June 8, 2001 Imagine turning on your faucet and watching water flow out and then flow right back up into the faucet. NASA scientists have observed a similar phenomenon by using superfluid helium-4 in laboratory research that could improve earthquake prediction and spacecraft navigation.
The team of scientists, led by Dr. Dave Pearson of NASA's Jet Propulsion Laboratory, Pasadena, Calif., is the first ever to observe this phenomenon, called the Josephson effect, in superfluid helium-4, the most common type of helium. Superfluids allow matter to flow without friction in the same way that electricity flows without resistance in a superconductor.
The Josephson effect was first predicted in 1962 by Nobel Prize Laureate Brian Josephson. For ordinary fluids, a pressure difference along a pipe causes fluid to flow from the high pressure to low pressure area; thus, water comes down out of a faucet and stays there. But with the Josephson effect, when pressure is applied, fluids begin to oscillate back and forth, or up and down, at a rate in direct proportion to the pressure difference. In essence, this effect enables a fluid to defy gravity.
"My colleagues and I used very high-resolution thermometers to precisely control the superfluid temperature to approximately two degrees above absolute zero," Pearson said. Absolute zero is the temperature at which scientists think that no further cooling can occur.
At this extreme cold, helium-4 enters a quantum state, in which its behavior becomes very odd. By using electrostatic forces to create a pressure difference across a pipe, Pearson and his colleagues saw that the fluid began to oscillate from one end to the other.
This strange effect is created because the fluid begins obeying laws of quantum mechanics, which govern how atoms behave at super-low temperatures. "What we see is quantum mechanics on the macroscopic scale," Pearson said. "This was very exciting for us, because we thought various technical factors would prevent the Josephson effect from occurring."
The successful observation of the Josephson effect in superfluid helium-4 allows measurements of very small rotation, enabling scientists to measure very precisely how fast Earth rotates. Monitoring Earth's rotation speed could yield information on minute movement of tectonic plates, which may eventually help predict earthquakes.
In addition, this research could lead to extremely precise, yet simple, gyroscopes to navigate spacecraft. Among the NASA missions that may benefit is the Terrestrial Planet Finder, which may use multiple spacecraft flying in very precise formation to image planets around other stars, looking for Earthlike planets that may harbor life.
The Josephson effect had been observed in superconductors in 1963, then in isotope helium-3 in 1987, but it has eluded researchers for 35 years in helium-4. Certain properties of helium-4 make it easier to work with in laboratories and in space. The research by Pearson and his team was conducted under a grant from NASA's Biological and Physical Research Program.
Pearson co-authored the quantum experiment paper, which appears in the May 17 issue of the journal Nature, with Drs. Talso Chui and Kalyani Sukhatme of JPL and collaborator Dr. Yury Mukharsky of CEA-DRECAM (Commissariat a l' Energie Atomique, Département de Recherche sur l 'Etat Condensé, les Atomes et les Molécules) from Saclay, France. More information on the BPR Fundamental Physics Program can be found at the following Web sites:
JPL manages the Fundamental Physics in Microgravity Research Program for NASA's Office of Biological and Physical Research, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.
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