# How could an engineer advance human civilization by time traveling to the past? [closed]

Earth in the near future (in 2081) is invaded by aliens who are just "a bit" more technologically advanced than humans. The war is not a one sided extermination of humans, but humans are about to lose anyway.

An engineer succeeds in building a time machine for a one way trip to the past. From How fast could a civilization advance if given access to information from future? I understand that there would be many problems, but this is the only option nonetheless.

He is one of the last surviving humans and he alone must depart as soon as possible.

There is some space in the time machine for luggage (think DeLorean from Back to the Future - it could be a bit bigger if need be, but not larger than a small truck) and the engineer takes a tablet with all human knowledge and an advanced AI that can function as a military, economic, medical, ... advisor (so the question is not about what knowledge he should bring, but to whom he should bring it), a Google Glass like device that can translate all ancient languages, a small fusion reactor - but then has to decide what else to bring with him (for example: penicillin mold, genetically modified seeds, ...). between bringing either:

• the latest computer with as many spare parts as can fit in the time machine (but eventually the spare parts will run out and you have limited number of computers in the world)
• all the tools (and tools to make tools) to start mass producing an 1955 era vacuum tube computers for the whole world (but this progress will be much slower)

What is the best option and how far back should he travel to benefit most from the technology of the time (so he can build on the existing infrastructure and knowledge of metallurgy, medicine, science, ... of the time and perhaps influence a great historical figure), but still advance the human civilization the most? 2000 AD? 1500 AD? 1000 AD? 500AD? 500 BC? 1000 BC? 1500 BC? 2000 BC?

### EDIT for "put on hold as too broad":

Thank you for so many great and interesting answers!

I see now that the question really is too broad and I have modified it in a way that hopefully leaves the existing answers still relevant, while being more specific. If the question is still too broad, I can narrow it further.

What I removed from the question is in strikethrough and what I added is in italic.

TL;DR: One of the last surviving humans must travel to the past to give the humanity a technological head start in the battle against invading aliens. His computer contains an advanced AI adviser with all human knowledge and the question is: to whom should he bring it to maximize the chances of success, considering that traveling further back in time increases the possible technological advances, but also the uncertainty of success?

## closed as too broad by Anketam, elemtilas, Trevor, 011358 smell, Ryan_LJul 25 at 18:37

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Been there, read that. amazon.com/Connecticut-Yankee-King-Arthurs-Court/dp/1948132877 – puppetsock Jul 24 at 13:31
• Leo Frankowski's Conrad Stargard (born Schwartz), The Cross-Time Engineer (link goes to Amazon), went from the 1986 People's Republic of Poland to the wretchedly fragmented 1231 Kingdom of Poland and, being a very good socialist engineer, succeeded into making medieval Poland into an invincible power... As for "all the tools (and tools to make tools) to start mass producing an 1955 era vacuum tube computers for the whole world", you do realize that he needs a very very very large time machine, yes? – AlexP Jul 24 at 13:42
• A better question would be what THINGS to take back given a compact form containing relevant knowledge. For instance take an assortment of modern seeds with you, skip several thousand years of selective breeding. instantly have agriculture that is highly nutritious and efficient.A sample of penicillin mold would be nice as well. – John Jul 25 at 0:06
• One of the major novels dealing with it is L. Sprague de Camp's "Lest the Darkness Fall"(1939) en.m.wikipedia.org/wiki/Lest_Darkness_Fall . The main hero is an archeologist not engineer, and he gets pushed to a critical point in Roman empire. He succeeds in averting the fall of the Roman empire and the following Dark Ages -- partially by not very complex technologies -- but mostly with applying his knowledge of history and diplomacy. This could change the following history considerably. – Gnudiff Jul 25 at 7:58
• Whatever time period you decide to visit, you need to change the course of history for the better and you need to do it quick before you succumb to the common illnesses and diseases of that era. Even more important than your tablet is going to be some sort of water purification system because I doubt that 7 days is enough time to achieve anything. – MonkeyZeus Jul 25 at 13:33

## 22 Answers

The engineer will have the most effect when they can leverage an existing community receptive to the ideas. In that way, a sustainable group can carry on the acceleration over history.

Heading to a largish city is important to this. Teaching a few bronze age shamen some tricks is at best going to create a brief flurry of power and die out.

Possibly look to great figures in history and enable them. For example Socrates/ Plato or Aristotle. Alternatively, wait until Galileo or Newton.

If heading to classical Greece, its not just engineering/ technical knowledge that is important. Use that to gain credibility, but then the real thing is the scientific method. Teach them how to fish as the proverb goes.

The economic concept is an interesting one. Actual execution on it seems hard. How to convince anybody to adopt your ideas, given the facts that economic are to say the least hard to prove, and in any case take a lot of time.

But on the economic side, think about the key revolutions. The agricultural revolution comes down to a scientific mindset coupled with a few basics like crop rotation. More food means more people means more room for overall economic development.

As well as considering the value of accelerating history boom times, consider how to avoid the busts. Perhaps bringing about an agricultural revolution in 200-300 AD would avoid Rome's decline. Problem is, it is hard to be sure about that. However, avoiding the relative slowdown in tech development for the thousand years prior to the renaissance would clearly be a huge accelerator.

So maybe visiting Alexandria in 250 AD, bringing crop rotation and the scientific method you might be able to really advance things. Just need to avoid global thermonuclear warfare in 1200 AD.

