How long would it take to build today's technology?

[manaiaK]

The question is a bit loose. By build, do you mean "re-invent" (have one example of) or "reproduce" (have today's technologies in widespread use)?

First rule of development projects: it always takes longer than you think, even when you allow for the first rule of development projects.

As was pointed out, the first thing that happens is that 80% of the population starves to death. The key thing about that, though, is that it's essentially 100% of the people in the more advanced areas of the world. People who aren't using today's technology are the ones who would survive. And if they're not using it now, why would they be motivated to reproduce it?

Second rule of development projects: it doesn't happen if it's not wanted enough.

Also. Just having 'unlimited' energy is not enough. The sun provides us with energy at the rate of about 85 petawatts, or usable energy (exergy - energy that can do work) of the order of 90 terawatts, five times as much as we globally produce and use currently. But we have machines to use it and networks to distribute it.

Assuming that somehow the survivors of this catastrophe want to reproduce today's technology as seen in the industrialized countries from scratch, I can't see that happening in less than 300 years. That's if everything goes perfectly smoothly. Probably more like 1000.

[Endersmens]

We need not worry about food. Seriously. All conditions are ignored except built time. Unlimited resources, no starvation. Just. Build. Time.

[Brethern]

We need not worry about food. Seriously. All conditions are ignored except built time. Unlimited resources, no starvation. Just. Build. Time.

Are we talking standard 8-5 or 8-8 working?

I'd say minimum of ten years. You can build something from schematics, but until you do so once you're not going to be able to build it fast for efficiently.

The Da vinci tank is a good example, you can build one for the plans, but unless you realize that he intentionally sabotaged it you're not going to be setting up a production line.

[Mazon Del]

The most difficult part of this is that the build time is entirely dependent on your existing industrial base, and your population size is largely dependent on your industrial base. You cannot say for example that "You have zero items, but you have 1 million clothed people, GO!" Because at time +1 month, a huge portion of those people are dead due to starvation and exposure to the elements. Eventually you get some random middle ground where enough people died while enough stuff got done to have some percentage of the original million still doing stuff, another percentage is alive only because they went far enough away from the main group that they could easily find resources for themselves to live but are now useless for the Challenge, and another (rather large) percentage that died. These people are more going to be tasked with expanding their own living infrastructure which does not directly mean expanding the useful infrastructure. Digging ditches for waste or setting up farms for example, helps them live but doesn't necessarily help their industry.

If you say that the million starts with the industrial base to keep them alive, then they get a bit of a jump start because they can choose to cannibalize some of that industrial base to skip ahead several eons on the tech tree.

Even if you assume your populace starts with a magical giant building that keeps them alive and fed, the primary limiter you are going to have on development is actually gathering resources rather than working. Need aluminum for something? Well, we have no idea where it is. Time to send out scouts! Then IF you find some, time to set up a mine!

In the end, if you finally assume your populace starts with a magical giant building that keeps them alive, fed, AND provides unlimited resources for them to work with, then the answer ends up being that in many ways it wouldn't take all that long. A day to set up your crappy stone furnace, start melting iron and converting it into wire. Eventually you have a nice spool of wire. Order some hematite (I am assuming you get it magnetized) and shove it in middle on a spinning shaft. Another day (probably much less, you have a lot of people, this is probably ready) to set up a system to turn that one fast. Bam! You have electricity, now you can use it to generate electricity necessary to make stronger magnets, which means more efficient conversion of motion to electricity. After a certain rather quick point, you now have the ability to make some crappy DC motors, and now you have the ability to make mills, you just need something strong enough to use as a cutting blade, but likely you (given the metallurgy knowledge you start with) also had someone else whip up something good. In relatively short order you have the ability to machine items to a precision we've had in roughly the last 50-80 years or so. With precision machining, most other things happen fairly quickly, it just again ends up a matter of throughput.

So really, with a big enough group of people and a sufficiently magical test area probably not more than 5 years to get up to something like pre-digital computer Earth and then 5-10 years after that to reach an acceptable level of "The digital age".

