Nathan Rosen

• 1. A Step Ahead

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  Nathan Rosen published a paper on the structure of the atomic nucleus in Physical Review in 1931. James Chadwick wouldn't formally discover the neutron until the following year. That gap is a signature of how Rosen worked. He was consistently reasoning toward particles and structures the instruments had not yet confirmed.

  He was born into a Jewish family in Brooklyn, New York, and attended MIT during the Great Depression. He earned a bachelor's degree in electromechanical engineering, then returned for a master's and a doctorate in physics. By 1932 that doctorate was complete, and he headed to Princeton for further research. In 1934 he became Albert Einstein's assistant at the Institute for Advanced Study in Princeton, New Jersey.

  The two years that followed produced ideas physicists are still working through today. One paper challenged whether quantum mechanics could be considered a complete description of reality. Another described a bridge connecting parallel layers of folded spacetime. That bridge now has a name: the Einstein-Rosen bridge, the first known kind of wormhole.

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• 2. A Revolution Taking Shape

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  Max Planck proposed the quantum theory in 1900, describing energy as moving in discrete amounts called quanta. Albert Einstein published his theory of special relativity in 1905. Around 1927, Niels Bohr and Werner Heisenberg, working with many other physicists, developed what became known as the Copenhagen interpretation of quantum theory. It described quantum particle behavior in terms of probability, not certainty.

  The Copenhagen interpretation drew a sharp line: quantum particles have no definite properties until they are measured. That claim was alive and contested when Nathan Rosen arrived at MIT during the Depression. The ideas shaping his field were less than three decades old. He would walk into the center of that argument and help plant one of its most pointed challenges.

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• 3. Entangled with Einstein

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  Boris Podolsky was the third name on a paper published in May 1935. Rosen had noticed peculiarities in Einstein's work on wave functions while the two were already collaborating at Princeton. Podolsky was brought in to help develop the theoretical argument. The resulting paper posed its central question as its title: "Can quantum-mechanical description of physical reality be considered complete?"

  The paper's foundation rested on work Rosen had already done on the hydrogen molecule. In that molecule, neither electron carries a definite quantum number on its own, but the pair together holds a pure state. To represent this, Rosen used what he called "entangled" wave functions: a single mathematical object for two particles treated as a unified system. The May 1935 paper extended that logic into a challenge. If measuring one particle in an entangled pair instantly fixes a property of the other, quantum mechanics had left something out. The effect operated regardless of any distance between the particles. That challenge became known as the Einstein-Podolsky-Rosen paradox, or EPR paradox.

  Two months after this paper appeared, Einstein and Rosen published something else.

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• 4. The Bridge Through Space

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  The July 1935 paper described spacetime folded into parallel layers, connected at a single point by a bridge. That bridge rested on two established frameworks: general relativity and Maxwell's equations. No new physics was required. The construction was the first known kind of wormhole.

  Einstein helped Rosen secure a position in the Soviet Union, writing to Molotov on his behalf. Rosen spent two years at the University of Kiev starting in 1936. In 1937, the two published "On Gravitational Waves," extending the spacetime model to configurations produced by rotating cylinders. Rosen pursued the subject independently after returning to the United States. "General Relativity and Flat Space" appeared in 1940. "Energy and momentum of cylindrical gravitational waves" appeared in 1958.

  In 1962, theoretical physicists John A. Wheeler and Robert W. Fuller published a paper showing the Einstein-Rosen bridge to be unstable. Subsequent researchers extended the concept. Robert Hjellming, in 1971, proposed a model in which a black hole draws matter inward while connected to a white hole in a distant location. That white hole, in Hjellming's model, expels the same matter. Kip Thorne and Mike Morris, in a 1988 paper, proposed that a wormhole could be stabilized by containing negative matter or energy. Neither of those proposals originated with Rosen.

  While others were extending the bridge concept through those decades, Rosen had turned his attention to building the institutions of Israeli science.

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• 5. Building Israeli Science

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  The University of North Carolina at Chapel Hill was Rosen's home institution from 1941 to 1952. In 1953 he made a permanent move to Israel, joining the Technion in Haifa. Among the students he advised at the Technion was Asher Peres. The institution later named a lecture series for him.

  Among the organizations he helped found were the Israel Academy of Sciences and Humanities and the Physical Society of Israel. He also helped establish the International Society on General Relativity and Gravitation. He served as president of the Physical Society of Israel from 1955 to 1957. From 1974 to 1977, he led the International Society on General Relativity and Gravitation as its president. In the 1970s he also served as President of Ben-Gurion University of the Negev. He commuted between that institution and the Technion from his home in Haifa.

  He died on the 18th of December 1995, at his home in Haifa, at the age of 86. A theoretical project that had occupied him for nearly fifty years had ended three years before.

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• 6. The Bimetric Effort

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  Between 1940 and 1989, Rosen published a series of articles on a version of gravity he called bimetric. The aim was to improve on general relativity by eliminating singularities from the equations. He also replaced pseudotensors with tensors to eliminate nonlocality from the standard framework.

  Pulsar observations in 1992 produced data that conflicted with the theory's predictions. The project was set aside after more than fifty years of development. The goal of removing singularities from a workable theory of gravity remained unachieved.

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