Posted on

Light: Preconditions for Visual Perception

Quote

If the doors of perception were cleansed everything would appear to man as it is, Infinite. For man has closed himself up, till he sees all things thro’ narrow chinks of his cavern.

William Blake, poet, painter, print-maker (1757–1827), The Marriage of Heaven and Hell

Introduction

Light is everywhere. Look around. If you can see something, then it is being illuminated by one or more light sources – sunlight, moonlight, firelight, streetlight, starlight, a firefly.

Light is primordial, it dates from the beginning of time, and is ubiquitous – it saturates the universe.

Light is primitive, curling yellow and red in prehistoric hearths, flashing and booming in the dead of night, deadly in the mid-day sun.

Light cuts through the darkness and through the shadows in our lives, drawing attention to things that would otherwise be hidden.

Light wages war upon us, polluting, burning and blinding. But, along with light comes illumination – insight, awe, wonder.

Just as we need light, we need darkness to retreat, rest, and sense the faint glimmer of things otherwise hidden.

Talking about seeing the light means to understand something more clearly or in new ways. As the veil of darkness lifts, personal realms are revealed – the mind’s eye, imagination, hallucinations and penetrating revelations.

If we want to see more, we turn up the light, point the torch more directly or concentrate our thoughts.

Film studios and theatres are full of banks of lights to make sure we see the action as intended. Shopping malls are full of spotlights to make sure we don’t miss any details of the latest display. There is an illuminated stage in our minds where flashes of creativity spark new ways of seeing and acting. As searing light sweeps away the old, previously unimagined possibilities dance before us.

If we can’t see things through direct observation, then we insert equipment into our line of sight. Microscopes, telescopes, spectroscopes and oscilloscopes are all technologies of choice to enable invisible stuff to materialize before our eyes. Gamma waves, microwaves and radio waves, for example, are all types of light that are outside the visible part of the spectrum but can be shifted to the range of wavelengths our eyes are best suited with the right piece of kit. Meanwhile, graphic visualizations can make data visible, MRI scanners create a kind of topology of the human body and 3D printers can create artifacts from non-visual information.

To get a grip on some of the important contemporary questions about light, and its connection to colour, vision and ways of seeing more, we are going to take a 13.8-billion-year step backwards to the beginning of the Universe. Our destination is a time shortly after the Big Bang. It involves a trip into the scientific worlds of cosmology and evolutionary biology to come to terms with core questions such as why do we have eyes in the first place?

In case you are already confused, cosmology is a branch of astronomy that studies the origin of the Universe, and particularly the way it has unfolded over time. Evolutionary biology studies the processes evident in nature (natural selection, common descent, speciation) that account for the diversity of life on Earth.

The underlying rationale for the route we will follow is that there is nothing random about the fact that eyes have evolved on several separate occasions in different species, that we see the world around us with such clarity, or that sight is so central to how we learn about and understand ourselves and the world. 1 There is a direct connection between the earliest history of the Universe, the formation of the first stars, the galaxies they exist within and the fact that almost all insects and animals have little light-sensitive balls stuck on the front of their faces. We will pass important sites on the road that can be thought of as preconditions for visual perception. So look out for the appearance of light, space-time and it’s geometry, the stability of the cosmos over time, material forms and embodied beings, biological life and photosynthesis, and finally, the emergence of eyes and human cognition.

let’s begin with a photograph of a somewhat self-satisfied looking gentleman smoking a pipe and directing his nicotine filled gaze into the machine that towers over him.2 He seems to want us to appreciate that he is making unparalleled discoveries about the night sky that will lead to brand new fields of scientific inquiry and a plethora of other remarkable discoveries. We now know that in less than a century his work will transform our understanding of the cosmos and play a critical role in scientific revolutions set to transform our lives. What is not clear from this portrait is whether he knew that as we learn to sense photons of light arriving from ever more distant reaches of space and time, decoding them to reveal their origins and some of the details of their travels, a parallel process enables us to reconsider the scope of human vision, the reach of our imagination and caste new light on what it means to be a human observer.

Quote

Quote

Edwin Hubble stands by the 48-inch telescope at Palomar Observatory, San Diego County, California.
(Carnegie Institution of Washington)

The big bang

In the photograph of Edwin Hubble introduced above, we see a scientist peer into the eyepiece of one of a new generation of powerful optical telescopes. What he saw was a total revelation! During his research at the Mount Wilson and Palomar Observatories, he made measurements and perceived details in the night sky not imagined by previous generations. Relying solely on evidence drawn from faint smudges of light, he was able to make unanticipated deductions about the scale and origins of the Universe.

