On November 16th, representatives from nearly 60 countries will gather in Versailles, France, to vote on a major change in how we define the kilogram and other key units of measurement. This meeting is a significant event in the history of the International System of Units (SI), as it aims to redefine four of the seven base SI units: the kilogram, kelvin (temperature), mole (amount of substance), and ampere (electric current).
Since 1799, the kilogram has been defined by a physical object: a platinum-iridium cylinder known as the International Prototype Kilogram, or “Big K,” stored in Paris. While this definition has worked for over 200 years, it has some issues. Scientists have found that the mass of Big K is changing when compared to other similar cylinders, raising concerns about its reliability. Additionally, access to Big K is limited, making precise measurements difficult.
To create a more consistent and universally accessible mass standard, scientists propose using Planck’s constant. This constant connects the frequency of a photon to its energy and is also linked to mass through Einstein’s equation, $E=mc^2$. Currently, Planck’s constant has some uncertainty in its last few decimal places, while the mass of the platinum-iridium cylinder is known with absolute certainty.
By redefining the kilogram using Planck’s constant, the physical object in Paris will no longer be the standard. Instead, Planck’s constant will be set to an exact value, becoming the new reference point for measuring mass.
Redefining the kilogram affects other base SI units that depend on it. For example, the mole is currently defined by the number of particles in 12 grams of carbon-12, which relies on the kilogram’s definition. After the vote, Avogadro’s constant will be fixed to an exact value that aligns with the new definition of Planck’s constant.
Similarly, the ampere will be redefined based on the fixed value of the charge of an electron, and the kelvin will be based on the Boltzmann constant, which relates temperature to the average kinetic energy of molecules. These changes will ensure that all units are consistent and reliable.
For most people, these changes won’t drastically alter everyday experiences. Food will still weigh the same, and temperature will continue to function as it always has. The main goal of these updates is to improve the consistency and reliability of measurements worldwide, removing the dependence on physical artifacts.
However, there will be minor adjustments in electrical measurements, with the volt changing by about one part in ten million. This is because previous decisions by electrical metrologists kept outdated values of Planck’s constant, which will now be updated based on more accurate measurements.
The motivation behind these changes is the quest for precision in scientific measurements. Accurate measurements are crucial for scientific inquiry, allowing researchers to make observations and draw conclusions about the universe. Historical figures like Kepler relied on precise measurements to understand planetary motion, and modern discoveries, such as the Higgs boson and gravitational waves, showcase the pinnacle of human achievement in science.
By moving away from physical objects and basing measurements on fundamental constants of nature, scientists can achieve a new level of precision. This shift represents a significant leap in our understanding of the universe, allowing for more reliable and consistent measurements that are accessible to everyone, everywhere.
In conclusion, the upcoming vote in Versailles is not just a technical adjustment; it symbolizes a transformative moment in the way we define and understand measurement in science. As we transition to a system based on the laws of nature, we pave the way for future discoveries and advancements in various fields.
Research and create a presentation on Planck’s constant. Explain its significance in physics and how it relates to the equation $E=mc^2$. Discuss how this constant will redefine the kilogram and its impact on scientific measurements.
Write an essay tracing the history of the kilogram from the International Prototype Kilogram to its redefinition using Planck’s constant. Highlight the challenges and limitations of using a physical object as a standard and the benefits of the new approach.
Create a concept map showing the interconnections between the kilogram, mole, ampere, and kelvin. Explain how changes in the definition of the kilogram affect these other units and the importance of consistency in the International System of Units.
Conduct a class debate on the importance of precision in scientific measurements. Use historical examples such as Kepler’s laws and modern discoveries like the Higgs boson to support your arguments. Discuss how redefining measurement standards can influence scientific progress.
Investigate and present on how the redefinition of measurement standards might affect industries such as electronics and pharmaceuticals. Discuss any potential challenges and benefits that these changes might bring to everyday life and technological advancements.
Kilogram – The base unit of mass in the International System of Units (SI), equivalent to the mass of the International Prototype of the Kilogram. – The mass of the object was measured to be 5 kilograms using a balance scale.
Measurement – The process of obtaining the magnitude of a quantity relative to an agreed standard. – Accurate measurement of the length of the pendulum is crucial for calculating its period.
Constant – A quantity that remains unchanged under specified conditions. – The speed of light in a vacuum, denoted as $c$, is a fundamental constant in physics with a value of approximately $3 times 10^8$ m/s.
Energy – The capacity to do work or produce change, often measured in joules. – The potential energy of an object at height $h$ is given by $E_p = mgh$, where $m$ is mass, $g$ is the acceleration due to gravity, and $h$ is the height.
Mass – A measure of the amount of matter in an object, typically measured in kilograms or grams. – The mass of the sample was determined to be 250 grams using a digital scale.
Photon – A quantum of electromagnetic radiation, which exhibits both wave-like and particle-like properties. – When an electron transitions between energy levels in an atom, it emits or absorbs a photon with energy $E = hf$, where $h$ is Planck’s constant and $f$ is the frequency of the radiation.
Precision – The degree to which repeated measurements under unchanged conditions show the same results. – The precision of the instrument was evident as it consistently measured the voltage to be 5.00 V with minimal variation.
Science – The systematic study of the structure and behavior of the physical and natural world through observation and experiment. – Science relies on empirical evidence and reproducible results to build and refine theories about the universe.
Units – Standard quantities used to specify measurements. – In physics, it’s essential to use consistent units, such as meters for length and seconds for time, to ensure accurate calculations.
Temperature – A measure of the average kinetic energy of the particles in a substance, typically measured in degrees Celsius, Fahrenheit, or Kelvin. – The temperature of the gas was measured to be 300 K, which is necessary for calculating its pressure using the ideal gas law.
