely strange: He is of excellent health (people needed to work extremely hard from childhood, damaging their bones and sinews, they had plagues and were badly nourished. Even the rich ones like nobility were eating too much wine and flesh, overweight and gout was rampant. While often very robust because they survived this environment, the body took damage). If he is a white-collar worker, his hands were soft which would indicate higher status but his behavior does not fit. His clothes were strange and if unlucky, could kill him at once. Wearing purple was reserved for nobility and punishments in medieaval society were almost always capital punishments.
It should be said that it must be a "him" because "her" survival would be either marriage (if lucky) or prostituition. Having no rights and respect at all it would be nearly impossible to get out of the trap.

As several people pointed out, the known sicknesses could kill him very easily because he is in another environment.
The lucky ones: Craftsman and ranchers who are still not fully technologized. They could be found e.g. in Amish cultures, rumors have it that even now there are blacksmiths, goldsmiths, bakers, carpenters which would be able to continue their work in a medieaval society. In cities there were guilds, so they needed to join them but I think it could be possible.

White-collar workers had a very good opportunity to survive: Healer

The knowledge of medicine was so unbelievingly abysmal that having visited a first aid course and common knowledge would set you apart. Barbers were responsible for teeth and chirurgy and were often quite competent at it, but the prohibition of sections meant that the knowledge teached were garbage. We know that the ancient ones did very good operations, but in medieaval time corpses had unsetted broken bones. What's better: Calling yourself a healer was not prohibited.

• Hygiene and sickness: People died on infected wounds all the time. The extremely painful tetanus infection killed many people. Appendicitis was a death sentence. Simply washing and sewing wounds were unknown.

• Bumbling: Bloodletting was the standard (and useless) procedure. If you have diarrhoea, you could expect that they tried to put a cork in the ass... I am not joking. Burns which could be treated with cold water were coated with butter.

• Mouth-to-nose insufflation. You could not believe that even in the middle of the 20th century drowned people were treated with arm aerobic. Alone using that on victims and resurrect someone would be unbelievable.

While having very advanced knowledge, you needed to learn herbology (by practitioners or reading) and chirurgy (probably self-taught: barbers were often competent, but had low social status).

• Medicine is something I have thought of, but besides the basics, he would be just as stumped as the others. He would also need to find proper replacements for modern tools and materials (disinfectant, etc). While these could be managed and he could very well achieve significant improvements regarding mortality, being branded as a heretic could still realistically happen if he wasn't careful enough with his words, methods and patients. Also, while back then death was much more accepted, I think some would attribute the death of a patient to his unproven, mystical ways instead of the disease. – zovits Mar 27 '15 at 6:52
• +1 Many great answers here, but I liked this one the most. Especially (but not only) because it's the only one that takes physical appearance into account. – Chanandler Bong Mar 27 '15 at 8:17
• And just to add something about the clothes - they would look so odd that many people would think of them as very expensive. If he's lucky he would be quickly running naked, if unlucky... well, the same, but not so much running :-) – Chanandler Bong Mar 27 '15 at 8:28
• contrary to popular modern opinion, bloodletting did actually have a couple valid and beneficial applications. Not many, but they worked. It would be better to say mostly useless. – hildred Mar 27 '15 at 22:59
• @zovits - A possible option might be looking for a job as a healer's assistant while figuring out the basics of the society, what methods the locals were familiar with, and how to talk about ideas like hygiene without sounding crazy or suspicious, before thinking about setting up independently. This is more or less my own plan if I should end up in such a storybook situation... although as a female, saying my Da is a doctor might be a better explanation with my partial knowledge (no actual herb-lore, but physical first aid and hygiene) and without stepping on too many toes. – Megha Mar 30 '17 at 4:43

The average human from the 21st Century would do as poorly or even more poorly as the pessimistic answers provided here. Even very smart people with advanced educations would typically not do much better - their knowledge would be too specialized.

I have multiple engineering degrees and interests in many other areas. But most highly technical people these days are way too specialized to be able see a project through from beginning (finding appropriate minerals) to end (fine tolerances of a gun's chamber). Furthermore people with the right knowledge may not be dropped into an environment where necessary resources are present (which of us could find iron ore in England?).

Given some local labor and proper mineralogy in the area, I would eventually be able to smelt high quality steels based upon my geology & metallurgy classes but I likely could not do it without local help and my first several batches would most likely fail.