[sojourner]

You guys would like the Crosstime Engineer book series. A chemical engineer get accidentally dropped into 12th century Poland and proceeds to turn it into the most advanced nation on earth.

[magnemoe]

Steam engines have to many mechanic parts that have sharp tolerances. Entry level electric power can be driven by water turbine, all thats required is a shaft and a plaform and a dynamo. Once you get an electric smelter then you can build the pressure hull for a steam engine. You have to be abke to heat iron/steel reliably hot enoughbso that it can be poured and rolled. If course the first parts you want to make are the steel working tools. This is all going to be done in initially wooden factories so we can expect quite a few to burn down.

Unless of course you find aluminum salts and bake lime from stone to make cement, which can be used to make foundaries of concrete beam, which of course needs reinforced iron rebar.

Its not simply regurgitating textbook knowledge, its a process that will take blood and sweat and a few lives while you worknthrough th low tech hazards phase.

Late steam engines had tolerance levels like early IC engines the first one had wide tolerances, this is a question of how good machine tools you have.

I agree that we will do things different than in history, electricity will come much faster for one.

- - - Updated - - -

You guys would like the Crosstime Engineer book series. A chemical engineer get accidentally dropped into 12th century Poland and proceeds to turn it into the most advanced nation on earth.

Plenty of books about this setting, isles and flints 1632 is just two.

The first one fits this setting as an island is sent back to BC2000 or something.

[Mazon Del]

1632 is pretty great, especially since he was given an actual inventory of a town (everything the people were willing to admit they had or knew they had) much like the one that got sent back in time. However it isn't really worth reading past book 4 or so. At that point he kind of gets into a war with his own readers concerning the Grantville Gazettes and his quality started to suffer a bit...then he got bored and started jumping ahead in his timeline, without filling in the blanks where other books were supposed to go...

[PB666]

The question is a bit loose. By build, do you mean "re-invent" (have one example of) or "reproduce" (have today's technologies in widespread use)?

First rule of development projects: it always takes longer than you think, even when you allow for the first rule of development projects.

As was pointed out, the first thing that happens is that 80% of the population starves to death.

80, try 99% prolly more like 99.9%. Since consider everything you eat, unless you live in the amazon is technically speaking a technology, and everything that people who lived where you live now ate, pretty much pushed off the landscape. I suspect that once 50% of the population has starved cannibalism will kick in and the population will begin to flatten out. Certainly in the big cities it would be like the siege of Stalingrad. The first skins and leathers will prolly be human. But anyway this would be a necessity, dead humans lying all around only foul the water supply and spread disease. Any one recall what Atilla the Hun did to 'Poland', you don't want that.

The key thing about that, though, is that it's essentially 100% of the people in the more advanced areas of the world. People who aren't using today's technology are the ones who would survive. And if they're not using it now, why would they be motivated to reproduce it?

Second rule of development projects: it doesn't happen if it's not wanted enough.

Hah, what about Windows 10! Well there are wants and then there are wants, and there are needs. The survival needs will occupy at least the full of 3 years. In great luck you will have housing within 6 months, for whoever figures out how to make stone axes or adzes. Don't forget also, for that technology to come, the ladies are going to have to start spending most of the day in domestic occupations, gardening and farming, child-rearing. You loose half your labor force right off the bat.

Also. Just having 'unlimited' energy is not enough. The sun provides us with energy at the rate of about 85 petawatts, or usable energy (exergy - energy that can do work) of the order of 90 terawatts, five times as much as we globally produce and use currently. But we have machines to use it and networks to distribute it.

Assuming that somehow the survivors of this catastrophe want to reproduce today's technology as seen in the industrialized countries from scratch, I can't see that happening in less than 300 years. That's if everything goes perfectly smoothly. Probably more like 1000.

Industrial steel working is key, the sooner you can get to that point the sooner you can make tractors for growing crops, pressure holds for building steam engines for trains and mechanical in factory's. You can't even have an oil industry without the ability to make a distillation apparatus or a cracking unit. So if its not a big rush to get steel plating its a fail.

