Reproduction, as described in the definition of life, is the ability to create offspring. Reiterative computer programs make copies of their components parts, life forms propagate whether it is from a single parent such as cell division (asexual) or two different parent organisms (sexual).

Mutation occurs when the offspring of an object is non-identical to it’s parent. If the offspring of an object were identical, then no diversity could occur within a population to factor in the final element, selection.

Selection is where particular objects in a given population are selected to survive based on particular attributes which they have either mutated or inherited from their parents that either other objects do not have.

The evolution of objects requires all three elements to occur. I use the term object as evolution theory can be applied to many different disciplines, notably computer science where programs that evolve are now common place.

Organisation is where an organism is made up of one or more cells. A cell is the fundamental building block to life. Cells are self-contained replicating units, from single cell bacteria to multi-cellular humans. All cells contain the ability of reproduction through cell division, the ability to divide into a near exact copy.

Metabolism, whether at a cellular or multi-cellular level, is the ability for an organism to take matter (photons in the form of photosynthesis, nutrients from other organisms, minerals from the environment) and convert it into organic matter (cells) that are useful to them (synthesis) and converting there own organic matter to inorganic matter through waste (catalysis).

Growth is where the rate of synthesis exceeds the rate of catalysis, so an organism become progressively larger.

Adaptation is where an organism is able to change (adapt), either by it’s own volition through modifying behaviour, or more commonly through heredity.

Response to stimuli is perhaps the most telling factor of whether an organism is alive. A rock rolling down a hill is not reacting to gravity, it is under the force of it. Plants rotate their leaves to follow the sun, animals experience physiological change when seeing prospective food, feeling the cold, mating etc.

Reproduction is the final common attribute. Living organisms must have an ability to reproduce themselves, whether it is from a single parent such as cell division (asexual) or two different parent organisms (sexual).

It is important to note that whilst these definitions in combination are a good way of describing life, there are many exceptions to the rules. When a horse and a donkey are cross-bred the offspring, called a mule, is infertile and incapable of bearing their own offspring. No one would doubt that a mule is alive. Conversely, most biologists actually regard viruses as not-alive as they do not move, metabolise or undergo waste (catalysis). Viruses require living organisms to survive, infecting their cells and using their hosts cellular makeup to propagate themselves.

Computer viruses which can be programmed to replicate and adapt to surroundings would not be classified as alive, yet raises a pertinent question, in line with the theme of artificial intelligence in the scientific novel ‘Do androids dream of electric sheep?’ by Philip K. Dick, as to when machines will be classified as alive.

The Earth was one of the objects that formed out of the flying debris that was the early solar system, and the moon is thought to have broken off from the Earth in a collision at some early point in its development. It is believed that the orbit of the moon around the Earth provides a stabalising effect on the Earth’s rotation and thus climate.

During the 20th Century, many great leaps were made in the science of astronomy. Possibly the most important were the observations of the astronomer Edwin Hubble, which reinforced the notion from Einstein’s Theory of Relativity that the Universe could not be a static shape. His observations were that all stars in different galaxies other than the Milky Way (our own galaxy) had a red shift, implying that they were moving away from us.

To reinforce this theory of an expanding Universe cosmologists (scientists who study the physical and theoretical nature of the Universe) predicted there would be an electromagnetic radiation (cosmic wave background radiation) as a lasting trace of the explosion, which was first detected in 1965.

The amount of the lighter elements apparent in the Universe (hydrogen and it’s isotopes, helium, lithium and beryllium) are also considered consistent with that predicted by Big Bang Theory.

Electro-magnetism is the force that is involved in charged phenomena, particles such as charged molecules and non-particles such as electrons and photons (light). Aside from gravity it is the force that explains nearly all phenomena that we witness in our day to day lives, from static electricity to radio and light waves.

The strong and weak nuclear forces are the forces that interact with sub-atomic particles and atomic particles. The strong nuclear force binds some of the components that make up a proton, and the weak nuclear force binds most other atomic particles (electrons etc). The laws governing the strong and weak nuclear forces come mainly from Quantum Mechanics.

Gravity is the most mysterious of the four forces, it’s effects can be observed and it’s behaviour predicted using General Relativity yet no one knows how it operates. The existence of a small particle called a Graviton has been speculated, but it has yet to be detected.

In classical physics there are two types of substance in the Universe, energy and matter which behave as waves and particles respectively. However truth is proving stranger than fiction, and many of the properties of either matter or energy are shared by the other. This combination is simply illustrated by Einstein’s equation e=mc2 where e is energy, m is mass, and c is the speed of light.