Researchers have proposed building a nuclear clock that would lose only one-tenth of a second over 14 billion years, the current age of the universe. The design would be 100 times more accurate than current atomic clocks and might be used in applications such as higher-precision GPS satellites and experiments that probe fundamental physics. Atomic clocks measure time using the oscillations of a single atom and are accurate to 17 decimal places. They are in widespread use for GPS measurements and synchronization in particle accelerator experiments, and you can even set your laptop to one. But errant magnetism, electrical fields and microscopic jostling would make atomic clocks drift about four seconds over the lifetime of the universe. The proposed clock would instead measure time based on the oscillations of a neutron, a particle that is found tightly packed inside an atomic nucleus and isn't susceptible to vibrations or electromagnetic forces. Researchers would excite a single thorium atom's nucleus with an ultraviolet laser, and then keep time using the oscillations of its neutrons. The whole system, meanwhile, would need to be cooled to just above absolute zero. While all the technical components are possible, it may be awhile before physicists can actually create the clock — they don't yet know the exact frequency of ultraviolet laser emissions can excite the thorium nucleus in just the right way. The research will appear in an upcoming issue of Physical Review Letters.
 Images: An ultra-high vacuum chamber houses an ion trap where single thorium atoms are suspended and laser-cooled to near absolute zero temperature. (Alexander Radnaev) |
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