The city of Paris owns a tiny and tucked away metal cylinder. We refer to it as Le Grand K. This hunk of 10% iridium and 90% platinum has been the prototype kilogram for about 130 years now . And this would mean that we measured all kilograms by this object. Let’s say that there were microscopic contaminants which made Le Grand K heavier. Then this unit of mass would also “gain” weight. Alternatively, if a tiny scratch or thorough cleaning affected it in a way that it made it lighter, then the kilogram would become lighter too.
Furthermore, experts state that, over the course of time, this important object has shed 50 micrograms of its mass. However, the absolute rule of Le Grand K ended. This object no longer defines the unit of mass. Namely, Planck’s constant, the basic property of nature, is now in charge of the kilogram. The value of this constant cannot vary. In this respect, it is similar to the speed of light. And it was created with absolute precision.
Stephan Schlamminger, a physicist at the National Institute of Standards and Technology, said that a fundamental constant could not alter. So a kilogram will weigh the same on Mars, Earth, or in the Andromeda galaxy. Researchers express that this new meaning of the kilogram (as well as certain changes to the ampere, the mole, and the kelvin) is a turning point for the world. In fact, Walter Copan, director of NIST, said that we were improving as species because we could measure something with increasing accuracy.
Of course, most of us will probably not even notice the change. So the weight of a chicken at your local grocery store or coffee beans at a café will be the same. Schlamminger stated that they were not in the business of disturbing the whole system.
How These Changes Came to Be
After much deliberation, delegates decided to redefine four base units in November last year. This was during the 26th General Conference on Weights and Measures in Versailles, France. And representatives from 60 member states gathered in a huge auditorium to cast their votes. The results were unanimous. This was followed by a standing ovation and a toast. Copan, a delegate from the USA, described the meeting as being a thrilling experience. According to him, it took them quite some time to reach this point.
What’s more, the creation of the metric system could be traced back to the French Revolution. People used about 250,000 different units of measurement in France back then. Undoubtedly, this made trade and commerce that much difficult. Now, many deem the new system to be universal and rational. Its units rely on properties of nature and not on any whims or royal decree.
Ken Alder, a science historian at Northwestern University, gave his opinion on this. He said that experts wanted to ensure that the measurements were the same across the globe. Also, they wanted people to use them forever. The meter was the basic unit of the system. And scientists wanted it to be one ten-millionth the distance from the North Pole to the equator along the Paris meridian. At the time, they made an error in their measurement. So the meter is actually longer for around 2 millimeters.
Moreover, they defined the kilogram as being the weight of 10 cubic centimeters of water which was at 4 degrees Celsius. The French Republic accepted these units back in 1795. But people actually utilized local measurements for years. As Barry Taylor stated, not everyone was in favor of the metric system from the get-go. This scientist emeritus at NIST concluded that this was not the case at all.
The Path of the Metric System
The metric system was accepted across Europe and South America in the 19th century. And 17 countries in total signed the Treaty of the Meter in 1875. It created a general system of units which was based on the kilogram, the meter, and the second. The first two were actually determined by metal artifacts even though they relied on the size of the Earth. They were created in London in 1889. And one could find them in a vault of the International Bureau of Weights and Measures in France. All member states got one of their own replicas.
This agreement also found the General Conference on Weights and Measures. As many might know, this is a group that researches and votes on any changes that might impact the units of measurements. Among other things, they approved three base units: the kelvin, the ampere, and the candela. Also, they made some changes to the second in 1967. In particular, they relied on the oscillations of a cesium-133 atom.
In addition, they altered the meter in 1983 as well. To be specific, they connected it with a basic property of the universe. And it became the distance taken by light in a vacuum in 1/299,792,458 of a second. Schlamminger says that we can count with precision the distance from our planet to a satellite which is 6,000 kilometers away. Nevertheless, Le Grand K still defined the kilogram. This object was so valuable that they would remove it from the vault every 40 years in order to take care of it.
The Change Was a Long Time in the Making
Experts have waited for the kilogram’s definition to change since the 1900s. However, it took some time for the option to measure Planck’s constant with precision to come to life. In addition, Planck’s constant connects the frequency of light with energy. This is similar to how pi links the diameter and circumference of a circle. The developments in technology that would repair the value of Planck’s constant occurred sporadically.
A number of scientists came up with a scale that would link mass with electromagnetic force in the 1970s. They called it the Kibble balance due to Bryan Kibble who invented it. Albeit, it was not as accurate, at least it was a breakthrough. Over time, the Kibble balance became better and more precise. This prompted a group of scientists to publish a study “Redefinition of the kilogram: a decision whose time has come.” According to Schlamminger, this paper was the starting point for everything.
And five years ago, experts concurred that national metrology institutes had to measure Planck’s constant with an accuracy of 20 parts per billion. Also, they needed to show that it would be possible to get the same answer by using different methods. Ian Robinson, a researcher at the National Physics Laboratory, explained that if you were to reach the same conclusion after utilizing two different methods, then it would indicate that you were not wrong.
The Kibble Balance
The Kibble balance gave only one value. One measurement included a sphere of enriched silicon. Its structure was beneficial in that scientists were able to determine Avogadro’s constant. With this, they were able to measure Planck’s constant. Taylor said that this silicon sphere was a check during this particular approach. And scientists use this fixed constant in the recent definitions of the kelvin, the mole, and the ampere. Starting from Monday, the mole would rely on the value of Avogadro’s constant. As for the kelvin, it would use the value of Boltzmann constant, while the ampere would utilize the value of the elementary charge.
Additionally, Schlamminger said that we all could use the fundamental constants. In fact, they do not discriminate against someone on the basis of anything. They do not differentiate between humans on Earth and those somewhere else in the universe. Who knows, maybe one day these new definitions could assist us in talking with extraterrestrials.
According to Schlamminger, if we ever get in contact with aliens, they would laugh at us for using a metal hunk to determine our units of measurements. At the moment, no one knows how the changes will influence the future. But scientists are almost certain they will. For instance, it is possible for us to measure the second so precisely that we can notice minor changes that might occur in the Earth’s gravitational field.
Copan went on to quote Lord Kelvin who said: “To measure is to know.” So it’s only logical that, by becoming more precise, our knowledge of the fundamentals of life and universe will expand. As for Robinson, he believes that the new definitions will make it possible for scientists to be creative when it comes to measurements. He concluded that they did not have to worry about this object in Paris. From now on, their only concern was physics.