[This episode is sponsored by Skillshare] [ INTRO].

Sit still for a second. What do you hear?

Maybe a siren across town? A jet overhead? But how about the really tiny noises?

Your breath? Your heart? Your bones grinding against each other?

These sounds are so quiet they’re barely there. But for some experiments, even the softest background noise is too much! So scientists have created rooms that are unimaginably still.

Take, for example, the room where LIGO conducted the first experiment that detected gravitational waves—tiny perturbations in spacetime—from two colliding black holes. It was an incredible triumph of science—but also of engineering: the equipment had to sense tiny fluctuations a mere fraction of the width of a proton in size! That meant eliminating every possible source of movement.

And they aren’t the only ones aiming for perfect stillness. If your telescope is looking for planets hundreds of light-years away, a little thermal expansion could mean the galactic equivalent of photographing your thumb. And if you’re working at the other size extreme, shooting electrons at individual molecules, even the light tug of a fridge magnet could be disruptive.

So scientists have resorted to extreme measures to build the stillest rooms in the world. That means, first and foremost, eliminating mechanical vibrations from things like trains, ocean waves, and footsteps. The simplest solutions are passive—they block vibrations just by sitting there.

For example, springs can provide isolation—they keep fast vibrations from being transmitted. Think of a car’s suspension on gravel: the springs mostly absorb the tightly spaced bumps. Of course, fatter bumps, like speed bumps, are too much for springs alone to hide.

That’s why cars also have shock absorbers, which use friction to dissipate any bouncing of the car body. That dissipation is called damping. Sensitive experiments need isolation and damping too.

Many labs use rubber pads or pneumatic table legs, which provide both isolation and damping for sensitive equipment. If you’re building an entire vibration-free room, though, you have more…hard-core options. The noise-free room in IBM’s nanotechnology lab outside Zurich is built deep underground— right on the bedrock.

That means any vibration is fighting the inertia of millions of tons of rock. And it, as well as the stillest lab at The National Institute of Standards and Technology in the US, also employs a more complex solution: active vibration control, where sensors detect small motions and counteract them. It’s like noise-canceling headphones, but for the ground.

And speaking of noise, you might need to block vibrations in the air, too—AKA sound. Obviously blocking sound is crucial for audio measurements, like testing a model concert hall or checking what background noises confuse Siri. But sounds also make equipment or samples quiver, which can lead to problems like blurry images.

To block outside noise, labs can be insulated with layers of concrete and air. Microsoft’s underground audio lab, for example, lives inside a six-layer concrete onion…. And on top of vibration-damping springs, of course.

To stifle noises from inside a room, the walls and even the floor can be plastered with wedge-shaped foam or fiberglass tiles. These break up and absorb sound waves, keeping them from echoing off the walls. Hence the name for such rooms: anechoic chambers.

Microsoft also paid special attention to little details like how cables enter the room, how the doors are sealed, and how air is circulated. All that effort paid off: in 2015,. Guinness certified the lab as the quietest place in the world at negative 20 decibels.

That’s barely louder than air molecules bouncing around! Some experiments need to go beyond vibrations, though: they need to control thermal expansions and contractions, too. Heat is especially important in experiments like that LIGO one that use interferometry, where miniscule lengths can be measured by looking at the effects of adding them to the paths of laser beams.

LIGO kept the temperature constant for that gravitational waves discovery by sucking out all the air in the room and hanging instruments from insulating glass rods. That obviously won’t cut it when suffocatable humans need access. In those settings, temperatures are normally stabilized by air circulation.

The problem, of course, is that air conditioning is loud! And the moving air can directly vibrate equipment. That’s why that IBM nanotechnology lab uses a gentle, upward-flowing ventilation system.

The lab’s not quite as quiet as Microsoft’s, but it does manage to keep temperature fluctuations to one hundredth of a degree Celsius! For experiments on the very smallest scales, even electrical or magnetic fields can disrupt the stillness. Some modern microscopes sense tiny forces between particles, and electronics manufacturers sometimes etch circuit patterns using beams of electrons.

Those critical particles can be deflected by electromagnetic fields from any nearby source, including things like power lines. So to block those out, high-precision measurement labs like the one at NIST wrap the whole room and sometimes the equipment in magnetic metals. Just two layers can cut magnetic fields to a third of the Earth’s normal field strength, and more layers push it down even further.

It’s only by blocking mechanical, acoustic, thermal, and electromagnetic noise that we can spy on distant black holes or watch molecules flow into and out of a single neuron. Not all experiments need all these measures, mind you, so different labs are quietest in different ways. The IBM lab is unusual in trying to block everything at once.

If you’re seeking peace and quiet, though, you might want to look elsewhere… these rooms are so silent many people can’t stand more than a few minutes in them. Me, I’ll take some nice wind in the trees. I’ll leave the true silence to the microscopes.

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