Physically speaking, life can universally be defined as an autonomous system of relatively negative entropy, which transduces, takes in and assimilates energy for self maintainence and survival as a single system, and autonomously replicates information about its own system of being, to propagate itself.
It is a rather beautiful set of parameters, as it would apply to all living organisms. These parameters ARE life. When we look at living organisms, and we try to extrapolate the biology to what we may expect from space, we’re taking a shot in the dark and in reality, whatever the environment and time allows, will evolve. So in theory, life can take almost any form. But we can be almost certain that any kind of ‘life’ woould have to conform to these laws. These parameters define what differentiates a cell from say, a planet or an ocean. Key concepts define life:
- Negative entropy
- Energy intake
Entropy is the measure of order or disorder in a system. The universe is one giant system which can then be divided into countless subsystems (subsystems including you and I… hello! From this point, I shall refer to living organisms as ‘living systems’ - in order to describe biology in it’s most fundamental form: A product of chemical and physical processes).
More entropy = more disorder. Less entropy = more order.
Life is a structured, ordered phenomenon. Molecules and structures must behave in set ways, and are utilised in different regions in living systems. In this way, Life is ordered, therefore it has a relatively low entropy compared to, say, a bottle of water or something. The water is sloshing around, and evaporating, and the molecules are all over the place, dispersed almost randomly. The water is approaching an equilibrium with it’s environment.
The 2nd law of thermodynamics is that everything in the universe tends towards maximum entropy. This means, everything tends towards max. disorder, over time. Disorder is thermodynamically stable. In this way, living systems cannot be thermodynamically stable. If we were, we’d be dead! A thermodynamically stable system would be at equilibrium with its environment, and a cell in equilibrium is dead. Living systems transiently reverse the natural trend towards entropy, by decreasing their own entropy, at the expense of the entropy around them. Or in laymans terms, as we build our ‘order’ or ‘structure’ up, there has to be a compromise in that it is reduced elsewhere. This ties in with the first law of thermodynamics that energy cannot be created or destroyed - only have its form changed, aka energy is transduced (eg, from light energy to potential energy).
Energy is taken in to living systems to maintain this negative entropy, as without external energy input, the living system would fall apart into disrepair. Energy intake enables the system to be maintained, and persist in the environment - thus it is surviving. Energy is taken in as organic molecules (food!). The energy is released from its molecular form and transduced into a more useable form which the system then uses to keep chemical processes going, reproduction, and maintaining structure (first law of thermodynamics again!) The universe doesn’t have any external energy source that we know of, and to try and reason this will require me going into a realm of physics which is clearly out of my depth. That being said, the universe will eventually stagnate as all molecules eventually decay and fall apart, in compliance with the 2nd law, a process known as ‘heat death’.
- A living system dies.
- Becomes molecules via some kind of decay/breakdown process.
- The molecules become atoms.
- The atoms decay into subatomic particles, which then decay further.
That all takes billions and billions of years, but it’s the fate of everything eventually.
As we have established, a living system is ordered. Something must define this order. There must be some sort of information within the system which coordinates all this order. In the case of Earth Biology, this information is DNA. This information must be reproducible, otherwise eventually that store of information would break down and fall apart (damn you 2nd law of thermodynamics!). This is where reproduction comes into the equation. The information must be reproduced to maintain its longevity, and it is the information which persists longer than the system it describes. After you die, your genes persist in any offspring you may have had. The body, brain and cells you are made up of are ultimately tools of survival for the set of chemicals known as your DNA. You are a survival machine for your genes, I suppose.
'…But how we survive, it's what makes us who we are.'
-‘Survive’ by Rise Against, from the album ‘The sufferer and the Witness’… It’s just so fitting!
Ultimately, it boils down to the fact that a genetic molecule has the means to preserve itself, that life actually exists. Current understanding is that genes came first. Cells and structures came later - via evolution, an aimless by-product of replication which helped the genes to persist longer. Evolution partially occurs because genetic copying mechanisms are imperfect.
DNA polymerase, the enzyme respnsible for DNA replication in many living systems
Because information must be replicated (eg, DNA replication), there can be errors in replication or even in information storage. This can be due to inefficient replication machinery. However, mistakes aren’t always a bad thing (we can also refer to them as mutations!). Evolution is actually the byproduct of a mixture of reproduction and competition. When organisms start competing for resources (eg. energy sources and things that help systems persist in the environment, and further replicate information), then the better adapted systems survive (survival of the fittest). The succesful systems are able to obtain energy, don’t fall into entropy and are able to persist long enough to replicate their underlying information which was able to underpin the advantage that conferred it persistence in the first place.
To surmise so far, Life exists to persist. If it didn’t do so, then it wouldn’t exist and we wouldn’t be reading this.
(Part 2 coming up very soon, to conclude all this. Splitting it into two otherwise it’d be one long-ass post)