James Wolcott raises an interesting point about Johnny Carson:
In retirement, Carson became appalled by the degeneration of cable news coverage and political discourse post 9/11. I received a wonderful note from him a few years ago–a note from Johnny Carson! I’ve never opened an envelope more gingerly–in which he lamented the dying out of voices of reason such as astronomer Carl Sagan, a frequent guest on his show. An astronomy buff himself, Carson prized science and reason. In his latter years he must have felt even more estranged from a country embracing its own hysteria.
David Letterman, of course, does occasionally have scientists on; Brian Greene did a yeomanlike job trying to explain string theory, and Sir Martin Rees was spectacular at talking about astronomy. But Letterman is ultimately too nihilistic to care too obviously about the state of the public discourse or any such thing. In that sense, the closest we have to Carson’s true heir is probably Jon Stewart.