The key multiplier is to remove sustenance farmer and put him in the factory, until you can get there you are still behind the game.

[sgt_flyer]

Well, even triying to list some of the basic key technologies needed is going to take some time

Though, among the earliest technologies, (with fire and stone tools) you would find pottery (helps holding liquids, notably water, for metal work, and you can make bricks to create some basic furnaces too. Besides, you'll also find use of ceramics for holding chemical products, notably for early acid uses. Add leatherworking, etc - (which you'll need for making bellows to stoke your furnaces.) and you're pretty much set for working with a lot of metals (and glass making - for easier distillation of chemicals )

Fast forward some technologies, and you'll have some insulated copper wire + magnetic iron (for your permanent magnets) - very easy from there to build crude dynamos and electric engines (though you might still rely on mechanical power until you have more precise and efficient electric engines) after this point there start to reach more modern & true precision stuff therés a lot of various technologies and industrial process involved - so you'll have a really big basic industry boom to simply be able to sustain the build of higher tech industries, and etc

Edited October 19, 2015 by sgt_flyer

[ChrisSpace]

So here is the question: With all of today's knowledge, how long would it take to go from nothing to having all the technology we have today?

Now, before you say instantly, think about this. While much of the time from the stone ages until now was spent in developing ideas and inventing, some of it was actually spent building. And, think about this. In order to make the computer you're likely reading this on, precision machines assemble precision parts together. In order to make those machines and parts, more precision machines are needed. To make those, precision hands are needed and premade materials. If we were to start over with nothing, this process would have to happen. The first tools would be used to make better tools, those tools to make even better ones, ect.

So, only taking into consideration build time, how long would it take to go from nothing to today's technology? Give your guess below! If I had to guess, purely on build time, I think we could go from nothing to today's technology in a matter of years, under a decade.

Pretty much all of my favorite Minecraft modpacks go off this concept: Starting in a completely untouched world with no humans on it, and slowly developing better things until you can build rockets, nukes and modern infrastructure. Of course, everything is overly simplified so my heavily modded Minecraft games can't really be accurately used to determine much. Still, I am very familiar with this concept.

This actually happened. Kinda. Tzarist russia before bolsheviks revolution was underdeveloped agricultural nation with almost nonexistent industry, all science and industry imported from west and ravaged with war to boot. Forty years later they beaten americans to space.

No. Russia was never anywhere near 'square one'. Relative to western Europe they were, but in total they were extremely more developed than a Russia-sized population of people just being dropped into the wilderness.

The first thing people will do, hopefully, is finding ways to record all knowledges right away, in some form that would last behind for a while with high fidelity, before the first generation who has all the current world knowledge and experiences die off and leaving a generation never seeing technology before behind.

A more interesting scenario would be if only a small and sterile (perhaps 100-200 people) group of people were dropped onto an uninhabited earth-sized planet but were completely immortal. On one hand, the population couldn't increase and you would only have a tiny population, but on the other hand, all the knowledge and memories stay in the population indefinitely. It would be interesting to see how fast this group could develop.

As for a time estimate, it depends entirely on the population you've got. If you dump 1 billion people on a virgin earth it will go much MUCH faster than when you send 10 guys.

If we go with my 'everyone is immortal but infertile' idea, this would probably become the biggest factor. I think it would be the most interesting to see what a group of 2000 or less people would do, but obviously more people would make things go along faster.

If you're interested in this stuff, You could try the book "The Knowledge: How to rebuild our world from scratch". It explains a lot about how to rebuild modern machines from scrap.

I will certainly look into that. Thanks!

At the time of posting I was ignoring resource gathering, which takes out agriculture and mines and such.

Oh. Yes. Agriculture. Umm... how would that work in an immortal scenario? Perhaps they can live forever if they just eat food / drink water?

and the technology, give the roman legions ak-47s, aircraft and nukes and see how long it takes them to take over/destroy the world.

Civilisation V in a nutshell.

13.82 billion years. Based on empirical evidence.

