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Colophon
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp iii-iii
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Frontmatter
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp i-ii
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RANDOM WALKS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 57-64
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Summary
Photons travel in vacuum following straight lines. Their eight-minute flight from the Sun to the surface of the Earth is a peaceful journey almost all the way through. Hundreds of kilometers before reaching the ground, though, they start facing several layers of obstacles. The upper atmosphere reflects the most energetic photons back into space. From the remaining photons, a portion is absorbed by some of the tens of molecules identified across the following layers of the atmosphere. The rest reach their destination on time, except for a few that may be still delayed in the next-to-last stop. Much like Ulysses in Homer's Odyssey, who spent ten years bouncing between islands and coasts to cross the few kilometers of Aegean waters from Troy to Ithaca, these last few photons undergo a random walk from molecule to molecule in the concluding layers of the atmosphere. Eventually they land, continuously and from all directions, filling with bright blue the eyes that look at the sky.
The above-described adventure of photons results in an inexhaustible source of information about the composition and behavior of atmospheric gases. The HITRAN (high resolution transmission molecular absorption) spectroscopic database, maintained and developed at the Harvard–Smithsonian Center for Astrophysics in Cambridge, Massachusetts, archives the spectral parameters (the identity card) of the molecules absorbing and scattering light in the sky. People working at HITRAN like to consider it as the genome project for molecules and their isotopic variants. HITRAN provides data to academia and industry around the world, aids in the remote sensing of other planets' atmospheres, and helps track the presence and concentration of polluting agents and allergens in the Earth's air.
Such analysis of absorption and scattering of light may be particularized for the detailed study of any diffusive medium. The specific study of the diffusion of light in human tissues is a resourceful method in medical sciences, where physiological features can be assessed non-invasively and often in real time.
ABOUT THE BOOk
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp x-xiv
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“The sun shone, having no alternative, on the nothing new.” Samuel Beckett's acclaimed opening words for Murphy appear to be somehow pessimistic. Yet actually, quite often, a distinctive control over light beams puts forward a path to the new. This book takes a glance over some of those paths.
Exploring the natural phenomena around us and across the Universe; pushing the limits of our understanding of Nature; and using the knowledge acquired to diagnose and cure disease, and to create devices and machines that make life safer, healthier, and more fulfilling is a program that many, throughout history, have found as captivating as compelling. Advancing such programs requires tools, which must be more and more sophisticated as the limits of knowledge move farther from our own scale and intuition. Really small or really large things, as well as really fast or really slow events, are particularly challenging, as neither our senses nor our ordinary gadgets are equipped to tackle them. We need powerful tools and technologies to enter such territories. The farther we aim to reach, the higher the performances that our toolkit must deliver.
Light is one of these wonderful tools. It is ubiquitous and universal, and can be outstandingly accurate and precise. During the past decades we have learnt not only how to generate and control light in exquisite ways – especially since the invention of the laser half a century ago – but also how to transmit it and display it in ways that used to be the realm of science fiction and novels.
As a result, light-based technologies are, literally, everywhere. And what is available today is just the beginning.
The book consists of sixteen chapters of the same length and structure, each addressing a particular scientific and technological challenge in which some of the multifaceted existing light–matter interactions take a leading role. Readers can go through the chapters following any order they want. Each chapter opens with a short story that aims at motivating a context in which the overall challenge to be addressed has an impact.
Contents
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp iv-v
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GENTLE
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 9-16
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Go – from the Japanese word igo, meaning “encircling game” – is a strategy board game that originated in China approximately 3500 years ago. The game starts with an empty grid set on a wooden board. Players then take turns to place black and white stones on the intersections of the crossing lines. The objective of each player is to capture the stones of the opponent. A stone – or chain of connected stones – is captured if all its four degrees of freedom (the four surrounding intersections) are occupied by an opponent's stones. Despite these simple rules, go is a game of extraordinary complexity and beauty. A player in any typical game among experts has an average of a few hundred choices per move, making strategies strongly tied to intuition, experience, and pattern recognition. The players' skills strengthen by learning to identify a certain balance between the territory they give away and the force they exert on the opponent. It is a gentle-strategy game.
The lack of skillfulness typically results in pushing the opponent's beads instead of encircling them. Successful encircling calls for a delicate, wise balance between force and territory, limiting and yielding, pushing and letting go. A suitable way to go: attack from the corners. Continue along the sides. Move into the center. Trap. The goal is to constrain the freedom of the opponent applying the minimum amount of force.
