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Michael_Sullivan comments on AI timeline predictions: are we getting better? - Less Wrong
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What people usually mean when they talk about flying cars is something as small, safe, convenient and cheap as a ground car.
There will never be any such thing. The basic problem with the skycar idea -- the "Model T" airplane for the masses -- is that skycars have inherent and substantial safety hazards compared to ground transport. If a groundcar goes wrong, you only have its kinetic energy to worry about, and it has brakes to deal with that. It can still kill people, and it does, tens of thousands every year, but there are far more minor accidents that do lesser damage, and an unmeasurable number of incidents where someone has avoided trouble by safely bringing the car to a stop.
For a skycar in flight, there is no such thing as a fender-bender. It not only travels faster (it has to, for lift, or the fuel consumption for hovering goes through the roof, and there goes the cheapness), but has in addition the gravitational energy to get rid of when it goes wrong. From just 400 feet up, it will crash at at least 100mph.
When it crashes, it could crash on anything. Nobody is safe from skycars. When a groundcar crashes, the danger zone is confined to the immediate vicinity of the road.
Controlling an aircraft is also far more difficult than controlling a car, taking far more training, partly because the task is inherently more complicated, and partly because the risks of a mistake are so much greater.
Optimistically, I can't see the Moller skycars or anything like them ever being more than a niche within general aviation.
You say that "There will never be any such thing", but your reasons tell only why the problem is hard and much harder than one might think at first, not why it is impossible. Surely the kind of tech needed for self-driving cars, perhaps an order of magnitude more complicated, would make it possible to have safe, convenient, cheap flying cars or their functional equivalent.
At worst, the reasons you state would make it AI-complete, and even that seems unreasonably pessimistic.
I'll cop to "never" being an exaggeration.
The safety issue is a showstopper right now, and will be until computer control reaches the point where cars and aircraft are routinely driven by computer, and air traffic control is also done by computer. Not before mid-century for this.
Then you have the problem of millions -- hundreds of millions? -- of vehicles in the air travelling on independent journeys. That's a problem that completely dwarfs present-day air traffic control. More computers needed.
They are also going to be using phenomenal amounts of fuel. Leaving aside sci-fi dreams of convenient new physics, those Moller craft have to be putting at least 100kW into just hovering. (Back of envelope calculation based on 1 ton weight and 25 m/s downdraft velocity, and ignoring gasoline-to-whirling-fan losses.) Where's that coming from? Cold fusion?
"Never" turns into "not this century", by my estimate.
Of course, if civilisation falls instead, "never" really does mean never, at least, never by humans.
Or new technology relying on existing physics? Then yes, conventional jets and turbines are not going to cut it.