The Big Bang is a scientific theory arising from measurements showing that the Universe is much bigger than had previously been realized, and is still expanding. Hubble was the first to make such observations and to publish his calculations (1929). Hubble and his contemporaries worked out that there are myriad galaxies located beyond the boundaries of our own, the Milky Way. Their results also showed that regardless of which direction we look in, that clusters of galaxies are moving away from us, and the ones that are farthest away are moving the fastest.


A timeline of the Universe. The far-left shows the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. The afterglow of the Big Bang, the Cosmic Microwave Background, began to be emitted about 400,000 years later. (Image: )

The remarkable thing that Hubble’s observations demonstrated was that unlike releasing a box of birds in an open field, enabling them to fly off through space towards the boundaries of the field, it was space itself and so the field that was expanding. Taking this analogy a little further, when Hubble made his observations, every bird (cluster of galaxies) appeared to have travelled a considerable distance from their point of origin, but it wasn’t so much that the birds were all flying away, it was the scale of the field itself that was expanding. As a result, we can imagine that even if each bird (or cluster of galaxies) where to be glued in position at some moment, the distance between them would continue to increase, not because they were going anywhere but because the volume of the field itself is exploding in size. This way in which the Universe was observed to be expanding came to be known as the Hubble Constant.

Of course, the Universe is not a field of birds among other grassy fields as suggested by the analogy above. Quite to the contrary, the Universe encompasses everything in existence, from the smallest sub-atomic particle to the sum-total of all galaxies everywhere and everything else besides.

Quote

This is the Abell Galaxy cluster. It is believed to consist of four thousand distinct galaxies, all bound together by gravity. It is 2.2 billion light years from planet Earth.

The Universe: past and future

But what will happen over time if galaxy clusters, some of the biggest structures we know of, are drifting away from one another as the size and geometry of space and time change in scale, leaving more and more empty spans in between? The answer seems to be that in the distant future they will eventually be so far away from one another and receding at such a speed, that their light will fade to nothing as they pass out of reach forever. From then on, other than the relatively small galaxy cluster around our own Milky Way, there will be nothing out there but an impenetrable empty void.

If that bleak picture lies in the future, what can we deduce about the past? What has brought us folk on planet Earth to this point in the history of the Universe? Hubble realized that if the rate at which the Universe is expanding is a constant, then not only is it constantly getting bigger as time goes on but looking back at its history, in the past, it must have been smaller than it is now.

Very slowly, let the air out of a party balloon at a constant speed and the speed at which it shrinks will also be constant. If we run the sequence of events that account for the evolution of the Universe in reverse, at a certain point, 13.82 billion years ago, it reaches a point where the scale of everything becomes so small it vanishes entirely. That vanishing point is the location of the Big Bang.

Big Bang! It’s a silly name, because at the moment the Universe first appears, there is no space, no time and no-one to hear the bang. But, be that as it may, the Big Bang theory suggests that because the total mass of everything that constitutes the Universe as we know it now was at one point in the past compressed into an infinitesimally small nothingness, that it was also off-the-scale hot.

A parallel example of how things that get compressed become hot is the way a bicycle pump heats up at the point where you force air into a tyre. Pressure doesn’t directly cause things to heat up, but compressing the same amount of gas into a smaller space does. The amount of heat in the gas remains constant, however in a smaller volume that heat is more concentrated, thus raising the temperature.

In the case of the Big Bang, heat is usually attributed not to pressure but to the wavelength of photons of light. As the Big Bang took place and space was in the first instant of materializing, there was only room for the very shortest wavelengths imaginable, at the top end of the electromagnetic spectrum where gamma rays are emitted. Gamma rays not only have the shortest of wavelengths, but they also transport the most energy. The more energy the greater the heat. The gamma radiation we are talking about here had the shortest of all possible wavelengths and harboured the sum total of energy that would ever exist anywhere, ever. This was not going to just be a bit of a pop, it truly will be a tremendous boom.

The Big Bang is the point from which everything in this article and the Universe itself unfolds. In an unimaginable brief amount of time, the infinitesimally small space between any two imaginary points inflates to 99.7 trillion kilometres, causing a previously non-existent steaming soup to actualize as a primordial plasma. As it decompresses, it cools to around ten thousand million degrees. After this initial fraction of time, a slower expansion and cooling process continues and according to a pattern that seems to conform to the Hubble Constant.

For those interested in such things, the unit of measurement for the Hubble Constant is estimated to be around 70.00 km per second per mega-parsec. A mega-parsec meanwhile is a million parsecs and as there are about 3.3 light-years to a parsec, a mega-parsec is, well, quite a distance.

