[♩INTRO ] When you hear “philosopher’s stone,”
the first thing that comes to mind might be Harry Potter trying to stop Lord Voldemort
from using it to restore his power. But the idea of a philosopher’s stone has
been around for thousands of years. For ancient alchemists, it was their ultimate
goal in life: to create some kind of object or process that could turn common metals into
gold. They mainly focused on lead, and the recipes
they came up with were as numerous and bizarre as the alchemists themselves. Some called for things like urine, bones,
and cat hairs. They never actually succeeded in their quest
to achieve transmutation—the conversion of one element into another. Or in creating an elixir that would make them
immortal, which is the other thing they thought a philosopher’s stone might be able to do. These days, we still can’t make ourselves
immortal. But with some serious equipment, we can change
atoms into different elements. We can even turn lead into gold. Elements are defined by the number of protons
their atoms have in their nuclei. Lead has 82 protons and gold has 79, so to
turn lead into gold, we would have to somehow force it to lose three of its protons. But that's not simple. The forces that hold nuclei together are incredibly
strong — I mean, literally, they're called the strong force. If an atom’s protons want to stay together,
all the cat hairs in the world aren't going to break them apart. But they don't always want to stay together. And in the early 20th century, scientists
discovered that sometimes, one type of atom will suddenly turn into another. In 1903, physicists Ernest Rutherford and
Frederick Soddy noticed that some thorium in their lab had converted itself into radium. We now know that's because thorium is radioactive,
meaning its nucleus is unstable — it doesn't have a good balance of positively-charged
protons and neutral neutrons. [pic on TB] To fix this, radioactive nuclei eject small
particles, which is what we call radioactive decay. That lowers the energy needed to keep everything
together, so the nucleus becomes more stable. And some forms of radioactive decay change
the number of protons in the nucleus — and therefore, the element itself. In Soddy and Rutherford’s lab, thorium,
which has 90 protons, underwent alpha decay, losing two protons and turning into radium,
which has 88 protons. Supposedly, Soddy said: “Rutherford, this
is transmutation!” and Rutherford replied, “Soddy, don't call it transmutation. They'll have our heads off as alchemists.” Soddy was right, though: it was transmutation,
and we now know it happens all the time with radioactive elements. But creating gold was another matter entirely. In 1923, Japanese physicist Hantaro Nagaoka
was studying the structure of atoms by looking at the light emitted from them when they were
excited by electricity, and realized that it might be possible to turn mercury into
gold. Mercury has 80 protons — just one more than
gold — and Nagaoka believed that with enough energy, you could rip protons off the mercury
atoms, forcing them to turn into gold. During one experiment, his team applied about
15,000 volts of electricity to mercury, and detected a small amount of gold in the residue. Their work caught the eye of German researcher
Adolf Miethe. He was intrigued because he’d found gold
in the residue from a mercury vapor lamp. So Miethe modified Nagaoka’s experiment
and ran a current through a mercury lamp for nearly 200 hours. He claimed to have made gold, and even filed
a patent for the process. But, there were many, many criticisms of his
methods, and efforts by other scientists to replicate his findings failed. Researchers weren’t completely sure mercury
could turn into gold until the 1940s, after they’d figured out how to force atoms to
release particles by bombarding them with tons of extra energy in the form of neutrons. But there was a problem—the isotopes of
gold that mercury turned into were radioactive. Isotopes are atoms that have the same number
of protons but different numbers of neutrons. They’re the same element, just lighter or
heavier. The isotope of gold we mine from the ground
isn’t radioactive, but plenty of the isotopes we can make artificially are. These particular radioactive isotopes were
heavier than natural gold, with 119 or 120 neutrons instead of the usual 118. And they actually decayed back into mercury,
through a process that involves ejecting an electron and turning one of their neutrons
into an extra proton. So, by the 1940s, physicists knew how to turn
mercury into gold. It was radioactive and unstable and not the
kind of thing you could make coins or jewelry out of, but it was something. Turning lead into gold is a lot harder, though. The lead nucleus is pretty stable — it can
hold a lot of neutrons before it becomes radioactive, which is why we use it to shield nuclear reactors. But once it does become radioactive, it undergoes
a type of decay that makes it gain a proton, turning into an isotope of bismuth. And we do know how to turn bismuth into gold. In the 1980s, researchers used carbon and
neon nuclei to blast protons out of a sheet of bismuth. They produced nine different isotopes of gold,
and the team was confident they’d transmuted at least a few thousand atoms. But a few thousand atoms isn’t much. I mean, we’re talking less than a billionth
of a billionth of a gram. That would be some very small bling. If this all sounds like a lot of work to create
a tiny amount of gold, that’s because it is. Using these transmutation methods, it costs
tens or even hundreds of thousands of dollars to produce miniscule amounts of gold — usually
radioactive gold. I know gold is expensive these days, but that
just doesn’t seem worth it. And yet, we’re still performing these kinds
of experiments all the time, because even though it isn’t a very good money-making
scheme, we can learn more from them than the ancient alchemists could ever have imagined. For example, in the late 1980s, researchers
at CERN discovered that the nuclei of some of the lighter isotopes of gold have different
shapes — some are close to spherical, but others are much more deformed. And physicists are still trying to figure
out exactly how that works. So even if we aren’t able to make vast quantities
of stable gold, I guess you could say we finally did discover the philosopher’s stone — or
maybe, the philosopher’s particle accelerator. It’s not making money or turning us immortal,
but it is teaching us a lot about physics. And we didn’t even have to use pee or cat
hair to make it happen. Thanks for watching this episode of SciShow,
brought to you by our patrons on Patreon. If you want to learn more about the science
of splitting atoms apart, you can check out our episode about the first human-made nuclear
reactor. [♩OUTRO ]
