A red sprite photographed by a team at the University of Alaska, Fairbanks. Sprites are emitted near the tops of thunderclouds and reach up into the ionosphere. The transmission line model for lightning shows a smooth upward curve of current. Lightning, however, is not a smooth and steady phenomena. The transmission line model is the oldest and simplest model about lightning, so it shouldn't work.
Lightning is much more complicated than that.
Lightning does not follow a simple path across the sky. For instance, downward lightning can meet upward lighting in the middle of a cloud. Despite the 'messiness' of lightning, it somehow still obeys the simple current curve of the transmission line model. Uman asked these questions because he believes most theorists are too intent on developing their own models. By posing these questions at the International Conference on Atmospheric Electricity, Uman hopes to stimulate further thought about the physics of lightning.