In Nature, a similar balance sustains the glide of a seagull on a current of air. The form of the wings separates the flow of air molecules so that moving air molecules passing underneath exert a lifting force larger than the downward pressure of those passing above. The resulting force is just enough to compensate gravity and keep the bird in a comfortable flight.
In spirit, a similar balance is the principle behind optical trapping. Photons can exert tiny – but observable – forces by exchanging momentum with very small particles. Without a good strategy, though, photons can only push.
RIDDLES
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 89-96
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A problem frowns, a riddle lifts an eyebrow, a paradox smiles: – X believes she is a hypochondriac. Is X a hypochondriac?
Define hypochondria as the unfounded belief of having a disease. Assume hypochondria is a disease. Then if X above is a hypochondriac, then X is not a hypochondriac. But if X is not a hypochondriac, then X is a hypochondriac.
There is something liberating in discovering flaws in rigid systems, as long as they don't threaten your own security. A paradox is a flaw on the rigid system of reasoning. Any formalization of reasoning can be pictured as a path to the top of a mountain. To answer a question, one has to climb to the right solution stepping on single rocks, which are intermediate states of certainty. A paradox is fun because it means bouncing forever between two rocks: it shows that the Mountain of Truth can be tricked. Although this is serious enough to deeply shake the foundations of mathematics, causing one of the greatest philosophical revolutions ever, for the layperson it is a guarantee that playing games on thought will never be over.
Paradoxes are not the only examples of exceptional climbing up the Mountain of Truth. There are questions with infinitely long paths of rocks, or with no path at all. There are questions with paths which, being finite, are so lengthy that it is not possible to reach the peak in trillions of years. If a given question is proved to have no answer, then one is allowed to devote efforts to more efficient tasks, but if a question has an answer and the problem is simply that all the time in a lifetime is not enough to reach the peak, then Mountain-of-Truth climbing deserves a revision. Classical Mountain-of-Truth climbing is characterized by the fact that one always steps on a single true rock at a time. To jump from one rock to another, one just has to give basic true/false answers. This finds a correspondence in classical physics, where things can be in only one place at a time.
SHARP
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 17-24
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Incisive, brilliant, discriminating, precise? Elementary: Sherlock Holmes. The master of observation and deduction, unmistakable in his cape, pipe, and magnifying glass, yet able to penetrate any layer of society when camouflaged in one of his thousands of disguises. Certainly not the tidiest man in his personal habits, but the most meticulous when dissecting a case, with an innate ability to single out guilt from innocence, discern minute details, avoid external bias, and operate at full power without drawing attention. A true detective of surgical methods. Not entirely fictional, for Sir Arthur Conan Doyle's inspiration for this character was his professor at the Edinburgh Medical School, the Scottish surgeon Dr. Joseph Bell – apparently, an extraordinary lecturer and physician, whose sharp eye and inference powers were frequently requested by the police in the toughest investigations.
During Conan Doyle's lifetime, especially during the last decades of the nineteenth century – while he still combined writing with medical practice – surgery became a wellestablished medical discipline. Two fundamental advances were involved: anesthesia and sterilization. In the 1840s, the discovery of ether and chloroform allowed doctors to overcome the barrier of pain, and surgeons were able to venture deeper, performing more elaborate operations. Long story short, in the 1860s, John Lister implemented sterilization for fighting infection, following the steps of the unfortunate Ignaz Semmelweis, and the groundbreaking experiments of Louis Pasteur, which led to the confirmation that infection was caused by microorganisms.
Modern surgery has continued to advance in the search for improved methods to fight pain and infection, while striving to minimize invasiveness, recovery time, and secondary effects. Instruments grew sharper and gentler in order to deal with smaller and more delicate objects. The advance of microscopy and computer-assisted manipulation now helps surgeons to go beyond the power of their eyes and hands to dissect and solve the most complex cases, sometimes hidden behind layers of tissue, as in the case of a blocked coronary artery or a leak of cerebrospinal fluid.
DISPLAYS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 65-72
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Vision strongly influences our perception. Examples are the McGurk effect, an auditory illusion where the visual component of speech clearly influences what a person hears; or the famous experiments conducted in 2001 by Brochet and Dubourdieu, involving 57 wine experts, in which every one of them failed to notice that it was actually a white wine with an odorless red dye what they were asked to rate as a red wine.