The same is true for gun powder and gun cotton. I understand the general methods of making these but don't know the proper ratios etc. It would take favorable local mineralogy, chemistry (how many of you can manufacture nitric acid or potassium nitrate?), and some willing local labor to put these things together.

I live on a hobby farm and know moderate amounts of animal husbandry and modern farming practices so I could probably help improve crop yields. But what use is my knowledge of growing melons and corn if I was dropped into Medieval Europe?

With modern wood working tools, I have created my own bow from local wood but have no idea about how to create the bowstring.

Unlike the protagonist of A Connecticut Yankee in King Arthur's Court, I haven't bothered to memorize eclipses from many hundreds of years ago, so that approach is right out.

So I suppose the real answer is on average, the modern man wouldn't do very well but some people might be able to do quite a bit if they were dropped in the right environment (near the necessary resources or otherwise where their knowledge would be applicable).

• Your answer is quite close to my initial thoughts about most sufficiently advanced technologies that could make a difference rely heavily on advancements in other fields that even an expert of the original topic might know only in theory, therefore creating a society of mutual dependence. I have asked this question mainly in order to gather ideas that would either reinforce or in some way refute this preconception, I think it has been an outstanding success so far. – zovits Mar 30 '15 at 6:06
• "How many of you can manufacture nitric acid or potassium nitrate?" I could. You leech it out of horse manure. – AJMansfield Mar 30 '15 at 19:32
• Yeah, I know that's how you can get potassium nitrate, I'm not sure about the nitric acid though. But how many people with those other skills know this? And how many people with access to nitric acid have access to cotton cloth? Cotton isn't available in Medieval Europe. It's a problem of getting the right knowledge, resources, and labor together. This is not easy in a Medieval society. – Jim2B Mar 30 '15 at 23:13
• I'm beginning to think that easier stuff like water wheels & plumbing might be the right place to start. Work on steel, gun powder, etc. later after you get some basic improvements going. Just putting up a simple farm water pump powered by a windmill would be a wonderful labor saver. – Jim2B Mar 30 '15 at 23:17

It might not sounds like much, but you could actually achieve quite a lot, assuming you could survive and convince a wealthy person that you have value.

1. Printing press. This was amazing, and the technology required for a basic version is virtually 0, it was just no-one had the idea first. For mass printing of something, say the bible, you can literally get a cylinder of metal with raised letters on it, cover it with ink and roll it down a page. Want to print 10,000 copies of the bible? Gonna be a lot quicker and more accurate with a bad printing press than by hand. This is widely credited as causing a dramatic increase in literacy rates, as there were a lot more books to read.
2. Weaponry. Forget guns, too hard. What is saltpeter anyway? Crossbows and pikes could be made easily by a time traveler and a couple of bowyers/blacksmiths. This made the poor significantly more even in combat against the rich (although I believe also led to people conscripting larger armies of farmers, and thus starvation) So maybe don't do this? If you wanted to make guns better, you would be best of creating a revolver (easy, all you need is a trigger that makes a hammer strike a bullet and rotates the chamber containing the bullets around. Easy enough for any blacksmith, and then when someone who knows chemistry comes along and discovers gunpowder, all they need to do is package it into bullets and you have advanced guns significantly.
3. Trains. Coal (I assume most people know of an abandoned coal mine?) gets burned, which heats water, which turns a fan, which turns an axle, which turns a wheel which runs along a metal track. Congratulations, you have revolutionised transport.
4. Science. Most people know enough science to help significantly. They would need to write down hundreds of facts that they learnt off the news, and run thousands of copies through the printing press they built. This is because 99% of these books will be burnt for heresy. After several of your scientific declarations are proved, people will start to take the rest seriously. Most people with a high school education would be able to; point out that light is a wave and a particle, if anyone doubts you, suggest they pass it through two slits and look at the interference, recommend pea plants as a good simple thing to look at when considering evolution and determining the difference between dominant and recessive traits, give scientists confidence that if they are looking for a particle that gives everything its mass, they just need to build a bigger circular ring and accelerate particles faster. Point out that matter is not made of plum puddings, point out that God does play dice with the universe, make the statement "lets assume that all observers see light at a constant speed relative to themselves, and thus time must dilate, length must contract, and mass must dilate." A mathematician would be able to go from there to relativity, relatively easily. Introduce the periodic table and fill it as far as you can remember. None of these would be useful immediately, but they would be extremely useful for the next 500 years.
5. OH&S - Give some dire warnings about the end of the world - asbestos, CFCs, CO2 emissions. As you are now the most famous scientist ever, people will listen to your warnings, even though you are long dead.

