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No. 130: JUL-AUG 2000

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Two Wrong-Way Phenomena!

Electrical currents flowing in opposite directions. How can this be? What about Ohm's Law? This counterintuitive situation was confirmed in a recent issue of Science.

Now two teams of researchers have induced millions of electrons to flow simultaneously both ways around a superconducting ring with a non-superconducting notch in it, a gizmo known as a superconducting quantum interference device, or SQUID.

This is all pretty weird but it just one more paradoxical phenomenon allowed by quantum mechanics. You see, in quantum mechanics, an object can exist in two or more states at the same time. This is, of course, a statement of fact rather than an explanation appealing to one's common sense -- a common occurrence in the quantum world.

(Cho, Advising "Physicists Unveil Schroedinger's SQUID," Science, 287:2395, 2000)

Heat flowing from cold to hot. The revered Second Law of Thermodynamics seems to tell us that heat always flows from hot to cold. But out in space, under special conditions, physicists seem to hedge a bit.

The groundbreaking experiment was carried out onboard the Mir space station last year as part of the French-Russian Perseus mission. By warming a copper-and sapphire-walled cell filled with a drop of liquid sulfur hexafluoride and one tiny bubble of gaseous sulfur hexafluoride in near-zero gravity, scientists triggered a slight compression of the bubble. That gentle squeeze raised the temperature of the gas above that of the cell walls. For this to happen, heat must have been transferred from the cooler walls to the hotter gas, scientists report in the 1 May Physical Review Letters.

This weird phenomenon can be tossed off as a "transient temperature overshoot." The Second Law didn't really apply because the system was not in thermodynamic equilibrium. Also, the Second Law really concerns changes in entropy rather than temperatures.

(Sincell, Mark; "Backward Heat Flow Bends the Law a Bit," Science, 288:789, 2000.)

From Science Frontiers #130, JUL-AUG 2000. 2000 William R. Corliss

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