Human engineering has produced marvelously complicated wonders — from space telescopes that can peer back nearly to the beginning of the universe to microchips packed with billions of transistors, all squeezed into the device in your pocket. However, these impressive feats of ingenuity aren’t just found in advanced laboratories — they’re all around you. Inside your home, the objects you use every day, often without a second thought, are quietly doing their own complex work. Here are a few objects you use every day that were once considered scientific miracles.

Refrigerator

Today’s refrigerators feature nonsensical technology and advanced “smart” features (you can even watch TV on them), but their basic design is devilishly inventive on its own. The concept of a fridge hinges on the idea that coldness doesn’t actually exist — but the absence of heat does. First, refrigerators are well insulated to not let heat inside, but the real magic happens with the refrigeration cycle. This cycle uses refrigerant that easily changes from a liquid to gas and back again. The fridge’s compressor squeezes the liquid, increasing its temperature, and passes it through the condenser releasing heat. When the liquid refrigerant moves through an expansion valve, it comes out the other side as a cold gas, which then moves through the interior of your fridge, absorbing heat inside. This gas then heads to the compressor, where the process begins again, continually keeping your favorite treats nice and cool.

Electrical Outlet

Electrical outlets transformed our homes from 19th-century dwellings to fully-electrified domiciles, and it all happened thanks to two types of wires: hot and neutral. When you plug a device into an outlet, you complete a circuit, allowing electricity to flow through the hot terminal, into the device, and back out through the neutral terminal to the breaker box, which monitors for overloads or faults (i.e. tripping the breaker). However, one of the more amazing aspects of outlets is that they’re the final destination for a flow of electrons that have traveled over hundreds of miles of wires, winding through generators, step-up transformers, high-transmission lines, step-down transformers, utility poles, and finally your home’s circuit breaker. This means the electrons powering your lamp were generated from natural gas turbines, solar panels, or nuclear power miles away before being used to generate light, heat, or motion inside your home.

Water Pressure

Delivering clean water to a growing population found a solution in a simple engineering truth: water flows from high pressure to low pressure. While that was the basic building blocks for Roman aqueducts, today’s cities use a variety of methods to funnel clean water through the pipes. Most cities in the U.S. rely on water pumps and water towers to reliably deliver water when the height of the local water source, such as a reservoir, doesn’t provide enough natural pressure to get the job done — as the weight of water at higher elevations applies this pressure via gravity. In New York, for example, buildings shorter than six stories don’t require pumps or water towers due to the natural location of reservoirs upstate, which provide enough natural pressure to get the water flowing. For buildings taller than six stories, water pumps store water in tanks during periods of low demand, typically overnight or in the middle of the day. Whether a giant tower in a small town of Manhattan, Kansas, or a small tower on an apartment building in Manhattan, New York, natural pressure from these mini-reservoirs safely supply water to all residents without fear of running out.

Coffee Maker

Coffee is a daily necessity for many, so coffee makers need to be both effective and affordable. Standard coffee makers have a large water reservoir in the back that eventually (when heated) makes your coffee while also containing a heating element in the base to keep the coffee hot when brewed. But how exactly does water get from the heating element at the bottom to the top of the machine to pour over the grounds? Instead of installing two heating elements — one at the top and one at the base — engineers devised an ingenious solution by using a one-way valve and heat-resistant tubing. This set-up creates a bubble pump, and it starts with the one-way valve at the base of the reservoir that uses a small ball that allows water to flow from the reservoir to the heating element but crucially doesn’t allow water to reverse flow back into the reservoir. As the water heats up, the boiling water creates bubbles of water vapor that in turn increases pressure inside the tube and these trapped bubbles eventually push water the only direction it can go — up the tube and out of the sprayer. The water then wets the grounds, creating a perfect pot of drip coffee in just a minute or two.

Ballpoint Pen

Although a big improvement over quill pens, fountain pens were well-known for leaking ink and constant smudging — in fact, an entire fashion accessory, the pocket protector, was designed to protect unwanted ink stains from damaging clothing. Then, on October 29, 1945, Gimbels department store in New York City began selling a new kind of writing tool — the ballpoint pen, the first ever sold in the U.S. Today, most ballpoint pens use a tiny ball bearing made of tungsten carbide to pull off two important jobs: To form a seal against the reservoir to prevent the ink from drying out and also control the ink’s flow rate via capillary action, which allows liquid to flow through narrow spaces without the need (or even opposition to) gravity. This capillary action allows the liquid to flow between the ballpoint and the paper to provide a consistent flow of ink. Unfortunately, the engineering of these pens became so good that they became a disposable commodity with billions of them finding their way to landfills. In recent years, companies like Bic have created eco-friendly versions of their pens that are made mostly of recycled plastic.