Monday, 4 January 2016



To simplify the language the word ‘light’ will be used to denote the whole spectrum  of energies of light, ranging from the lowest energy (radiowaves), through microwaves, infrared, visible and ultraviolet to the very highest energy light known as gamma radiation.

From the beginning
Light is made up of photons, the very first stable particles in the Big Bang event 13.8 billion years ago. Photons began only one hundredth of a billionth of a second after the creation of space-time, the very first entities of the natural world, existing before atoms, neutrons, protons and electrons. They are eternal, i.e. they do not decay like other particles, and without mass.

Absolute as a frame of reference
Light is the only real frame of reference in the universe. If you try to measure the speed of anything else you get a result which depends on the relative speed between you and whatever object you are measuring. (Einstein, Special Theory of Relativity, 1905).  This is not so with light. Even if you travel at 99.999% the speed of light in any direction you will still measure the speed of a passing beam of photons as the same speed as if you were completely stationary. This absoluteness of speed, which defies common sense, is the basis of GPS navigation, accurate time keeping and much else upon which the modern world depends.

Wave particle duality
Light behaves in two fundamentally different ways: as particles of electromagnetic energy called photons or waves of energy called electromagnetic waves. Which of these natural forms of energy is observed depends on how they are observed. (This is best illustrated by the double slit experiment but there is no need to go into this here. See this YouTube video .) Beams of other particles, such as electrons, protons, neutrons and molecules also behave in this strange way. It is known as wave-particle duality and is revolutionizing our understanding of the natural world as well as imposing limits on what science can be used to investigate.

Information carrying power
The internet depends very much on the ability of light passing through fibre-optic cables to carry vast amounts of data around the world at the speed of light (8 times round the globe in one second). Telescopes, binoculars, microscopes and fibre optic medical imaging all exploit light’s properties. Microwaves, radar, radio waves, infrared rays, optical light, ultraviolet, gamma rays and X-rays are all forms of light of different wavelengths and energies which carry information as well as energy. We also rely on light to tell us almost everything we know about the history of the universe (e.g. through the cosmic microwave background, radiation from the universe when it was only 1/3rd of a million years old). It is not commonly realized that if the nearest star (alpha centaura proxima, 4.2 light years away) vanished into nothingness we would not know for at least 4.2 years. If the first stars stopped existing now this information would not arrive for over 13 billion years, long after we had become extinct.

Eyes and brains  formed to use light
543 million years ago, as oxygen concentration reached 10% of the atmosphere most of the skeletal architectures  used by organisms of all shapes and sizes today sprung up in what is referred to as the Cambrian explosion. In particular all the forms of eye existing today appeared, including compound eyes, inset eyes and eyes on stalks. Light played a crucial role, in particular because our yellow dwarf sun   emits visible light which is maximally transmitted through water (at other wavelengths than this water is almost opaque, so that underwater information transfer at the rates required for an underwater ecosystem would be impossible).  Once hunter and prey could see each other their hunting and evading behaviour grew rapidly in complexity along with  the neural networks needed to process and respond to the optical information.

Circadian rhythms
These diurnal cycles of biological activity are universal and basic to the whole natural world. They are synchronised to the daily  cycle of light and dark and have been for billions of years, right back to the time when the earth rotated once in 22 hours. No other rhythm in nature is so fundamental in governing the behaviour and well being of an organism.  Each of the 10 trillion cells in the body is governed by it and works in cooperation with all the others, either directly or through a hierarchy of sophisticated networks that sprung up suddenly in the Cambrian explosion.  The whole biosphere is synchronized to it.

The source of all energy and matter
Nothing could exist without light. Not only does it power nature directly through photosynthesis (by which light is captured by leaves and converted to the nutrients and energy sources needed by the plant and animals which eat it) but human civilization depends on it for firewood, fossil fuels, solar generated electricity, wave power (ocean waves owe their existence to radiant heat from the sun), tidal energy (the sun and moon came  from the photons in the Big Bang like everything else) and hydroelectric power (rivers and lakes depend on water evaporated from the sea by the sun). Light preceded matter in the Big Bang so everything of which we are aware ultimately comes from the first photons colliding to produce elementary particles, the constituents of everything we know exists.

And there was light…
So it would seem that the God-inspired writer(s) of the Genesis creation poem had some inkling of light’s crucial role in the history and origin of the universe:
‘And God said let there be light, and there was light, and God saw that it was good.’  Gen 1:3-4. 

 It is not surprising that it was and is to this day  used as a metaphor for the spiritual power which drives away darkness and wins over spiritual evil. Jesus Christ, for instance, is referred to and pronounces himself as the light of the world. 


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