In 1994, a massive earthquake shook the Northridge suburb of Los Angeles, killing 57 people and injuring over 5000. The cost of damages was in excess of $20 billion. It's
earthquakes like this one that make us question just how solid is the earth beneath our feet, and what does it mean to be solid anyway?
At first glance, pitch looks like a solid, but it's not. It's actually a liquid at room temperature—just a very viscous one. Viscosity is a measure of resistance to flow—what we
often think of as the "thickness" of a liquid. Olive oil is nearly 100 times more viscous than water, and honey is about 100 times more viscous than that. Meanwhile, pitch has a
viscosity 2.3×10¹¹ times that of water. At the university of Queensland in Australia, pitch is the subject of the world's longest running lab experiment, and it's still going to this day.
Back in 1927, this glob of pitch was placed into a funnel, and ever since then, in nearly 90 years, it has produced only 9 drips—roughly 1 a decade—and no one has ever been in the
room to see a drop fall. Though in 1988, the former custodian of the experiment, John Mainstone, came very close to observing a drip fall, except he stepped out of the room
for just a few minutes to get a cup of tea. Now, you can actually watch this experiment live—there's a link in the description—but since the last drop happened in 2014, I think
you'll probably be waiting a while. Another substance that you may have heard is a very viscous liquid is glass. If you look
at the stained glass windows of old churches, you'll find the bottom of the pane is decidedly thicker than the top, and that's because the glass has been flowing down over
