Greg Egan's SF scenarios are about as complex and mind-boggling as anything Stephen Hawking would come up with. His stuff earns the Capital S in SF.

I just finished "Distress": quite nice, relatively accessible. "Diaspora" was an extremely weird tale, as was "Quarantine". So far, my personal favourite among his books is "Permutation City". You can tell that he's a programmer, but he must be smoking Good Stuff at times...