In the earliest days of optics
Since the dawn of time, people have found the nature of light to be interesting. Many cultures have given the Sun, the source of the light that lights us and gives us life, the status of a god, while the stars, as sources of light that brighten the night, have served as a source of inspiration for intellectuals and scientists. These views might seem out of date now, yet back then, people grappled with issues like what light is. Is its speed bounded or unbounded? Why does a light beam change direction when it hits water or reflects off a mirror? Etc. The most brilliant minds were motivated to find the answers to those first questions, and through their investigation, they created the scientific theories that currently underpin the body of knowledge that humanity values.
Ancient Egyptians and Mesopotamians began polishing crystals (typically quartz) around 700 BC in an effort to duplicate the optical properties that they had observed could be created with water. Nimrud lens is among the most well-known examples of those unique lenses (Figure 1). This lens, which was made in ancient Assyria between 750 and 710 BC, was used as a decorative item, a magnifying glass, or a fire-starting tool. African and Middle Eastern optics pioneers’ efforts only served to inspire the Greek and Roman mathematicians, physicists, and innovators whose experiments served as the foundation for
classical optics.
Figure 1. The Nimrud lens, commonly known as the Layard lens, is a piece of rock crystal dating to the eighth century BC that was found by Austen Henry Layard in 1850 at the Assyrian palace of Nimrud in present-day Iraq. It might have been a piece of beautiful inlay, a magnifying glass, a burning glass for lighting fires by concentrating sunlight, or both.
Credits: British Museum
The “emission theory” developed by Platon, the “intro mission theory” backed by Democritus, Epicurus, and Aristotle, and the “geometrical optics” developed by Euclid several hundred years after Plato were the three most well-known schools of optics thought at the time. Sadly, with the fall of the Roman Empire, all of these theories vanished from scientific circles in Europe. However, they managed to persist in the Middle East, where Muslim scientists continued to create new methods for analyzing the qualities of light.
Al-Kindi (801–873), the Persian mathematician Ibn Sahl, and Alhazen were among the most well-known authors of the era. Through his important “Book of Optics,” Alhazen was able to reintroduce contemporary views of the characteristics of light to Europe in the 1200s. One of the most significant optical texts in Europe long into the 17th century was this book, which made the first claim that light travels in a straight line and can bounce off of all matter.
With the construction of the first wearable eyeglass in 1284 by Friar Salvino D’Armate, optics history underwent a significant change. Before the second decade was up, Italian engineers and innovators in Venice founded the first Eyeglass guild and launched a full-scale investigation into this fascinating scientific topic. Especially in the Netherlands and Germany, which developed into centers for the manufacture of eyeglasses in the 14th and 15th centuries, this new industry quickly spread throughout Europe. Scientists were quickly able to make astonishing discoveries thanks to the development of optics study. In his early 17th century publications, Johannes Kepler developed geometric optics, producing the first accurate theories regarding the inner workings of the human retina, convex and concave lenses, as well as many other features of the light and astronomical events. With the efforts of René Descartes, Robert Hooke, Christian Huygens, and Isaac Newton, whose book “Opticks” was regarded as the greatest contribution to light research at the time, optic discoveries proceeded.
The evolution and advancement of humanity have been significantly influenced by light and the phenomena associated with it. Therefore, it is not surprising that optics was one of the first divisions of the natural sciences to develop. On the other hand, light, or a lack of it has had a tremendous impact on the evolution and diversification of life on earth. Therefore, it is not unexpected that nature is where optics was originally discovered and used.
