@willpayton: They are smaller and lighter because of a hundred year innovative advantage in that direction. We know more about expansion rates, lubrication, and kinetic application than we did back in its day.
It's certainly possible that with more development that small steam engines could get better, but part of the problem is just physics. Also, it's not like steam engines arent used today and we're talking about current ICEs versus old steam engines. Steam engines are used all the time in power plants. It's just that they have inherent problems that keep them from being used on small scales like for cards.
Alternative Energy is perfectly applicable when applied to this discussion because its an alternative to fossil fuel. By your definition, there's nothing alternative about, say, solar. Early on, batteries would still be as necessary as they are in ICE. We still use a battery to start it, we would surely still use a battery to start a steam car as well. But once its going, there's no reason it can't be exclusively steam the same way hybrid cars work. If its true that steam can't be miniaturized to the degree of an ICE, there's still no reason we can't have hybrid steam trucks starting out. Look at the one Jay Leno is driving in the video I shared. It still would be less pollution than the electric cars running around with the eternal pollutants in their batteries, imho..
Steam engines are not "an alternative to fossil fuel". Steam engines are just a different type of engine. They still need a fuel source exactly the same as ICEs, the difference is that they use external combustion instead of internal.
Engine type and fuel source are two completely different things. You can power steam engines with solar just like you can power them with gasoline or coal.
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