- Person
- Richard Feynman
- Lived
- 1918–1988
- Field
- Physics
- From
- American
The story
When liquid helium is cooled to just a few degrees above absolute zero, it behaves in bizarre ways. It flows without any viscosity at all, creeping up the walls of containers and passing through tiny gaps that would stop any ordinary liquid. The Soviet physicist Lev Landau had proposed a theory of this superfluidity but its microscopic basis was unclear.
Richard Feynman tackled the problem after moving to the California Institute of Technology in the early 1950s, fresh from his work on quantum electrodynamics. Applying the Schrödinger equation, he provided a quantum mechanical explanation for Landau's theory and showed that the superfluid was displaying quantum behaviour on a scale large enough to see. Building on earlier work by Arie Bijl in the 1940s, he developed around 1955 a microscopic theory of the roton, which was soon observed in experiments that scattered neutrons off liquid helium. Feynman later admitted that his model gave only qualitative agreement with experiment.
He also studied how a superfluid can rotate. Landau had thought that rotation entered the liquid through vortex sheets, but these were later shown to be unstable. Lars Onsager and, independently, Feynman showed instead that rotation enters through quantised vortex lines, thin whirlpools each carrying a fixed amount of circulation, and they developed the idea of quantum vortex rings.
It was a striking example of Feynman's ability to take a puzzle that others had described only in broad strokes and explain the physics underneath it. The work helped researchers think about a related problem, superconductivity, the flow of electricity without resistance in certain materials at low temperatures. Feynman himself did not solve that puzzle. It was explained in 1957 by John Bardeen, Leon Cooper and John Robert Schrieffer in the BCS theory.
Superfluid helium remains one of the clearest examples of quantum mechanics acting on a visible scale. Feynman's work on it is still cited among his major achievements, alongside quantum electrodynamics and the parton model, and the quantised vortex lines he described with Onsager are a standard part of the modern understanding of superfluids.
Why it matters
Feynman's insights helped make superfluidity one of the clearest examples of quantum mechanics acting on a visible scale.
About Richard Feynman
Nobel laureate in physics; quantum electrodynamics, the Manhattan Project, beloved teacher and storyteller.
More about Richard Feynman
- Feynman offered $1,000 prizes for tiny machinesTo spur progress toward nanotechnology, Richard Feynman offered two $1,000 prizes for miniaturisation challenges. William McLellan and Tom Newman claimed them.
- Feynman showed why the Challenger shuttle failedOn the commission investigating the 1986 Challenger disaster, Richard Feynman dipped a sample of O-ring material in ice water on live TV to show it lost resilience in the cold.
- Feynman invented diagrams that physicists still useRichard Feynman devised simple pictures, now called Feynman diagrams, to represent the mathematics of how subatomic particles interact. They remain widely used today.
- The Feynman Lectures on Physics inspired generationsIn the early 1960s Richard Feynman spent three years rethinking Caltech's introductory physics course. His lectures became The Feynman Lectures on Physics, a classic still read today.
- Feynman was among the first to propose quantum computersRichard Feynman was one of the first scientists to conceive of quantum computers, arguing that only a machine following quantum rules could efficiently simulate nature.
- Feynman's 1959 talk launched the idea of nanotechnologyIn a 1959 Caltech lecture, There's Plenty of Room at the Bottom, Richard Feynman imagined machines and writing on the scale of atoms, introducing the concept of nanotechnology.
Sources
- Richard Feynman Wikipedia
- Superfluid helium-4 Wikipedia
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