1. Other engineering stuff I thought of now. Abacus (assuming you land in Europe and not somewhere it already exists), penny-farthing bicycle (no need for rubber wheels). There are a lot of inventions that you could vaguely discuss/draw picutres of, which would assist real inventors down the track. As with almost everything I have suggested, it would help years after you were dead. I'm trying to help humanity, not the time traveler. Trebuchet (just a catapult where the rock is in a sling attached to the end of the arm), the concept of arch/suspension bridges. Arguably, you could invent a relatively decent typewriter, although it might end up breaking too much.

2. Health - propose washing of hands, eating lemons to avoid scurvy, moving latrines further from food preparation, and recommend people investigate moldy bread to prevent infections. As with science, all of this will be ignored immediately, it just means that when one of these things is accepted, all the rest will be investigated.

3. Extremely modern stuff that you could describe, write about and draw, thus cause to be invented a bit early. The roller-ball mouse, airbags, dvorak keyboards, snuggie

• The printing press is a genius idea, I really haven't thought of that. While trains and revolvers might prove too problematic (due to the lack of metalworking skills and general low precision of the age), writing down his basic facts could very well ensure his going down in history as the greatest scientist ever. The catch is of course this would mostly happen after his life, so it would be the ultimate case of misunderstood genius. – zovits Mar 27 '15 at 6:34
• Also, there is a subtle catch in your point #5. He can't just write "Do not use asbestos", because people at that age wouldn't know what it is. His warning would only create a fear of something called asbestos, without a mental link to the material itself, possibly giving roots of various superstitions. He could of course explain the concept and give ample reasoning why it is dangerous, but first he has to think of it :) – zovits Mar 27 '15 at 15:45
• Really nice job; +1. I do object to "point out that God does play dice with the universe", because that was just Einstein getting rather annoyed at quantum theory. – HDE 226868 Mar 28 '15 at 21:38
• The pike is basically just a long spear. I doubt mediaevals needed time travelers to point out the idea. Also, why on earth would most scientific facts be considered heresy? There's a lot of simple chemical concepts that the traveler might be able to introduce, such as the concept of chemical elements, compounds, and knowledge about which substances are which. – zeta Mar 29 '15 at 8:16
• Also, I was just thinking that while crossbows existed in medieval times, longbows were much faster to reload. The problem with a longbow was the skill necessary to aim accurately while keeping it under tension. Today's compound bows use fancy modern materials, but even with medieval technology I would think the principles could be used to fashion a compound longbow that would could be used accurately by a much wider range of people. – supercat Mar 29 '15 at 17:56

There are many low tech inventions, and conceptual frameworks that could turn the tide of a war or make a person rich.

## Scientific method

The idea that you can understand the world through iterative experimentation comes from the enlightenment. This is a powerful framework in which to work.

## Bicycles

Constructing a simple bicycle requires a decent knowledge of ironwork. An army equipped with bicycles could cover 100 miles in a day and arrive fresher than an army which has marched the same distance.

## Batteries

Construct a battery from steel and copper plates plus lemon juice. stack enough of these together and you might even be able to create an arclight.

## Carbon Steel

Cast iron is brittle. The addition of Carbon atoms, readily available from wood makes iron much stronger. Take your molten iron and chuck in some branches. Presto, your swords are sharper and stronger than the warlord next door.

## Generator

Generate electricity by spinning a magnet in a copper coil. A piece of magnetite should do the job. This also possibly opens the way to induction hardening.

We don't know for sure when people first realised that a piece of magnetite floating in water would align itself north-south. It may have been as late as the 15th century. A magnetic compass would provide an obvious advantage to anyone wishing to navigate on a cloudy night.

## Crossbows

Crossbows are simple powerful, quiet weapons. The man who invents the crossbow would be put in charge of many things.

## Kites

Kites are simple to construct. A large enough kite can carry a man, giving a medieval warlord superior scouting capabilities.

## Central heating

The Romans knew about this, it's not hard. Have a slave heat water in a boiler, then pump it under the floor. A nice warm house for a nobleman.

