There would be costs associated with running the lasers that power the cars up the ribbon, as well as simpler costs associated with transferring goods to the platform at the bottom of the ribbon, which will be located in the ocean.

Another person at the conference asked about why the current model has just three cars that could climb up and down at once -- why not six? It's possible, Laubscher said, but someone would have to work out how they'd pass each other on the ribbon and the elevator would require six laser beaming stations if they all were to climb at the same time. That would require more study.

Some enthusiasts are investigating ways to use solar panels on the ribbon in order to provide power, rather than using lasers beamed up from Earth. Peter Swan, a scientist who has worked for the U.S. Air Force and worked on the Iridium satellite system for Motorola, is collaborating with 27 other authors on a book on the feasibility of the space elevator, and they have begun looking into the possibility of using solar panels along the ribbon.

But why not put the solar panels on the cars, one attendee wondered. It's possible, Laubscher said, but the idea would need to be investigated in terms of the mass the panels would add to the cars.

Another person wondered if an efficient way to build multiple elevators could be to construct the first one twice as wide as necessary so that it could be then split in half. "No one's really looked into it," Laubscher said.