Further off senses, images enjoy the power of acting as a kind invitation, a call to mind, of more abstract ideas. In geometry, the most visual part of mathematics, the flow of reasoning can generally be followed by looking at images. Elsewhere in the sciences and the arts, production of explanatory, enlightning, summarizing pictures are often the basis of a successfull spread.
Currently, technology is working in optimal displays to make the power of vision even stronger.
Displays are indeed the material interface in which the invisible gets converted into the visible. They provide graphical interpretations of realities beyond the capacity of our senses. For example, most information in the non-visible regions of the spectrum, from the gamma and X-ray to the radiowave, is translated into the visible, incorporating the nanoworld and the astronomical world – from the ultra-small and the ultra-large, and from the ultra-fast and the ultra-slow – into human-scale perception. Displaying artistic images of phenomena that are not encountered in the macroscopic world, such as the operation of the intra-cellular molecular machinery, opens the imagination to a whole new world.
In a connected world, where technology struggles every day to store and transmit bigger, faster loads of information, within a knowledge-based society depending on its capacity of aquiring, integrating, and distributing such information, the massive and global wiring of data might be rendered incomplete without an appropriate canvas to display it at the other side.
A good canvas does not necessarily imply a high resolution, as the power of images does not always lie in being an exact representation of reality.
ACKNOWLEDGMENTS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp ix-ix
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VIRUS ATTACK
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 33-40
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In classical science fiction, alien attacks are perpetrated by oddly shaped creatures from outer space. Since the turn of the century, the genre has taken a more disturbing turn: invaders are earthly viruses. Although fictional, these new plots are based on a threat already experienced by a reliable majority: influenza, a well-known virus as small as 100 nm, infects millions of people every year, spreading the flu worldwide via airborne or direct transmission.
One of these fictional plots could feature Sarah, a young virologist facing the spread of an unknown virus threatening humanity. After a first observation of the symptoms and the evolution of patients, she sits at the microscope to focus on virus–cell interactions. Such interactions are fundamental to initiate an infection, since viruses need the machinery of the cell to be replicated and expressed.
Hers is a first-class standard microscope. It has the best components and offers images of the best possible resolution, but it is limited by the basic laws of light ray transmission. These are the same principles that explain rainbows and lenses, and were already beautifully summarized by Pierre Fermat in The Principle of Least Time: “Out of all the possible paths that light might take to go from one point to another, it takes the path that requires the shortest time.” Since Fermat, scientists have learnt that this principle is not completely general, but they have put forward modern refined versions that are.
When Sarah switches on the white lamp under the sample dish, the rays take Fermat's path, bending and refracting as they travel through different mediums in a labyrinth of crystal lenses, air, and mirrors. As a result, a greyish image of deformed cells reaches her eyes, indicating the infection is on course. She needs to understand how the virus is attacking; otherwise she will not be able to find a way to block or divert its maneuvers before every human dies. However, the image of the cells, an amalgam of indistinct moving grey shapes, does not give enough contrast to clearly identify the agents involved in the invasion.
NEW MATERIALS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 97-104
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The term “material world” refers in some contexts to the limitations of our will, the wall on which ideas crash to become just reality. And yet materials are – with all their imperfections – one of the ultimate fabrics for testing our thoughts. Fortunately, between the world of pure ideas and the actual material reality, there exists an exciting third region: the region of possibilities. This region is occupied by materials not forbidden by Nature that, however, do not actually occur (or occur very rarely). It contains everything we can soundly think of, but that is too odd as to have been inspected by Nature. A family of such entities is formed by what is termed “metamaterials.”
Optical metamaterials are man-made materials whose peculiar properties emerge from an artificial inner structure, carefully crafted at the nanoscale. It is possible (yet not easy) to produce materials whose fine structure tricks visible light to bend in unconventional (yet not impossible) ways. These severe alterations of the refraction properties of a material might produce supermagnifying lenses – with enough power to see directly a DNA chain – or even guide the trajectory of light around an object and render it invisible: light would illuminate the metamaterial covering the object and travel along it to emerge to our eyes in the same direction and carrying the same information it had prior to illumination. No reflection, no absorption: a true invisibility cloak.