## Plumbing

Water can be transported from place to place via a lead pipe. A low tech solution that makes a fashionable nobleman's life better, until he goes mad from lead poisoning of course.

## Cryptography

Medieval codes were simple substitution cyphers. A modern person with a basic knowledge of probability ought to be able to crack such a code with ease, and could easily come up with a stronger code.

## Triangular sails

Medieval ships had square sails which meant they could only move if they had a following wind. More modern ships have a triangular sail with a swinging boom, plus a deep keel. This means they can sail across the wind and tack into the wind. The advantages here in terms of warfare and commerce are obvious.

## Mechanical loom

A mechanical loom can be constructed from wood. With a little thought our modern human might be able to work one out.

## Ball bearings

Ball bearings dramatically reduce the friction in a wheel. A coach or chariot equipped with ball bearings can move faster with the same number of horses.

## Sprung suspension

Stagecoaches used a large metal spring on which the coach itself was suspended. A simple innovation providing greater comfort for travelling royalty on bumpy roads.

Slightly trickier this one, but presumably long sightedness among older people was an issue in the middle ages just as it is today. Glass was available in medieval Europe. Given time and persistence it could be shaped into a convex lens of great value.

A convex lens can also be used to start a fire in sunshine, which presumably would have looked like the most extraordinary alchemy.

## Burning glass weapon

A large concave mirror made of polished metal can concentrate the sun's rays on a target, perhaps a ship, a siege weapon, or an enemy general. A burning glass may have been used by Archimedes as early as 212BC. Of course you would need sunshine for it to be effective.

## Printing press

Books were expensive. The concept of movable type would not be hard to replicate. A person with a printing press could be rich.

## Zippo lighter

An oil soaked rag in a metal box, plus a flint and steel. Magic instant fire in the palm of your hand.

• Postal service safe and secure how? – Pimgd Mar 30 '15 at 11:48
• The postal service as an idea didn't exist in mediaeval times. Making it secure would be an implementation issue. I would suggest big men with swords would be a good option. – superluminary Mar 30 '15 at 12:35
• @superluminary - postal service existed as far back as Roman Empire. The trouble in medieval times was that there was no market (people with the means and the need to communicate already used messengers). – user4239 Mar 30 '15 at 16:39
• Bicycles aren't that useful without roads. – Oldcat Mar 30 '15 at 18:04
• You can make a bicycle out of wood - no need for metal. – AJMansfield Mar 30 '15 at 19:35

John Doe would know some very important facts.... he would be able to draw a map of the shape of the world freehand. He would know where the largest oil deposits in the world are and what oil can be used for. He might know where the largest Gold deposits and diamond deposits could be found. He would be able to predict the future to some extent. Every place he went he would see people doing things in ways that could be improved.. printing presses, looms, plows, dams, mills, etc. He would make alliances with kings and probably become so powerful he would be get himself beheaded.

• While I agree with you in the regard that he knows these, would any of these be reasonably achievable for a commoner in the middle ages? He knows the rough layout of the continents, but he has no ship, no crew, no funds for an expedition. He knows where oil can be found, but he is far from the middle east, has no obvious way of getting there, no means of getting land ownership there, but most importantly no use of oil for several hundred years. With diamonds he might know that central Africa would be the palce, but then the concrete location is still unknown, besides the "getting there" part. – zovits Mar 27 '15 at 14:27
• For technological advancements, he would certainly have many ideas, but he can't get them implemented initially due to lack of skill, tools and trust. Maybe when he has his reputation established, but even then, he would most probably fail lots of times, and engineering failures tend to be costly and maybe dangerous. I can still agree wholeheartedly with the last part, he would need to be cautious and not draw too much attention if he wishes to keep his head in an age when jealousy and heresy could easily end his life. – zovits Mar 27 '15 at 14:32
• No one starts out with a reputation. It is built over time. As he travels, he will need to work to get food. As he works, he will not be satisfied toiling in the muck with stone age tools. He will create tools. He will engineer processes. He will leave behind him a wake of new inventions. His expertise will become more valuable. He will eventually gain audience with the royals. And, he has seen enough movies of the period to know how to keep his head. – Jason Williams Mar 27 '15 at 15:48
• Do you know where gold and diamond mines are? Not something vague, like "I think somewhere in southern Africa", but precise enough that you could actually lead someone to the spot and dig up some gold and diamonds? I certainly don't. – Jay Mar 27 '15 at 21:53
• You probably know if you went to Alaska, you would be able to find a big river with loads of gold. If you went to South Africa, you could ask the locals where the transparent rocks come from. But, if you are asking if I personally know where some Gold mines are, then, yeah. I could take you there and show you where to dig... Gold Hill, OR or Virginia City, MT. But, I am not John Doe. Not sure if John Doe would know what I know. He would have other info. Maybe better. Everyone does. – Jason Williams Mar 27 '15 at 22:54

