Boulder group

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The Boulder Group is a group that has performed the most accurate measurement of the speed of light on behalf of the National Bureau of Standards . Ken Evenson was the project manager . Other project members were Bruce Danielson , Gordon W. Day , Dick Barger , John L. Hall , Russ Petersen and Joe Wells .

The end of the measurement of the speed of light

The National Bureau of Standards in the USA had a long tradition of measuring the speed of light (see Rosa and Dorsey 1907).

The Boulder group tried to develop a method to determine the speed of light. In 1972 an asymmetry was found in the krypton line , which until then had been the basis of the definition of the meter and thus made an exact measurement impossible. In contrast, the time could be measured very precisely with the cesium atomic clock - as was the speed of light, which was published in 1973 at 299,792,457.4 m / s.

So now the problem was the meter. The experiment was repeated and improved several times by other laboratories in order to answer the question of whether a more precise definition of the meter was possible with the aid of the speed of light. All that was needed was an accurate measurement of higher visible wavelengths for verification. The Boulder group took on a leading role again this time and made the first direct measurement of the frequency of light with an iodine-stabilized helium-neon laser at 633 nm and also at 576 nm wavelength. This was verified again in other laboratories around the world and cleared the way for a new definition of the meter.

At the 17th General Assembly for Weights and Measures in 1983, the speed of light in a vacuum was defined as c = 299,792,458 m / s. This crooked value was chosen to have the smallest possible deviation from the original meter.

Furthermore, the definition of the meter was changed from: "A meter is 1,650,763.73 times the wavelength of the radiation propagating in a vacuum, which is emitted by atoms of the nuclide krypton-86 during the transition from state 5d5 to state 2p10" One meter is the distance that light travels in a vacuum in a time of 1 / 299.792.458 seconds “changed.

literature

  • Edward Bennett Rosa & Noah E. Dorsey: A new determination of the Ratio of the Electromagnetic to the Electrostatic Unit of Electricity . Bulletin of the Bureau of Standards 3 (1907) 433-604.
  • Edward Bennett Rosa & Noah E. Dorsey: A comparison of the various methods of determining the ratio of the electromagnetic to the electrostatic unit of electricity . Bulletin of the Bureau of Standards 3 (1907) 605-622.

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