It’s impossible to visualize the matter-radiation plasma soup immediately after the Big Bang because even if we leave out its unimaginable explosive force, it’s defining features, including structure, density and temperature, were smoothly and indistinguishably distributed in all directions to infinity. As a result, the preconditions for the usual way human beings think of things, in terms of specific locations in space and time and with a point of view on distinctive surroundings didn’t yet exist. Everything was absolutely identical everywhere.

Title

The Holmdel Horn Antenna was constructed in 1959 as a communications satellite but discovered radiation from the Cosmic Microwave Background. (NASA / Public domain)

Cosmic Microwave Background

With the previous two sections in place, it is time to talk about light!

Around 400,000 years after the Big Bang, things began to happen that are still evident today and are of particular relevance to the concerns of this article. Using our latest technologies, such as the European Space Agency’s Planck satellite, we have been able to study the Cosmic Microwave Background (CMB), a relic of the oldest known electromagnetic radiation in the universe. It began to be emitted as the chemistry of the opaque plasma soup, mentioned in the previous section, began to alter. This happening, in which photons of light begin to be distinguishable within the preceding opaque plasma. It occurred as the first forms of matter condensed sufficiently to produce discrete atoms of hydrogen and helium. It heralded an increasingly transparent future because the new atomic structures had empty spaces between them through which photons of light could squeeze. The process of the decoupling of matter and energy continued for 600,000 years. Images of the CMB dating from that epoch provide evidence of the very first visible signs of the Universe we inhabit today.

The Cosmic Microwave Background is the afterglow of Big Bang. This image shows tiny temperature fluctuations. Red regions are warmer and blue regions are colder by about 0.0002 degrees. The average overall temperature today is 2.725 Kelvin degrees above absolute zero. (http://wmap.gsfc.nasa.gov/media/101080)

The Cosmic Microwave Background is radiation left over from the Big Bang and, as the word microwave reveals, it is electromagnetic radiation in the microwave part of the electromagnetic spectrum. Microwaves have a peak wavelength of 1.9mm. This is however the wavelengths we see today. They have been stretched since their point of origin.

The Cosmic Microwave Background was discovered by accident in 1965 by researchers building a new type of radio telescope. The telescope looked like a huge horn and was intended to be used as a satellite communications antenna. But things weren’t going well because the scientists were puzzled by the constant hiss of noise it produced. They soon realized the noise came uniformly from all over the sky. Physicists, who had first predicted the existence of the Cosmic Microwave Background in 1948, then realized the static was what they had been looking for.

It took a further 50 years (2009-2013) before Plank and it’s sister satellites revealed that whilst being smooth and uniform in every other way, at a sufficiently high resolution, images of the CMB contain very small fluctuations in temperature. These fluctuations represent tiny irregularities that would, as the Universe evolved further, precipitate the formation of ever more complex forms of matter and lead to the evolution of galaxies, their stars, and all the other structure we see around us today.

It’s important to be clear about how we can possibly observe evidence of CMB radiation if it was emitted so soon after the Big Bang.

Microwaves are a type of electromagnetic radiation (EM radiation), which we often simply call light. The visible light we humans see is different from microwaves, ultra-violet light, x-rays, gamma rays and radio waves in that they are all invisible to the human eye. The only difference between visible light and the other kinds is that they belong to a different band of wavelengths and frequencies that we divide EM radiation into. All forms of EM radiation fall somewhere on the electromagnetic spectrum.

Electromagnetic spectrum

Since all forms of light (EM radiation) travel at a speed of just under 300,00 km per second (the speed of light) though empty space, there is a delay between the moment light is emitted and its arrival at distant destinations. The delay between radiation emitted by the Sun arriving at our home planet is eight minutes. As distances get bigger the time delay gets longer and eventually has to be measured in light-years, the distance light travels in a year. The delay between transmission and reception for light travelling across our local cluster of galaxies is 9.8 million light-years. At a bigger scale, there are three million galaxies within a billion light-years of our solar system. This means that as light arrives we see things as they were all that time ago.  The light from the CMB has travelled further than any other before being picked up by equipment like the Plank satellite – telescopes designed to pick out the CMB from all the other types of EM radiation that fill the sky. When astronomers observe the CMB they see it as it was more than 13 billion light-years ago.

The CMB appears to be the same distance away in every direction. The implications of this are that we can think of ourselves as having a viewpoint on the Universe from which the CMB forms a sphere around us. But it’s not that it’s all laid out just for us. The fact is, as far as we know, whatever the viewpoint within the known Universe, it’s so huge that the CMB would always form an identical sphere. This is hard to visualize as is the fact that it has now cooled to just a couple of degrees above absolute zero (minus 459.67 degrees Fahrenheit, or minus 273.15 degrees Celsius).

