In a closed system, entropy will maximise. A gas will spread over a larger space, a stone will evaporate etc. Living organisms, however, tend to grow: they will get more organised.

This is a very short post with a thought of today… I just saw a clip on youtube about what life is.

When is something alive, when is it not?
Thinking about this, I came up with the following definition:

Something is alive when it uses energy to decrease entropy.

In a closed system, you would expect entropy (a vague term, I admit) to increase. A gas will spread over a larger space, a stone will evaporate etc.
Living organisms, however, tend to grow: they will get more organised.

In other words, if something is not alive, it will dissolve in it’s environment. It’s entropy will increase, it will become more ‘chaotic’.
So, according to this definition, here are some examples of living organisms:

  • Animals
  • Plants
  • Bacteria, some cells
  • Viruses
  • DNA
  • Proteins

Not living then:

  • Rocks
  • Cars
  • Computers
  • Computer programs (Artificial Intelligence, Computer Virusses) Even if they are Artificial Intelligence: leave a computer for a number of years and it will decay. The ‘direction’ is for increasing entropy.

Alternative and more practical definition of life (16/8/2019):

Life = organisms based on DNA/cell mechanisms

This will classify the same categories as above.

Origin of life

Open question remains what the origin of life is?

How did a primal soup of decaying chemicals turn into an energy consuming mechanism that recreates itself?

In other words, how did non-living materials turn into living (DNA based) cells?

The DNA/cell mechanism is complex: it involves chains of amino acids, that are translated into proteins that have many different nano-robotic functions. These form into cells that work together to form more complex beings. These beings (us!) work together to procreate and form a society.

Even the basic DNA mechanism appears too complex to have evolved from random chemicals. Or is it?

Could it have evolved in a number of simpler steps by chance?

Evolution evolves

The mechanism of cell division is part of the cell life cycle. The whole internal mechanism of the cell (excluding mitochondria) is coded for in the DNA of that cell.

As such, evolution itself is encoded in the DNA and subject to evolution.

This means that in the past, evolution may have been much simpler and it also means that the way evolution works differs between species.

Inheritance works differently for humans as compared to other living beings.

Parts of living organisms and survival

Looking at the proposed list of living organisms above, there are some that many would consider at least questionable.

A virus, for example, or even a single protein.

They will need a host cell to increase entropy of the population. A virus cannot survive by itself.

In the normal course of development, the virus will die at some point and so in future its entropy will decline.

The bigger population it is part of though, in principle, could survive forever. The same would hold for cells in animals and even for the whole animal.

Humans die, the human population survives. Which is alive?

As such, is a virus alive? I guess it is part of a living system and I would therefore define it as alive.

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