May 29, 2019
Did you here this... the unit of measurement known as a kilogram will no longer be defined by physical object? This is news to me! Come on science! What's going on over there?
Learn about this and more interesting stories from the scientific community in today's issue.
*-- Kilogram to be based on physical absolute instead of single, physical object --*
The kilogram is no longer defined by a physical object. Instead, from here on out, the unit of measurement will be based on fundamental constants, atomic properties and physical absolutes.
Scientists around the world will be able to reproduce the mass constant.
Until now, a kilogram unit was based on the mass of a cylinder made of platinum-iridium alloy. Housed in Paris, the cylinder has been the standard-bearer for the base unit of mass for 130 years.
Of course, physical objects change. Each time the cylinder was hauled out of storage to calibrate an instrument, the object shed a handful of atoms. Over the last 130 years, the cylinder lost 50 micrograms.
The abandonment of the physical kilogram was made official on May 20, 2019, which is World Metrology Day, a celebration of the Meter Convention held in 1875, where scientific leaders agreed upon the International System of Units.
With the official change in the definition of the kilogram, as well as changes to the definitions for the base units of charge, temperature, and mole, all international units are now defined by physical constants. Other common units, like the meter, made the switch years ago.
"The [International System of Units] is now based on a set of definitions each linked to the laws of physics and have the advantage of being able to embrace further improvements in measurement science and technology to meet the needs of future users for many years to come," scientists at the Meter Convention announced in a news release.
From now on, the definition of a kilogram will be based on the Planck constant, which is based on the energy of a photon to its frequency. A single kilogram is equal to 6.62607015 times 10^34 kilograms times square meters per second.
Nobel laureate Wolfgang Ketterle, a professor of physics at MIT, explained the change during a lecture on Monday, commemorating World Metrology Day.
"Conceptually, the explanation is that 1 kg is now the mass of a defined number of photons, 1.4755214*10^40, at the frequency of the cesium atomic clock," according to Ketterle.
The change doesn't mean scientists will now have to count photons. As Ketterle explained, there is a multi-step process for using physics and math to precisely define a kilogram.
"If you win a million dollars, and it is paid in pennies, you don't want to count pennies. You will first exchange the pennies into dollar bills, and then the dollar bills into 100 dollar bills, and then you count them," Ketterle told MIT News.
"In metrology, something analogous is done by comparing the atomic clock frequency of the cesium atoms to a much higher atomic frequency. Then you use this frequency to measure the mass of the electron or of a single atom, and only then you start counting," he said.
*-- Scientists extract yeast from ancient pottery, recreate 5,000-year-old beer --*
When researchers in Israel examined fragments of clay jars used to house beer and mead several thousand years ago, they discovered colonies of yeast hiding in the shards' nano-sized pores.
To help them extract the long-dormant yeast, scientists recruited the help of winemakers with experience aging wine in clay pots.
Archaeologists dated the clay fragments to several different historical periods, including the reign of Egyptian Pharaoh Narmer, who ruled Judea between 3100 and 3050 BC. Scientists also identified and extracted yeast from ceramic pieces dated to the reign of Aramean King Hazael, whose rule lasted from 842 to 800 BC. Several jugs dated to Judea's Persian rule during the 5th century BC were also used to isolate ancient beer yeast.
"We dug at Ramat Rachel, the largest Persian site in the Judaean kingdom, and found a large concentration of jugs," Yuval Gadot, an archaeologist at Tel Aviv University, said in a press rleease. "In a royal site like Ramat Rachel it makes sense that alcohol would be consumed at the home of the Persian governor."
Previous studies have shown there is a long history of beer making in the Near East.
In total, six strains of viable yeast were isolated from the pottery pieces and used to brew a handful of beer varieties.
"The greatest wonder here is that the yeast colonies survived within the vessel for thousands of years -- just waiting to be excavated and grown," said Hebrew University researcher Ronen Hazan. "This ancient yeast allowed us to create beer that lets us know what ancient Philistine and Egyptian beer tasted like."
Scientists have previously created beers inspired by the ingredients of ancient alcohol beverages, but researchers in Israel claim this is the first time ancient yeast have been used to brew ancient beers.
Because the researchers were able to isolate only a few yeast strains, it's hard to know how similar the beer they produced and drank was to the varieties consumed during ancient times. The beers brewed and consumed several thousands years ago were likely made using dozens of yeast varieties, produced by unique combinations of ancient grains.
Still, the feat of brewing 5,000-year-old beer is significant.
"Aside from the gimmick of drinking beer from the time of King Pharaoh, this research is extremely important to the field of experimental archaeology -- a field that seeks to reconstruct the past," Hazan said. "Our research offers new tools to examine ancient methods, and enables us to taste the flavors of the past."