The remarkable thing about all this is that planet Earth, an unremarkable ball of matter in an unremarkable corner of the Milky Way has developed blobs of biological matter that are able not only to feely-crawly themselves about the ground but can also look up at the sky and sense some of the forces that have shaped everything that has ever existed, anywhere, since the beginnings of time. Life on planet earth is truly insignificant, yet human eyes and human minds are literally tuned to some of the cosmic forces that have shaped the largest things we can imagine right down to the traces of iron in our blood.

Before looking at the statements in this last paragraph in greater detail, let’s tidy up loose ends.

I am text block. Click edit button to change this text. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.

theatre, stage, actors

So let’s set out an ordered series of prerequisites for and interconnections between the cosmological and biological dimensions of our lives that might help to account for vision. We need to look even more closely at the inter-relationships between this phenomenon we call light, our extant lives and vision. It might help to think of human life as a play. Here we are, acting out the things we do best. Then there is the stage, the natural world within which we have an ecological niche. Housing all that is the theatre.

The fact that microwave radiation preceded the formation of the first stars has been discussed above. Cosmic Microwave Background radiation was the first manifestation of light in the Universe – electromagnetic radiation is literally part of its essential workings. Light is also em-meshed into the laws of physics that help us account for the consistent forms and properties of the heavens across all space and time.

The fact that photons of light began to escape the preceding torrid, isotropic mass of plasma and traverse the empty spaces between emerging atomic structures accounts for the fabric of space-time. Both space and time are the fundamental prerequisites for a living Universe. All forms of matter, including very living thing, must have geometric coordinates in which to exist, and this is exactly what space-time provides. Space-time is the theatre, and the physical and temporal dimensions of the stage on which we find ourselves determine the locations from which we participate in and observe the play folding and unfolding. Each of us is an actor, swept forwards by the tides of time, caught in the action as things emerge, evolve, change and become different.

It would be billions of years after space-time emerged that creatures evolved on planet Earth able to reflect upon their place in this matrix and trace its history back over aeons to its origins. But eventually, the living generations of which we are all a part are the ones who are finally able to see and to consciously appreciate that our very existence is predicated upon conditions that emerged in the earliest phases of the evolution of the Universe. How remarkable that we can describe ourselves in these terms!

With the theatre in place, we need to consider another critical detail! Where do our bodies come from? In other words, what are the preconditions for the embodied existence of anything?  To grasp this, we must target the physical matter that everything from our own to heavenly bodies is constructed from.

In addition to Cosmic Background Radiation, the Big Bang left behind another important relic: all of the matter in the universe today. CMB radiation was emitted by newly forming atoms of hydrogen and helium. Initially these were the only forms of matter and even today, hydrogen is the most abundant element in the Universe. As we extrapolate the inter-connections between light and vision we also need to keep in mind the very material fabric of our existence.

From the start, hydrogen atoms began to clump together under the effect of their own gravitational attraction forming sheets, walls and filaments, separated by immense voids and creating the vast structures sometimes called the cosmic web.

As ever larger quantities of hydrogen were drawn together, gravitational attraction increased, compressing more gas into every smaller and hotter regions until the first stars were born. Stars are balls of burning matter undergoing nuclear fusion within their cores and forcing atomic nuclei to fuse and produce new, heavier elements. During the fusion of two hydrogen nuclei to form helium, for example, a little less than one percent of their mass is emitted as energy. Within our own solar system today, it is this ongoing process of fusing hydrogen nuclei that releases the radiant energy and bathes our world in light every day.

Credit: https://sciencenotes.org/what-are-the-naturally-occurring-elements-elements-found-in-nature/

Whilst the first stars were composed solely of hydrogen and helium, all the other 92 elements (lithium to plutonium) found in nature are the result of nuclear fusion within later generations of stars and from catastrophic stellar explosions known as supernovae. The most common elements, like carbon and nitrogen, are created in the cores of most stars. Only the most massive of stars produce heavier elements such as iron.

A star becomes a supernova when it runs out of fuel. Normally, gravity pulls the contents of stars together whilst fusion pushes them apart. The two balance each other perfectly until fusion stops causing the outer layers to explode and the core to implode. It takes about a quarter of a second for the entire core of a sun to collapse in on itself. The massive increase in pressure in the extreme conditions of a supernova adds new elements to the periodic table –  cobalt (Cb) to plutonium (Pm).

