This is more of an engineering question than a physics one, but I thought you might enjoy mulling it over: you know that trope in sci fi stories where someone brings an ipod or a laptop or a mobile phone or something either back in time, or to a significantly less technologically developed civilization, and it dramatically accelerates their technological progress? Would you like to speculate about the sociological and technical factors governing the ability to exploit such a windfall?
OK, so, there are kind of two parts of this question: first of all what use would a smartphone or laptop, or the technology you might find by reverse-engineering one, be in (very broadly speaking) non-industrial times? And second, what hope do you have of manufacturing more of them? (A third question: if you’re planning on time travelling, what should you bring with you?)
General difficulties of time travel
Before we talk about electronics, however: travelling into the past is not going to be easy. You will not speak the language. (If you’ve studied surviving literature from the period, you may be able to read and write it to an extent.) Your information about politics and society at the time will be limited to the very skewed representation in whatever accounts are left, and a lot of speculation. You will not fit in. You will not know what you are doing.
Before you communicate anything about technology, you will have to work out the basics of talking to people, getting enough to eat, having a safe place to sleep, and so on. You won’t know more than the vaguest ideas about the most basic ways of living in this culture - don’t imagine that because you’re from the future, you know anything about how to live in this different society.
You also don’t necessarily know how you’ll be understood in relation to ethnicity, gender, etc. Or perhaps you do know, and it’s helpful/unhelpful. For most parts of the world, statistically, you’ll look like someone not from there I guess? Though no doubt people will find a way to make sense of you.
And of course, regardless of how hygienic your living conditions are, you will get sick. You’re facing an entirely different population of diseases, some of which may no longer exist where you live, others simply in different forms that your immune system is not familiar with. (Consider how adaptable the flu virus is, even year-to-year.) There’s an excellent chance that, no matter what medicine you take with you, you’ll die within months of arrival.
Additionally, the chances of creating a system of production on the scale we depend on today to produce devices like iPhones, within your lifetime, are pretty much negligible.
But let’s say you won’t let that stop you.
One other thing: ‘technological progress’ is… less than sensible as an idea. There’s no straightforward progression of technologies except insofar as everything works within the same rules of physics. There’s no reason to assume any individual technology, broadly interpreted, adopted by our particular weird global capitalist society would have cropped up if history had gone a different way.
Infrastructure is quite important, actually
Anyway! Let’s start with the really big limitations.
So the first problem of using any electronic device is the absence of a way to power it. There’s no electricity grid, naturally, and to charge a phone you need a stable source of electrical power, whether AC or DC. (Mains chargers generally convert their input power to DC.)
If you have time to prepare for your trip to the past, there are solutions, the most straightforward being bringing a solar charger (or a few) for your phone. The life of a solar charger is probably measured in years; you’d also want to bring a supply of batteries, because batteries only last for so many charging cycles. (Of course, your batteries can die even if you don’t charge them.) There are probably other forms of charger, e.g. hand-cranked, or ones you can attach to a bike. (Having a bike with you would be a fantastic idea!)
All of them will have a limited life - they’re built in a society which expects such objects will constantly be manufactured, so when they fail, they can be easily replaced. Off the top of my head, I can’t say how long you can hope to get out of them.
Planned obsolescence will also be a problem for your device. Most smartphones are probably designed to last for a few years before the user is expected to get a new, “better” model. Partly this is a function of marketing, of course, but with that lifetime in mind, phones aren’t really built to last decades. Laptops probably have a longer life in mind, but not hugely longer - I think I can be vaguely confident saying most people replace their laptop within a decade. (The laptop I’m typing this on is now… probably about five years old, I think.)
I have no idea what the statistics are for when people replace their phones. At a guess, a lot of phones probably die through accidents that crack screens, or they fall in the toilet, or whatever. If you have the only smartphone(s) in the world, you would have to be extraordinarily careful not to allow them to break.
