Unraveling the mysteries of the universe, physicists have an unexpected ally: ancient Roman lead. But here's where it gets controversial...
In a fascinating twist, a 2,000-year-old Roman shipwreck off Sardinia's coast sparked excitement not only for archaeologists but also for particle physicists. Dr. Ettore Fiorini, a visionary physicist, saw beyond the ship's historical value; he envisioned its lead cargo as a key to unlocking the universe's secrets.
Ancient lead, it turns out, is an ideal material for sensitive physics experiments due to its lack of radioactivity, which can interfere with observations. When studying elementary particles, the building blocks of reality, physicists must eliminate all background noise. This is why particle detectors are often placed deep underground, away from cosmic rays, which are high-energy particles from space that can disrupt experiments.
"Every second, every part of our body is crossed by a particle," says Paolo Gorla, an INFN physicist. Going underground provides a cosmic silence, a quiet space for these delicate experiments.
But even underground, there's radioactivity to contend with. Lead, with its super-dense nature, is an excellent shield against this noise. However, freshly mined lead has its own radioactivity due to the presence of lead-210, an unstable isotope. This means that while lead can protect against external radiation, it can also generate particles that disturb the experiment.
The solution? Ancient lead. Over time, the radioactivity in lead decays, leaving behind stable lead that's perfect for shielding. This is why physicists like Dr. Fiorini are on the hunt for lead from ancient Roman times, which has had centuries to stabilize.
But this pursuit has sparked a heated debate. While some argue that using ancient lead is a necessary sacrifice for scientific progress, others, like Elena Perez-Alvaro, an underwater cultural heritage researcher, believe it destroys historical records and artifacts.
"Everything taken out of the water without proper archaeological documentation is lost information," Dr. Perez-Alvaro says. "Where the ship came from, where it was going—this is basic knowledge for understanding the past."
This dilemma has divided the scientific community, pitting those who defend the past against those who advocate for the future.
Despite the controversy, there's a growing consensus that ancient lead can be used ethically in experiments, provided it's properly documented and recovered.
"Sometimes, having 1,000 ingots in a museum warehouse isn't useful," Dr. Perez-Alvaro concedes.
Dr. Fiorini's experiment, shielded by ancient Roman lead, is designed to detect dark matter, an elusive phenomenon that's thought to make up 85% of the universe's mass. Dark matter is an invisible substance that interacts with gravity but not light, and its existence is inferred from gravitational anomalies observed by astronomers in the 1930s.
The Cryogenic Underground Observatory for Rare Events (CUORE), located under Italy's Gran Sasso mountain, is one such experiment. The CUORE detector, kept in dilution refrigerators colder than outer space, is designed to detect the elementary particles that give our universe structure.
While CUORE hasn't made any major discoveries yet, it will soon be upgraded to CUPID, and the ancient Roman lead shield will remain in place.
"Without the quality of the shield, we wouldn't have been able to measure at this level," Dr. Gorla says.
Another observatory under Gran Sasso, called DAMA/LIBRA, has been detecting a signal believed to be dark matter for 20 years. However, other teams have failed to replicate the experiment, leading to controversy.
This is where Australia steps in. The SABRE South detector, located in Victoria's Stawell gold mine, aims to replicate the DAMA/LIBRA experiment and confirm whether the signal is indeed dark matter or an error.
"Understanding what 85% of our universe is made of will help us understand our place within it," says Theresa Fruth, an astroparticle physicist at the University of Sydney.
The pursuit of dark matter and the use of ancient Roman lead in physics experiments showcase the delicate balance between scientific progress and historical preservation. It's a battle between the past and the future, and the outcome will shape our understanding of the universe and our place within it.