Without supernovae, life as we know it would not be possible. Earth would be a very different place without the heavier elements created in stars and supernova explosions. Without all the natural occurring elements of the periodic table, there would be no matter to build a planet out of – no seas, no mountains, no clouds – and no life. We need the air in our atmosphere to breathe. Our blood has iron in its hemoglobin to carry oxygen to every cell in our bodies. Nitrogen enriches our planet’s soil and is a vital component of chlorophyll. Chlorophyll is the compound by which plants use sunlight to produce sugars from water and carbon dioxide (photosynthesis). Nitrogen is also a major component of amino acids, the building blocks of proteins. Without proteins, plants and bodies wither and die.

To fully appreciate the materiality of our bodies we must remember that the idea we are stardust is not just a poetic metaphor. The entirety of our solar system is composed of material from the cosmic web and past generations of stars. Every atom in our bodies has an extraterrestrial origin. And when people muse about whether there are aliens out there is space, they forget that our bodies are where the real aliens are hiding, it’s just that they are the hidden building blocks of every molecule and compound in our bodies. But whilst the matter that forms the bodies we live in is extraterrestrial in origin, there is, as yet, no compelling evidence that life itself originated elsewhere.

Bodies, beings, organisms, entities, and multicellular life-forms, these are some of the names we give to the living creatures we share our biophysiology with. Every plant and animal is distinguished by an individual existence bounded by birth at one end and death at the other. This is life as we know it, and every instance represents another example of the interaction between matter and energy. All the different things living organisms do with light account for the shear abundant volume of our shared biosphere, its spread, diversity and evolution. Seen as a whole, we must look once more to light to account for the has animation of matter, bringing it to life and accounting for the entire biosphere . It is photosynthesis that is at the heart of that interface.

Life has been shaped and driven by photosynthesis and it forms a key part of the root of life’s family tree. Photosynthesis is the process by which plants convert the electromagnetic radiation transported by light into chemical energy. There are two types, oxygenic and anoxygenic photosynthesis. The general principles of both are similar, but oxygenic photosynthesis is the most common and is seen in plants, algae and cyanobacteria.

Chlorophyll within leaves and stems absorbs the light and synthesises carbohydrates such as sugars using carbon dioxide and water drawn from the environment. Different wavelengths within the visible spectrum, corresponding with particular colours, play an important role in photosynthesis but plants don’t absorb all colours evenly. Chlorophyll absorbs violet- blue and red but all green wavelengths are reflected, hence the greenness of nature.

If evolution hadn’t come up with photosynthesis, there would be no oxygen in the atmosphere, no protective ozone layer above it, and probably no life on dry land. Planet Earth minus the invention of photosynthesis would be inhospitable for all higher organisms that are around today, and would be peopled only by primitive bacteria in the oceans or under the surface of the Earth. (Light and Life By Kenneth R. Yeager)

Since the advent of photosynthesis, organic life and the planet have coevolved. Forests turn to coal. Seashells turn to limestone. Plants draw the nutrients and water they need from the soil. Even plate tectonics may play a critical role in nourishing life. Organisms and bio-systems draw upon what remains of the light absorbed by the generations of life-forms that have preceded them. The continuity and unity of life that we know today is evident in the uniformity of genetic systems, the molecular composition of living cells and the chemistry.

Our human existence has in turn been shaped

Time fame
Cone System
4.6 billion years agoEarth forms
3.4 billion years agoFirst photosynthetic bacteria appear
2.7 billion years agoCyanobacteria become the first oxygen producers
2.4 billion years agoEarliest evidence (from rocks) that oxygen was in the atmosphere
1.2 billion years agoRed and brown algae become structurally more complex than bacteria
750 million years agoGreen algae outperform red and brown algae in the strong light of shallow water
470 million years agoFirst land plants – mosses and liverworts
420 million years agoVascular plant tissue evolve, responsible for transporting water, minerals, and products of photosynthesis
200,000 years agoHomo Sapens

Photosynthesis has played a central role in the evolution of life. (https://en.wikipedia.org/wiki/Evolution_of_photosynthesis)

 

Eyes

A critical connection between photons and nature comes about when cells begin to be photosensitive. In The Origin of Species Charles Darwin noted:

How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but . . as some of the lowest organisms . . are known to be sensitive to light, it does not seem impossible that certain elements . . should become aggregated and developed into nerves endowed with this special sensibility.

Some of the early forms of eyes looked like small spots before evolving into concave cups and then developing lenses and so a more successful and competitive organ for sight. The process probably required 364,000 generations, so as short a period as half a million years.

When light strikes a photo-sensitive rod or cone cell in the retina of the eye, it releases energy and triggers a chemical reaction which in turn produces an electrical impulse that after processing is transmitted to the brain.

It is likely that from the moment the chemical reaction begins that the energy received contributes in one way or another to visual perception and so to conscious experience.

Initially eyes probably could distinguish between light and dark. But it is theorised that the prototypical ability to distinguish between organism and environment may have been an early function.

