At Yale University in the United States, researchers have built a tiny circuit through which water flows. At first glance, it looks like a set of small pipes. Yet it can retain information about what happened previously, simply through the movement of the liquid.
To understand the trick, you need to look inside these channels, whose depth is about half the thickness of a hair. The researchers placed tiny flexible fibers inside them. When water flows, it pushes against these fibers and can make them switch from one position to another.
The most interesting point is that a fiber does not necessarily return to its initial position as soon as the flow decreases. To make it switch sides, the flow sometimes needs to be increased sufficiently, then reduced further to produce the opposite movement. It can therefore retain two stable positions, depending on what it has experienced previously.
This property is what serves as memory. A fiber positioned one way can represent a 0, and the other way a 1, just like the binary system used in computers. Two circuits carrying the same amount of water can therefore be in different states because they have not experienced the same history.
The researchers went further by connecting several channels. When a fiber changes position, it alters the way the water is distributed. This can push another fiber to switch, followed by a third. The circuit therefore does more than memorize a state: its different parts can also act on one another.
However, this circuit is not a computer powered by water. It does not run programs and has not learned to make decisions. For now, the researchers have demonstrated a form of physical memory: the information is stored in the shape of the fibers, without needing an electronic component to record it.
What could this be used for? Engineers are considering soft robots, which already use liquids or pressurized air to move. A network of small channels could one day help them react to their environment without electronics.
It remains to be shown that these circuits can perform genuinely useful tasks. But this experiment shows that memory does not always need electronic chips and can work with nothing more than water... "Water memory"?