• The idea to enable great figures in history is very appealing! If you travel to 1510 you can contact Leonardo da Vinci about 9 years before his death (and possibly prolong his life) and if you live long enough (living up to 100 could be plausible in near future) you can pass on the work to the young Galileo Galilei in 1570. – Jinjinov Jul 25 at 8:58
• This question reminds me of one of my favorite stand-up comedy bits (Nate Bargatze): youtu.be/QXy3uII-xn0 and I think your point about leveraging a receptive community is spot-on. – Ryan Jul 25 at 14:22

Your engineer needs to forego the trip and send an economist instead, specialising in development economics. The main obstacle to technological development throughout history hasn’t been lack of knowledge, it’s been lack of incentives. There were things like steam engines and electric batteries in the classical world, but they were largely seen as toys or amusements. Those on top don’t want to shake things up, because it might dislodge them from the top. What you need is to create the economic conditions that encourage the rapid development of technology, much earlier than they actually occurred in 18th century England. I think Diocletian is the chap to target — he identified deep-seated issues in the Roman economy and introduced far-reaching measures to correct them, but because he didn’t know what he was doing he made things worse in the long term.

• That's not really true though. Rome had a lot of very good engineers and scientists, as proven by the fact that it took roughly a thousand years from the fall of the Roman Empire until Europe could build similar structures again. And they all talked, and worked together, and bounced ideas off each other. The reason we (incorrectly) have the impression that's all they were considered is because the records we have were kept by Christian clergy, who did have that attitude, and they did not keep any of the technical docs. – Graham Jul 24 at 22:58
• An economist can go back and tell you all about capitalism, but the ruling class already owned everything and had very little motivation to switch to a capitalist society (if they cared about innovation they would already be funding it). Merchants might be a better target, but they didn't have that much power until the renaissance, at which point capitalism is on the verge of happening all by itself. Economic systems arise from culture, and culture is next to impossible to force. – Turksarama Jul 24 at 22:59
• I disagree about economist/incentives as the "main obstacle" ... no, in Human history there has been one and only one "main obstacle" to ... well everything: Religion – CGCampbell Jul 25 at 11:34
• @CGCampbell But then would you consider religion to be the true obstacle, or is religion a consequence of some greater obstacle, such as power imbalance? – JMac Jul 25 at 15:00

# For best effect, head for either UK or USA any time from 1939 to 1989.

The last few decades have brought the most rapid advances in technology and the greatest focus on advancing technology, during WWII and the Cold War this was often regardless of the cost. Anything to get an edge over either the Nazis or the Russians during the appropriate periods was grabbed with both hands and tried with gusto, often no matter how daft it appeared to be.

Of course if your intent is purely to advance technology regardless of cost, then you could head for any of the opposing powers who also had much the same mindset, but the outcome would be ... different.

You could consider the argument that the efficiency of the German war machine during WWII would give humanity the an advantage over the aliens during the future encounter. Their willingness to pursue technological development without regard to inconveniences like ethics gives them a lead and that handing them the technology to overwhelmingly win the war gives the only positive outcome in the future conflict.

• I have thought of that, but wouldn't traveling back to 1500 AD to Leonardo da Vinci get you better results, even if it would take 300 years to understand and implement the knowledge, you would still benefit about 300 years - better than the 100 years or so from WWII ? – Jinjinov Jul 24 at 14:07
• @Jinjinov, but can you bootstrap the industrialisation of technological development without the population of the modern world? There's just no need for it at that point. It's not until the era of global warfare that it suddenly becomes a major factor. – Separatrix Jul 24 at 14:08
• @Jinjinov No need and more importantly not enough population density to make it possible. – Ash Jul 24 at 14:22
• Efficiency of the German war machine? When they put time and materials into creating increasingly impractical weapons instead of churning out as many Pz IVs and Panthers as they could? That said, they did develop the first space-going vehicle... – Baldrickk Jul 25 at 9:28
• I upvoted your answer because it is the closer to what I think. Why go thousands of years in the past where people will barely understand what you give them when you can jump a few decades back where what you bring will almost be instantly assimilated. Moreover, in the far past the travel of information was very bad and the mission could fail very easily. Aiming for recent times allow success wherever you go ! – Echox Jul 25 at 10:11

Take the tools, a gun, and a few cool tricks

The main problem here is that you can show up in history and claim you're from the future and know everything, at which point you will either be burnt at the stake for being a witch/heathen/rival witch/rival heathen, or told to get in line behind everyone else who very clearly knows the future and they have astrology, not some weird magic ... thing.

The best idea here seems to take a leaf out of a sci-fi, specifically Foundation's psychohistory. More specifically, when the Foundation decides to make a religion out of there superior tech. You want to go far back in time - basically to the dawn of human civilization (the more time the better). Good location include, but are not limited to: The Fertile Crescent of Mesopotamia, the Olmecs of Mesoamerica, or perhaps the ancient Chinese. You're looking for two key components. The first is they have a primitive religious mindset, and the second is that they look different from you. Wow them a bit by demonstrating your superiority, claim that you're a superior being, and take their children. (Not kidnap, just take them under your personal tutelage.) It's also a good idea to take a consort and have children that way. (Advantage here is to males whose limits is the number of females they have, and don't have to personally endure risky childbearing.)

