AIP History Center Newsletter
Volume XXXVIII , No. 2, Fall 2006


Niels Bohr and Werner Heisenberg engaged in a long and intimate collaboration through the 1930s, creating the quantum physics that has radically transformed philosophy and daily life. Michael Frayn’s recent play Copenhagen is bringing this extraordinary chapter in the history of physics to a wide audience, portraying the collaboration’s deep friendship, intellectual rivalry, and final collapse. As a side-effect of the play’s popularity, the Center for History of Physics has received dozens of requests for copies of the photograph shown here. The image
illuminates, in a compact and moving fashion, the collaboration of the two great physicists at its peak.

This is one of two photographs taken in 1934 by a teenage boy, Paul Ehrenfest, Jr., son of the noted physicist Ehrenfest senior. Copies wound up in the hands of Victor Weisskopf, another of the many outstanding scientists who passed through Bohr’s institute in Copenhagen. Weisskopf eventually donated his photograph collection to the Center. Ehrenfest’s snapshots are now included in the selection of images (about one-third of AIP’s holdings) available online in the Center’s Emilio Segrè Visual Archives at

We stand as silent visitors in the lunchroom of Bohr’s institute. Note the Carlsberg beer bottles: Bohr and his group were partly supported by a bequest from the founder of the brewery. The world-famous teacher and his greatest student are eating, drinking, laughing and — as usual — vigorously arguing.

Somebody, presumably Weisskopf or Ehrenfest junior, wrote on the back of this photo that shows Bohr speaking: “Ja, ja, Heisenberg, aber– ” (“Yes, yes, Heisenberg, but– ”).

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