[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. If you’re looking for a silent room to record
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by clicking on the link in the description and thanks. [ OUTRO]
