Let's Say You've Gone Back in Time

April 14, 2009 9:16 AM

What knowledge would a time traveler find most useful in uplifting an ancient civilization or establishing personal wealth?

I came across this poster a few hours ago, which details what a time traveler in the vein of a Connecticut yankee or archaeologist would find useful.

The list interests me, but I know that the chemistry information at least is incomplete (ie. Knowing some isoform of C20H26O2 is a birth control is meaningless, but bauxite isn't described). Pasteurization and waterwheel -> electricity are examples of the list's strengths.

So, what snippets of scientific information would be good additions to this list? Anything that would improve the ancient society or the traveler's place in it is fair game, provided it can be applied with the tools on hand, or is readily available from simpler knowledge (nuclear fission is out of reach and e=mc^2 useless).

For the purposes of this question, assume the traveler arrives sometime around 200BC in the Mediterranean, with no tools or books. Knowledge of the particular political climate isn't important, I'm more interested in the technology.

posted by Orange Pamplemousse to science & nature (46 answers total)

Germ theory.
posted by kldickson at 9:18 AM on April 14, 2009

That's already on the list, first line beside "Health".
posted by Orange Pamplemousse at 9:22 AM on April 14, 2009

Scientific method.
posted by kuujjuarapik at 9:22 AM on April 14, 2009

In addition to knowing one should wash oneself (listed on the poster), one might also want to know how to make soap.
posted by yohko at 9:24 AM on April 14, 2009

assume the traveler arrives sometime around 200BC in the Mediterranean, with no tools or books

Ancient Greek would be helpful.
posted by Civil_Disobedient at 9:26 AM on April 14, 2009

Stirrups. The Romans didn't have stirrups. With stirrups, you can have heavy cavalry.

The longbow. The compound bow.

Arabic numbers, including 0. Simple to teach, simple to learn, much easier to use than Roman numerals.

The axle. Roman carts couldn't turn.

A general sense of where the continents are, and where the Mediterranean climates are to be found in them. Found the first Roman colony at Cape Town, and you're off to the races.

The lateen sail.

Ocean currents. Crucial to sailing in the Atlantic; barely present in the Med.

Has the arch been invented yet?
posted by musofire at 9:30 AM on April 14, 2009 [3 favorites]

How to make a telescope. I seem to recall reading (thought I don't remember where) that decent telescopes could have been made with the technology available centuries before they actually were.
posted by DevilsAdvocate at 9:35 AM on April 14, 2009

The moldboard plow and the horse collar. Those revolutionized agriculture in the Middle Ages.

The flea vector in plague. The mosquito vector in malaria.

Smallpox vaccination via cowpox.

The formula for gunpowder (and how to extract saltpeter.)

The trebuchet -- easy to build, not invented until c. 14th C.

The catamaran.
posted by musofire at 9:35 AM on April 14, 2009 [1 favorite]

Religion tends to be science's older brother. What we understand and can control doesn't scare us, hence religion doesn't need to help us deal with it. 200BCE we're still doing polytheism and the like, so look to the gods people worship (sun, war, underworld, etc.) for examples of what enlightenment you can bring. For the sun setup an eternal flame in a room with vents that don't allow light in and grow plants by the light of the flame to show it is just a big flame in the sky but doesn't burn us, so it's ok. For War do projects in psychology. Demystify death by showing the weight of dying person/animal/plant doesn't change when they die. Show how composting creates great fertilizer and thus the circle of life. The flame experiment helps with this. Death+sun=rebirth.

For profit do all this to show you control these things and are therefore a god. Deny knowledge on how you did them, just show the before and after. Be prepared to deal with folks that see you as competition for power. Most will try to kill you very quickly.

The merchant route might also work. Use projects designed to uncover "new" knowledge people can use in their daily lives and have them pay to access it, get rare materials from you, etc.
posted by jwells at 9:35 AM on April 14, 2009

How to build good sewers.
posted by edd at 9:36 AM on April 14, 2009

I like musofire's examples, but agriculture was pretty important too.
Crop rotation
Cross-breeding favorable types of plants
The plow.
The compass.
GPS (just kidding!)