If you don’t accidentally break your phone, sooner or later electronic components will fail. Exactly which components will fail first, I’m not sure. A guess would be the battery. Your processor will very slowly die over about 10-20 years. Your flash memory will slowly become unable to hold a state after enough years, so your phone will no longer have storage - and I guess that will mean you lose the operating system as well. One way or another, your phone will die.
Your laptop will have a similar fate. Its hard drive is particularly likely to go, so take a lot of backup hard drives and keep your data backed up regularly. So is your power supply and fan. These at least are relatively easy to replace. But bring spares.
If you take good care of it, though, perhaps a laptop or phone can have a relatively long life…
What's the point of a phone?
So what good would it actually be for the time you have it? Let’s start with using a smartphone after you’ve travelled back in time…
So, like, As You Know, a smartphone relies very heavily on connecting to external networks for most of its services.
Probably the first use of a ‘phone’ is communication. Now, you can’t call or text another phone (assuming you brought more than one) in the absence of a cell network. Nor can you use instant-messaging or email services designed to send messages to be routed through the internet. So you’re instead relying on direct, peer-to-peer protocols; Bluetooth is one but it has a very limited range; for technical reasons, smartphones can’t communicate peer-to-peer.
This is still useful, of course: instant, silent communication through any barrier short of a thick stone wall would be immensely useful in all kinds of situations where simply shouting is difficult. Spying on someone, communicating in a noisy situation - valuable things. Still, it’s not the same world-changing thing as long-range communications, and bringing a set of handheld radios would be more immediately practical.
Another one we rely on our phones for constantly is navigation. Phones do not usually store their maps on board the device, but stream them from remote servers. Likewise, without at least 3 (or is it four?) GPS satellites above the horizon broadcasting the time to immense precision, the phone’s GPS will do nothing at all.
So if you want to pick a mapping app to use for your time travel, you need to pre-load maps data for all relevant areas. Of course modern-day streetmaps will be meaningless (except maybe as a novelty, ‘one day they’ll put all these roads here’), but maps of elevation might be useful (if potentially inaccurate as land rises and falls). Having precise data of coastlines and elevation would potentially be incredibly useful for cartographers wherever you end up, assuming you can find a way communicate meaningfully about the mathematical details of projections and so on.
You’d also want to be able to add points to the map persistently, so you could build up a new map of human-built areas. Probably you’d do this on the laptop (if you have one too).
Your smartphone probably has a compass, but in most times and places, compasses (or comparable methods of navigation) would already have been developed, so an unreliable compass that depends on electrical power would perhaps not be entirely useful.
One of the most useful features of your phone would actually be the extremely precise and accurate clock. You’ve probably heard the story of how in the 1700s, a guy called (*looks up*) John Harrison won a very large amount of money from the British government by developing increasingly precise clocks, allowing ships to determine their longitude precisely at sea.
(This is usually presented as a “what a clever guy” story with a dash of “wow can you believe the government arrogantly refused to recognise this humble carpenter’s amazing invention” but like, given that this kind of navigation technology allowed European sailors to colonise the world and carry out genocide on an unprecedented scale, I’m far from convinced it’s something to celebrate…)
That said, a single smartphone is of limited utility as a clock, because it can’t be reproduced, and it’s so reliant on electrical power. A bag of cheap watches would be more useful.
The other use of a smartphone is a small portable general-purpose computer, able to run arbitrary mathematical calculations and computer programs. We’ll talk more about that in a second when we go into laptops.
Incidentally, I note the main calculator program I use on my phone, Wolfram Alpha, is totally dependent on a connection to a server to interpret its input, do calculations, and provide data. But I’m sure you could load a copy of Matlab or something onto a phone.
A pocket calculator, by contrast to a phone, is much more limited in its computing abilities, but has a much longer life. Bringing a scientific calculator would probably be more useful for most calculations. Though indeed, a slide rule would last even longer, and be much easier to reproduce!