Technology has only been developing for a few million years of that. We aren't building a universe here.

well, to help 'restart from zero' we would also need to refill all the surface deposits of minerals first

Yes. In my little scenario I set everything back to how it was around 4000BCE, minus the humans, human artifacts and now-extinct species.

You guys would like the Crosstime Engineer book series. A chemical engineer get accidentally dropped into 12th century Poland and proceeds to turn it into the most advanced nation on earth.

My face after reading that second sentence...

Plenty of books about this setting, isles and flints 1632 is just two.

Okay i'll read that as well.

[Mazon Del]

Incidentally, if any of you like this concept, you should check out the game Factorio. *drools*

[wumpus]

That's still not nothing..

There are several technological cycles required to get to steel production.

Food cycles, domestication cycles, natural product extraction cycles

just to get electrical smelting operations, 10 to 20 years.

Once there its a matter of ramping up coal fired power plants.

So we are talking minimally 60 years.

And btw, all the schematics for building things, all now stored on computers. They are lost, anything that does not have a paper copy would be lost. And to copy paper, you have to build paper making and printing technologies. So the ability to distribute information basically collapses to hand transported and people hovering over diagrams in library transcribing (pencil technology, iron gaul ink technology) until you have a modem and an 8088 or Z80 processor. By the time we got to the point we could actually build an 8088, all the people who would have been familiar with its manufacturing would be long dead, so you hope that you made paper and writing quickly as to understand what they did to make those chips.

[How big is the population? My guess is the question implies some sort of spaceship lands with zero tools (God/Vulcan made the first blacksmith gloves...) but with a full library, living quarters, food supply (quick, trick it into supplying vegetable oil for a diesel engine).]

Except that to build an ENIAC you need the ability to make reliable* vacuum tubes and a lot of wire. To *run* the ENIAC you need ridiculous amounts of electricity (said to be enough to dim the lights of Philadelphia). You wouldn't build an ENIAC: you would make sure you had magnetic core memory first, and use that instead of the SRAM-like vacuum tube disaster that ENIAC used (you also get to put your software into the core memory instead of using wire jumpers like ENIAC used. You then make something like a PDP-7 tuned to feed some sort of vector floating-point processor (assuming you need math tables for whatever reason. If you are heading straight to recreating the internet, maybe some sort of SMT design for multi-users).

This pretty much means that you don't care about existing schematics/PCB/IC layout. While schematics might be on computers, they typically assumed a full computer-controlled PCB manufacturing process plus pick and place (I'm furiously ignoring a bit in the 90s where that wasn't quite true in a lot of places, including where I worked). You don't want a 8088 in much the same way you don't want an ENIAC because the 8088 was a gawdawful kludge. You would go from something like a Chuck Moore (the Forth guy, not the Intel co-founder) Forth chip (for absolutely minimal transistor availability) straight to something like ARM or Alpha.

Reproducing Moore's Law would largely depend on population. Obviously, the whole question should be man-years, not just years. Easily the biggest reason Moore's law has worked the past 40+ years is that we have been buying every transistor that the Silicon Valley (and other places) can make. If you can't spend billions on a fab, you don't get a fab (and haven't gotten one for years). Of course, you could easily declare ".28um is good enough", in the 20th century a smaller chip was faster, cheaper, and used less power. Nowadays it is pick just one (usually low power).

* reliable vacuum tube is pretty much a contradiction, but at some point the thing has to run long enough to make progress. Without using vacuum tubes for memory you should need a lot less tubes.

[PB666]

You don't need to invent vacuum tubes to make transistors, and its a completely different technique to make microprosessor. Your target level processorcis the. 8080 or the Z80.....,assuming someone etched the schematics and/pricess into a gold brick and burued it some place convinient. Another target is the 200 baud modem and RS232 communications relay (a technology that is still being used). CRT are optional, but ossciloscope is stll useful for other things.