Just be careful not to be accused of witchcraft, or whatever the period equivalent would be.
posted by JuiceBoxHero at 9:40 AM on April 14, 2009

Generally any sort of more advanced projectile weapon. A zip gun would blow most past peoples' minds.
posted by Inspector.Gadget at 9:41 AM on April 14, 2009

The piston made steam power useful. The Greeks knew about steam, but couldn't do anything with it because they didn't have the piston. With the screw propellor, you can then make steamships.

The windmill.

Distillation. (THAT will go over big time.)

The Vauban-style star-shaped fortress.

The limited liability company.

Morse code (for communicating via smoke signals / signal fires).

The canoe and kayak.

The hot air balloon.

(The overshot water wheel has probably already been invented, and they definitely had soap.)
posted by musofire at 9:42 AM on April 14, 2009

Gunpowder's not so hard to make. A decent firearm is hard to make, but you could make small bombs.

I think Greece c. 200 BCE would be up to making paper from textiles and a Gutenberg-style movable type press with metal type. That'd be huge.

Simply knowing where there are valuable metal deposits, like the silver mines at Joachimstal, could be useful.

Knowledge of math and astronomy might be useful to impress the local intelligentsia, but of limited utility for its own sake.

The lateen sail hadn't made it to Greece at that point. Navigation by compass didn't exist yet, and cartography was crude -- projections useful for navigation (and a jump on knowing the world's geography) could make a big difference.
posted by Zed at 9:48 AM on April 14, 2009

This article from Marginal Revolution is chock full of great stuff. Targeted to 1000 AD, but still good. Amazing way to kill a few hours at work... if you're into that sort of thing.
posted by jasondbarr at 9:49 AM on April 14, 2009 [3 favorites]

Ah yes ... and cryptography. The Romans had substitution codes, but not multi-letter substitution codes.

Actually, ancient mathematicians could have handled public key cryptography, using short keys. Take PGP to Julius Caesar and he'd know exactly how valuable it was.

But if you really want to change the world -- reveal a popular, evangelizing religion. Religion can be regarded as a "technology," setting aside its truth value. 200 BC was a fertile period for world religion, and people were ready for something new. The major religions had drawbacks -- Mithraism was only for men, Judaism only for Jews, few of the elites really believed in polytheism. It's no accident that Christianity exploded when it did. Just stay out of reach of the authorities until you can convert them.
posted by musofire at 9:52 AM on April 14, 2009

For personal wealth, you want something that you can produce that people will want, and more importantly understand that they might want it. Finally, it needs to be something your could actually do. It's fine to know that sewers are important, for example, but how are you going to build them? Do you know how to build a stone arch, dig trenches by hand without having them fall in, how to build a water-tight pipe with only wood materials?

So, some simple things, that one or a few people could do to make (a lot of) money:
- Paper making. If you can make a high quality paper to compete with vellum, you could be very rich.
- Printing. If you can figure out how to set lead type, you've changed the world 1600 years early.
- Weaving, especially if you can figure out a pattern loom. There's a lot of money to be made in textiles in this time period.
- Dyes and mordants: if you can make bright dyes that are colour-fast, you'll clean up. Petroleum is available in natural seeps around the Mediterranean. Aniline dyes should be doable if you know some practical chemistry. That same infrastructure can be used to kick-start drugs too (aspirin, for example).

Knowing where minerals are isn't really useful: mining technology isn't up to the task without an industrial revolution. Also land ownership is closely related to who has the biggest gang. Gemstones, though, are possible to collect by hand on the surface. Northern India for emeralds, Africa for diamonds.
posted by bonehead at 9:55 AM on April 14, 2009

If you're looking for your first stake -- study the probabilities of various games of chance, and play the odds till you're rich.

Or, invent Texas Hold'em.