Yes he will, but don't expect anything fancy. I'll try to explain why. First, even if he had his gadgets on him, they would either not work (e.g. no Internet to look something up on his smartphone) or would not work for very long (i.e. no power to (re)charge the device). So, John has to work from memory to get things done.

As you postulate, John isn't very skilled at anything in particular so he would need others to help him. Charity used to be something very different from what is nowadays considered to be the least one can do for another, so John doesn't have to count on anyone helping him getting food, shelter etc. He needs to have or do something to earn it. He will not be able to build something to aid him in his quest for his basic, everyday needs, so he will have to put his knowledge from the future to good use. As he only knows some high school topics (and probably not with a great deal of depth or precision), he will not have some "magic knowledge" readily at hand to make people stand in awe. He will not have or be given the time to experiment with what he remembers to get something.

What he can do, is get a job like anyone else. Working as household staff or joining some noblemans private army will get him a roof over his head and food. It will not be a live in luxury.

I really see only one way out for him to use his knowledge to acquire wealth and fame: if he is able to whip up something that can be used as a weapon, that will give him a chance to win over the favor of a nobleman. If he succeeds at that, he might survive.

• The smartest move would be to declare yourself as a pligrim on the way to some moderately far off holy site. Then most would feel obligated to give some aid along the way. – Oldcat Mar 26 '15 at 18:45
• @Oldcat: That has the advantage of explaining your poor command of the language. – Charles Mar 26 '15 at 20:23

Lets say this guy gets past the first hurtles of surviving. Finds a place in a village where he can live a life, although a short life. I think this is perhaps the crux of the question, the guy arrives, settles in for a time, ponders what he could do to change the world with his advanced perspective. What could he possibly come up with, given the lack of resources and technology of the time he found himself in?

The printing press is the thing. Easily built by a dedicated hobbyist that has been able to secure a few connections with a furniture maker, maybe a black smith and a supply of lead. To the basic machine, improvements would come later. We know it can be built at the time in question, because it was.

Knowledge is power, but knowledge is useless if there is no medium for it. The most talked about thing in Western history is Martin Luther's thesis, and how everything changed in the religious world when he posted them on the door. Luther did not have an original concept on that door. John Calvin pretty much had said everything Luther posted a century before.

I believe that it was about a half a century after Calvin's time that Guttenberg invented the printing press and the another five decades before Luther posted the thesis. During that time the printing press was catching on. Literacy rates were climbing, more people had access to printed material. In towns mass advertising was beginning to appear (Yes Spam!). All the things that helped Luther become the father of the reformation were in place.

The reformation was the biggest, but by no means all that was going on. Knowledge was being recorded and much more widely distributed with each passing year. This spread has not stopped the Internet and SE being direct descendants of the Guttenberg printing press.

It is said that the ancient Greeks were on the edge of an industrial revolution, but then the library burned, no back ups, no redundant storage, information was not widely known, most of it was lost. If they would of had a printing press, who knows we might be in the dark ages now having ran out of oil a couple of thousand years earlier.

All the things that came after the printing press if not made possible by the printing press they certainly made more practical. Everything simply changed and became more accelerated as the flow and archiving of knowledge increased. The invention of the printing press marks the beginning of the modern era, without that acceleration in the archiving and dispersion of ideals, invention, communication etc., we would still be in the dark ages.

The guy would likely die in obscurity, start ups at the time being pretty rough. That's one thing he could put together to change everything.