The children are the key. If you can train them to work with your technology, then you can restart the modern human times and rebuild humanity at whatever point in time you want. It'll take a while to build the industry back up, but with modern knowledge, you can make defensible structures and deadly weapons until that point, after which you can more or less conquer the world. (You may be dead at that point, so leave a good set of instructions.) At which point, we'll have around 2k-3k years of progress on our modern one in present day. Hopefully you won't wind up up with some totalitarian empire after your absolute power corrupts your descendants absolutely, but even if you do, the human race isn't wiped out so ... win?

• Modern skills are pathetically useless in dawn of humanity ages where chasing down prey and defending yourself were a teensy bit more important. You need infrastructure to support physically wimpy people sitting at computers thinking about whether it's a better user experience for the button to be blue or green. – Muuski Jul 24 at 14:40
• @Muuski That's where religion comes into play. The technologists are treated as the priest class, which should be simple, seeing as you can do what they would consider to be miracles. – Halfthawed Jul 24 at 15:08
• @Muuski: With a few modern plant seeds, bows&arrows (or crossbows) and basic knowledge of hygiene, pottery, glass, metallurgy etc. survival should be much easier. – Michael Jul 25 at 6:40
• -1 for blatant bigotry. The "primitive" religious mindset was actually what gave us science as we know it today. The ancient Greek mathematicians saw their calculations as an important part of the worship of the Gods, and virtually all of the great medieval scientists, the fathers of the Scientific Method, were priests specifically seeking to bring man closer to God by understanding how His creation worked. Isaac Newton actually considered his research on theology far more important than his research on physics! – Mason Wheeler Jul 25 at 11:35
• @Mason Wheeler If you use the definition of the word primitive to mean the initial state of something before it evolves into something else then that word is very compatible with what you just described. You even say "what gave us science as we know it today" which implies an evolution from a primitive state to a modern state. – Muuski Jul 25 at 15:28

You just jump back to shortly before the war with the aliens.

Assume you jump back 2000 years. You may achieve a lot there (or not, but that's a different story), but you are still leaving a lot of the outcome to chance. Just look at how much of ancient knowledge was lost for a long time, plus what might be lost forever after the burning of the great library.
That is definitely taking too many chances, when all of mankind is at stake.

You state that the humans aren't massacred, but they are losing anyway. That means, with some luck and some foresight, it might go the other way.
We cannot craft luck, but we can craft foresight.

I assume that the first skirmishes resulted in either side finding out what weapons are effective and what wasn't. Jumping back to before the war eliminates this part on our side, giving us a slight edge.
Also, i assume we were quite surprised by their arrival, and by the first hostilities. We can eliminate that, too: By traveling back, you can make sure we know when and where they appear, and when and where they will strike. And we already know which weapons work. We can prepare for an all-out preemptive strike the moment they arrive, cutting the war short, and avoiding all sorts of strange developments that are bound to occur when you travel too far back.

• Very interesting answer! I agree that going back one year before the invasion would give the humanity a significant edge just with the knowledge. But, thinking further, going back 10 years would give the same edge and provide more time to build weapons. The only problem is the possibility that nobody would take you seriously. If you want to avoid that, traveling to the start of WWII seems a safer choice. – Jinjinov Jul 25 at 9:22
• @Jinjinov you might (or might not...) get better weaponry out of a longer jump. But would you really? what if you just shortened WWII, and even prevented the cold war? Then you would be left with 1960s weapon tech, making you easy prey for the aliens. There is just too much you need to consider and control when you jump further back. – Burki Jul 25 at 9:48
• You have a point there! What about going back to 1975 or 1976 when Microsoft and Apple were founded and influencing the engineers, investing in the companies and later also in Google in 1998 and in SpaceX in 2002, bringing them solutions beyond their knowledge, but still plausible so as not to be suspicious? – Jinjinov Jul 25 at 10:31
• "Hi! I'm Future Man!! You're about to be attacked by aliens and must build weapons to these specifications I've got here!!!" "Yeah, sure thing, buddy. Now just come along quiet - we've got a nice padded cell all ready for ya..." "But OFFICER!!! The Fate Of The Free World Rests In Our Hands!!!!" "Uh-huh. That's what they all say..." – Bob Jarvis Jul 25 at 11:22
• If the engineer is in contact with some very powerful people, they will probably get access to the protocols to confirm a successful time travel (I do hope everyone agrees that these exist somewhere). Then, the engineer can confirm that they are a time traveler to the early version of the powerful people (or those occupying that place), and they should be easily believed. Also, the engineer can probably bring some knowledge useful to prove the alien invasion, like space coordinates where you can see the aliens coming if you point a really powerful telescope (if they don't go too far back) – Blueriver Jul 25 at 20:51

It makes no difference.

Traveling back in time with technology does not, in and of itself, improve human civilization.

You just get a different civilization.

Let's say you give the Roman Empire basic computers. This means they can e.g. count better, maybe do some calculations better, probably all you've done is let their tax people work better. But no matter what technology you gave them (or any other faction), you don't change the politics or religious and social norms.

At any period in history all you can do is (maybe) influence who gets more powerful or richer. You can change how they do things (what tools or weapons they use), but not why they use them or for what goals. The goals remain the same - power.

Let's again consider Rome. Would Rome still fall ? Yes - the pressures that brought it down were complex, a mix on internal and external political, social, religious and economic factors. Would your engineer be able to change those ? Not enough.

You might change some things but your engineer cannot change everything. He/she can't change what Gods people believe in, or what social norms are in force in any location. They can't really control the whims of kings, queens, generals and politicians. They can't stop armies from breaking under attacks.