Also, invent the (sheep-gut) condom and the (copper) IUD.
posted by musofire at 9:56 AM on April 14, 2009

Boil water before drinking it.
posted by Cool Papa Bell at 9:58 AM on April 14, 2009

The hardest part about this time travel is that you'd be arriving with no starting capital. You'd be a tall barbarian, whose accent would sound like reeeeeeally messed up german to the people you met, if you knew the language. Boiling and washing is all very well and good, but with no tools you can't do either until you get your homestead established. Or I guess you could rent a flat in Rome, depending on where you landed. Arrive with an immunization to a bunch of the third world parasites and be ready to get the trots anyway, seeing as the bacteria would be a bit exotic. If you can bring clothes from out of period, wear two layers of socks (so you have a change if you need it) and some sturdy hiking boots, as well as your work clothing.

I would guess that knowing how to mix various building materials (cement, etc) and primative blacksmithing would work. You might not have tools, but if you knew the right mixture to make cement from scratch and landed in an area with the right sort of lime and other matrials, plus you knew about building a forge, you could hook up with the short little metal workers of the area and help out with you huge western diet induced frame until they let you tinker with their stuff to improve it. The Romans were pretty sophisticated, so if you took up with them, you wouldn't be a voting citizen, but you could always eke by.

You could become a tutour, if your knowledge of ancient languages and things like math were sophisticated enough. You could arrive with a head of long hair (take prenatal vitamins before you leave?) and sell that too.

200 BC is also a good time to carve yourself some moveable type out of wood, and once you had the captial, get the local metal casters to make you a lead alphabet. And you could probaly make some cash sellying people stamped illustrations of themselves to give to all their friends and family. If you knew how to build an industrial level grinding machine you could get paper off the ground early... though in 200 BC you could still count on papyrus.

Early industrialization would probably be a good idea once you could afford some slaves. With the printing press brinnging in cash, building some early industrial weaving looms could help fill your pockets.

Invent the reaping machine early (called a valus). Those don't come along until AD, and until that point grain would be harvested by hand. You could also probably build primative wind/water mills, and gradually introduce modern engineering knowledge.

A modern medical degree could also help. Surgery in that era was a little hit or miss, and if you knew how to refine poppies into morphine and take out gallstones, there'd be some very, very happy Roman upper class showering you with sestertii. Ditto midwifing, if you were the right gender and could handle epitiotomy that didn't kill the patient half the time.

If you're good with your hands, you could try clockwork. You already know the basics so you wouldn't have to reinvent the grasshopper escapement, just know how to build teeny parts. With a clock you could improve navigation and have your trading vessels reach far and wide.
posted by Phalene at 10:03 AM on April 14, 2009 [2 favorites]

Gunpowder + Metalworking = Artillery, Guns = Military domination

How to Build a Clock + Sextant + Your Mental Globe + Artillery = Longitude, Latitude, Cannon = Naval Dominance, Colonization, Control of Trade

Crop Rotation, Composting, Hygiene, Penicillin = Plenty, Population Growth, Social Stability = Superior Nation/Culture to those surrounding you

Knowledge of ancient mining sites = monopolistic control over precious/useful metals = vast wealth.

Knowledge of route to India/The East = Mercantile Opportunity (should you base yourself in Europe) = Vast Wealth

You could also preempt Jesus or Mohammed and create a tide of religious fervor to carry you to wealth and power.

I'd be tempted to go with either China, Rome, or The Seleucids as my base of operations.
posted by Any Moose In a Storm at 10:04 AM on April 14, 2009

The split axle. Roman carts couldn't turn.

Just needed a little edit to musofire's entry. Romans had a straight axle and that's why their carts couldn't turn well. Of course to get the strength of a strait axle and the turning of a split axle you could just "invent" the four wheeled cart and have the front wheels pivot with the horses.

Some of the stuff on that poster is a waste of time. Why do you need to build radar or sonar in times before powered flight or warships with the capability of attacking out of visual range?
posted by Pollomacho at 10:14 AM on April 14, 2009

Now, anyone want to speculate what 30,000 people from an advanced technological society might have been able to teach human beings at about 150,000 BC?
posted by musofire at 10:16 AM on April 14, 2009 [1 favorite]

Phalene: The hardest part about this time travel is that you'd be arriving with no starting capital.

