[SciShow intro plays]

Michael: Wouldn’t it be nice if our transportation was as sleek as in The Jetsons or Futurama? Flying cars are cool, but I’m talking about a giant network of human-sized tubes that run through buildings and across entire cities. You could step in one and be swept off to your destination in a rush of air -- quick, simple, and none of the stress of waiting in traffic jams.

We’ve been dreaming of futuristic travel for decades. But, in fact, these pneumatic tubes already exist, and have been used to transport small things from mail to medical samples. People... not so much. Or, at least, not yet.

Pneumatic tubes were invented in the early 19th century by the Scottish engineer William Murdoch. And by the late 1800s, some cities like London had tens of kilometers of pneumatic tubing -- mostly in businesses and mail rooms -- which were used to transport millions of letters each year. Since then, pneumatic tubes have been used around the world to deliver medicine, money, and even McDonald's hamburgers. They’re fast, easy to use, and the design isn’t all that complicated.

Let’s say, for example, you worked in an office building back in the day -- like, before email and texting were a thing. And you wanted to send some important paperwork -- or a secret message -- to your friend who works in the other side of the building. Instead of making the trek to their office, you seal up your message in an air-tight canister and place it at your end of the pneumatic tube -- the sending station. Now, imagine this tube as a giant metal straw. At first, the air pressure is the same throughout the entire tube -- there’s a bunch of air molecules moving around and pushing on the canister the same amount in every direction.

But then, you press the “go” button and all that changes. A fan activates at the receiving station in your friend’s office, it starts sucking air out of their end of the pneumatic tube, and creates a partial vacuum. Just like sucking on a straw. Suddenly, there’s not much air in the tube pushing down on the top of the canister. But there are lots of air molecules at your end still pushing up from the bottom of the canister. This difference in air pressure creates a powerful force that propels the canister through the tube. So, a few seconds later, the canister will arrive at the receiving station, and your friend can read your message!

Pneumatic tubes worked well enough for quick and easy mail delivery in the 19th century, but they weren’t perfect. For one thing, you needed to build a new tube to every place you wanted to send something. Eventually, these pneumatic networks got pretty complex -- with switches and trap doors to adjust the route of each canister, and more possibility for mistakes or collisions. And if you wanted to send more packages, farther, cars were just more efficient than building and operating giant pneumatic tube systems. So as cities grew, pneumatic tubes were mostly left in the past. Although, they’re still used today in some buildings -- like to transport medical samples in hospitals, or checks in bank drive-thrus.

But could they ever be used to send something as large and fragile as a human? Well... maybe. Way back in 1869, Alfred Ely Beach developed New York City’s first ever subway line using pneumatic power -- a small, one-car shuttle called the Beach Pneumatic Transit. It was really short -- like, less than 100 meters long -- and mostly an experiment. It closed down after 3 years, but over time, different engineers have proposed their own designs for creating trains inside partial vacuums -- or vactrains -- like Daryl Oster’s ET3 and Elon Musk’s Hyperloop.

A lot of these designs combine the idea of pneumatic tubes with magnetic levitation -- using large magnets to make the train float above the track -- to reduce air resistance and friction. But these specific designs don’t actually use air pressure to move the trains. Instead, the ET3 uses electric motors to gain speed, and the Hyperloop train has electromagnetic motors similar to the ones in Tesla cars.

So we don’t really send letters by pneumatic tube anymore. And we’re probably not going to live the futuristic cartoon dream and fly above cities in them. But maybe someday, we’ll be sending humans cross-country by tube -- in super-fast trains.

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