Monthly Archives: April 2018

Arts, History, Philosophy, Science

Philosophy: The four elements and atomism

GREEK PHILOSOPHY

The dawn of scientific thought in Ancient Greece.

THE question of what the universe is made of was still a major concern of Greek philosophers in the fifth century BCE. A native of Akragas in Sicily named Empedocles thought that everything was composed of a single element (known as the Milesian line of thought). Later, however, he took this a step further, identifying four distinct elements – earth, water, air and fire – which in different proportions formed all the different substances in the universe. Developing his ideas from the monism of Parmenides, he argued that these elements must therefore be eternal and unalterable, but reasoned that change was possible if some sort of force altered the mixture of elements.

He suggested that two opposing forces, which he poetically called ‘Love’ and ‘Strife’, caused attraction or separation of the elements and brought about changes in the composition of substances. His classification of the substances later known as the four classical elements was widely accepted by philosophers and was a cornerstone of alchemy until the Renaissance (the transition from the Middle Ages to the Modern Era and covering the span between the 14th and 17th centuries).

Democritus and Leucippus: atomism

A theory of matter proposed by Leucippus and his pupil Democritus was less influential at the time than the ‘four elements’ proposed by their contemporary Empedocles. In retrospect, it seems closer to modern scientific understanding. They suggested that everything in the universe is composed of minute, unalterable and indivisible particles, which they called atoms (from the Greek atomos, uncuttable). These, they argued, are free to move through empty space, combining in constantly changing configurations.

The assertion there is such a thing as a void, an empty space, may be one reason these ideas were originally considered unacceptable. According to their theory, the number of atoms is infinite, and different kinds of atoms with different characteristics determine the properties of the substance they form together. Because the atoms are indestructible, when a substance, or even a human body decays, its atoms are dispersed and reconstituted in another form.

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Science

Questions of Science: Free the atoms

Oxygen has a slightly greater density than nitrogen. Why, then, don’t these main constituents of air separate out?

MD overlapGAS MOLECULES move rapidly at room temperature, with oxygen and nitrogen travelling at around 500 metres per second, so they obviously collide frequently. This allows the oxygen and nitrogen molecules to mingle and mix, rather like large numbers of people on a nightclub dance floor, in a process known as diffusion. Convection, the transfer of heat within the atmosphere, also plays an important role in this gas mixing process.

Gas mixing is a spontaneous process. This means that if you had a container with two compartments separated by a barrier, with one compartment containing pure nitrogen and the other pure oxygen, the two gases would automatically mix or diffuse as soon as the barrier was removed.

A change in the ratio of oxygen to nitrogen would be expected in a hypothetical quiescent atmosphere. However, constant mixing occurs in the real atmosphere, driven by the Earth’s rotation and by differences in density between hot air at the Earth’s surface and colder air higher up.

Up to altitudes of between 80 and 120 kilometres this mixing results in a uniform concentration of oxygen and nitrogen – which respectively make up approximately 21 per cent and 78 per cent of the atmosphere.

This region is known as the homosphere. Partial stratification of the two gases does occur above 120 kilometres, in the heterosphere, where the density of air is much lower than at the surface and the efficiency of bulk mixing processes is reduced.

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If there were no circulation in the atmosphere, the oxygen would tend to concentrate in the lower strata. This process would take millions of years once circulation ceased because molecules of oxygen (and, indeed, nitrogen) are constantly colliding with other molecules. This means it would take a long time for a particular molecule to fall from its starting point to the ground. Once it hit the ground, it would bounce and eventually rise again to a great height, only to fall again. This would be repeated frequently if no other variable, such as temperature, changed.

Although the individual molecules continue to travel up and down, each ‘species’ of oxygen and nitrogen would eventually reach an equilibrium distribution of molecules per unit volume as a function of height. This species density will decrease with height by an amount that depends on the molecular weight of the species. So, the oxygen would fall off with height slightly faster than the nitrogen. At high altitudes, the air would become richer in nitrogen, but then other gases such as water vapour, neon, methane, helium and hydrogen would dominate.

