Gregory Benford has written some of the best "extreme SF" of recent years. Just check out his collection on Worlds Vast and Various (2000) for some examples. Benford (b. 1941) is a professor of physics at the University of California, Irvine, specializing in plasma turbulence and astrophysics He advises NASA on national space policy and has been heavily involved in the Mars exploration programme.
His novels, The Martian Race (1999) and The Sunborn (2005), are generally regarded as amongst the most authentic considerations of the race to and exploration of Mars. In 1995 he received the prestigious Lord Foundation award for scientific achievement.
In the world of science fiction, Benford has received many awards including the Nebula for Timescape (1980), still one of the most realistic time-travel novels. His most sustained sequence of books is the Galactic Centre series, tracing the continuing conflict between organic life forms and AI machines. The series began with Across the Sea of Suns (1983).
Amongst his more recent novels perhaps the most extreme is Cosm (1998) involving an artificially created micro-universe.