Edited October 21, 2015 by PB666

[magnemoe]

1632 is pretty great, especially since he was given an actual inventory of a town (everything the people were willing to admit they had or knew they had) much like the one that got sent back in time. However it isn't really worth reading past book 4 or so. At that point he kind of gets into a war with his own readers concerning the Grantville Gazettes and his quality started to suffer a bit...then he got bored and started jumping ahead in his timeline, without filling in the blanks where other books were supposed to go...

Agree here, note that 1632 got it easy they landed an place who was pretty ready for an industrial revolution.

Isles in the sea of time had an harder time 3000 year earlier, they did not get past the early industrial phase in the books outside of scavenge technology, Example: use an motorcycle engine for an ultralight plane and you have air recon for your musketeers, elite snipers had modern guns. They managed to build an long range airship out of various parts for strategic airlift and recon

- - - Updated - - -

You don't need to invent vacuum tubes to make transistors, and its a completely different technique to make microprosessor. Your target level processorcis the. 8080 or the Z80.....,assuming someone etched the schematics and/pricess into a gold brick and burued it some place convinient. Another target is the 200 baud modem and RS232 communications relay (a technology that is still being used). CRT are optional, but ossciloscope is stll usefuk for ither thungs.

Yes, you would probably never use vacuum tubes for computers, transistors even very primitive integrated circuits is not so hard.

You will use them for radios, its 19th century technology not way harder than light bulbs.

CRT is also not so hard, say its on line with transistors.

[sal_vager]

Oscilloscopes are indeed useful.

And there are other displays older than CRT.

[wumpus]

Are making transistors (who have some unbelievable purity requirements) really that easy? I guess it depends on how far along you have your chemical industry. I think there is a patent on the transistor from the 1920s. The kicker is that the patent describes an incorrect process: all working transistors from that era included contaminants (presumably the doping "real" transistors need).

And for the ~Z80 level integration, I'd prefer a 6502 but you really want to stick a stack in there. Not necessarily a full-blown Forth chip like I alluded to, but would probably crank up C as well (at least the C that fits in a few kbytes). The followup chip would be strongly stack oriented (mostly so you could have all sorts of on-chip DRAM for whatever registers you need. Stacks mean everything but one register need only one R/W port). Unfortunately, this is a dead end as well and it is off to ARM/Alpha land a few more shrinks down the road.

I still think the key is to skip as many disasters as possible: non-transistors alternatives to core, move to DRAM as soon as possible, understand most of the issues behind floating point. Understanding the break points between structured and OO code (don't ever use spaghetti code, and switch to OO when your data>>code). Don't use anything like x86 (mainly the segments, but really everything). Don't use anything like DOS. Don't trust anything from the 'net (i.e. don't use anything like windows* [or at least any of the "run anything it sees" model splattered across all windows editions]"

* while I'm writing this from Linux I almost always play KSP under windows. Not sure which version it was, but I suspect my nvidia drivers had more bugs than 64-bit windows (yes, ran it for awhile) KSP.

PS. Note that most of these "don't do that" are all about using the benefits of hindsight (there was no excuse for releasing activeX in 1996). As much as the 8088 segmenting model was hated, if it was just stretched a little further (over 8 bits instead of 4) it would roughly lasted until replaced by 386 flat addressing. In 1977 64k was a ton of memory (and using memory in 256 chunks at a time would seem wasteful), so they didn't (I suspect that the real reason was the extra 4 pins or so, motorola made a similar "mistake" ignoring the upper 8 bits of addressing words. Quite useful on the 68000, incompatible on the 68020.

While I recommend jumping to stack/Forth chips as soon as possible, it badly limits pipelining and executing multiple instructions (possible with completely new architecture, but not really worth it). Who knows, maybe it will get the idea of multi-threading started early enough in the industry (these small fast stack chips should be much smaller than deeply pipelined multiple execution units). Note that this should also skip the "close the semantic gap" issue: when assembler was still fashionable, it made sense to make architectures that could be easily programmed in assembler. This lead to lots of ways to address memory. It turns out that the real benefit to RISC (reduced instruction set computing) should really be called (reduced instruction set complexity) and that the complexity of the addressing modes (so loved by assembler writers) were the biggest (and really only insurmountable) one. Basically you would go from stack chips to modern Out-of-order chips written in C-ish (obviously the string library would be sanely written, malock-free would presumably be more careful (I don't know the whole story on this) and other pitfalls more carefully avoided (I'm guessing that C would be designed to compile under Objective-C and C++ would never get used).