In fact, atmospheric circulation and turbulence prevents this from happening in the lower atmosphere. But in the very high atmosphere there is not much circulation and the composition does become dominated by atomic oxygen. Above 600 kilometres this is superseded by helium, and eventually by atomic hydrogen.

science in motion

Science-in-motion: a series of short articles following topics in science.

. Molecular geometry

This describes the overall shape of a molecule in terms of how the atoms inside it are arranged. Examples of simple structures are linear molecules like carbon dioxide (O=C=O) and tetrahedral molecules like methane, which consists of a carbon atom with four hydrogen atoms surrounding it at the corners of a tetrahedron.

Trigonal-bipyramidal molecules are shaped like two pyramids back to back, while octahedral molecules have a shape like an eight-sided solid. Octahedral molecules include the compound sulphur hexafluoride (SF6).

‘Isomers’ are compounds that have the same chemical formula but different molecular structures. For instance, the sugar fructose is an isomer of glucose – they have the same formula C6H12O6, but their atoms are arranged in different ways. Sometimes, two isomers are mirror images of each other, in which case the molecule is said to be ‘chiral’ and the two mirror-image forms are called enantiomers. Chiral molecules include most amino acids (which are the building blocks of proteins).

Molecular Geometry

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Philosophy, Science

Philosophy and Science

REASONING

Einstein

THROUGHOUT much of the history of philosophy, there was no such thing as science in its modern form: in fact, it was from philosophical enquiry that modern science has evolved. The questions that metaphysics set out to answer about the structure and substance of the universe prompted theories that later became the foundations of natural philosophy, the precursor of what we now call physics. The process of rational argument, meanwhile, underpins the ‘scientific method’.

. Previously (Philosophy) Essential Thinkers: Friedrich Nietzsche

Since the 18th century, many of the original questions of metaphysics have been answered by observation, experiment and measurement, and philosophy appeared to be redundant in these areas. Philosophers have since changed their focus to examine science itself. Some, like Hume, challenged the validity of inductive reasoning (empiricism) in science, while others sought to clarify the meaning of terms used by science, opening up a ‘philosophy of science’ that considers areas such as scientific ethics and the way science makes progress.

Logic

In seeking answers to questions about the universe and our place in it, philosophy is distinguished from religion or mere convention by its use of reasoning. Philosophy proposes ideas because of thought with the assertions justified with sound rational argument. Convention or mere belief is not enough. Various logical techniques have been devised to show whether an argument is valid or fallacious.

In simple terms, logic is the process of inferring a conclusion from statements known as premises, either deriving a general principle from specific examples (inductive reasoning) or reaching a conclusion from general statements (deductive reasoning). The classical form of logical argument, the syllogism, consisting of two premises and a conclusion, was officially formalised by Aristotle and has remained the mainstay of philosophical logic until advances in mathematical logic brought in new ideas in the 19th century. Later, in the 20th century, symbolic logic opened new fields still further within philosophy.

Metaphysics

For the first philosophers, the burning question was: ‘What is everything made of?’ At its most basic, this is the central question of a branch of philosophy known as metaphysics. Many of the theories proposed by the ancient Greek philosophers – the notions of elements, atoms, and so on – formed the basis of modern science, which has since provided evidence-based explanations for these fundamental questions.

Metaphysics, however, has evolved into a field of enquiry beyond the realms of science: as well as dealing with the make-up of the cosmos, it examines the nature of what exists, including such ideas as the properties of material things, the difference between mind and matter, cause and effect, and the nature of existence, being and reality (ontology).

Although some philosophers have challenged the validity of metaphysics in the face of scientific discovery, recent developments in areas such as quantum mechanics have renewed interest in metaphysical theories.

. See also Philosophy: An introduction…
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