The Einstein–Rosen Bridge

What They Were Trying to Do

In 1935 Einstein and Nathan Rosen published "The Particle Problem in the General Theory of Relativity." Their aim had nothing to do with travel. Einstein disliked the way physics treated particles as points where the equations blow up to infinity. He hoped that matter could instead be described entirely by smooth fields, with particles appearing as features of the geometry.

Examining the equations for the space around a compact mass, the two found that the troublesome central point could be avoided. The geometry could be continued through a narrow throat into a second, identical sheet of space. They called the connection a "bridge," and proposed that an elementary particle might be such a bridge between two sheets.

What Became of It

As a theory of particles, the idea did not work. But the geometry is a genuine solution of general relativity, and it took on a life of its own.

In a 1957 paper with Charles Misner, John Wheeler gave such structures the name wormhole. In 1962 Wheeler and Robert Fuller showed that the Einstein–Rosen bridge is not something one could pass through. The throat pinches shut so quickly that not even light can cross from one side to the other.

Later theoretical work found that a wormhole could in principle be held open, but only by a kind of matter with negative energy that has never been observed in the amounts required.

What People Get Wrong

• Einstein did not predict tunnels through space for travelers. The bridge was a model of a particle.
• There is no observational evidence that wormholes of any kind exist. They are a mathematical possibility permitted by the theory, not a discovery.

Where It Stands

The bridge survives as a striking feature of the mathematics of black holes, and as an active topic in theoretical research on how gravity and quantum theory fit together. In popular culture it has done rather better.