Such response of light to structure is possible because light is an electromagnetic wave. Indeed light, as described by Maxwell's laws, consists of an electric field and a magnetic field whose spatiotemporal variations are related to each other, to their sources, and to the characteristics of the medium through which it propagates. If the “tricks” introduced in the structure of the material are smaller than the wavelength of light, then, although microscopically the passage of light through the material is extremely intricate, macroscopically it can be described in terms of the new characteristics of the effective medium, that turn out to be extraordinary. Invisibility cloaks and supermagnifying lenses, although amazing, are still in their infancy.
FOCUS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 25-32
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Focus is the principle behind vision. First, attention is focused on an object. Then a lens in the eye collects and focuses onto the retina (the screen of the eye) the light reflected or emitted by every point of the selected object. Finally, the information thus gathered is processed by the brain to construct a meaningful image.
In order to offer a distinct, significant, and almost instantaneous image of the world around us, the brain is obliged to focus on a narrow subset of relevant information. The input provided by our senses is selectively picked out, since processing the whole set of data would exceed the brain's computational capacity. (That might explain why evolution did not burden us with the power of microscopic vision: it would mean way too much information to process!)
To see small details beyond the limits reached by evolution, the aid of more-powerful tools is needed. Larger and stronger lenses in microscopes overcome the capacity of the human eye's lenses to collect and separately focus on the screen the light that arrives from two very near points of the sample. As a result, features of a structure indiscernible to the naked eye appear clearly differentiated. However, focus (and hence vision) is limited by a fundamental fact: light is a wave.
The wavelength of light involved in vision is approximately 500 nm. Points spaced apart by 200–300 nm cannot be distinguished by any conventional lens, for diffraction will cause two overlapping blurred spots instead of two well-differentiated image points. This fundamental limit for resolution is known as the diffraction limit of light. Scientists are currently busy trying to beat it using a variety of tricks, including the use of certain exceptional materials – metamaterials – to fabricate the future so-called super-lenses. However, current technology can already achieve an extraordinary control of the interaction of light and matter at the nanoscale, providing a set of alternative methods to image details under the diffraction limit of light. These techniques constitute the field of super-resolution microscopy.
COLD
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 1-8
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In the nineteenth century it was discovered that matter could not get colder than –273.15 degrees in the Celsius scale. A new temperature scale named Kelvin – after physicist William Thomson, Lord Kelvin – renumbered Celsius to assign zero to that newfound lower bound. Zero degrees Kelvin corresponds to the absolute zero of temperature, the absolute cold.
At the absolute zero all motion ceases to exist. The random movement of the microscopic constituents of matter ceases, and every degree of freedom remains frozen and under control. This is certainly not a pleasant place to be, but those are the idyllic conditions for errorless machine performance, in which computers, precision instruments, compasses, and diagnosis tools will work unaffected by the detrimental effects of thermal noise.
As appealing as it seems, the absolute zero is unreachable. Even in deep space, the background radiation filling the whole Universe since the Big Bang “keeps the vibe” at 3 K. If you were lucky enough to get to some interstellar objects made of expanding gases, like the Boomerang nebula, you could get cooler than that and drop to 1 K. Indeed, cooling by expansion of gases is the principle behind freezers and air conditioning, and it also explains why spray deodorants are so cold. The principle was discovered (again) by Lord Kelvin and had a central role in the development of thermodynamics, the physics of heat and cold. Learning to direct heat pushed steam trains forward while schemes to procure cold revolutionized the industry and commerce of food and products. At a more fundamental level, it propelled low-temperature labs worldwide into a hectic race to get closer and closer to the unreachable absolute zero. This race holds the key to understanding why we are now reaching temperatures of only millionths of billionths of a degree (and dropping).
In 1908, the physicist Heike Kamerlingh Onnes got himself a prominent place in the competition, achieving a record temperature of 2.4 K with the liquefaction of helium. However, Onnes was not interested in the record itself, rather his motivation was confirming the existing theories about the behavior of metals at very low temperatures. He did not, however, find what he expected.
The Wonders of Light
- Marta García-Matos, Lluís Torner
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- Published online:
- 05 July 2015
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- 18 June 2015
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Discover the spectacular power of light with this visually stunning celebration of the multitude of ways in which light-based technology has shaped our society. Be inspired by state-of-the-art science: sixteen beautiful, straightforward chapters demonstrate the science behind the fascinating and surprising ways in which light can be harnessed and used, from displays, solar cells and the Internet to advanced quantum technologies. Be dazzled by brilliant color: dramatic design and radiant color illustrations bring cutting-edge science and groundbreaking innovations to life, clearly explaining the fundamental principles behind them. Be part of something bigger: published in association with the Institute of Photonic Sciences (ICFO) to celebrate the 2015 UNESCO International Year of Light, it is perfect for anyone interested in the frontiers of science, engineering or medicine, and in the phenomenal technological advances that have been made possible by human innovation.