I think all of the "invent X years before you're supposed to" are all well and good, but you'll have a hard time because of this excellent point.

Far more useful, IMO, would be an understanding of things like military tactics and the assembly line.
posted by mkultra at 10:18 AM on April 14, 2009

musofire: Arabic numbers, including 0. Simple to teach, simple to learn, much easier to use than Roman numerals.

Rome was not by any stretch the dominant culture in the Mediterranean in the second century BC. It took political power in that century, but the Macedonian empire was still having its effects even in its decline. In fact, even for the Romans, Roman numerals were significantly different in that century, given that they were still similar to the old Etruscan tick-marks from which they developed; and, while the Macedonian Greeks used a similar system of tick-marks, starting in the second century they also used the system which they still used today, a good, simple base-10 system based on their alphabet. In fact, the lowercase letters actually came from this number system, which consisted of smaller versions of the standard system of capital letters. (This is also the source of the order of the alphabet.)

Moreover, I would argue that the study of mathematics reached its peak in the second century, with the great mathematician Apollonius of Perga. I know I'm in the minority on that opinion, but it's easily argued that mathematics was quite developed, and had been for at least two hundred years, by the second century.

I think you're making a mistake that lots of people in this century have: you're confusing the symbols with the things themselves. The truth is, people who used Roman numerals were just as good at thinking about math, since math was the same thing then as it is now.
posted by koeselitz at 10:59 AM on April 14, 2009

Orange Pamplemousse: So, what snippets of scientific information would be good additions to this list? Anything that would improve the ancient society or the traveler's place in it is fair game, provided it can be applied with the tools on hand, or is readily available from simpler knowledge (nuclear fission is out of reach and e=mc^2 useless).

For the purposes of this question, assume the traveler arrives sometime around 200BC in the Mediterranean, with no tools or books. Knowledge of the particular political climate isn't important, I'm more interested in the technology.

I have a different answer to this question to this question than those above.

Maybe this is because I'm very interested in the particular time period that you've pulled out of the air here, but I think the question is sort of beside the point. The second century BC was a damned good century; Alexander's conquests had, if nothing else, laid out a large swath of territory where there was a single government and brought, for the first time, a society where people didn't have to spend a large amount of time thinking about defense of the city or forging alliances with neighbors. Remember that this represented the first significant step away from the city-states that dominated the political landscape in the Mediterranean into the third century BC. The, for lack of a better term, 'conservative' factions in Sparta and elsewhere lost out, because of the rise of commerce and political interconnectedness, to the Athenian cosmopolitan openness. In short, what I'm saying is that, in the second century in the Mediterranean, you could expect that people were more willing and able to move about between different cities and nations and more open to other societies than previous generations and previous societies; centuries of expanding trade meant that people at least in most larger cities were used to seeing foreigners and hearing strange languages.

Because of this, people were relatively insulated from the caprices of bad crop years and natural disasters; if a terrible epidemic happened, neighboring cities or a central government could be counted on to provide support, and if agriculture went through difficult times, trade meant that people generally didn't have to go hungry. A rich literature and culture meant that people had diversions and thought about music, art, philosophy, and beauty. Yes, it is true that there weren't printed books, but old things were remembered and recited more often; as Plato pointed out, writing can destroy memory much more often than it can assist it, and the new schools (in places like Alexandria) were rising while the old schools (in places like Athens) were declining.

What I'm trying to say, I guess, is that most 'scientific advances' that you could bring to this culture wouldn't mean much to people. It would be nice to cure a few diseases, but disease didn't ravage second-century Mediterranean culture in any significant way, and people generally were used to whatever sicknesses they encountered and thought of them as normal. The ability to print books would have been an interesting novelty but would not by any stretch have changed society, given that people were attached to the old ways and still relied on spoken history - not to mention the fact that most people were illiterate anyhow. Some farming techniques might have been helpful, but even farming was relatively advanced by this time; if you examine Xenophon's Oeconomicus, you'll see that even two hundred years before the second century farming was studied carefully as an important art.