Edited October 21, 2015 by wumpus
lots of blather added to justify my "don't do that " comments

[manaiaK]

non-transistors alternatives to core, move to DRAM as soon as possible, understand most of the issues behind floating point.

Non-transistor memory? For a good chunk of computing's history that's what we had. Way more reliable than vacuum tubes and early transistors. DRAM uses CMOS transistors which are fairly sophisticated devices: you're not going to get to being able to make them any time soon.

But we're down in the weeds here. I laugh when people say "we're good when we can make steel". To make steel you need high-purity oxygen. Once you have mild steel you're just at the start. There isn't just one kind of steel, there are over a hundred steels in common use, each with differing amounts of alloying elements: chrome, nickel, vanadium, molybdenum, silicon, boron, copper, aluminum, etc., etc., etc. To make "steel", i.e. fit-for-purpose machine tools as well as tin cans and paper clips, you need to be able to isolate and refine a lot of other elements as well (for that, you need acids, for a start), and you need to be able combine them predictably and precisely. Similarly, there isn't just one "concrete", one "glass", etc.

Likewise: steel totally sucks as an electrical conductor. If you want electric light or power (and you do!) you need "copper" and all the technologies that go with making the different alloys and workings of copper. And so on. There is a lot of knowledge that's completely invisible to the average person.

What I'm saying here is that you can't focus on one or two "key materials" and ignore the industrial infrastructure they're built on. It's all necessary ... except for telephone sanitisers, as Douglas Adams showed us .

[sgt_flyer]

There has been other methods of making steel way before using pure oxygen.

(Crucible steel was used for a very long time, but the process was not suited for industrial use)

For industrial processes, Using normal air had the problem of embrittlement due to the nitrogen,

However, some industrial processes were very controllable and eliminated the nitrogen problem (it was much slower than which pure oxygen, but you can increase the number of factories to make up for it until you can use pure oxygen directly) :

https://en.m.wikipedia.org/wiki/Open_hearth_furnace

The key point was that they made use of the oxygen trapped in Iron oxides to remove the excess carbon in pig iron to create steel

And structures similar to the open earth furnaces have been found dating all the way back to 8th century (ok, they don't know if it was used for actual steelmaking, but if the basic structure could be built in the 8th century, someone with the appropriate knowledge would have been able to make basic steels - steels that he'll be able to use to create far more durable and precise tools than Iron tools to help you build the next generation of even more precise machines

Edited October 23, 2015 by sgt_flyer

[wumpus]

Follow some of the above links to see why rebuilding today's tech might take hundreds (or thousands) of years.

You need a blast furnace: easy? You get to make the whole thing out of bricks (you can't reinforce concrete. You can't really find anything better than brick. You get to hand mold and fire the bricks nearly individually). You dig the foundation with shovels. Any roads built to bring coal and/or ore also are dug by shovels (any guesses why Pittsburgh is a mountainous horror for modern drivers but does contain 3 rivers (and very expensive bridges)?). Once that is built you can *start* by building low quality machine tools (to build medium quality machine tools that might somehow cut the improved steel you need for 19th century machine tools...).

The sheer amount of infrastructure needed to build each level boggles the mind. The biggest difference is that during actual history 90% of the population was out in the fields producing food, presumably this thread requires wildly less population than the original method. Amdahl's law (which states that computers [really algorithms] are limited by the serial portions and that adding more parallel hardware stops increasing speed far earlier than you thought) applies here as well. You aren't progressing up the tech tree until you have finished *all* of each level of said tree. James Burke [see Connections] has built an entire career out of pointing this out (well worth seeing if this isn't obvious to you, if you know it better you will find some really iffy connections).

