I like to think that life is a thermodynamic mechanism that:
- locally reduces entropy by consuming
lower-entropy energy and casting out
higher entropy stuff
- reproduces
by which definition stars are almost alive. I say "almost" because stars only manage to keep local entropy from growing very fast, but they don't manage to reduce it.
For example, life on Earth consumes low-entropy (because colimated and short-ish wavelength) sunlight and molecules of various types (e.g., CO2) and uses that to build locally-lower-entropy things (plankton, plants, animals, ...), in the process emitting lower entropy things like detritus, feces, etc., but especially longer-wavelength light in all directions. Because Earth's climate is roughly in equilibrium, if you examine all the light going in (colimated, low-wavelength sunlight) and all the light going out (longer-wavelength IR in all directions), the energy must balance, but the entropy must be much higher on the outbound side. Similarly, Venus must be dead because it reflects so much sunlight, thus failing to use it to improve local entropy, thus it must be dead.
Inspired by Erwin Schrödinger - "What Is Life? The Physical Aspect of the Living Cell" from 1944 ?
> Schrödinger explains that living matter evades the decay to thermodynamical equilibrium by homeostatically maintaining negative entropy in an open system.
Oh, I'm certain that Asimov wasn't the first to think of it. It could have been thought up in the 19th century, and it would be very surprising if Asimov was the first to write down the idea.
This is negentropy (not my fav. word, but it is the term used). Indeed it's the signature of life, although I think there would be a threshold that all living creatures meet, but non-living systems do not. In other words life produces lots of negentropy, probably exponentially, unlike other systems like celestial bodies.
There was a recent podcast episode from Sean Carroll's Mindscape [1] where they focus on and around the Krebs Cycle and discuss it as an example of Entropy. Turns out Entropy really is fatal.
> In other words life produces lots of negentropy, probably exponentially, unlike other systems like celestial bodies.
Exponentially? I guess, in the sense that from fertilized egg to adult, lifeforms grow exponentially, you're right, but adults usually do not keep growing. So I would say "sustained", and once the negentropy (I don't like that term either) operation is no longer sustained -and so local entropy is once more on the rise-, then the being has died.
For stars, I think the issue is that local entropy does not go down. Collapse is avoided on a sustained basis, and when that stops being so, the star dies (and possibly leads to the creation of new stars, which looks like reproduction). That looks like life, but it isn't because local entropy still goes up.
Oh, I meant the totality of life. If we consider how life evolved over the 4 billion years, at first it was super slow and then it accelerates into a variety of lifeforms, eventually humans, and then civilization and all its complexities in just a few thousand years.
Asimov was way ahead of TFA :)
I like to think that life is a thermodynamic mechanism that:
by which definition stars are almost alive. I say "almost" because stars only manage to keep local entropy from growing very fast, but they don't manage to reduce it.For example, life on Earth consumes low-entropy (because colimated and short-ish wavelength) sunlight and molecules of various types (e.g., CO2) and uses that to build locally-lower-entropy things (plankton, plants, animals, ...), in the process emitting lower entropy things like detritus, feces, etc., but especially longer-wavelength light in all directions. Because Earth's climate is roughly in equilibrium, if you examine all the light going in (colimated, low-wavelength sunlight) and all the light going out (longer-wavelength IR in all directions), the energy must balance, but the entropy must be much higher on the outbound side. Similarly, Venus must be dead because it reflects so much sunlight, thus failing to use it to improve local entropy, thus it must be dead.