Which song was used as the original unaired pilot's theme?

The original unaired pilot of The Big Bang Theory used Thomas Dolby’s “She Blinded Me with Science” as its theme song.

That pilot was produced for the 2006–07 television season but was not broadcast. It differed substantially from the familiar series: Penny, Howard, and Raj were absent, while Amanda Walsh played Katie and Iris Bahr played Gilda. After CBS passed on that version, creators Chuck Lorre and Bill Prady reworked the concept and produced the pilot that led to the series.

The aired version replaced Dolby’s song with the theme written and recorded by Barenaked Ladies. That later song is often informally called “History of Everything,” because of its opening lyric, but the group’s single credits it as “Big Bang Theory Theme.”

The title “Weird Science” is an understandable distractor because it is another science-themed song, but it was not the original pilot’s theme. “Particle Man” likewise belongs to They Might Be Giants, not this unaired pilot.