PORTLAND, Ore. -- Perpetual motion is forbidden by the laws of classical physics, but in the quantum realm frictionless motion is possible. For instance, a closed loop of superconducting wire can exhibit perpetual motion, albeit only for electrons traveling around the frictionless loop of wire. If only such frictionless motion could be demonstrated for a fluid, then "superfluidity" could realize the frictionless motion of atoms around a torus, thereby enabling ultra-sensitive rotational sensors to be built.
Now the frictionless motion of superfluidity has been demonstrated at the National Institute of Standards and Technology and the Joint Quantum Institute at the University of Maryland. True perpetual motion is still years away, but the agency recently demonstrated a proof-of-concept--what it called "persistent" motion--using an ultra-cold form of matter called a Bose"Einstein condensate. NIST predicts that eventually it will harness the quantum effects of superfluidity for the frictionless motion of matter, much like the frictionless motion of electrons in superconductors. Such superfluids could enable NIST to build ultra-sensitive navigation sensors not possible using classical materials.
Predicted by Einstein
Bose"Einstein condensates were predicted by Albert Einstein, but were conceived in 1925 by Satyendra Nath Bose. However, it was not until 1995 that scientists demonstrated them in the lab. Bose"Einstein condensates are a state of matter so cold that all the atoms are in their lowest energy state, thereby permitting quantum effects to manifest at a macroscopic scale. Composed of bosons, which are usually associated with electromagnetic waves because they can occupy the same space at the same time, this state of matter is often referred to as a superfluid--exhibiting motion without the friction of "bumping" each other.
Since the first demonstration of a Bose"Einstein condensate, such superfluids have been pursued by laboratories around the world. The University of Amsterdam, for instance, recently demonstrated Bose"Einstein condensates on-a-chip. However, these labs have been content to demonstrate the mere existence of their Bose"Einstein condensate, whereas the NIST demonstration is the world's first to harness a superfluid in a proof-of-concept for perpetual motion.
The key to NIST's demonstration was its formation of a torus (donut) trap using magnetic fields to contain supercooled sodium atoms that were stirred into motion by lasers. So far, the "perpetual" motion has only lasted for 10 seconds--prompting the "persistent" label rather than "perpetual." Future prototypes will aim to improve the length of time, as well as build-in compensation for losses by using bursts to stir the fluid. Eventually, such frictionless flows of atoms could enable ultra-sensitive navigational sensors to be based on the frictionless rotation of atoms around a torus etched into the surface of a chip.