From air conditioning to fridges and freezers, cooling is a crucial part of the modern world. It is also a part that requires a lot of electricity, but this might not be the case in the future. Researchers have now shown that it is possible to build devices that produce cooling without consuming energy.

The breakthrough was made by researchers at the University of Zurich. They constructed a device that acted as a thermal oscillating circuit, a system that can make heat flow from a hotter body to a colder one and, more importantly, do the opposite. The oscillation is such that it is possible for the colder object to end up at a temperature lower than its surroundings.

Thanks to their device, the researchers were able to cool a 9-gram (0.3-ounce) piece of copper from the temperature of boiling water to a few degrees below room temperature. The results are reported in Science Advances. The importance of this work is that the thermal oscillating circuit was not powered by an external power supply.

The team used a Peltier element, a device that can transform electrical currents into temperature differences. They are commonly used to cool minibars in hotel rooms. With that, the researchers were able to reduce the temperature of the copper piece by about 2°C (3.6°F) with respect to the surrounding temperature of 22°C (72°F).

This might not be enough to create powerless fridges, but the researchers argue that this was achieved with commercially available components. Ideal elements could achieve temperatures tens of degrees below zero. They are yet to be built but they certainly have alluring applications.

“Theoretically, this experimental device could turn boiling water to ice, without using any energy,” lead author Professor Andreas Schilling said in a statement. “With this very simple technology, large amounts of hot solid, liquid or gaseous materials could be cooled to well below room temperature without any energy consumption.”

You might be wondering “what’s the catch?”

While this certainly seems too good to be true, apparently, it is not. In physics, the “too good to be true” is usually delivered in one form or another by the second law of thermodynamics. It tells us that the entropy of a system always increases. So things age, break, and get messy. It also tells us that you can’t get more work than you put in, so you can't have perpetual motion machines that output something out of nothing.

But despite not receiving any active power supply, the device is still receiving power passively. It receives enough power to generate the temperature change and behaves in accordance with one of the crucial laws of the cosmos.