what happens if the cable is cut four feet above the ground? does it come crashing down to earth? does it fly off into space?
My question is Why? Why would I want to go 22,500 miles on a friggin' elevator? And that's just to get TO space. And this bit about counting on Solar to power the thing? How much power do they count on it taking to power 13 tons 20, 000 miles? I've heard of this before, I think it is a scam.
"what happens if the cable is cut four feet above the ground? does it come crashing down to earth? does it fly off into space?"
It should fly off into space. The way that it works is that the ribbon is counterweighted at the far end in order to provide centrifugal force that overcomes earth's gravity. This makes the entire ribbon stable in an epic zero-sum game.
Now, what you should REALLY worry about is what happens if an asteriod knocks some of the counterweights off. Of course, the chance of that happening are extremely slim.
It moves into space; the big problem is if the elevator parts above the midpoint... It fall to earth at hypersonic speeds wrapping around the planet!
Assuming of course it doesn't burn up.
First, you'd need a device strong enough to cut it.
It goes flying into space (and likely wipes out a good percentage of geosynchronous comm sattelites in the process). Actually, I would hate to see us put all our eggs in this basket, while it has been discussed by brighter people than my own fine self, in theoretical terms for over a hundred years, a lot of details need yet to be hammered out. Carbon fiber may well be a good start, depending on the structure, carbon makes a fantastically strong molecular bond.
I am just glad to see someone get serious about something besides the overpriced, overly complicated, all too delicate shuttle as a primary Earth to orbit conveyance. The NASA people who are still serious about space as opposed to waiting on their pensions, know full well the shuttle is an overpriced piece of crap.