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20101112

-              v3
+              v4
 the key to understanding the nature of gravity, the history of cosmic
 expansion, the origins of supermassive black holes, and the physics of
 quasars.  I will describe (i) why astronomers expect supermassive
+black holes to collide, and (ii) the history, current status and
 future prospects of the scientific quest for the answer to the title.
+quasars.  I will describe how the scientists' view of the question has evolved
+over the years, from the preliminary work of Stephen Hawking and others,
+to recent breakthroughs, current research and future experiments.