From darkness to light the Light Switch Theory
For over three billion years, the only living things were bacteria, plankton, rudimentary algae, or at most, tiny creatures a few millimeters in length. Between 1,000 and 850 million years ago, the earliest organisms of a particular size, including sponges, jellyfish, and bilateria (the first animals with bilateral symmetry), first appeared. However, the Cambrian era (the Cambrian Period marks the beginning of the Paleozoic era, which is itself the beginning of the Phanerozoic eon) saw the emergence of the earliest animal optical instruments. Around 508 million years ago (Ma), the first reflector was discovered. Around 521 Ma, the first eyes with lenses appeared. A theory for the cause of evolution’s Big Bang the Cambrian explosion is developed in light of the evolution of eyesight. Between 520 and 515 Ma, a sudden and mysterious explosion of the range and variety of life forms occurred. There has never been such profusion, such exuberance, and such overwhelming diversity in so little time, within a million years, in the Earth’s history. The cause of the so-called “Cambrian explosion” the sudden “explosion” of life has been extensively studied, including by Charles Darwin. He saw it as an argument against his theory of natural selection. Darwin struggled to understand how life diversity could emerge so suddenly because natural selection emphasized small gradual changes over a long period of time. The Light Switch Theory attempts to fill this void.
All animals were soft-bodied and mostly worm-like before the Cambrian explosion event, as they had been for millions of years before that. However, many of the major animal groups found on Earth today independently evolved their hard body components for the first time during the Cambrian explosion. According to the Light Switch Theory, as soon as atmospheric changes during the Cambrian epoch enhanced the amount of light reaching Earth, sight quickly became advantageous for evolution. Because vision allowed predators to perceive, pursue, and kill their prey, predation was launched. Teeth and jaws, which aid in predation, quickly protruded. To combat the predators, defensive hard components like shells evolved in order to shield smaller animals. From this point on, the vision took center stage in evolution, giving rise to the eyes and reflective optics we see in modern nature.
The earliest optical gadgets in living creatures
Many different types of life have the potential to react to light, but only animals have eyes with mechanisms that divide environmental light according to its direction of origin. At its most basic, an eye might be made up of a few light-responsive receptors in a pigmented pit that casts shadows on some receptors from light coming from one direction and others from another. Even while no eyes have been found in Precambrian fossils, it is likely that eyes similar to these were present from the beginning of the evolution of the Bilateria, far before the Cambrian boom.
There are many different types of lenses found in eyes, such as the compound eyes of insects and the graded-refractive-index lenses seen in fish (Figure 2). By directing rays coming from various parts of the lens onto one focal plane the retina the latter avoids spherical aberration. The mirror-box lenses and parabolic reflectors of some crab eyes, as well as the telephoto lens component in a jumping spider eye, are examples of complicated optical processes found in some eyes. The bristle star’s micro-lens array, which consists of sparsely spaced, tiny convex lenses formed of calcite, is a more recent finding in the field of eyes. The bristle star lens is a light sensor that ascertains the specific lighting conditions in its environment rather than being a part of the entire visual system. It’s important to note that the trilobites, the sole other animal groups to have calcitic lenses, were also the first to have fully-focused eyes.
Figure 2. The size of the eyes needed for high-resolution vision would make compound eyes impracticable for huge animals. Credits Егор Камелев from Unsplash
The optical function of the human eyes
The eye of a human being is a stunningly intricate organ. It functions like a camera, gathering and concentrating light before converting it to an electrical signal that the brain interprets as images (Figure 3). The Nimrud lens, commonly known as the Layard lens, is a piece of rock crystal dating to the eighth century BC that was found by Austen Henry Layard in 1850 at the Assyrian palace of Nimrud in present-day Iraq. It might have been a piece of beautiful inlay, a magnifying glass, a burning glass for lighting fires by concentrating sunlight, or both. Credits: British Museum. However, it has a highly sophisticated retina instead of photographic film that detects light and uses dozens of different types of neurons to process the signals. The eye is so complicated that creationists and supporters of intelligent design have long cited it as a prime example of what they refer to as irreducible complexity, a system that cannot function without any of its components and thus cannot have evolved naturally from a more primitive form. Indeed, Charles Darwin acknowledged in On the Origin of Species that, it may appear absurd to believe that the eye was formed by natural selection. Despite the lack of evidence for intermediate forms at the time, Darwin’s theory of how the eye developed gradually through evolution was simple and straightforward.