• I think the printing press and movable type would be the lesser problem, proper ink being the main one – and lack of paper, of course. – Crissov Dec 13 '15 at 21:25

Most of the other answers here present suitably pessimistic assumptions, but you should remember that you do not have deviate that far from normal to invalidate your core assumptions. For example if my uncles were sent back, they would do just fine. D is a blacksmith and shepard, is building a bloomery and an accomplished storyteller. S is also a blacksmith best known for his decorative work and an instrument maker. My father would either become a well respected teacher or killed by the catholic church for his knowledge of the scriptures. But for some real outliers, just step back a generation. My paternal grandfather built a crane from scrap, cut gears by hand and was an acceptable farmer. On the other hand my maternal grandmother would have been burned as a witch.

Let's assume he lands near a village. First off, since he has no clue that he's just time travelled, he will try to figure out what is going on. After several failed explanations, he will try to communicate with the locals, who will consider him half-mad, one, for the lack of language skills, and two, for asking stuff like "Do you know where I came from?" or "What is this place?". He will take a lot of time (if he didn't take history lessons) to realize that he has, in fact, time travelled.

After that, he can either try to convince the people that he is from the future (which will lead to him being laughed at and considered totally mad) or he can accept the fact that he has to live there for the rest of his life. He will have to learn the ways of the people, including the language, the culture, and get to know their level of basic understanding of science. Having a high school level education might be of some help. But that is just a possibility. Most probably, if he tries to teach the locals science, no one would even bother to pay attention (because he is considered mad). However, it could happen that for example a travelling local discovers a new fruit from a new land (which is widely available in modern times) and our hero predicts it's taste and other properties. That would hardly be enough for the locals believe that he isn't mad, though. After a series of events like this (very improbable) maybe the locals would start to listen to him.

Still, as mentioned in other answers, building his own weapons and tools would be hard because of his lack of smithing knowledge and/or unavailability of the proper materials. Applying his high school knowledge, thus, would be very difficult. Assuming everything goes his way, he will find a person that knows how valuable he is. If that person is 'good', he will help our hero with whatever he wants to do (example taking up some job or writing books, as mentioned in other answers). If the person is 'bad', he will lock up and torture our hero and will gain as much information as possible and credit it all to himself. In the end, our hero will either be dead, tortured to the brink, gone insane, or, in the best case, be doing well.

This is all assuming that he doesn't die/get injured of other causes first, like diseases and/or war.

Seems like a terrible omission to not include the wonderfully funny work of Dara O'Briain (4min video)...

In short, we'd be useless even if taken seriously!

While we're great users of modern technology extremely few people know enough about what we use everyday to be able to guide someone trying to recreate it. Dara works this by explaining that even if we know how our computers and toaster etc... work we draw a blank at what happens after they connect to "the wall".

• Updated, better? – Daniel Mar 30 '15 at 3:19
• It is a funny video and relevant to the question, but I have a feeling that if John tried a bit harder, he could remember things about electricity, plumbing and maybe the operating principles of several modern inventions. A car can be explained by telling that there are many tiny explosions in a strong metal box that rotate the wheels through pistons and cogs. This explanation can be taken by a genius designer of the age and made into a crude design. Of course the available precision doesn't let it work, but still. The problem of getting enough credibility to talk to a genius is there though. – zovits Mar 30 '15 at 5:56

Presuming weve got past the language / culture / disease issues mentioned in other answers, you might be able to do demonstrate something useful with electromagnetism.

Even without any hands on experience, anyone one with a reasonable high / secondary school education should have a basic understanding of the key concepts.

Iron would be relatively easy to get hold of, copper aswell. Providing you can find some way to create copper wire, fashioning a basic electromagnet should be relatively simple.

Getting a relatively constant supply of electricity would be more complicated, but linking up your electromagnet to a rotating wheel would at least allow you to prove the concept. Provided the locals dont decide to burn you as a heretic, you should have attracted enough attention!

• Getting some metal wire wouldn't be very hard, but getting insulated wire suitable for creating a strong enough electromagnet that can be used for anything more serious than being branded as the devil's accomplice. Uninsulated wire or core would just result in short circuits and lots of heat. He could get electricity from wet piles, provided he finds a way to support his "hobby". – zovits Mar 27 '15 at 15:41
• I think the metal wire would be harder than the insulation, Even for a significant time into the twentieth century the normal form of insulation was woven cotton; I would think that if one had a length of wire and some spools of thread, one could hand-wind the insulation well enough to be usable. – supercat Mar 28 '15 at 22:04
• What would be the point? With enormous effort, you could perhaps make sparks, but a telegraph would require miles of copper wire, let alone more elaborate electrical devices. – user243 Mar 30 '15 at 16:52

I suspect surviving in this situation might be easier for someone without a high school education, a child. Providing someone picked them up and cared for them (I think this much more likely for a child, children were valued for manual labour), they could grow into a normal medieval adult. Children learn quickly, and often more readily except things they don't know, so I think a child might be able to adapt to this situation much easier than an adult.

