Steven Chu, the Nobel Prize-winning physicist who has served for four years as President Barack Obama’s Energy Secretary, announced his resignation on Friday.

As of this weekend, Chu will become the nation’s longest-serving energy secretary, a record previously held by Spencer Abraham, who served in the Cabinet post under President George W. Bush. The former director of Lawrence Berkeley National Lab, Chu was largely a newcomer to politics when he took on the post in 2009.

He said he will stay on as head of the Department of Energy at least until the end of this month, and possibly until a successor is confirmed.

“During his time as Secretary, Steve helped my Administration move America towards real