Large airships could have been developed much earlier. The biggest problem was funding. There were many airship designs advanced between 1845 and 1855, but none of them were built. But certainly had any one of the inventors gotten commercial backing airships could easily have been a reality by the late 1850's.
People may take exception to the fact that some of the Airships in books are far too heavy. They have sails, steel and wooden hulls, dreadnought guns, and lots of brass. They wouldn't fly today either.
But this may or may not be a problem, depending on the kind of book you are writing. The question is whether the fiction is immersive enough to make the reader forget his current reality.
When it comes to this sort of thing, I like to think of the difference between accuracy and authenticity. Not a steampunk example, but this is what the creators of HBO's Rome went for when they were designing and writing that series. The historical events weren't completely accurate. They compressed timelines, merged some historical figures together into one character, left some bits out, added some bits in... but they weren't trying to make a documentary. They were trying to make an entertaining show. And so they went for authenticity, which they talk about in a lot of the special features. They wanted their Rome to feel like ancient Rome, to have that ambiance, to have the right colours and textures, to have the right attitude. And that's how I look at steampunk. I don't mind inaccuracies -- it is, as others have pointed out, alternate history. If nothing was changed, it wouldn't be fiction. But I do mind inauthenticities, and I do mind in-world inconsistencies. Everything needs to fit within the bounds that an author sets -- but those bounds don't have to be "accurate".
I think Cass has hit the nail on the head here. The way she explained it made me think of Mexican food, or more precisely what us non-Mexicans think of as Mexican food. Go into most 'Authentic Mexican Restaurants' and what you're getting is what, if the propriater is doing their job right, the locals think is the food they eat in Mexico. But if a Mexcian walked in they woudl most likely laugh or be insulted, but ultimately it doesn't matter because that's what the public wants.
NB - This post is purely the view of Michael Grey, and any likeness to the views of SWAG, Restauranters or Latin Americans is purely coincidental.
totally true :DI have friends that are hispanic and what they cook at home is 'authentic'... why? because they are hispanic so it's authentic hispanic food... but is it the ONLY hispanic food? no.. it's been filtered and enhanced through the hands and stomachs of many people in their family... so why knock the colorful additions of individuals that change the scope of food... and science... :D
I agree absolutely, if the world is intensely immersive, (authentic) then the reader will be drawn into it.
I think that this also related to the debate within science fiction regarding its hardness vs. softness. For those that don't know "hard" science fiction is that which adheres as stringently as possible to known scientific principles whereas "soft" science fiction is that which doesn't let science get in the way of the plot.
I'll give you an example from short story I worked on: Basically it was about an immigrant coming to Ellis Island, only one in which difference engines and various other mechanical computers helped to sort out and process the new immigrants to the US (this was based on what seemed like the mind blowing idea that civil servants could process thousands of immigrants in a day without the aid computer). I decided to give this a semi-realistic setting, since I was writing about real world places circa 1900.
At first I wanted my character to come from Ireland aboard an airship, but on further reflection I decided that such transportation, even in a steampunk world, would have been far to expensive for an immigrant, especially one emigrating from Ireland due to a criminal background, so I put him in steerage with the other immigrants (also where's steerage on an airship?). While I'm still revising this story I wanted to try and blend realistic with fantastic and I hope it comes out well.
So, as long as you can write it immersively, and can get the reader to suspend disbelief, you're doing a good job. As for anything else, well, that can just be a fun debate.
My problem has been - and remains - that there is often little, if any, in-story justification for these changes. You can't say 'I have a steam-powered A.I.' without some major crazyness - and that's okay. But there is no way even hyper-advanced steam power could create artificial intelligence.
A lot of technology could have come about earlier than it did in reality, however. There was simply no need for the tank before WWI, and the major difficulty with heavier-than-air flight like the plane was not aerodynamics, but control; no one understood how to control a vehicle in three dimensions, as everything prior was all in two. The ship, the cart, the car. All they needed was left, right, forward and back. Adding up-down and tilt controls confounded people for almost fifty years. You could arguably have steam-powered tanks and planes and, given enough technological advancement, powered armour and robots, in the 1880's or earlier with only slight derivations from history. Beyond that (or things related), you start getting into hand-waving and 'just because' excuses, which must be used sparingly.
Most fiction fails to do so, and these stories tend to fall into mediocrity and the murk of forgotten novels. But in every other genre, this is a bad thing; bad writing kept these books down, and these mistakes are learned from. Steampunk seems to be far more accepting of these mistakes, and no one learns from them. Making crap up without justification or explanation is just plain bad writing. The farther out of reality you go, the more you a) need to explain it, or b) need to control and limit it. Things can be mysterious and unexplained - I love Boilerplate, for example, despite A.I. being my main beef with Steampunk. But these mysteries cannot solve plot points or diffuse dangerous situations, because it feels like cheating.
The ability to solve problems is directly related to how well the audience understands the methods being used. Usually this is used as a rule in magic systems in fantasy, but I think it applies to anything in fiction. Tolkien's Gandalf is mysterious, all powerful, completely unexplained. Solves almost nothing with magic and is still an awesome force in the Lord of the Rings. Brandon Sanderson goes the total opposite; his magic systems are frighteningly well documented and explored, and his characters solve all kinds of problems with it. If Gandalf did the same, it would feel like cheating because he has no explanations. The characters get in trouble, Gandalf swings in and everything is solved for no reason. This would not be interesting. And it's not interesting in Steampunk.
While I'm not disagreeing with the point behind your post, John, this sentence jumped out at me:
"Making crap up without justification or explanation is just plain bad writing."
(Excuse me if this sounds disjointed - I just wrote out a reply and the forum only posted the first line so I'm having to go off memory).
China Mieville's The City & The City and more recently Embessytown are two exmaples of spec fic where the origins of the two unique settings are not explained, and in the case of Embassytown not even hinted at.
I think it comes down to each individual peice of writing as to whether an explaination is required or not.
Now if I could just teach myself to write like Mieville I too could skim the details.