I think there is less chance of a child being seen as a witch, or knowing too much that they get on the wrong side of a noble.

Obviously you do have the problems of children being less resistant to disease, wanting mummy, etc.

(Perhaps this is not what you were imagining in answering the question, but maybe it was interesting)

• Yes, a child is much more flexible and moldable by external forces, making the situation much more predictable. His / her life wouldn't be a lot more different than of every other children (of the same sex), maybe apart from a lingering dreamlike memory of a strange world throughout adulthood. This could in theory make our protagonist a prophet, speaking of the coming of a world where buildings reach the sky, everyone has magical boxes that can do wonders, metal chariots roam endless roads and huge birds cross oceans with people in their bellies. Others would find this entertainingly crazy. – zovits Mar 30 '15 at 5:45

If our time-traveler is a fan of Dinosaur Comics, there is any chance they have a copy of the Time Traveler Cheat Sheet either memorized or printed out and stored in their wallet. Assuming the latter everything will go great, they'll be "inventing" and "discovering" all sorts of useful stuff until one day a jealous cohort will notice them looking at their cheat sheet, realize it is the source of their "power" and kill them, steal the sheet and take their place as the provider of awesome anachronistic newness!

• While this sheet is nice, there are lots of subtleties. Right there it admits that finding magnets is a bit hard, and nearly every other thing requires lots of manual work, therefore lots of time or money to hire craftsmen. Also, nothing really goes right on the first try, and there are lots of tiny details that make or break an invention. While it is true that a certain mold produces penicillin, good luck isolating the exact kind and finding the right dosage that does heal but does not kill. All in all, it is a good summary, but only a summary. – zovits Mar 30 '15 at 15:45

He could have a profound impact If he established himself to the point where he become known as a learned individual.

If he was able to source metal and magnets (both of which are available), he would be able to at the very least demonstrate and create short range electrical signal system.

If he paid attention in high school physics he should be able to be a huge teacher of basic math, and even calculus, surpassing easily the smartest scholars.

I'd he paid attention in physics, he should be able to derive Newtonian mechanics, which would have a profound impact on builders no longer having to build by trial and error at full scale.

His biggest impact would be in health. Simply knowing about germs and washing hands, boiling things to clean them, or before surgery, segregating those coffing/sick covering mouth etc. Would have a profound impact on the spread and rate of sickness.

If he knew principles like how to conduct double blind experiments, he would certainly leave a foundation for renaissance, as he would be able to prove things to people.

Even basic things like using metal tools for farming was not done in the middle ages because people were worried about poisoning food, no one ever thought of testing it though, it was superstition that didn't break until the American revolution!!!

I think he could have a profound impact. He would need to keep all this uber his hat until some community accepted him. And he would need to roll them out in a way where it was seen as natural and beneficial.

• As this answer pointed out, the contemporary reaction to Ignaz Semmelweis rather argues against the effect a lone individual might rapidly achieve "simply by knowing" about germs and washing hands. It also argues against the effectiveness in "proving something" to people who have fixed ideas contrary to what you are demonstrating. – Wildcard Aug 27 '16 at 1:11

He might be able to make a go of things if he knows foreign languages, such as Spanish, French or German (if he is an American it is unlikely that he would have learned Latin).

Although these languages will also be very different from their current versions, he will still have the ability to communicate with foreigners, such as merchants and sailors or foreign mercenaries. These are skills which the nobility and various guilds will be very interested in, and constant application and practice will improve his skills rather quickly.

