Living things move. In fact our visual system uses the way things move to decide whether or not an object has agency and is able to move on its own. In the pre-technological world only things that are alive have agency, but in the technological era we have animatronics and animated video that can mimic the movement of living things and trick our brains into treating objects or representations as if they are alive.

There are several applications for detecting the signatures of life. So far such efforts have focused mainly on chemical signatures – looking for the products of biochemistry. Researchers publishing in PNAS, however, have taken a new approach.  They are trying to detect the motion signatures of life at a microscopic scale.

They use nanoscale motion detectors that are actually tiny cantilevers. Even a single bacterium twirling its flagella can cause the cantilever to move. Lasers then detect the motion of the cantilever, and that motion is analyzed for the signatures of life. The researchers tested their setup on soil and pond water, and found that it accurately detected microscopic life. They then used drugs to kill any living cells, and the detection stopped. 

The most immediate application of this technology would be in drug development and research. If, for example, an antibiotic or anti-cancer agent is being studied, it could quickly be detected if the bacteria or cancer cells were dying off. This could accelerate the process of such research.

Perhaps the more interesting application, and of course the one that the press release focused on, is detecting life in extreme conditions, including extraterrestrial life. Such an apparatus could, for example, be included in a Mars probe, or one to Europa or Enceladus. If the Martian soil contains any living microorganisms, regardless of their chemistry, this technique might be able to detect them.

In fact, movement may be a more universal signature of living things than any particular chemical reaction. We currently only have one example of biochemistry, and that is from life on Earth, all of which is related. Scientists and science fiction writers have speculated about what kinds of alien biochemistry might exist, but it is all speculation. It’s interesting to think about silicon-based life instead of carbon, for example. Some doubt the plausibility of this because silicon, while similar to carbon, does not have its chemical flexibility. Others have speculated about hydrogen breathers, methane breathers, and life in conditions vastly different from those on Earth.

Using chemical signatures we can look for what we know, but might completely miss the unknown.

With movement, all we would need to have a suspicion of life is any movement, particularly movement that is non-inertial, meaning that it cannot be explained by passive movement  following the laws of physics.

I find it hopeful that this technology has some immediate practical applications, such as in drug development. This makes it more likely that it will be fully developed, and therefore be available for less commercially viable applications.