LIGHTING
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 113-120
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A steady light for reading in bed and keeping moving shadows at bay. Neons and LEDs fused with the city landscape. Candles on table-tops beside theaters. This is life after sunset. For many people growing up today, it is hard to grasp what it is like living without lightbulbs. The major impact of lighting technologies is directly addressed on their way and their quality of life. Besides enabling basic tasks, these technologies afford people the mere aesthetic pleasure of being surrounded by a particular play of light, one that they can design and control. In order to celebrate the ability to shape atmospheres with light, let's bring up the eloquence of three famous light-shaped scenes.
Gaslight (George Cukor, 1944) – life before electricity. London, late 1800s. Paula Alquist, a young woman recently married, starts to believe that she is losing her mind. Missing objects, fading lights, a number of minute details around her start changing, apparently unnoticed by others. After a bright night at the theater, Paula arrives home reassured. She's undressing when one of the gaslights in the room starts fading again. Her face turns from liveliness to suspicion and then panic. As the lights fade, and amidst the increasing shadows, she seems to bid farewell to the lights of her own sanity.
Rear Window (Alfred Hitchcock, 1955) – the lightbulb. The whole movie looks like a tribute to optics. The hero of the story, J. B. Jeffries, is a photojournalist, with the walls of his austere apartment in the Village covered with many of his award-winning photographs. His telephoto lens got him into the drama and the lights of his flash gave him a way out, blinding the murderer he helped to unveil. But it was a lightbulb (three, to be precise) that brought us here. While sleeping by the rear window, in almost complete darkness, a shadow approaches Jeff's face.
FAST
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 49-56
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Time is measured by changes, e.g. heartbeats count instants, moving shadows over a landscape mark the hours, and the births and deaths of our loved ones evidence the passing of the years. Periods longer than a lifetime are increasingly difficult to properly accommodate in our mental space. Indeed, while we describe art movements in terms of centuries, and millennia might give a framework to the duration of a civilization, a block of hundreds of thousands of years lies beyond the magnitude of our imagination. We need tangible changes to understand (how much) time passes. For this reason, when a paleontologist explains that 3.5 billion years elapsed between the first signs of life on Earth and the appearance of the Homo sapiens, we allow our mind to open to a new unit of time.
Similarly, it is difficult to grasp time blocks that are shorter than a heartbeat. Anything happening in less than a thousandth of a second falls under the wide label of “very fast.” But, how many degrees of “fast” are there? The flapping of a bee's wings, the scattering of the pieces of an exploding balloon, the functioning of modern chips, each of these processes is a thousand times faster than the previous, but all are equally indiscernible to our eye–brain system, which is limited to less than a few dozen images per second. However, there is a way of introducing ourselves as natural observers of the super-fast: splitting the whole process into still pictures. Each shot needs to record the entrance of light during a short-enough lapse of time, otherwise we would get a blurred image. Shots, moreover, should come up at a tuned pace, otherwise we would miss some relevant steps while the light is off. A stroboscopic lamp, for instance, with flashes of microseconds shooting at intervals of hundredths of a second, offers a clear sequence of the trajectory of an object as fast as a flying bullet.
CONNECTED
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 05 July 2015
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- 18 June 2015, pp 73-80
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August in a small Mediterranean village. Too hot to leave the shade of the vines and fig trees in the courtyard, the day goes by reading, chewing fruits, playing cards. Two hours after sunset, it's time to leave for the fields and listen to the crickets. A remote memory from childhood appears: somebody's grandfather is explaining a story, an old rural formula to judge the air's temperature from the frequency of the crickets’ song. A sudden jolt of restlessness. Could that be true? Oh, never mind. We're lost, on holidays, in the middle of nowhere; sitting over subterranean water streams, among soft hills, under the stars. Only time comes along. Over three hours, according to the smartphone, which besides such information displays several apps to measure the air's temperature from the crickets' song. Apparently, the phone did not forget about that brief inquisitive moment a few hours ago. It's the first event of the day that happens fast.