• Why would he be any more interesting than people of that time who already know the contemporary versions of those languages, and are probably better at speaking them? It's not like learning foreign languages is a modern advantage. – zeta Mar 29 '15 at 8:24
• I'm American, and I know Latin... – Jimmy360 Mar 31 '15 at 5:13

Many answers have told the pessimistic view. Since I don't know exactly the year which he arrived, I guess he could do/teach the following technologies:

• hot air baloons

• steam machines

• steel and nitriding steel

• gunpowder (he might not know the exact composition, but might have some idea which would accelerate experiments to build it)

• galvanic cells

• radio trasmission (using sparks from galvanic cells)

• advanced mathmatics (one doesn't need to know by heart all the values of sin(), cos(), if they know how to calculate them)

• I'm afraid many of these depend on either specific knowledge (e.g. I don't even know what is "nitriding steel") or the tiny details (getting saltpeter, fabricating an airtight seal, machining a piston with the right tolerances) so his ideas would be hard to implement even if he manages to find an understanding audience and the necessary resources. I'd be gladly proven otherwise (I really don't know how difficult was it to create an airtight piston back then), but until then I'll remain sceptical. The hot air balloon is a neat idea, I haven't thought of that yet. – zovits Mar 31 '15 at 18:10
• Yes, that depends a lot on what your "average" man knows. And the time-traveler wouldn't know the exact details, but he would have a better knowledge than many at that time. It's much easier to build steel when you know that it's made of iron and carbon, even if you don't know the correct %, than not knowing it. The same to steam, gunpowder, galvanic cells... – woliveirajr Mar 31 '15 at 19:59
• Or, put it another way: perhaps you don't know that penicillin comes from a specific fungus. But knowing that penicillin exists and comes from some fungus gives you a great advantage. The man won't have some immediate benefit, but he knows what he is looking for and have some clues on where that will come from. – woliveirajr Mar 31 '15 at 20:02

The average human did not live to adulthood. Just by being around, he's not average, but lucky, fortunate, and skilled enough at surviving. The last item is still important even if you postulate that an adult popped back in time without having to survive up to that age in that environment.

Knowing how to use a crosswalk safely in a busy urban center, the emergency services phone number, how to use credit cards wisely, etc. will not help continued survival. An average random person, even after removing those who died from disease or poor fortune, does not survive. One has to develop skills for surviving in that environment, and your traveller will be rather poor off in that regard.

• "even if you postulate that an adult popped back in time without having to survive up to that age in that environment" Yes, this is the basic premise. John Doe was born in 1980 (or so), lived until 2015 and was somehow transported back to the medieval ages with his skills, memories and body. Most of his learned skills are not usable there, since they depend on the work of other people, tools or information sources. His manners are suited to a completely different world. Even his language is more or less different. How could he survive, establish himself, maybe even become famous? – zovits Apr 1 '15 at 13:25

From another perspective, there are many novels which explore how to bring primitive humans up to "modern" or even more advanced technologies. One such example is the Safehold Novels.

In the case of these specific novels, the protagonist has many non-primitive resources to fall back upon to aid in his advancing the primitive culture. However, other novels using different assumptions are available.

In Earth Abides, the protagonist attempts to first bring primitive technologies to the survivors and then help them advance.

I suggest exploring the available fictional novels available for various treatments of the issue.

• In Safehold, the protagonist has the high-tech with him and is trying uplift the world. A lone time traveller would not have this advantage. – Oldcat Jul 20 '15 at 23:55

Rock and roll star (yes, I'm serious here!)

He probably doesn't remember any of the formulas for useful medicines or inventions, but he DOES have a recollection of centuries of popular culture which he has consumed his whole life. He probably couldn't recreate movies in play form (though on second thought, that would be pretty cool), but he can rework popular songs to suit local (temporal) tastes. He doesn't really even need to know much about music, just find a minstrel and hum him the tunes. If this works, he could even end up with royal patronage like Mozart got (this guy probably recalls some Mozart, so this isn't too unrealistic).

Your modern basic understanding of how things work would put you under continuous stress to play dumb. Any exhibition of superior intellect would bring immediate suspicion from those you try help. You would either be killed or jailed as a heretic by the Church or nobility or burned as a witch by ignorant locals. Ultimately it would be living conditions that would do you in. You would be unable to eat without contracting some food bourne illness like cholera. General lack of sanitation would expose you to plague,tuberculosis,flu,pox...etc. If you managed to avoid those things, your best hope would be to gain the favor of some noble by mastering the improvement of some of their weapons if your level of knowledge would permit that. As a peasant, your access to the nobility to even accomplish this would severely limited.

• Could you explain why this is? At the moment this answer is just a set of statements without much explanation: if you can add some, the quality will improve dramatically. – ArtOfCode Apr 4 '15 at 21:21