One rather nice use of a phone I can think of is as an astronomical tool. There are many astronomy apps available which provide a very detailed map of astronomical bodies and predictions of their orbits, and a phone has the advantage of using its compass to allow you to point it directly at the sky. The app I use, Mobile Observatory, has a lot of data pre-loaded onto the phone, with periodic updates to its catalogue. I doubt it goes too far back in time, though.
Using a phone in this way would be very useful to any astronomers and astrologers you might meet, but also a detailed map of the night sky would be very valuable for navigation by the stars.
Another, personal use for your smartphone is to help you monitor nutrition, medicine schedules, and that kind of thing.
Finally, I almost forgot, your smartphone almost certainly has a camera on it. This is immensely useful: you can bring photographically detailed images around with you from one place to another. Not as useful as being able to send them via the internet, but still. Of course, your camera lens can easily get scratched or filled with dirt, and if so, it will be very hard to replace.
I think that covers the main smartphone-specific features. Basically, without network support, your phone would be a great deal more limited, but it would still have some extremely useful features.
OK, a laptop - or indeed, a computer in general.
You have no internet, of course - the only other device you can communicate with is your phone.
Fortunately, nowadays it’s common for laptop hard drives to be 500GB+ in size, so depending how you encode it, you could carry a vast amount of information with you. (Video files may be impressive, but you can take a ridiculously larger amount of text, in a clear searchable format.)
If you know you’re going to time travel, you would want to absolutely pack your laptop with detailed technical information on engineering very simple, practical but important machines, as well as all the information we have on the place and time. And you’ll have a lot to learn, so you’ll want to make notes.
In terms of software to bring, if you’re hoping to introduce new technologies to the people you meet, this is what comes to mind for me: an engineering programming environment like Matlab, some CAD software, libraries of data on material properties, physical simulation software, astronomical catalogues and navigation software. Also, I don’t really know what’s available in this field, but software to help you monitor your own health, and access relevant medical information.
I would imagine that having this kind of software available will be a huge help when it comes to designing machinery with locally available materials and methods. But also take your cues from the local builders and craftspeople, who will already be extremely familiar with whatever they’re working with. Abstract mathematical knowledge is likely to be very hard to translate, and you’ll probably miss a lot of nuance that comes from working with the materials and techniques the people you meet will know intimately.
If you want to persuade the people you visit to build something, you need to respect their work. Lots of time travel stories have the time traveller descending from on high with perfectly applicable future knowledge - this is very silly. Whatever you achieve will *not* be “let’s get my willing workers to make me new iPhones” - it’ll be a process of working together with whoever you meet to combine your abstract engineering knowledge with what they know. Depending where you go, I guess builders would appreciate things like precise knowledge of how to build an arch that won’t fall down, or new processes for producing certain materials.
Potentially, you could bring peripherals to your laptop such as scientific monitoring equipment that would be useful in getting some process or another started, monitoring temperatures and so on.
It would likely be very useful to bring educational software or information to help others learn to use your laptop, and help you teach about the information you have stored on it. That said, teaching any kind of science is very difficult, it takes years and years; understanding the knowledge and preconceptions and mental models of the people you meet will likely take a lot of time, and adapting the information you have to be accessible to them might be very difficult.
Ultimately, something will render your laptop and phone unusuable. By this point you need to have substitutions - enough knowledge shared with the people you now know, ways to perform calculations without writing a program to do it, etc. etc.
I do think both a laptop and phone would be very useful, and probably worth bringing. They wouldn’t on their own change the world the way the widespread adoption of computers and now phones has.
Could you replace them?
OK, so the second question is, how do you build a laptop? Or a phone?
Actually, someone has done their best to answer a question a bit like that - by building his own toaster from raw materials. A toaster seems like an extremely simple device, but as the guy found here it really isn’t in the least bit simple to even produce the basic materials of a toaster, such as iron and the plastic shell.
That said, he was working alone (more or less), and you might have a group of people working together and refining their methods. Perhaps in time you could reliably make a toaster that doesn’t catch on fire.
