Over the years, I've several times skirted the edge of this issue. When blogging at Control Engineering, I went on a rather lengthy rant comparing the intelligence of the then most advanced autonomous systems to that of various life forms. As I recall (I no longer have access to the manuscript), I concluded that robots compared well to life forms somewhere between viruses and amoebas. Certainly, they didn't have the brains God gave a potato bug.
More recently, in my novel Vengeance Is Mine! (available in PDF format as a free download from my website at www.cgmasi.com), fictional technology maven Doc Manchek voices the opinion that "I think we're going to have to clarify what we mean by ‘life' very soon."
This is a question also posed by the 2004 film I, Robot, which was based on stories written by Isaac Asimov in the middle 20th Century. Asimov seemed to feel there was an important dividing line related to the concept of free will.
I think that's asking too much. Can anyone seriously impute free will to one of my wife's orchid plants? They're certainly alive, but notoriously poor at independent thought. Creativity just isn't there.
In Vengeance Is Mine! Manchek makes a more practical suggestion. Speaking of automated systems, he says: "They certainly are capable of goal-directed behavior. It's a short step from there to defining their own goals, such as wanting to keep their batteries charged, and avoiding being run over by a truck."
A key capability required of all life forms is the ability to seek out and obtain nourishment. Another is, as Manchek points out, a desire for self-preservation. Perhaps the most significant capability shared by all natural life forms, however, is the ability to self-replicate. That is probably the most important life-form capability of all.
The system that is probably closest to the dividing line between living and non-living things is a virus. A virus is a packet of DNA enclosed in a wrapper. It reproduces by injecting itself in a living cell, taking over the cell's DNA-replication equipment, and using that equipment to punch out bazillions of copies of itself. They can't reproduce on their own, but the dang things do a bang-up job of self-replicating - just ask anyone with the flu!
So, does a robot vacuum cleaner that finds its way back to its charging station count as a life form? It shows goal-directed behavior. It finds its way home to find nourishment (in the form of electric power). I have never, however, heard of one producing baby vacuum cleaners.
So, no, they're not alive.
C.G. Masi has been blogging about technology and society since 2006. In a career spanning more than a quarter century, he has written more than 400 articles for scholarly and technical journals, and six novels dealing with automation's place in technically advanced society. For more information, visit www.cgmasi.com.