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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.
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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.
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