You can't stop one faction or race or religion hating another. The drives are too much for a technology or devices to change. What you change is the details, but it's too chaotic to control it all. Many have tried, all have ultimately failed.

How imagine your engineer (somehow) gains control of e.g. the Roman Empire and sets out to make it a force for improving civilization (something it actually was by the standards of the day). Your engineer can't do that forever and has now started history on a new path and does not know what will happen. Your engineer has no more control over who will invade, attack, stop trading, increase prices, what peoples will migrate and to where and all those other details, than any Emperor ever had. When the engineer dies history will go about it's own path. The Roman Empire of Engineer the First may last a hundred years and then collapse under more or less the same pressures our Roman Empire did. Who knows.

But there's no way to guarantee improvement only differences.

Take along something that helps record and spread knowledge of a few basic principles. The problem is not that people "way back when" were stupid - it's that ideas weren't able to be recorded, disseminated, and improved upon.

Consider - the Antikythera mechanism, a geared analog computer for predicting astronomical positions and eclipses, was built circa 100 BC and lost in a shipwreck approx. 30 years later. It was a revolutionary geared mechanism unlike any other known from the ancient world. Nothing else like it was known for another 1500 years - but it was apparently a one-off which wasn't mentioned in "recorded history". Had this technology come into common usage who can say how people could have used it? Or - if a simple low pressure steam engine had been built in the early Iron Age, it might have dramatically affected the civilization which could build and reproduce it. But again, the know-how to do this would have to be spread out to keep it alive, and to stop wars, pestilence, and the death of the one mad genius who knew the secrets of steam from putting an end to this idea.

Maybe educational picture books would help spread knowledge. Maybe getting writing out of the hands of the priests and into the hands of, at least, the aristocracy on a regular basis might have allowed knowledge to be recorded and diffused. But it's more about recording and communication than it is about twisting nuts or stringing wires. That, and lots of time - because one man, brief in space, must spread his ideas across a period of many years if he is to have a chance of succeeding.

Ancient Greece

The ancient Greeks has the boiler and the piston developed already but just never thought to put the two together to make the steam engine.

If that had happened, the industrial revolution could have happened two thousand years earlier.

Give them the secret of gunpowder and the basics of electricity all which can be built using their level of technology.

Basically anyone with a high school level science ability spending ten minutes with someone like Pythagoras and the world would be thousands of years more advanced that where we are now (or extinct much sooner if they follow the same path as humanity)

• It's unlikely that they could have gotten the industrial revolution that early, as their primitive metallurgy wouldn't have been able to cope with the high pressures involved in industrial steam engines. There's a good reason they didn't consider it anything more than a toy: serious steam pressure requires good-quality steel and will tear apart lesser metals. And we didn't get industrial steel until the dawn of the Industrial Revolution--3000 years after the earliest known steel samples!--for complex societal reasons that can't be solved by simply handing technology to someone. – Mason Wheeler Jul 25 at 10:28

Go back to the day that Julius Caesar crossed the Rubicon. Shoot him in the head with your sniper rifle before that. That keeps the Roman Republic from turning into the Roman Empire for at least a few more years.

Now go find the scientists of that day and give them translated textbooks. Build a library and store engineering diagrams in it. Build a factory and make things from the seventeenth and eighteenth centuries. And yes, a school teaching the scientific method.

If you can prevent the Romans from turning to an imperial government, you can avoid a thousand years of grief. Think about it. That alone could put humanity a thousand years ahead. If you add to it the basic mathematical and scientific discoveries of the last five hundred years, that's going to put things way ahead.

If another tyrant arises during your lifetime, well, you still have your sniper rifle, don't you? Leave it to a dedicated secret society for the prevention of future tyrants.

After Rome, you need to wait a thousand years to have the same sort of technological base. So you only move things up a few hundred years. Before Rome, you have to build the Roman base before you can do anything. You only move things up a few hundred more years, plus you still need to conquer a larger area. Rome is as good as it gets in terms of having a large civilized area with superior technology for the time.

Alexandrian Macedonia has some of that, but it didn't survive Alexander. You'd have to find a way to fix that. Also, it wasn't quite as advanced as Rome.

• What prevents the secret society of becoming tyranic? You just switched out a visible tyrann with an invisible one, which sounds like it would make things worse. The rest sounds good. – Hakaishin Jul 25 at 5:40

Taking a different approach here,

The more distance the engineer travel through time the greatest the risk of someone killing him/her because of his/hers differences, and it is not his/hers goal either, the objective its to win the war NOT improve mankind to its limits, so the best option would be a couples months before the alien invasion.

Let's say the war lasted until now five years, the alien "a bit" more technologically advanced than humans, meaning that the humans learned a lot during the war (alien battle tactics, Alien hierarchy, their technology, intelligence on the alien command at some specific time and so on) and the knowledge would be more decisive than betting that mankind would improve to be better at war than the aliens in the future.

A few different people have mentioned the concept of "start the Industrial Revolution early", and the idea that if only we could teach the ancients how to make a steam engine, everything would be awesome.

This, in and of itself, won't work.

The first steam engine to do any useful industrial-grade work, (pumping water out of a mine,) was invented in 1606. But James Watt's steam engine design, generally associated with the Industrial Revolution, wasn't produced until 1765. A bunch of things changed in science and engineering during those 165 years, (it spans the entire lifetime of Isaac Newton, just for starters!), but one of the most significant happened in 1740: Benjamin Huntsman invented a process for making good-quality steel in large quantities.