Our eyes exactly respond to this band of energy between red and violet that makes its way through the atmosphere. And that it is this same range of wavelengths that powers the entire canopy of plant life that covers the surface of the planet on land and at sea. Heat, photosynthesis, temperature of biosphere, climate.

In the meantime, we humans will continue trying to interpret and explain the causes of evolution and the mechanisms and laws governing the universe in which we exist. Our species, at least to our knowledge, in the solar system, is the only one that asks itself for its past and tries to regulate its future. Without humans, Earth and the solar system will exist, yes, but nobody would interpret them, nobody would notice the wonders of nature. Nobody would see the forces and the logic of the universe.

Loose ends

Before steering towards conclusions, let’s make sure the vocabulary used so far and the way terms fit together has been properly explained.

Electromagnetic radiation

Electromagnetic radiation is a type of energy more commonly simply called light. Detached from its source, it is transported by electromagnetic waves (or their quanta, photons) and propagates through space.

  • Electromagnetic radiation (EM radiation or EMR) includes radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays.
  • Man-made technologies that produce electromagnetic radiation include radio and TV transmitters, radar, MRI scanners, microwave ovens, computer screens, mobile phones, all types of lights and lamps, electric blankets, electric bar heaters, lasers and x-ray machines.
  • At the quantum scale of electromagnetism, electromagnetic radiation is described in terms of photons rather than waves. Photons are elementary particles responsible for all electromagnetic phenomena.
  • The term quantum refers to the smallest quantity into which something can be divided. A quantum of a thing is indivisible into smaller units so they have no sub-structure.  A photon is a quantum of electromagnetic radiation.
  • A single photon with a wavelength coresponding with gamma rays might carry 100,000 times the energy of a single photon of visible light.

Visible light

Visible light is the range of wavelengths of electromagnetic radiation perceived as colour by human observers.

  • Visible light is a form of electromagnetic radiation.
  • Other forms of electromagnetic radiation include radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays.
  • Visible light is perceived by a human observer as all the spectral colours between red and violet plus all other colours that result from combining wavelengths together in different proportions.
  • A spectral colour is produced by a single wavelength of light.
  • The complete range of colours that can be perceived by a human observer is called the visible spectrum.
  • The range of wavelengths that produce visible light is a very small part of the electromagnetic spectrum.

Electromagnetic spectrum

The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths (and corresponding frequencies) of electromagnetic radiation, ranging from low energy radio waves through visible light to high energy gamma rays.

Cosmic microwave background

The Cosmic Microwave Background (CMB) is a form of electromagnetic radiation dating from an early stage of the Universe. It is the oldest known form of electromagnetic radiation. With a traditional optical telescope, the space between stars and galaxies is completely dark but a sufficiently sensitive radio telescope reveals the CMB as a faint glow not associated with any star, galaxy, or other objects.

  • The glow of the cosmic microwave background is strongest in the microwave region of the electromagnetic spectrum.
  • The CMB is an emission of uniform thermal energy coming from all parts of the sky. As a result, it is often described as being homogeneous and isotropic.
  • The CMB is considered to provide demonstrable evidence for the Big Bang theory.

Photon

A photon is the basic building block of light. A photon is a single indivisible bundle of energy (or particle) within an electromagnetic field.

  • In the field of optics, light is explained in terms of waves (wavelength, frequency and energy) but this description doesn’t always fit the evidence. It became clear during the 20th century that light sometimes exhibits wave-like behaviour, at others both waves and particles, or just particles.
  • Contemporary physics considers that electromagnetic fields propagate through space configured as bundles of energy. These are bundles of photons.
  • Photons are the force carriers of radiant energy (electromagnetic radiation).
  • A photon is a type of elementary particle and represents a quantum of light (eg. visible light). Another way of putting this is that a photon is the smallest quantity (quantum, plural quanta) into which light can be divided.

Wavelength

Wavelength is a measurement from any point on the path of a wave to the same point on its next oscillation. The measurement is made parallel to the centre-line of a wave.

  • The wavelength of an electromagnetic wave is measured in metres.
  • Each type of electromagnetic radiation, such as radio waves, visible light and gamma waves,  forms a band of wavelengths on the electromagnetic spectrum.
  • The visible part of the electromagnetic spectrum is composed of the range of wavelengths that correspond with all the different colours we see in the world.
  • Human beings don’t see wavelengths of visible light, but they do see the spectral colours that correspond with each wavelength and the other colours produced when different wavelengths are combined.
  • The wavelength of visible light is measured in nanometres. There are 1,000,000,000 nanometres to a metre.

