Chapter 1: The Creation of the Roundest Object

In 2011, a remarkable achievement was realized by the Australian Centre for Precision Optics when they crafted the world's most spherical object: a small silicon sphere valued at approximately £2.5 million (about $3.25 million). This sphere, measuring less than 10 cm in diameter, is so precisely shaped that if it were scaled to the size of Earth, the difference between its highest and lowest points would be a mere 2.4 meters. The single isotope of silicon used in its creation was worth over a million euros at the time. The question arises: why was such a significant sum invested in this extraordinary object, and what purpose does it serve?

To understand the significance of this sphere, it's important to delve into the historical context surrounding the kilogram, the only fundamental unit of measurement with a prefix in its name.

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Section 1.1: The Historical Context of the Kilogram

In the wake of the French Revolution in 1793, a committee that included the renowned chemist and physicist Antoine Lavoisier proposed that the fundamental measure of weight would be the grav, equivalent to the weight of a cube of water with 0.1 m edges at 0 degrees Celsius. However, before this term could gain traction, Lavoisier and many others met a tragic fate during the revolution. Interestingly, he used his final moments to conduct a unique experiment, attempting to blink for as long as possible post-execution, with his assistant timing the effort. According to his assistant, Lavoisier managed to blink for approximately 15 to 20 seconds.

Section 1.2: The Evolution of Measurement

The grav, despite its initial endorsement, fell out of favor, as it reminded many of the title "graw," associated with nobility. Consequently, the smaller unit, the gram, was introduced but proved inconvenient for practical use. Eventually, the grav was rebranded as the kilogram, becoming the only basic unit with a prefix. Over time, the definition of the kilogram evolved, and in 1799, it was redefined as the mass of a liter of water at 4 degrees Celsius. A platinum cylinder was created to serve as the official kilogram standard, which was later refined into an alloy of platinum and iridium, securely stored at the International Bureau of Weights and Measures in Sèvres, near Paris.

Chapter 2: The Roundest Object's Purpose

Despite the meticulous safeguards for the kilogram standard, discrepancies arose when the original was compared with copies worldwide, revealing variations up to 50 micrograms. This seemingly minor difference can be significant in fields like medicine, where accuracy is crucial. To remedy this, a new approach was needed.

The first video titled "World's Roundest Object!" explores the creation and significance of this extraordinary sphere, detailing its journey from conception to realization.

To establish a more reliable standard for the kilogram, scientists sought to redefine it using physical constants, leading to the creation of the silicon sphere. This sphere, due to its highly ordered structure, allowed researchers to measure the number of atoms it contained with remarkable precision. The project, aptly named the Avogadro project, aimed to determine Avogadro's constant, which is the number of particles in one mole of a substance.

The second video titled "The Roundest Object in Existence" provides insights into the scientific principles behind Avogadro's constant and its implications for measurement standards.

The successful determination of Avogadro's constant enabled the recalibration of the kilogram, freeing it from reliance on physical objects. This advancement was officially recognized on November 16, 2018, during the 26th General Conference on Weights and Measures, which announced that, effective May 20, 2019, the kilogram would be defined by Planck's constant, allowing the original standard to retire gracefully.

As a result of this groundbreaking research, several similar silicon spheres were produced, each crafted with different isotopes but maintaining the same high value.