It looks like you're using an Ad Blocker.
Please white-list or disable AboveTopSecret.com in your ad-blocking tool.
Some features of ATS will be disabled while you continue to use an ad-blocker.
One of the ways we measure a beam of light is through its angular momentum - a constant quantity that measures how much light is rotating. And until now, it was thought that for all forms of light, the angular momentum would be a whole number (known as an integer) multiple of Planck's constant - a physical constant that sets the scale of quantum effects.
But researchers led by Trinity College Dublin have now demonstrated that a new form of light exists, where the angular momentum is only half of this value.
The end result of all this hard work is an instrument known as the Kibble balance. This was invented in 1975 by British physicist Bryan Kibble, and has been optimized since to reach new levels of accuracy. Despite its complications, the Kibble balance works like a traditional set of scales or beam balance, just like those you might use to weigh groceries. But while these scales usually weigh one mass against another, the Kibble balance weighs mass against an electromagnetic force which can be measured extremely accurately.
This electromagnetic force is generated using a coil of wire surrounded by permanent magnets. This setup can create two different methods of weighing. In the first, you run a current through the coil of wire to generate electromagnetic pull. In the second, you physically move the coil up and down like a piston, which has the same effect. Due to a number of recent discoveries (including those Nobel Prizes we mentioned), we can measure some of the forces involved in both of the weighing modes with incredible precision. And by combining this knowledge, we can measure the mass on one side of the Kibble balance using Planck’s constant. This is what allows scientists to create a new definition for the kilogram: measuring the fundamentals of the physical world down to what is essentially the smallest possible physical action.
The new definition of the kilogram uses a measurement from another fixed value from nature, Planck's constant (h), which will be defined as 6.62607015×10−34 joule seconds. Planck's constant can be found by dividing the electromagnetic frequency of a particle of light or "photon" by the amount of energy it carries.
The constant is usually measured in joule seconds but this can also be expressed as kilogram square metres per second. We know what a second and a metre is from the other definitions. So by adding these measurements, along with an exact knowledge of Planck's constant, we can get a new, very precise definition of the kilogram.
The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 × 10^–23 when expressed in the unit J K^–1, which is equal to kg m^2 s^–2 K^–1, where the kilogram, metre and second are defined in terms of h, c and ∆ν(sub Cs).
Scientists, for whom the update represented decades of work, clapped, cheered and even wept as delegates gathered in Versailles one by one said "yes" or "oui" to the change, hailed as a revolution in how humanity measures and quantifies its world.
The redefinition of the kilogram, the globally approved unit of mass, was the mostly hotly anticipated change. For more than a century, the kilogram has been defined as the mass of a cylinder of platinum-iridium alloy kept in a high-security vault in France. That artefact, nicknamed "Le Grand K," has been the world's sole true kilogram since 1889 .
Now, with the vote, the kilogram and all of the other main measurement units will be defined using numerical values that fit handily onto a wallet card. Those numbers were read to the national delegates before they voted. The update will take effect May 20.