People of this time were concerned with trying to stabilize the political climate created by the void that Alexander left, and with rearranging their individual cities around the emergence of the nation-state. They were facing the religious challenges of this rearrangement and its modification of the sacred rites of the family and the city and the innovations on this front that Roman culture brought. They were dealing with newfound freedoms and exposure to differing cultures.

What I'm saying is that I don't think you could have enriched the second century much. We don't have much to teach it. They have much to teach us. In particular, there is no sense in which we've attained any superior political knowledge. Moreover, I believe that it would be ridiculously difficult to enrich yourself by ingenious or scientific means if thrust randomly into that time period; wealth just wasn't transferred often enough to make this easy. It was generally against the law (and a major taboo) to sell land in the second century, for example. Even an expert in the second-century civilization (not me, I'm just an amateur) would have a hell of a time learning all the multifarious ways of life in those or any times. No one would give you the time of day in any time, especially right now in our incredibly insular and backward culture, until you'd gotten well acquainted with the traditions and practices that were common.

The one thing that might save you if you went back in time is a good facility with languages. As I say, even an expert classicist would be entirely out of his element speaking Macedonian Greek or Pre-empire Latin; you'd have to spend a long, long time learning the language and culture before you could get anywhere, and making that process easier would probably be the difference between hating the experience and getting something good out of it.
posted by koeselitz at 11:45 AM on April 14, 2009 [6 favorites]

I guess you've read Lest Darkness Fall?
posted by gregr at 11:46 AM on April 14, 2009

We moderns tend to vastly underestimate the differences between our time and earlier times; that's part of our extraordinary backwardness and provinciality, which I believe is unparalleled in history. We generally know less about and take less of an interest in cultures and peoples that came before us than any society in the history of the world. As such, I don't think we properly understand just how difficult time travel would be.

I recommend as strongly as I possibly can a fantastic book about ancient societies and the way people lived called The Ancient City [full English translation in pdf] and written by Numa Denis Fustel de Coulanges. This book is one of the few books I've read that actually vividly recreates the ways of life of those times and gives the reader an idea of what they cared about.
posted by koeselitz at 11:53 AM on April 14, 2009 [6 favorites]

If I were a bit more emotionally invested in it, I might even say that this question seems almost insulting. Think about what it sounds like to ask this question in geographical terms instead of temporal terms; what would we think of someone who asked, "what amazing technologies could I bring to Mexico to either get rich or surprise and enrich their backward culture?"
posted by koeselitz at 11:58 AM on April 14, 2009 [1 favorite]

The Cross-Time Engineer had to luck into finding a patron that kept him alive so he could do his "magic".

So, seeds, a tent, sleeping bag, and a rich cousin who is thoughtful enough to inoculate you after/before the fact.
posted by lysdexic at 12:06 PM on April 14, 2009

psst, koeslitz:
7 All streams flow into the sea,
yet the sea is never full.
To the place the streams come from,
there they return again.

8 All things are wearisome,
more than one can say.
The eye never has enough of seeing,
nor the ear its fill of hearing.

9 What has been will be again,
what has been done will be done again;
there is nothing new under the sun.


It's a fun what-if discussion, and I'm enjoying the links to things I've never seen.

posted by lysdexic at 12:11 PM on April 14, 2009 [1 favorite]

Previously on the Blue. "How to rock the Middle Ages with your bad 2008 self."

Of course, first you'd have to travel back in time to 2008...
posted by yeti at 12:24 PM on April 14, 2009

koeselitz, I don't doubt that merely surviving in 200BC would be a significant challenge for any would-be time traveler. The language and cultural barrier alone would render it difficult to establish oneself before hunger or disease took their toll, and I can't imagine foreigners were common (except maybe as slaves).

