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Redefining time

According to reports published in the Physical Review Letter, the National Institute of Standards Technology (NIST) published a paper indicating that it had discovered a new type of atomic clock based on mercury-ion. The report said that the new atomic clock is so accurate it's nearly 6 times more precise than the current cesium-based atomic clock.

The report said that the NIST currently operates a cesium-based atomic clock called the NIST-F1, which is accurate for roughly 70 million years. If operated continuously, the NIST-F1 would only be off by 1 second after 70 million years. The new mercury-ion atomic clock on the other hand will take 400 million years.

The new experimental clock measures the atomic resonance frequency of a mercury atom. The atom itself is electrically charged and kept in an extremely cold suspension. Using the new mercury-ion atomic clock, scientists at the NIST say that they will be able to conduct more precise experiments and further develop applications that rely on atomic-time accuracy such as GPS systems. Currently, the international standard that defines what one second is relies on cesium-based atomic clocks -- 9,192,631,770 radiation cycles of the change between two energy levels of a cesium atom. The NIST says that it will be five to ten years before we see mercury-ion clocks replace cesium ones.



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By FoxFour on 8/2/2006 12:41:35 AM , Rating: 3
quote:
The report said that the new atomic clock is so accurate it's nearly 6 times more precise than the current cesium-based atomic clock.

The report said that the NIST currently operates a cesium-based atomic clock called the NIST-F1, which is accurate for roughly 70 million years. If operated continuously, the NIST-F1 would only be off by 1 second after 70 million years. The new mercury-ion atomic clock on the other hand will take 400 million years.


Accuracy and precision are very different quantities. Accuracy is an estimate of how closely the reading from a measuring instrument correlates to the actual value. Precision describes the granularity of measurements that can be taken with the instrument. The two terms should not be used together in the context of the first paragraph I quoted.

Also, the 70-million-year (and 400-million-year) accuracies stated in this article are highly arbitrary. I could also say that a cesium clock is only accurate for 70 years, if I was concerned about measuring a time interval to within a few millionths of a second of the true elapsed time (assuming that such a clock has the necessary precision to measure to millionths of a second).

This is an important issue for anyone in science or engineering disciplines, so it would be nice to see more careful wording in future. It will not be unappreciated.





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