Still, the point of this is, “technological development” is not simply accumulation of knowledge and theory - this happened in parallel with, and interdependent with, massive changes in how our society was organised, how labour is performed, where materials can be sourced from, what workers know how to build, etc. etc. It’s no good having a theory of semiconductor junctions if you don’t have a way to get some appropriate-quality silicon.
So what would it take to build a computer?
The most basic form of computer is not electronic, but purely mechanical. This has the advantage of not requiring an electric power source, though the first fully programmable computer to be conceived of, Babbage’s analytical engine, would have required a steam engine or similar drive system.
To make a mechanical computer, even a simpler calculating device than the Analytical Engine, you would need to be able to cast thousands of identical components to a sufficent degree of reliability. Making the Difference Engine (but perhaps not the Analytical Engine) was possible in Victorian times, when industrial manufacturing was already well underway.
I don’t really have a clear idea of what it takes to make sufficiently small and precise mechanisms to build a mechanical computer, but we do know from the Antikythera Mechanism that the ancient Greeks were capable of building some very sophisticated machinery as early as 205-100BC. Wikipedia also claims that it took until the 1300s in Europe to produce a similary complex device. (Prior to that, Sū Sòng produced a clock with some of the first instances of mechanisms like escapements in the 1000s in China, and Al-Jazari apparently described a complicated clock in 1206, so… perhaps this is missing some stuff?)
Is the level of engineering skill needed to build an Antikythera Mechanism sufficient to make a Difference Engine? Honestly I have no idea.
Given a more detailed knowledge of what a computer might eventually be capable of, as well as CAD software to assist in designing the components and checking they work in theory before you commit to building the thing, perhaps you could develop a few bulky mechanical computers much faster than Babbage and Lovelace managed. But, you know. Maybe.
Now, everything in a modern computer is totally dependent on silicon integrated circuits. Without this, you need to use very large arrays of unreliable vacuum tubes or transistors, wired up. Which requires the ability to make vacuum tubes or transistors.
Reading Wikipedia’s detailed history, it seems like the integrated circuit was almost an inevitable development of its time and the limitations of World War II-era vacuum-tube based computers such as ENIAC. Early integrated components were able to be produced by hand out of a germanium chip in a lab, but I’m not sure how Texas Instruments were providing the germanium chips.
In any case, if I’m following the history correctly, the earliest integrated circuits only had up to tens of transistors, but even these were very useful in planes and missiles.
Per this wiki page, the early integrated circuits with up to a few hundred transistors were able to be produced by engineers hand-cutting a 'masking film’ known as Rubylith to create a mask for etching, which was then 'photo reduced up to 100 times’. So you’d have to make Rubylith, or something equivalent. And then develop a way of etching integrated circuits.
More complicated integrated circuits, with thousands of transistors or more, basically require you to already have a computer in order to create them.
Of course, creating an succession of increasingly dense integrated circuits is a tiny part of the story of creating a computer. Before you even get close to that, you need to be able to reliably extrude conductive wires, and connect components up with solder or something else. This is not actually as unreasonable as it sounds - you’d need to find a jewelry-maker familiar with the production of wires.
Historically people have created wire in various ways; wire has been produced as far back as the Second Dynasty of ancient Egypt (c.2890-c.2686 BC). In any case, the concept of wire drawing is relatively simple. You should bring some sample wires to show what you need.
There’s a huge difference, of course, between drawing wires and producing integrated circuits with transistors, and the kinds of computers we have today. And unless you somehow precipitated massive, sweeping changes in the entirety of how the society you visit is organised, you are not going to make very many computers this way.
It’s getting late and I’m kind of too tired, but I will continue this train of thought later. I would love technical, sociological, archaeological, engineering, physical corrections and further input. Because I bet I’m missing a ton of limitations here, even having already concluded it’s basically impossible to take a laptop and a smartphone and start producing more laptops and smartphones.