Scientists have updated the definition of “life” many times, and with increasing frequency.
Philosophers have debated what “life” is for millennia — it is one of the cornerstone topics in philosophy.
I claim that those debates are destined to lead nowhere, because there is no such thing as “life”.
But wait a minute: we are alive, aren’t we?
Yes, we are. But the idea that we are alive is all mixed up with the idea that we are sentient. We are that, I think (how would I prove it?). But if you separate “alive” from “sentient” as two different things, that is where we run into trouble.
Is a worm alive?
What about a cell?
Scientists say yes — these are alive. But most would say that worms and cells are not sentient (although again, how would they prove that?)
What makes scientists consider a cell to be alive is that it meets some very convoluted criteria in a list that, as I said, keeps changing. The current list includes things like “biological” processes such as signaling and self-sustaining processes. But wait a second: doesn’t that list preclude, by definition, that a machine can never be alive because it is not biological?
What if we create a machine that claims to be sentient? When other humans claim they are sentient, we believe them, because we relate personally to it. But what if a machine can be sentient? What if our neuromorphic technologies become so advanced, that they start to contain hundreds of billions of non-biological neuron-like elements, and the machine says that it is aware? Will we insist that it is not alive because it is not biological?
So the requirement for “biological” seems arbitrary and limited to life forms that we currently know of, and precludes those that might exist but that we simply do not know of. What if aliens land and they are not biological as we know it: they are based on an alien chemistry? Do we claim that they are not alive?
What about the requirement that they are “signaling”? Machines can be signaling. Computers are. So let’s skip that one. What about the requirement that life be self-sustaining? That’s the core one, I think.
But again, a machine could do that. What if we create self-replicating machines? Imagine a robot that makes other robots. Imagine the “gray goo” of fiction — self-replicating nanobots that take over the world, eating away at everything for food and blanketing the world in an ocean of themselves. What a horrible thought, but would it be alive? And yet, it would be based on something non-biological. Yet if we step back to the robot example, a robot is surely not alive just because it is programmed to be able to create other robots. So that definition seems to not work.
And here is my premise: that we never will come up with a meaningful definition, because the term “life” really has no clearly definable meaning.
We intuitively think we can recognize something that is alive when we see it, but our intuition is based on experience, not logic. We have seen animals and people and plants and they all grow and consume and eventually pass on. We call that “life”, but that is just a characterization, not a definition.
Life is like a color, like “brown”: we know it when we see it, but it is our perception. “Brown” is something that is relative. Scientists have identified a blend of spectral ranges that, when combined, are experienced by most people as something they call “brown”, but some people do not see brown, and some people see an enhanced version of brown. So it is relative: it is not precise. “Brown” is a perception. Color perception is a human biological phenomenon: there is no “brown” on the spectrum, because “brown” is a combination of colors, and is the result of how we perceive it. We have retinal receptors that perceive overlapping ranges of what we normally think of as blue, green, and red. Our brain constructs what we perceive as brown.
The whole debate about “what is life” is meaningless. It is tautological: it will always be the ever-changing definition that we fabricate for it. But the universe has no concept of life. The universe only has things that are ever changing. Some of those things replicate, and we — as part of the universe — will eventually create more kinds of things that replicate. We have already.
But are all of those alive? The question is meaningless.
Are they sentient? That is a lot more interesting. But if you can find the answer to that one, you will win a Nobel Prize, and probably change us forever.