It’s not just a surprisingly common topic
for song lyrics for the last several centuries, scientists
have been fascinated by what happens to materials when they’re
under pressure. The hope is that with these experiments, we can model the chemistry of places we’ll
never be able to visit, like deep inside the Earth, or Saturn, or
the Sun. And with the help of some diamonds, they’re already able to push some things
to galactic extremes. By definition, pressure is the amount of force
exerted over a given area. So there are two basic ways to increase that
pressure: increase the amount of force you’re using,
or decrease the area. As all good Jedi padawans know, generating more force isn’t always simple. Which means the easiest way to increase pressure is to decrease the area on which the force
is acting. That’s why shark teeth have points. One of the most common ways scientists do
this is by using a Diamond Anvil Cell, or DAC, so named because two flawless, cut diamonds
are used as anvils to squeeze a sample, which exerts a lot of
force over a tiny area. The area doing the pressing is a teeny facet at the bottom of each diamond call the culet. It can be as small as 50 microns, or millionths
of a meter across. Whatever scientists want to study is sandwiched between two of these culets, suspended in
a bit of fluid. Then, they push the diamonds together. Really hard. Pressures of standard DACs can get into the hundreds of gigapascals that’s millions of times more than the pressure that you feel standing on the ground, and equivalent to what we think is happening
in the Earth’s core. Where, to be clear, you would not be able
to stand. Because the pressure would crush you into
molecular mush. There’s also a special class of DAC called
double-DAC, which takes each diamond tip and attaches
an even smaller, specially-grown hemisphere of diamond — only
10-20 microns across. Then the super-mini diamond does the pushing, confining the force to an even smaller area. A double-DAC developed in 2015 is capable of generating 1000 gigapascals,
or 1 terapascal, of pressure enough to begin to explore the physics of
more massive planets. Astronomers think that’s roughly how strong
the pressure is in Saturn’s core, for example. One main reason we use diamonds is that they’re the hardest substance readily
available. But it’s also nice that they happen to be
transparent to a wide range of electromagnetic wavelengths, because that allows scientists to X-ray the
sample while it’s being squashed so they can see
what’s happening. And these DACs provide researchers with essentially
unlimited time to do that data collection, because they exert
static pressure that is, a fixed, continuous pressure on their
samples. But to really get at what’s happening elsewhere in the universe, you need a lot more pressure. And that means turning to dynamic experiments, which allow for much greater pressures, but less time to see what happens. There are dynamic DACs that can quickly vary the amount of pressure delivered over time, but the diamonds themselves can only handle
so much pushing before they shatter. So when scientists want to generate pressures too strong for the diamonds to withstand, they use lasers to vaporize them instead. You know, as you do. The National Ignition Facility in Livermore,
California is equipped with almost 200 super-powerful
laser beams. And researchers have used those lasers to pump so much energy into diamonds that
they start to vaporize. That creates an incredibly strong wave of
pressure known as a ramp compression wave, without
producing too much heat. This whole vaporization process takes about
ten billionths of a second, which is actually relatively slow and gentle as far as the diamond is concerned. The increase in pressure is gradual enough that it won’t necessarily destroy the sample, and you can get up to 5 terapascals of pressure
this way. That’s on par with the center of Jupiter, or even bigger super planets that exist in
distant star systems. Still, 5 terapascals is nothing compared to the kind of pressure a shock wave can generate. If the researchers are willing to sacrifice
their diamonds and maybe even their sample, they can generate twenty times that much pressure
using a device that looks a lot like a normal diamond anvil
cell, but with a twist. Instead of just pressing things together, you point a bunch of intense laser beams at
one of the diamond anvils, heating it up kind of like how focusing light with a magnifying
glass can light things on fire. The light heats the diamond so much so quickly in about a trillionth of a second that the outer layer vaporizes instantly. The rapid expansion of the carbon atoms creates
a one-time shock wave that travels into the sample faster than the
speed of sound, vaporizing both it and the other diamond anvil
it’s pressed against and then I assume everybody in the lab just
jumps and down and are like, “yes!!” Why? I don’t know. We did that! Theoretically, if the sample is already compressed
at the time, the pressure on it could be as much as 100
terapascals. That’s a billion times Earth's atmospheric
pressure. But if you really need as much pressure as
you can muster to get closer to what’s happening inside
of stars, for example you’re gonna need to use the shockwave from something a little more destructive. Or a lot more destructive. Yeah, I’m talking about nukes. Back during the Cold War, underground nuclear
explosions were used to study the compression of metals. The shockwaves those explosions created regularly
reached up to pressures of 20 terapascals, and some Soviet scientists reportedly reached a record of 700 terapascals of pressure in
1983. Granted, we try to stay away from the whole setting-off-nuclear-explosions kind of thing
these days, so we’re probably not going to replicate those experiments any time
soon. Still, all these high pressure experiments
can tell us a lot about what’s going on inside planets in
our own galaxy by creating some super weird things. In February 2018, for example, researchers
vaporized diamond to create what they think is superionic ice the stuff astronomers predict is in Neptune
and Uranus’s cores. That’s ice that’s compressed so much that
it becomes a lattice of oxygens surrounded by flowing
hydrogens which behaves like a solid and a liquid at
the same time. And that’s just the tip of the superionic
iceberg. While physicists have some ideas about will
happen at really high pressures, they won’t know
for sure if they’re right until engineers find a way to push things
to the extreme. So they’re just going to have to keep pushing
things, and pushing them real good. Thank you for watching this episode of SciShow! To learn more about the results of these nifty
machines, you might want to watch our episode on matter under extreme pressures. And thank you for watching and thank you for
subscribing, and if you haven’t subscribed, then now you feel bad that I thanked you and
you’re not a subscriber so you have to do it now. Just youtube.com/scishow, subscribe. Or there’s a button right under the video,
probably. Depends. Bye.