Steel had been around practically forever. The earliest known samples date back to around 1400 BC, and high-quality wootz (aka Damascus Steel) to 300 BC. But wootz was never manufactured in any large amount, and eventually the knowledge of how to make it died out.

Good steel is crucial for the Industrial Revolution. The ancient Greeks knew how to make toy steam engines, but it was never considered anything more than a toy, because with their primitive metallurgy they weren't capable of doing anything useful with it. The high pressures involved in industrial work require good-quality steel (or more modern metals, of course); it will tear apart anything less. And it wasn't until 1740 that the world got a way to produce it in moderately large amounts, and not until 1856, with Henry Bessemer's steelmaking process, that we got a way to produce it in truly large amounts.

Huntsman's steelmaking technique coincided with the Industrial Revolution, and Bessemer's with the so-called "Second Industrial Revolution", the one that truly gave us the modern world. This isn't really a coincidence; steel gave us the (literal) engines of industrial power. Huntsman's allowed for wide-scale production of Watt's steam engine, and a very interesting thing happened within a decade of Bessemer's patent expiring, handing the technology over to the public domain for unrestricted wide-scale production: a man named Karl Benz, an engineer who had worked on steam engines, came up with the novel idea of putting the burning fuel inside the piston itself. He used a commercial solvent called "gasoline"--easily available at your local chemist's shop for cleaning purposes--as the fuel, and the rest is history. Today we know the name "Benz" as one of the prestige-grade manufacturers of the machine Benz invented, which reshaped the entire world. But it would never have been possible without tough steel pistons capable of withstanding the insane pressures of exploding gasoline at a rate of a few thousand RPM.

If you really want to start the Industrial Revolution early, the key is not the steam engine; it's the Bessemer Converter. Knowledge of electricity would also be useful, as a few people have mentioned, but there's one thing I'm a bit shocked no one has brought up yet.

The tipping point that gave us the internal combustion engine and the automobile wasn't the creation of the Bessemer Converter; it was its patent expiration and release into the public domain. It was the widespread availability of the technology to any smith who cared to try his hand at it. If you really want to start the Industrial Revolution early, it's not enough to have someone know how to make good-quality steel. We had that with wootz and it still took another 2000 years to get the ball rolling, because it was always held as a carefully-guarded trade secret by the smiths who knew the trick to it, and then the knowledge would die out and have to be rediscovered, again and again. No, what you need is for everybody to know how to make it!

If you really want to start the Industrial Revolution early... steel and the steam engine aren't enough. Give them the printing press too.

• Wow, only one mentioned the press? – Anton Sherwood Jul 30 at 16:03

The first week of may 1953, you don't take tools or tools to make tools, you take information (your tablet) and a couple of live kidnapped aliens in the boot of the "DeLorean".

You turn-up in the laboratory of Watson and Crick a couple of weeks after the groundbreaking discovery of the structure of DNA.

Get them to examine the alien's tissues, show them video footage of the future destruction of human civilization. Get them to invite the Government from every first-world country to examine the aliens - they were so celebrated around the time of the discovery that an invitation to the Government's science-advisers, and leading technologists of the age would be sure to be taken seriously and ensure good attendance.

Hijack the presentation, show the aliens, the footage - explain the problem of the invasion. You're sure to be arrested, interrogated without creature comforts and with psychoactive drugs - but eventually, you just might be taken seriously - they might think the film footage is faked, but they can't deny the live aliens.

Just stick to the truth, they'll come around, and instead of that silly cold-war leading to the space race, a space-race/bio-tech-race/weapons-race can all be funded together with shared objectives to defeat a common outside threat.

You now have your own suite of rooms in area 51, one of the aliens has been dissected, the other has given birth - the brood is being tested for it's physical/mental/immunological tolerances by the Mengele process. World peace is achieved, the alien threat is neutralized, your conscience is troubled by dreams of a misunderstood civilization about to be destroyed.

• What a great, funny answer! :) And totally plausible to boot! All I would change is that I would use a force filed based hologram of myself to deliver the aliens... I don't fancy small padded rooms with no windows... – Jinjinov Jul 26 at 7:29

Knowledge of history and some lower tech gear and a few key ideas might allow for more advances than high technology because you can go back farther and introduce some key concepts at far earlier dates.

Population density is a limiting factor when it comes to technological progress, if you don't have enough people you can't maintain the specialised labour that supports higher technology. To that end antiseptic child-birth and city sanitation for example would allow you to create a sustained population explosion if you could introduce them to the Bronze Age. Taking the synthesis of streptomycin, or smallpox vaccine back would prevent the black death and possibly the Greek dark ages respectively both large setbacks to population density. Once you have the higher populations you need you can have your followers work on other innovations in later generations.

My advice would be to go back to 1500BC, with gold and trinkets to get taken seriously one should be rich and generous, iron smelting, gun powder, germ theory, detailed history books, mineral surveys, a plan outlining soil and wildlife conservation, and population-technology supports and linkages.

The absolute best thing for your engineer is to go back as far as possible and cause the Industrial Revolution.