Figure 3. A representation of the human eye; the most intriguing features from an optical perspective are the patterned iris diaphragm and the black middle circle, which is the pupil area. Foto de v2osk on Unsplash
It has remained challenging to find direct evidence. Whereas soft-tissue structures hardly ever become fossilized, which makes it difficult for researchers who study skeletal evolution to trace its transformation in the fossil record. Even when they do, the fossils do not retain nearly enough information to show how the architecture changed over time. However, by examining how the eye develops in developing embryos and comparing eye anatomy and genes across animals, biologists have recently made substantial progress in identifying the origin of the eye. The findings show that our form of eye, the type common to vertebrates, evolved from a basic light sensor for circadian (daily) and seasonal rhythms approximately 600 million years ago to a complex optical and neurological organ by 500 million years ago, taking shape in less than 100 million years.
Each of our eyes receives information-packed light from the objects around us. From one point in the image, rays begin to spread out in all directions, but we only see the ones that move in the direction of the eye and enter it through the pupil’s black hole. The cornea, the outer membrane in touch with the air, the aqueous humor, the crystalline lens, and the vitreous humour a clear, gelatinous material that fills the whole interior of the eye are all transparent tissues that the rays pass through on their route through the eye. The light beams are conveniently bent as they travel through the various bodily fluids and tissues to create a crisp image on the retina, a screen covered in biological sensors.
In the human eye, certain muscles contract when an item is close and the crystalline lens, the inner lens, thickens, increasing its curvature. Conversely, when an object is far away, the muscles relax and the lens becomes less curved. The retina is a screen made of photosensitive cells that is significantly more advanced than any photographic sensor that has ever been made by mankind. When ambient light is abundant, the human retina is equipped to distinguish colors thanks to its approximately 7 million cone cells, which are divided into three types and are each specifically designed to capture the three primary colors of blue, red, and green. When lighting conditions are poor, however, an additional 115 million rod cells enter the picture and provide grayscale data. In a straightforward analogy, the human eye would resemble a camera with more than 120 megapixels if each sensor cell represented a single information pixel. We can see in a variety of lighting settings, including bright sunlight and deep darkness, thanks to the rods and cones in our eyes. These biological photoreceptors connect to the brain, which is the ultimate architect of vision. The brain is a remarkably potent processor that combines such a vast amount of information in real-time that it renders even the most advanced cameras as low as a shoe shine.
Vision has been crucial to life ever since the Cambrian period. Today, eyes are present in more than 95% of multicellular creatures. You won’t find many animals in a field full of them since life is sight-adapted, unlike the primitive light sensors that existed before the Cambrian and couldn’t create images. The plethora of optical or photonic devices that can be found in nature today is another adaptation to vision. The origin of this is explained by the light switch hypothesis. According to what I can tell, a predator (a trilobite) was the first to evolve a useful visual system, and it was so successful that other animals had to evolve hard parts to live, resulting in the so-called Cambrian explosion. Today after millions of years, sentient life on earth (assuming it is a human) was able to find the characteristics and laws that govern visual phenomena, manipulating and profiting from them.
References
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- Artal, P., Benito, A. & Tabernero, J. The human eye is an example of robust optical design. J. Vis. 6, 1 (2006).
- Navarro, R. The Optical Design of the Human Eye: a Critical Review. J. Optom. 2, 3–18 (2009).
- Lamb, T. D. EVOLUTION OF THE EYE. Sci. Am. 305, 64–69 (2011).
- Parker, A. R. On the origin of optics. Opt. Laser Technol. 43, 323–329 (2011).
- Tanaka, G. ‘The Light-Switch Hypothesis’ and the Cambrian explosion. Fossils 16–30 (2012).
