Thought Experiment: world without fossil fuels

[CapelDodger]

Oh, right ... but somehow we have concrete roads, bridges, arches, and aqueducts made from concrete and rock by the Romans something on the order of two thousand years ago.

You just have to design a road or a bridge for the load it is designed to carry and for the lifetime it will have to last, it's not difficult. Adding pre-stressed iron or steel is better but not necessary.

Cement is fine for arches and domes, where the stresses are all compressive, but arched bridges without re-bar have their limitations. They can be pretty slendid, though. http://en.wikipedia.org/wiki/Pontcysyllte_Aqueduct. (Hat-tip to Telford for that one; the waterway itself is actually made of iron pans.)

Concrete roads suffer from surface flaking (spalling) and I don't know of any extant examples from Roman times. They adapted methods developed in Persia ~6thBCE.

Concrete certainly has its place, though.

 

[CapelDodger]

I might be able to, but would it ? And how far could it take it, given the reduced population ?

There was plenty of innovation with 19thCE populations so I don't think there'd be a problem with, say, a 1 billion global population. Quite enough mass there for mass markets (and mass warfare, another motivating factor).

 

[jimbob]

I don't think there'd be a limit, but it would have taken much longer to get there (or here, for that matter). It wouldn't have prevented the Enlightenment or the early (water-driven) Industrial Revolution, but without coal Peak Wood would have put a severe brake on the latter.

Much of the effort which went into the science and technology of steam-power would, I think, have gone into electricity - batteries and solar power in particular. Necessity is, after all, the mother of invention.

Very late to the party, but the mass production of iron (and later steel) was pretty important for later Victorian engineering. Fossil fuels would have affected this.