The earlier you cause the Industrial Revolution, the faster your humans will advance. There are several points in human history where we came close to starting the revolution, but missed out. The most important thing here is to create the steam engine and get it to stick. What you're trying to do is get civilization to invent a machine that will make slavery obsolete. Before the IR, we used people and animals to do all of our work. People are expensive to own. You have to feed them, clothe them, and house them, and at the end of the day you need a lot of them to do anything.

The average human male laborer uses about 0.5 kilowatt-hours worth of energy per day. Compare this to the modern American that uses around 29 kilowatt-hours worth of electricity per day. This means that a single American person today essentially owns the equivalent of 60 slaves in Roman times, just from an energy standpoint.

This free availability of energy is what you need for technological advancement. With the labor requirements of your society filled by machines instead of slaves, you not only have more people to carry out intellectual jobs, but you have the free time as well.

It's no coincidence that the rate of technological advancement became exponential as soon as we mastered the steam engine.

There were points that we came close to sparking the Industrial Revolution during Roman times, but they simply didn't recognize the value in a machine that could do work using steam, as they had slaves to do all the work for them that animals couldn't do. It wasn't until we had an economical need to produce things faster and more efficiently than slave labor could do that we took the idea of powered machines seriously. Your world-saving engineer will need to overcome this and show applications where industry beats slave labor. Once the revolution is started, your engineer's work is done, as the avalanche of advancement will carry itself forward. Take the Roman example, if we as a species got our head start 2000 years earlier, where would our technology be today?

I would say right after end of WW2 and start of Cold War. Make sure you take plans and detailed scientific papers for atomic weapons, nuclear power plants, rocketry and computers. Possibly take some basic computer, but make sure it is durable and won't need maintenance.

Going further back than industrial revolution would be ineffective. Culture back then would prevent any attempts at convincing both rich and poor about the improvements. And finding educated people to implement future ideas would be extra hard.

World Wars are a double-edged sword in these circumstances. Sure, lots of people died and lots of cities got destroyed. But technology, especially military tech, had huge advancements. So changing the future so that World wars wouldn't happen would make the new future too unpredictable.

The huge advantage of going back only few decades would be that it would be easy to convince people that you come from the future. You can tell them scientific and technological improvements that would be done in next ten years and they can easily confirm them. They will understand the computer and will know how to use it. And when you get their trust, you can tell them about the alien invasion so they can be better prepared.

Knowing what works and what doesn't will make the economics much efficient. The governments will be spending on research and development of computers, internet, rocketry and more advanced and safer nuclear plants. And thanks to exponential growth of today's economy, getting computers and internet a decade earlier would be huge boost. And knowing the aliens are coming would allow for development of weapons specifically build to fight them.

All the answers until now have focused on the European theatre. Not that I don't approve, but we're not the only ones out there.

China especially was also very advanced very early, just think of fireworks. The problem is that they stagnated - while Europe moved past them. One of the biggest reasons for this is that China was a land of china - by which I mean porcelain. Makes for lovely dinnerware, not so good for scientific discoveries, as even slightly volatile components will react with their container... In Europe, we instead used glass, which is of course known for being pretty inert.

So we take back the "secrets" of working with glass to ancient China, and let them go from there.

They also have/drink tea - something that was of underestimated importance in Britain during the industrial revolution. Boiling water for tea purified it, and meant that even with the dense populations the industrial revolution brought with it, disease didn't run rampant. They have this protection by default!

• An interesting answer! Reading all the other answers, I see that preventing disease and insuring longevity is just as important as advancing technology! – Jinjinov Jul 25 at 10:35

I think no matter what you do it is extremely hard to prepare humanity for the extraterrestrial event, because you cannot really foresee he consequences of your actions. I think the key is not so much in bringing technology back and advancing humanity, but rather warning them. Given that you already have the time machine, going back 50-30ish years with proof of what it is going to happen, data about the alien attack and the latest scientific advancements may be your most reliable plan. Consider that periods of rapid advancements within our current age are centered about conflicts. This approach wont give you a completely different humanity, but one that you know will be at least more prepared than the current one, and at the same time you will be avoiding the possibility of a random nuclear war or some similar event. It is also hard to know whether advancing humanity would advance their weaponry, so this way you are making sure that they focus in what it is really needed.

## Rifle technology, China, slightly before 1416

I would introduce rifles and the technologies to mass produce them (e.g. screws, interchangeable parts, assembly lines) to Ming-dynasty China. The precursor technologies were already present before 1416:

The Huolongjing, compiled by Jiao Yu and Liu Bowen sometime before the latter's death on 16 May 1375 (with a preface added by Jiao in 1412), featured many types of cutting-edge gunpowder weaponry for the time. This includes hollow, gunpowder-filled exploding cannonballs, land mines that used a complex trigger mechanism of falling weights, pins, and a steel wheellock to ignite the train of fuses, naval mines, fin-mounted winged rockets for aerodynamic control, multistage rockets propelled by booster rockets before igniting a swarm of smaller rockets issuing forth from the end of the missile (shaped like a dragon's head), and hand cannons that had up to ten barrels.

Rifle prototypes would not appear for another half-century, in Europe. They were not manufactured in significant amounts until the 18th century. The technologies involved lead directly to many other inventions.

