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12 Jun 2019 James Dacey / Physcis World
The ancient Egyptians believed their gods had shimmering skin made from gold. While the Aztec word for gold, teocuitlatl, literally translates as “excrement of the gods”. From ancient Rome to the California gold rush, this dense shimmering metal has been immutably connected with divine quality and the sense of opportunity. The reason for this is simple: gold is the most special element of them all.
Gold is so revered because of its irresistible combination of beauty and rarity. All the gold mined in the history of mankind would fit into an Olympic swimming pool, so they say. Today, we present our loved ones with gold rings to symbolize lifelong bonds. Governments hoard gold bars to safeguard their futures, and the finest athletes on the planet compete for gold medals. Even the idea of gold permeates our cultures, as we speak about “golden hearts”, “gold standards” and “golden opportunities”.
Gold standard for electronics
But it’s not just bankers and newlyweds that have a special relationship with gold. Scientists and engineers also covet gold on account of its superlative and complementary properties. Gold is a great conductor of electricity and heat, while being hard and resistant to corrosion. It’s also freakishly malleable, meaning a little can go a long way. According to the Encyclopaedia Britannica, an ounce of gold can be beaten into thin gold leaf sheets of 187 square feet. This winning combination is particularly useful in electronics for creating robust switches and connectors in the computers and phones that have transformed our societies.
In the emerging field of nanotechnology, gold is proving itself to be the gold standard once again. Due to their unique physio-chemical properties, gold nanoparticles (GNPs) are showing promise as a carrier for delivering drugs to tumours in a highly targeted manner. For energy applications, GNPs have also been used to improve the efficiency of solar cells. Particles embedded into polymer structures can trigger an effect known as surface plasmon resonance – collective excitations of electrons that interact very strongly with light.
We may snigger now to think that Egyptians and Aztecs believed gold had divine origins. But scientists have also struggled to fully understand the origins of gold, often with a desire to produce it for themselves. Indeed, despite revolutionizing our understanding of the mechanics of the universe, Newton actually spent a fair chunk of his time doing alchemy, seeking ways of converting less valuable base metals into gold.
Excreted from a kilonova
We know that gold – atomic number 79 – is present across the world in small quantities in igneous rocks, formed when molten material from the Earth’s interior finds its way to the surface. What scientists struggled to understand was how that gold came into existence in the first place. Some argued that heavy elements such as gold and platinum could form from lighter elements fusing together inside a supernova. Others argued that even the conditions inside an exploding star would not be sufficiently extreme for that process.
Remarkably, the answer only arrived in 2017 with the first ever detection of gravitational waves, by the LIGO and Virgo collaborations. Those waves were produced by the merger of two neutron stars in an event known as a kilonova. With the birth of multimessenger astronomer, astrophysicists pointed their optical telescopes at the source of gravitational waves to discover the signatures of gold and platinum in significant quantities. At long last, we had discovered our cosmic deity capable of excreting gold!
For their pioneering work in the LIGO/Virgo Collaboration, Rainer Weiss, Barry Barish and Kip Thorne were awarded the 2017 Nobel Prize for Physics. What did they receive at the award ceremony in Stockholm to acknowledge that their work shines above the rest? A 175 g medal made from 23 carat gold. Of course.
James Dacey is multimedia projects editor, Physics World