Connected and immediate. The sign of our times involves an overwhelming flow of information from long-distance sources, primarily supported by optical fiber technology. A large part of the flow of information started leaving the saturated radio and microwave frequencies years ago. Almost all long-haul telephony and data communication today is efficiently packed into near-infrared light travelling on glass fibers. But, why light?
The very basic principle is simple. The frequency of the electromagnetic waves in the optical range is much higher than that of radio and microwaves, meaning that in a second there are more wave peaks to modulate for the encoding of information. Therefore, more ones and zeros – the alphabet of digital information – can be packed in less time.
Notwithstanding how simple the basic principle might seem, its practical implementation for the accurate transmission of information over long distances represents a serious challenge.
Alexander Graham Bell managed to send voice and other sounds encoded in a beam of sunlight. He called his invention the photophone. Until his death, he considered the prospects of the photophone to be more promising even than those of the telephone. And he has been proved right.
OPTOGENETICS
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 18 June 2015, pp 41-48
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He had no acquaintances at the party, and was not really an extrovert. The food was not tasty, the music insipid, and thus – forced to stay by external circumstances, and not wanting to give the impression of being idle – he turned to the single occupation he found worth trying: looking at people's behavior. How they chose to dress, what they chose to eat, where they chose to sit. It was entertaining – just entertaining, he was aware he would probably miss in all his conclusions – to try to discover their motivations, the root of their choices. Well… as if such thing as having a choice ever existed. He smiled in amusement thinking about Buridan's ass.
Buridan's ass is a thought experiment, dating back to medieval times, devised precisely to discuss whether a choice is always based on a rational decision. It presents an ass, equally thirsty and hungry, and equally distanced from a pile of hay and a bucket of water. Since the animal cannot find a reason to prefer one option to the other, unable to take action, he dies, of both hunger and thirst. The thought experiment, that exposes the complex nature of free will by reducing its assumption to an absurd situation, is framed in a (perhaps endless) discussion that for centuries was the battleground of philosophers, now joined by neuroscientists.
For an experimental neuroscientist, analyzing behavior is a phenomenal task. The patterns behind choices and actions are woven up from tens of millions of interconnected neurons, whose firing activity takes place in a millisecond timescale. To understand in full any of those events, to lay any causal connection between them, it is necessary to have certain control of the neuronal activity, exciting and inhibiting it on demand. An example of an external tool for such control is the use of electrodes, but those may cause unintentional firing in the surroundings of the targeted neuron. Luckily for researchers, there exist algae and bacteria that find in sunlight the reason to excite or inhibit their behavior.
SENSING
- Marta García-Matos, Lluís Torner
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- The Wonders of Light
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- 18 June 2015, pp 121-129
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The different information channels that keep the human body in contact with the environment are traditionally grouped into five senses: taste, smell, touch, hearing, and sight. Taste and smell are mediated by chemical reactions at the nose and mouth; touch includes all the data gathered at diverse skin receptors: texture, temperature, pressure, humidity; hearing results from a mechanical process in the tympanum; and sight involves the interaction of light with the eye. However mediated through independent physical phenomena, human senses are not completely isolated from each other. They contribute to perception as an active team led by the brain to furnish every person with their own notion of what lies ahead.
In front of a coffee cup, senses complement, influence, and even compete with each other, to offer a full and personal impression of the coffee-drinking experience. Taste and smell lead to the flavor appreciation under a mutual influence. Touch and hearing may eventually supply conclusive details about the porcelain, complementing the visual inspection of the cup, which, in turn, exerts a non-negligible dominance on taste. Further connections, in every way more mysterious, are revealed by the synesthetic condition of some hypothetical individuals to whom the coffee's aroma might sound like an Elgar march.
Synesthesia is a peculiarity in perception that occurs when a stimulus over one sensorial channel triggers the perception of a different sense. It grounds the basis of some artificial approaches to sensing, since it implies the possibility of deliberately causing a sensorial impression without a direct stimulus. Certain sensorial impairments, like color-blindness, may be partially overcome by means of an implanted device that transduces the frequency of light corresponding to each color into a different sound frequency. As a result, colors, the notes of light, can be distinctively heard.
A beam of light has physical properties other than its color; like intensity, direction of propagation, or polarization. These properties may be affected in the interaction of light with different objects, revealing in the process diverse characteristics of such objects.