I chose 1416 because that was around the peak of China's status as a military, economic, and political superpower. This was largely due to the Ming treasure voyages. The Ming navy had up to 2868 ships, which would not be matched until World War I. Over seven voyages, the treasure fleet visited what is now Vietnam, Thailand and Sri Lanka; Malacca (Indonesia); Bengal and Calcutta (India); Hormuz (Iran); Aden, Mecca, Jedda and Medina (Arabia); and Mogadishu (Somalia). Those kingdoms which were visited were forced to enter into trade pacts and pay tribute to China, in return for naval protection. The fleet brought back to China

silver, spices, sandalwood, precious stones, ivory, ebony, camphor, tin, deer hides, coral, kingfisher feathers, tortoise shells, gums and resin, rhinoceros horn, sapanwood and safflower (for dyes and drugs), Indian cotton cloth, and ambergris (for perfume).

The beautiful cobalt blue that Ming vases are famous for? That's not from China; it was imported from Iran during the treasure voyages.

So I would introduce the mass-production of rifles during this period. It would make me wealthy and influential within China. However, I'm not doing this for the sake of the technology, but to curry influence with the Emperor to prevent the country's downfall.

You see, '16 was about the time that the Emperor got the idea that he needed to build a wall to keep out foreigners. They already had a wall, but this wall would be bigger and beautiful. It would be Great. But the Emperor needed money to build the wall, and so he shifted resources from international trade. This ended the treasure voyages, severed diplomatic ties with allies, and caused economic collapse at home. China would cease to be a superpower for nearly 600 years. Oh, and the wall didn't work -- they were invaded anyway.

So I'd use my wealth and influence to stop the Emperor from building his stupid wall. All of the workers who built the wall should instead be patrolling the border -- with my rifles, of course. And China would have 600 years of technological development as a global superpower.

• Great answer, different form the rest in a good way! The rifle technology is a great idea and it could be a perfect combination with some modern medicine, like penicillin - the soldiers have better offense and a greater chance of survival! – Jinjinov Jul 26 at 9:22
• There's a very unexpected reason why, despite China developing gunpowder, proper guns weren't developed until Europeans got ahold of it. And like the steam engine I've discussed elsewhere on here, it has to do with quality metallurgy. The Chinese didn't know how to produce metal tough enough to serve as a gun barrel; that gunpowder explosion produces some intense pressure, and if you're going to shoot it over and over, you need some really tough metal. The Chinese didn't have this, but the Europeans did, because of their long tradition of producing church bells, of all things! – Mason Wheeler Jul 29 at 15:15

Forget Engineer or Economist. We Need to Send Back a Sick Megalomaniac with Serious Delusions of Grandeur

Carefully reading again your question, the purpose of the time-travel is to help humanity overcome a [slightly] superior alien race invading earth, in a war where humans are about to lose.

For humans to win, humanity needs to be prepared to fight an Armageddon war of survival over a superior alien race. Superior technology is important but not enough (Nazi Germany was slightly technologically superior over the allied forces but still lost)!

Preparing humanity to fight a decisive battle for its survival is a colossal task. one that would require multiple centuries if not more. That rules out a short jump back in time.

Given our knowledge of human history, the only conceptual vessel that can withstand millennia and propel the necessary technological, social and intellectual colossal build-up of humanity to win a fight for its very survival is religion.

To my opinion, the only means by which humanity can be empowered to prepare for such a doomsday fight is to go back in time and either intervene/change/mold an existing religion or inspire the creation of a new religion.

The new religion will need to revolve around the war that is to come, teach all that is to know about the alien race that is to invade, promote and reward all human practices that may be advantageous for winning that war (technological advancement is one but there are other human traits like leadership, spartanism, discipline, etc.) and remove other human-nature obstacles like pacifism, dispossession or racism which may derail humanity from being well prepared. I can totally imagine a scenario where aliens invade earth and we waste valuable time trying to negotiate with them, compromise with them or appease them in various ways. If we have the benefit of knowing their genocidal goals today, a pacifist approach need to be discouraged in the past.

Given the magnitude of religiously inspired human achievements throughout history, from the building of the pyramids to the colonization of the Americas, the new religion will direct human ingenuity and human creativity to advance constantly in the path of assuring superiority.

The only problem with religion is that there is a huge difference between what we are taught and what historically happened. Therefore, sending someone back to somehow influence Christ or Moses may be a futile task because he might very well discover that non of them really existed. This is why I will opt for the creation of a new religion rather than influencing an existing one by "hooking up" with its believed founder.

Therefore, to my opinion, the best person to send back is not an engineer (although solid engineering knowledge is a must) and certainly not an economist. The ideal time traveler for the task is a gifted demagogue with proven abilities of mobilizing hoards of people. He would have to be extremely intelligent with degraded morals and serious delusions of grandeur, with a psychological need for people to follow him/her because this will be a lifetime mission. He would need to be propelled by deep psychological motives so we can all trust him to stay on course and not fall in love with a disciple and forget about it all (I have a list of historical figures who would fit the bill, you're probably thinking the same).

The task of those who send him back in time would be to equip him with the necessary means to practice as much influence as possible, over as many people as possible in as short of a time as possible. These means will have to include punitive and rewarding technologies, because punishment and reward are the best human motivators. He would need to have the power to inflict deadly diseases and cure them just as fast. He would need to be able to show deadly displays of force but also spectacular demonstrations mercy and generosity. He would need to be able to defend against the many attempts to end his life because like all people of great influence, there is always someone who wants to kill them.

