Let’s talk about steam. I don’t mean the malware installed on most gamers’ computers, but the real thing: hot, evaporated water. You may see it as just something given off by boiling stew or dying cars, but it’s so much more than that. For steam was the fluid that carried us into the Industrial Revolution.
And whenever we talk of the Industrial Revolution, it’s only natural to think about its timing. Did steam power really have to wait until the 18th century? Is there a way to push back its development by a hundred, or even a thousand, years? We can’t know for sure, but maybe we can make an educated guess or two.
Intro
Obviously, knowledge of steam itself dates back to the first time anybody ever cooked a pot of stew or boiled their day’s catch. Probably earlier than that, if you consider natural hot springs. However you take it, they didn’t have to wait around for a Renaissance and an Enlightenment. Steam itself is embarrassingly easy to make.
Steam is a gas; it’s the gaseous form of water, in the same way that ice is its solid form. Now, ice forms naturally if the temperature gets below 0°C (32°F), so quite a lot of places on Earth can find some way of getting to it. Steam, on the other hand requires us to take water to its boiling point of 100°C (212°F) at sea level, slightly lower at altitude. Even the hottest parts of the world never get temperatures that high, so steam is, with a few exceptions like that hot spring I mentioned, purely artificial.
Cooking is the main way we come into contact with steam, now and in ages past. Modern times have added others, like radiators, but the general principle holds: steam is what we get when we boil water. Liquid turns to gas, and that’s where the fun begins.
Theory
The ideal gas law tells us how an ideal gas behaves. Now, that’s not entirely appropriate for gases in the real world, but it’s a good enough approximation most of the time. In algebraic form, it’s PV = nRT, and it’s the key to seeing why steam is so useful, so world-changing. Ignore R, because it’s a constant that doesn’t concern us here; the other four variables are where we get our interesting effects. In order: P is the pressure of a gas, V is its volume, n is how much of it there is (in moles), and T is its temperature.
You don’t need to know how to measure moles to see what happens. When we turn water into steam, we do so by raising its temperature. By the ideal gas law, increasing T must be balanced out by a proportional increase on the other side of the equation. We’ve got two choices there, and you’ve no doubt seen them both in action.
First, gases have a natural tendency to expand to fill their containers. That’s why smoke dissipates outdoors, and it’s why that steam rising from the pot gets everywhere. Thus, increasing V is the first choice in reaction to higher temperatures. But what if that’s not possible? What if the gas is trapped inside a solid vessel, one that won’t let it expand? Then it’s the backup option: pressure.
A trapped gas that is heated increases in pressure, and that is the power of steam. Think of a pressure cooker or a kettle, either of them placed on a hot stove. With nowhere to go, the steam builds and builds, until it finds relief one way or another. (With some gases, this can come in the more dramatic form of a rupture, but household appliances rarely get that far.)
As pressure is force per unit of area, and there’s not a lot of area in the spout of a teapot, the rising temperatures can cause a lot of force. Enough to scald, enough to push. Enough to…move?
Practice
That is the basis for steam power and, by extension, many of the methods of power generation we still use today. A lot of steam funneled through a small area produces a great amount of force. That force is then able to run a pump, a turbine, or whatever is needed, from boats to trains. (And even cars: some of the first automobiles were steam-powered.)
Steam made the Industrial Revolution possible. It made most of what came after possible, as well. And it gave birth to the retro fad of steampunk, because many people find the elaborate contraptions needed to haul superheated water vapor around to be aesthetically pleasing. Yet there is a problem. We’ve found steam-powered automata (e.g., toys, “magic” temple doors) from the Roman era, so what happened? Why did we need over 1,500 years to get from bot to Watt?
Unlike electricity, where there’s no obvious technological roadblock standing between Antiquity and advancement, steam power might legitimately be beyond classical civilizations. Generation of steam is easy—as I’ve said, that was done with the first cooking pot at the latest. And you don’t need an ideal gas law to observe the steam in your teapot shooting a cork out of the spout. From there, it’s not too far a leap to see how else that rather violent power can be utilized.
No, generating small amounts of steam is easy, and it’s clear that the Romans (and probably the Greeks, Chinese, and others) could do it. They could even use it, as the toys and temples show. So why didn’t they take that next giant leap?
The answer here may be a combination of factors. First is fuel. Large steam installations require metaphorical and literal tons of fuel. The Victorian era thrived on coal, as we know, but coal is a comparatively recent discovery. The Romans didn’t have it available. They could get by with charcoal, but you need a lot of that, and they had much better uses for it. It wouldn’t do to cut down a few acres of forest just to run a chariot down to Ravenna, even for an emperor. Nowadays, we can make steam by many different methods, including renewable variations like solar boilers, but that wasn’t an option back then. Without a massive fuel source, steam—pardon the pun—couldn’t get off the ground.
Second, and equally important, is the quality of the materials that were available. A boiler, in addition to eating fuel at a frantic pace, also has some pretty exacting specifications. It has to be built strong enough to withstand the intense pressures that steam can create (remember our ideal gas law); ruptures were a deadly fixture of the 19th century, and that was with steel. Imagine trying to do it all with brass, bronze, and iron! On top of that, all your valves, tubes, and other machinery must be built to the same high standard. It’s not just a gas leaking out, but efficiency.
The ancients couldn’t pull that off. Not from lacking of trying, mind you, but they weren’t really equipped for the rigors of steam power. Steel was unknown, except in a few special cases. Rubber was an ocean away, on a continent they didn’t know existed. Welding (a requirement for sealing two metal pipes together so air can’t escape) probably wasn’t happening.
Thus, steam power may be too far into the future to plausibly fit into a distant “retro-tech” setting. It really needs improvements in a lot of different areas. That’s not to say that steam itself can’t fit—we know it can—but you’re not getting Roman railroads. On a small scale, using steam is entirely possible, but you can’t build a classical civilization around it. Probably not even a medieval one, at that.
No, it seems that steam as a major power source must wait until the rest of technology catches up. You need a fuel source, whether coal or something else. You absolutely must have ways of creating airtight seals. And you’ll need a way to create strong pressure vessels, which implies some more advanced metallurgy. On the other hand, the science isn’t entirely necessary; if your people don’t know the ideal gas law yet, they’ll probably figure it out pretty soon after the first steam engine starts up. And as for finding uses, well, they’d get to that part without much help, because that’s just what we do.