What interests me is the general portability of technology, and the benefit of hindsight. Things that seem obvious to us, such as stirrups or distillation can be simply implemented and have far reaching effects. I know little about applied science or ancient life and so don't know where the old technology was lacking, hence the question.


I would argue though that the reasons you give for this era to be difficult to enrich could be strengths of the time as well. An unstable political climate (such as that brought by Alexander's death) breeds invention, in war if nothing else. Growing interconnectivity between cities and nations should also open the possibility of more expansive trade routes, and the mixing of cultures would pre-expose people to new traditions, and aid acceptance of a time traveler's new ideas (although germ theory would certainly be a tough sell). For example, building a more efficient loom or dye could strengthen one of the local cities trade goods, allowing it to out-compete neighbouring wares and bringing in significant wealth. A simplification of the times sure, but I think that new technology could always be useful (hence my comment about the political climate). There certainly is no time in history when invention wholly ceased.


The reason for naming both time and place was mostly to limit the question to an area that I have at least cursory knowledge of. I haven't read history extensively, but I at least know a few of the major nations in that area. The timing places it before the dominance of the Roman empire but after Alexander, simply because I thought the borders and beliefs would be a little more varied (not that I gave it much thought). No insult was intended.
posted by Orange Pamplemousse at 12:33 PM on April 14, 2009

moonwalk
posted by ouke at 12:54 PM on April 14, 2009

Now, anyone want to speculate what 30,000 people from an advanced technological society might have been able to teach human beings at about 150,000 BC?
posted by musofire

Nothing, since you've thrown away all your tools.
posted by Marky at 1:03 PM on April 14, 2009

Knowing how to make porcelain would mean instant riches in any non-Chinese civilisation before 1700. Before 1300, the longbow was a force multiplier roughly equivalent to the long-range bomber - get it first and you'll be the first power to be able to destroy an army you can hardly see.
posted by WPW at 1:37 PM on April 14, 2009

Wow! Lots of good suggestions so far. Here's my hack at it.

Alcohol for sterilization.

Barometer: Thin latex sheet (made from a rubber tree) stretched over the mouth of a glass (the ancients had glass) bottle with a thin, light writing instrument attached. Helps you predict the weather.

Aspirin: From willow plants. I made it in high school chemistry. Bring the wonder drug to the ancients!

Barbed Wire: Military and livestock applications.

Bicycle

Compass: Invented in China at around the same time as your timeline you could bring navigation to the west early and you could correct the north/south mixup the west made but the Chinese avoided.

Cotton Gin

Geodesic dome: Using wood or metal shafts

Electricity: The original steam engine was a toy built by Archemedes (and stayed merely a toy for centuries) and consisted of a globe held over a fire with two steam jets designed to rotate the globe around a horizontal axle. You could hook that axle up to a magnet that rotates inside a coil of wire and you have electricity tens of centuries early. Then improve on it by heating the globe with coal fire (known to the ancients). (Please swap the signs for positive and negative charge while you're at it.)

Glue: First patent was around 1750

Lens Grinding: Bend light early. Then invent the microscope, telescope, and optics.

Layden Jars: Store your new invention of electricity in the earliest batteries known.

Mouse traps: Better than cats. The world will beat a path to your door.

Rockets: Assuming you invent gunpowder. The Chinese had 'em hundreds of years later. Why not you, now?

Steel: They had the beginnings of iron smelting. Improve their process by adding air and reading up on the rather simple Bessemer process.
posted by Lord Fancy Pants at 3:07 PM on April 14, 2009

Antibiotics. I'm certainly no doctor, but it occurred to me that if you knew how, the manufacture of something like penicillan (and a rudimentary syringe) could be duplicated with the available technology. The first wealthy patrons child you saved from some common infection that normally would have killed them would make you famous overnight. Oh sure, you'd be called a sorcerer or alchemist and everyone would fear you and you'd never get laid, but hey, you'd be a star!