Last but not least, assuming there is a room for a computer to send with him, that computer should be functioning as his most trusted aid. A powerful artificial intelligence that can provide solutions to problems by drawing on vast historical and scientific knowledge. Nevertheless, the biggest, most complex task of that artificial intelligence would be hidden from our megalomaniac time-traveler. The hidden task of the artificial intelligence would be to end the life of our time-traveler in the most perfectly orchestrated manor to assure best conditions for our time-traveler will become a Martyr, because throughout human history, the sacrificing of one's life for a cause had always been the best motivator for others to do the same.

Bottom line... given we send him enough time back (like a millennia or two) we might actually succeed in creating a dominant lasting religion, based on the ethos of winning that Armageddon war that is to come, with enough of humanity following it (at least enough to dominate the rest). That religion will guide generations of humans to invest the necessary means to assure human development in the desired direction.

The only problem is... although we might live to win the war, i'm not sure it would be any fun living as a human.

• Interesting and a bit scary... :) While it might work and the benefits would be great if it does, it might also fail with disastrous consequences. Also, this answer is so far the only answer that makes use of the advanced computer brought from the future. – Jinjinov Jul 26 at 7:49

I agree with the others on the point that close to 2000 AD would be the best time period to go, give or take a couple of decades. The most important info to bring would be the blueprints for future batteries and power sources and technology relevant to their production. Because that is the greatest limiting factor of today's tech. Everything else has been miniaturized today to ridiculous levels. We also have conceptual design of highly advanced tech and weaponry, but their power requirements are equally huge and current power supplies are simply too inefficient. So the progress of current humanity is actually being held back by the lack of suitable power source.

Of additional importance would be an efficient power transmission system, since preventing leakage and waste of power during conversion is just as problematic.

Finally, make sure to bring a proper data and power converter/adapter/connecter for your storage device. You don't have to be from the future to know the disaster of not having one when you need it.

Saturate the human race and it's history with the knowledge of time travel. Godhood will follow.

If you can take knowledge back in time little by little and educate our ancestors, the future will become more and more advanced.

Pass all your knowledge to an earlier form of yourself (providing you exists in the present and past simultaneously in your scenario) or another scientists. Let them repeat this process. Accruing the knowledge earlier allows for more expansion upon it later. If you repeat this process you can have the first man have the knowledge of time travel. Repeat with the knowledge of manufacturing the required technology and all that will keep you back eventually is a workforce.

Imagine, if you will, the Pharaohs using their workers to build time machines, tanks and jets rather than pyramids. The Romans of ancient Greece making use of drones and nightvision goggles in their armies. The Crusades happening with motorbikes and sub-machine guns.

The human race's history would radically change. In what ways would be up to you as the writer.

These kind of questions are typically within the restriction of a mind in 3D conditions. We humans tend to think of physical devices and technology, finding a way to travel in time. Just for argumentation and pondering, imagine a level of consciousness where materialization and dematerialization is a natural ability in living conscious beings. Keep in mind that levels of consciousness can be compared to the bandwidths of a radio, those that are shown on the device as L M FM etc. Instead of tinkering with mechanics, one could look into an entirely unknown and unexplored direction, the power of the mind.

Time travel happened, sort of by accident, during the Philadelphia Experiment in Montauk. There's a book about this event, that ended horribly wrong. Part of that experiment was dematerialization and materialization, in that order. A vessel and its crew were involved and after it showed up again, members of the crew were found merged with the body of the vessel. An experiment that was one of the first tryouts with human lives at risk. There's a youtube video with Bieleck Cameron, who joined the crew with his brother Duncan. In an interview he talks about his time travel to the future. https://www.youtube.com/watch?v=HyH3yjupayA

• Well, i'm not sure if you really think that or if it's just a fictional answer. Anyway, trying to clarify for other readers: the Philadelphia Experiment is a hoax. Anyway, that's not a proper answer to the question. – theGarz Jul 25 at 7:24
• If you're throwing out information that is based on hearsay, I'm doubtful if I'm in the right place here. You need to do your homework, theGarz. – Marian B. Jul 25 at 12:58
• First: It's not me that's "throwing out information that is based on hearsay" and i don't accept your suggestion to do homework. I already did mine studyng Russel and his teapot. en.wikipedia.org/wiki/Russell%27s_teapot You, not me, are supporting facts contrary to the physical laws known so far, then we can disscuss it but the burden of proof -the homework- is up to you. Also, Occam's razor suggests that's you, and not the entire scientific community, that's wrong about the so called Philadelphia Experiment (an oxymoron, actually). – theGarz Jul 25 at 14:29
• Second: even in this very section, worldbuilding, you answer is definitely OFF TOPIC! Op asked about a time travelling ENGINEER, you replied with something about "levels of consciousness" and a trivial-to-be-debunked event. There's a book about it? Nice, who cares? Guess what, there's a book also about Lord Of The Ring. Your answer simply doesn't fit the question. Nothing personal in my first comment and, thanks to another philosophical razor, the Hanlon's razor, i'll skip my usual reply for those who flaunt mental superiority. – theGarz Jul 25 at 14:29
• PS: i also doubt that you are in the right place. I'm not the questioner, it should be self evident, but more important is that you totally missed the way this site works (and it works, BTW). Some citations: "This site is all about getting answers. It's not a discussion forum. There's no chit-chat." "Read the question carefully. What, specifically, is the question asking for? Make sure your answer provides that" "Good answers are voted up and rise to the top." "The person who asked can mark one answer as "accepted"." I'm totally entitled to downvote an (your) answer. – theGarz Jul 25 at 14:31