Matter

Matter is anything that has mass as distinct from energy and occupies space by having volume.

  • Matter is distinct from energy.
  • Matter describes the physical things around us – earth, air and any object that can be named.
  • Matter is made up of particles – atoms and molecules.
  • Energy is a property of matter.
  • Einstein’s equation E=MC2 suggests that anything having mass has an equivalent amount of energy and vice versa.

Energy

Energy is a property of matter.

  • Everything contains energy including all forms of matter and so all objects.
  • Energy is evident in all forms of movement, interactions between, and changes to the forms and properties of matter.
  • At an atomic level, energy is evident in the movement of electrons around the nucleus of an atom. Energy is stored in the nucleus of atoms as a result of the forces that bind protons and neutrons together.
  • Energy can be transferred between objects, and converted from one form to another, but cannot be created or destroyed.
  • Everything in the universe uses energy of one form or another all the time.
  • When it comes down to it, even matter is a type of energy.
  • Light has energy but no mass, so does not occupy space and has no volume.
  • Energy is often described as either being potential energy or kinetic energy.
  • Energy is measured in joules.

Force

Forces bind things together and push things apart. The push-pull interactions between things are described as the interplay of forces. Forces explain how anything interacts with anything else in the whole of the natural world. Forces produce motion and can cause any object with mass to change velocity. This includes causing things to start moving from a state of rest, to accelerate or slow down. Quarks and leptons, the two fundamental particles present in all forms of matter, are bound together by fundamental forces.

Fundamental forces

There are four fundamental forces that account for all the forms of pulling and pushing between things that continually play out between everything in the Universe. To make sense of this, we need to understand that everything, everywhere is in motion. We must also realise that wherever there is a concentration of stuff, in planets, suns or galaxies, that is where most of the push-pulls happen.

The main points here are:

  • Nothing in the Universe is stationary unless its temperature is reduced to absolute zero. But nothing can be cooled to a temperature of exactly absolute zero.
  • Motion applies to things like objects, bodies, matter, particles, radiation and space-time. We also refer to the motion of images, shapes and boundaries. So motion signifies a change in the position of the elements of a physical system. An object’s motion, and so its momentum stays the same unless a force acts on it.
  • Whenever there is a push-pull interaction between two objects, forces are being applied to each of them. When the interaction ceases, the two objects no longer experience the force and their momentum continues uninterrupted.

The four fundamental forces of nature are:

  • Gravitational force: Gravity is the phenomenon that causes things with mass or energy to gravitate towards one another. Planets, stars, galaxies, and even light are all affected by gravity. The effect of gravity on small things like human beings when in the vicinity of something big like a planet is obvious. It is the Moon’s gravity that causes ocean tides on Earth. Gravity accounts for physical objects having weight. Gravity has an infinite range, although its effects become weaker as objects get further away from one another.
  • Weak Nuclear force: In nuclear physics and particle physics, the weak nuclear force explains the interaction between subatomic particles that is responsible for the radioactive decay of atoms. The weak nuclear force doesn’t affect electromagnetic radiation.
  • Strong Nuclear force: The strong nuclear force holds matter together. It binds the sub-atomic particles, protons and neutrons, that form the nucleus of an atom. Whilst repulsive electromagnetic forces push them apart, the attractive nuclear force is strong enough to overcome them at short range. The range at work here is measured in femtometres. The nuclear force plays an essential role in storing energy that is used in nuclear power and nuclear weapons.
  • Electromagnetic force: The electromagnetic force is the force that occurs between electrically charged particles, such as electrons, and is described as either a positive or negative charge. Objects with opposite charges produce an attractive force between them, while objects with the same charge produce a repulsive force. The electromagnetic force is carried by photons in the form of electric and magnetic fields that propagate at the speed of light.

Caption

 

 

Editing currently in progress. Please call back tomorrow 🙂

Get a grip on contemporary perspectives on light, and its connection to colour, vision and ways of seeing

  • there is nothing random about the fact that eyes have evolved on several separate occasions in different species,
  • that we see the world around us with such clarity
  • that sight is so central to how we learn about and understand ourselves and the world.

There are a direct connections between

  • the earliest history of the Universe
  • the formation of the first stars
  • the galaxies they exist within
  • and the fact that almost all insects and animals have little light-sensitive balls stuck on the front of their faces.

we can

  • sense many of the forces that have shaped everything that has ever existed, anywhere, since the beginnings of time.
  • human eyes and human minds are tuned to the cosmos and to processes that shape the largest objects imaginable and at the same time account for traces of iron in our blood.

as we find ways to sense photons of light arriving from ever more distant reaches of space and time, 

a parallel process enables us to reconfigure the scope of human vision, the reach of our imagination and caste new light on what it means to be a human observer.

