[viciousambition]

The problem with this is that it assumes progress in these areas is linear. For example, it's easier to leap from bi-plane to jets than it is to go from jet airliner to something faster because a system gets more complex based on both its components and the connections between them. Simply put--there's more that can go wrong.

"Why can't I travel to my destination is less than 8 hours?" isn't so much the question as "Can we carry enough fuel to power an engine that's faster?", "Do we need entirely new propulsion?", "If elevation could help, how do we keep this thing skirting the edge of the atmosphere and still function?" etc. I don't know anything about aeronautics, so forgive my oversimplification, but this seemed like an easy to grasp example of what I'm talking about.