Oh, and teach them to brush and floss. Seriously. Dentistry (the barbaric version) goes back to something like 7000 BC, but it was little more than yanking bad teeth until centuries later. Might not make you famous or wealthy, but may make your stay there a little better. Who wants to put the moves on a village girl with only half her teeth?
posted by elendil71 at 3:37 PM on April 14, 2009

You could do well selling/introducing modern innovations on the street in fun, simple forms, I think, if we ignore the language barrier. A few examples:

• You could add dye to wax and make the first crayons.
• Literate, affluent Romans would LOVE crosswords and Scrabble. Scrabble could be made of stone or wood; crosswords could be more a trend in which people made them for friends rather than a printed thing in the paper.
• Speaking of games: chess.
• Two mirrors and a long box: periscope!
• Basketball or volleyball could work well as military training/team-building exercises.
• Tea bags would be good for all the herbal remedies the classical world imbibed.
• Sandwiches? Panini?!
• Kites.

Other interesting ideas that might have been worth mentioning to the Romans once you'd got the Senate's ear:

• traffic management on busy roads: lanes, people directing traffic
• wheelbarrows
• tsunamis: people should get away from the coast when there's an earthquake
posted by mdonley at 4:58 PM on April 14, 2009 [1 favorite]

As a slight aside, Orson Scott Card wrote a really memorable sf novel called Pastwatch that asks the question What if the natives of Central and South America were immune to the diseases that Europeans brought over? That plus a few more advances (I forget exactly which). So via time travel, someone does just that (though of course that's just the short version). An interesting read.
posted by zardoz at 7:18 PM on April 14, 2009

Electroplating.

A simple battery can be made with copper, iron and vinegar.

1) Make electricity
2) Plate gold onto base metals
3) Profit!

BTW: Layden Jars: Store your new invention of electricity in the earliest batteries known.
Leyden jars are capacitors, not batteries.
posted by HiroProtagonist at 7:27 PM on April 14, 2009

If you really want to do it right, you need to take a whole town. But not to 200 BC. Make it 1632.
posted by lysdexic at 7:59 PM on April 14, 2009

Of all inventions, these:

Watt's Improved Steam Engine (fired by coal and/or fuel oil) and water suction, railroad transport, steamship, (and later) automobile applications.

You could skip the telegraph and go straight to shortwave radio technology I suppose.

The artillery shell + cannon + Vauban fortification as above

Agreed about the moveable type printing press. Good bang for the buck there.

Pennicillin and the polio vaccine.

and koeseitz, get over yourself. I think the visitor from 4000AD would have plenty of useful wealth-creation gadgets and tidbits of knowledge to impart to us now.
posted by mrt at 8:09 PM on April 14, 2009

I think the answer has already been put in song, a major answer there being the Haber process (fertilizer, bombs, etc.), but other easy examples are movable type, telescopes, interchangeable parts, assembly lines, quality control, penicillin, vaccination, steam engine, electricity, probability, and calculous. I'd say calculous alone will solve your survival issues if you can reach a court astronomer quickly.
posted by jeffburdges at 2:34 AM on April 15, 2009 [2 favorites]

Sandwiches! Totally!
Forget all this stuff about stirrups and whatnot.
posted by exceptinsects at 11:17 AM on April 15, 2009 [1 favorite]

Great stuff! A working clock ought to be easy to make and not beyond technology of the time -- like the Antikythera mechanism. I also second the compass, especially since it's so easy to make. Magnetite was well-known in ancient Greece.

How would you support yourself? Easiest if you're an entertainer. There was no mass media to mollify the masses, after all, so singing or street performance might yield a good wage.

One area where you could really revolutionize things is in art. I'd set up a school to teach theories and techniques relating to perspective, light and shadow, space, value, balance, and so on, to mate up with the Grecian obsession with anatomy. Imagine if the equivalent to the Italian Renaissance in art came 1700 years earlier (political situation permitting).

Also -- no one's yet mentioned the laws of Newtonian physics?
posted by Wyrmspace at 12:29 PM on April 15, 2009