Why do we have eyes!

The opening paragraph of this article centred attention on the connections between light and sight and the question of why so many creatures have developed eyes. Subsequent paragraphs provided a brief tour of the early Universe and our contemporary scientific understandings of light. There is room in this section to add more detail to substantiate the links between the dawn of the cosmos, the evolution of sight, and the scope of human vision and imagination.The aim is not to be prescriptive but only suggest the outlines of complementary motifs and patterns that readers can frame for themselves.

The links are also emergent in form in the sense that the whole is greater than the sum of the parts,meaning the whole has properties its parts do not have. These properties come about because of interactions among the parts. In this sense, life as studied in biology is an emergent property of chemistry.

But there is a third way of reading the motif.

Recognition of this connection between the primordial nature of light and the contemporary existence of vision. Just as our connection to antiquity – small tribes of humans pushing through tall grasses on the plains of prehistoric Africa, the first city states built upon trade and new forms of agriculture, the erection of pyramids and similar artifacts from massive blocks of stone,

The central point is, without eyes there would be no experience of light, and, had eyes not evolved, we would not only be unable to see, but there would be no visual component to our world. Can you imagine a world in which the sense of sight never existed? Until life developed on Earth, the Universe had never seen itself. Only living things can sense the existence of the world. Without us living beings, nothing from a grain of sand to the whole of the night sky knows anything about this reality. Without us, matter and energy exist but they don’t know themselves! Eyes connect our experience directly and instantly to electromagnetic radiation, to the visible spectrum, to colour and to everything between here and eternity that we can describe in terms of visual perceptual.

Without our eyes, the cosmological scale of the Universe would be beyond the reach of our other senses. It would be impossible to picture what is out there beyond earshot and the sense of smell – it’s scale, how it changes, it’s history or future. Without images of these objective dimensions of our world, our images of ourselves and our own lives would be similarly blinkered. Without the benefits of visual perception, we would be little more than squishy slime-balls, stuck by gravity to the surface of an insignificant sphere of rock, blindly living out our lives within its narrow envelope of atmosphere, with nothing beyond.

It’s easy to take our sensory experiences for granted, but because so much of our day-to-day lives centre on images, vision is, without any doubt, the faculty we need to be most critically aware of. Unless we explore and critique the economic, social, political and cultural forces that shape our perspectives, our horizons remain narrow and parochial. Left alone, most of our experiences, whilst figuring so prominently in our worldviews, largely exclude an ability to cognize the implications of our own every-day behaviour, the road our species is taking or the direction in which it is heading. Environmental degradation, starvation, illness, poverty, slavery, violence, war, homelessness, social inequalities, prejudice and racism, among others, affects billions of human beings and our natural world every day. To recognize, understand and know how to address such issues requires a type of vision that can only be developed over time. The powers of discrimination that enable us to decode the ways we see and understand the world, must be nurtured to prevent the wool being drawn over our eyes. We must constantly re-envision ourselves, our lives and our potential.

As far as we know, life on Earth is the only form of life anywhere. At best, we barely exist in relation to the scale of everything around us. The lifetime of even the most enduring species are brief sparks in the history of our solar system. In terms of the size of the Milky Way, there just are no dots small enough to represent ourselves. The existence of life itself registers only in our own minds and those of a small family of animals around us. The news has yet to reach the galaxy next door that Homo Sapien’s evolution is immanent – the Andromeda Galaxy is 2.537 million light years away. Beyond that, galaxies like our own, huge as they, are motes of dust.

 

A bigger picture. This scope of the way that we imagine ourselves. If we look outwards we seem small in relation to everything around us. If we look inwards we may c isolated organism. Look a little further is the biosphere the solar system and we are all that as well. If we choose to constrain ourselves we draw the frame tightly around us. But a large frame let’s in more and more of life. We choose. Select a frame to become more human. Select another to become more animal. Beacon light. Become matter. Beacon Timeless. More than anything watch and listen. Pick up a pattern full stop pick up a refrain.

  1. Eye sight is not a faculty that is universally enjoyed. An estimated 36 million people world-wide can’t see. Even when blind from birth, sightless people understand how others see the world even though they have never personally experienced visual images, according to a study conducted by researchers from the Massachusetts Institute of Technology and Johns Hopkins University.
  2. For much of the fist half of the 20th century women where excluded from many scientific and academic opportunities and institutions. The astronomer Vera Rubin was the first woman to use the Palomar telescope legally in 1963-64. The application form she was given stated at the top, “Due to limited facilities, it is not possible to accept application from women”. The limited facilities referred to was the presence of only one toilet at the observatory!