Want to build a printing press? You need paper (it doesn't work all that well on sheepskin). You need fine metal casting (Guetenburg was a goldsmith...). You need a new type of ink (lampblack, cottonseed oil and gum arabic in roughly equal quantities will do). You need a [grape] press (probably the easiest part, often seen as the "invention" by those who never looked closely). Keep looking deeper and you only run into more issues that have to be engineered out, and expect to run into issues that absolutely require an intact infrastructure to build (the Wright Brothers knew they were not flying until they had at least an 8 hp engine under 200lbs (it actually made 12hp)). Get a 25hp engine at that weight and you can start to make a brick fly...

Personally, I'd expect to have vacuum tubes before transistors, but the existence of a 1920's transistor and assuming a textbook explaining how they work might make it possible. Presumably you could make vacuum tubes with 18th century tech, but slowly building up the tech to generate electricity would be a killer. My guess is that you absolutely *need* that electricity for your chemical industry: that would be the reason it gets built. Whenever a computer gets built is dependent on the tech level the power is available (also assuming a bias towards computers that our hypothetical population probably wouldn't have).

[magnemoe]

Follow some of the above links to see why rebuilding today's tech might take hundreds (or thousands) of years.

You need a blast furnace: easy? You get to make the whole thing out of bricks (you can't reinforce concrete. You can't really find anything better than brick. You get to hand mold and fire the bricks nearly individually). You dig the foundation with shovels. Any roads built to bring coal and/or ore also are dug by shovels (any guesses why Pittsburgh is a mountainous horror for modern drivers but does contain 3 rivers (and very expensive bridges)?). Once that is built you can *start* by building low quality machine tools (to build medium quality machine tools that might somehow cut the improved steel you need for 19th century machine tools...).

The sheer amount of infrastructure needed to build each level boggles the mind. The biggest difference is that during actual history 90% of the population was out in the fields producing food, presumably this thread requires wildly less population than the original method. Amdahl's law (which states that computers [really algorithms] are limited by the serial portions and that adding more parallel hardware stops increasing speed far earlier than you thought) applies here as well. You aren't progressing up the tech tree until you have finished *all* of each level of said tree. James Burke [see Connections] has built an entire career out of pointing this out (well worth seeing if this isn't obvious to you, if you know it better you will find some really iffy connections).

Want to build a printing press? You need paper (it doesn't work all that well on sheepskin). You need fine metal casting (Guetenburg was a goldsmith...). You need a new type of ink (lampblack, cottonseed oil and gum arabic in roughly equal quantities will do). You need a [grape] press (probably the easiest part, often seen as the "invention" by those who never looked closely). Keep looking deeper and you only run into more issues that have to be engineered out, and expect to run into issues that absolutely require an intact infrastructure to build (the Wright Brothers knew they were not flying until they had at least an 8 hp engine under 200lbs (it actually made 12hp)). Get a 25hp engine at that weight and you can start to make a brick fly...

Personally, I'd expect to have vacuum tubes before transistors, but the existence of a 1920's transistor and assuming a textbook explaining how they work might make it possible. Presumably you could make vacuum tubes with 18th century tech, but slowly building up the tech to generate electricity would be a killer. My guess is that you absolutely *need* that electricity for your chemical industry: that would be the reason it gets built. Whenever a computer gets built is dependent on the tech level the power is available (also assuming a bias towards computers that our hypothetical population probably wouldn't have).

Then you get into 1900 level technology the main constrain become population and that restrain will grow exponential as you go up.

You can do 1850 level technology in an decent sized village however even here you run into issues as lots of stuff require factories to be economical and the factory need an marked to make sense.

The time traveler going back to say roman time has the benefit that Rome was an million city, the 1632 series had the benefit of landing in an place who was pretty ready for an industrial revolution, after 5 years the locals do most of the inventions.

Say you dump 100 people on an empty earth and it will take generations, if you make them sterile and immortal they probably reach the iron age but might stay hunter gatherer as its easier than farming. They will not go farther as its take more resources than the benefit it give.