## Thursday, November 2, 2017

### Fundamental Constants No Longer Constant?

In November 2018, the physics world might be changed when the International Committee of Weights and Measures meets at the General Conference of Weights and Measures to vote on the changing (or fine tuning) four fundamental constants. They are proposing revised values for electron charge, the Boltzmann constant, the Planck Constant and the Avogadro constant. We might not have seen these values in our class yet, but they play an integral role in the way to measure and calculate many things. Additionally, the constants inform other derivative values. The electron charge will help redefine the ampere, the Boltzmann constant will help redefine the Kelvin, and the Planck constant will redefine the kilogram. One significant figure will be added to the Boltzmann constant to make it have eight digits, where the last digit will be 0. The Plank constant will be lowered by 15 parts per billion.

This article led me to wonder how we define a kilogram. Interestingly, the kilogram is based off o the mass of a platinum-iridium cylinder in Sevres, France. This block is called the International prototype kilogram (or "Le Grand K"), and was cast in 1889. Because the mass of the kilogram is defined by a physical object, the mass of the kilogram has been changing throughout years. While this change is only in terms of micrograms, this proves to be an issue when trying to measure something very tiny or very large quantities (where the micrograms can quickly add up to be significant). This is unacceptable to most scientists, and thus now scientists are hoping to redefine the kilogram in terms of the Planck's constant (similar to how we define the meter in terms of the speed of light), which is why the redefinition of the Planck's constant in the most accurate terms is important.

Now, these changes are not enormous, but they are very important when experimenting on extreme limits with high precision. Luckily, this means our physics class will not be affected.

These changes to the SI system are expected to be officially announced on World Metrology Day on May 20, 2019. The scientists state what after this update the Planck's constant will truly be a constant and researchers will stop trying to measure it and instead focus on the kilogram

I thought this news was interesting because I did not even consider these values were up for debate. Stay tuned!