Opening remarks Before embarking on a journey into the world of light

Chapter 1: Strange Waves of Light
We are so close to waves | Which way do waves move? | Let's name each and every part of the wave | Let's calculate the speed of the wave | What transmits light? | Light is both a wave and a particle
Chapter 2 Beyond the Visible Light: The Invisible Light
Strong Family, Gentle Family, Electromagnetic Family | Visible Light, Visible Light | Light Beyond Red | Light Beyond Violet
Chapter 3: Light traveling straight ahead, light reflecting, and light bending
Light travels in a straight line, but it also reflects | How do images enter the eye? | Light bends | Why do objects in water appear curved? | The refraction of light creates rainbow colors | Trapped light, using trapped light | Loading information into light, at the speed of light
Chapter 4: Bright Light, Dark Light, and Curving Light
When Waves Meet Waves | The Secret of the Rainbow Discovered Underfoot | Uncovering a 1.3 Billion-Year-Old Secret | Light Bends When They Meet
Chapter 5: A Colorful World Painted with Light
Eyes and Visual Cells | Cone Cells, Coloring the World | The First Way to Create Color: Mixing | The Second Way to Create Color: Absorbing | Reflecting Properly Is Pretty
Chapter 6: The Birth and Evolution of Light
The History of Electricity, the Light that Brightened Humanity's Night | The First Incandescent Light Bulb | The Fluorescent Light, the Trend of Electric Lighting | The Future of Electric Lighting, LED | The Light of Displays | Under What Light Will We Read This Book in the Future?
Chapter 7: Please Take Care of Our Universe
In Search of Heavenly Secrets | The Dance of Atomic and Molecule Dances | How Light Divides and Spectra | The Dance of Atoms is Inscribed in the Spectrum | Where Can Spectroscopy Be Used?
Chapter 8: A New World Revealed by the Science of Light
In Search of New Light | Carrying Information with Light | Networks in the Digital Age | Concluding the Journey
Conclusion Through light, to our origins and further afield

Additional Notes | References

From the early light that illuminated the night to the light that is now at the heart of modern physics.

Laser printers, supermarket barcode scanners, LASIK surgery, optical fiber networks, X-rays, astronomical telescopes… What do these all have in common? They are all the result of scientific technology that harnesses the properties of light.
The light we see is light that left the sun 8 minutes ago.
Light reaches Earth and becomes a source of energy.
Artificial light sources created by humans brightened the night in primitive times and gradually played a decisive role in expanding the scope of activity.
Light allows us to perceive objects and enjoy the benefits of numerous cutting-edge technologies.
Thanks to the optical communication network that connects the world, we have overcome the limitations of distance, and we are also finding clues to solving the most serious environmental problems facing the Earth, such as global warming and energy problems, in optical technology that utilizes light.

Light has always been, and will become even more, a key player in illuminating civilization.
So, what's the point of exploring the background and development path of optical technology, rather than simply reaping the sweet fruits of light-based technologies? When science and technology advance, most people tend to become bystanders.
The more advanced it becomes, the more it goes beyond the scope of understanding of the general public.
But some scientists still want to make science known to the public.
This is especially true for the growing generation.
Because, as people living in an age of technological advancement, we need to monitor whether scientific advancements are leading to the happiness of humanity.
Surveillance is an expression of the will not to be dragged along by scientific advancement.
In that sense, any citizen living in modern society needs to have at least a minimum level of knowledge about science.
The purpose of "Teenagers Who Know a Little About Light" is to provide teenagers with the basic knowledge to enable them to live as active citizens in an era dominated by science and technology, especially optical technology.



Light is the most powerful means of understanding the world.

Light, as it is dealt with in physics, is not easy to understand.
Not only are properties such as the movement of light difficult to intuitively understand, but there are also many aspects that have not been properly elucidated to date.
Although the theory of relativity and quantum mechanics are at the core of modern physics, they are notoriously difficult.
In that sense, 『10 Years Who Know a Little Light』 shines more and more the more you read it.
The author's effort to explain the properties of light using a rich and diverse vocabulary and by relating them to familiar situations creates a sense of piecing together a world puzzle, connecting with how the properties of light are used in modern science.

Let's say we have the knowledge that when light passes through a prism, it disperses into various colors that make up the rainbow.
What use is there? Few people have not pondered this question while studying science.
This book explains that the field of spectroscopy has developed by utilizing the property of light being dispersed into various colors, and that this can be used not only to explore the secrets of the distant past, but also to glimpse the possibility of expanding the stage of human activity into space.
Knowing the properties of light is essential for understanding modern society, armed with science and technology.

What would the world look like without light? Humans process a significant portion of external information through visual information.
Seeing, that is, sight, is the most powerful means by which we perceive the world.
Light plays the most crucial role here.
So modern science has been developing the most beautiful and natural-looking displays and developing artificial light sources.
By building an optical communication network that can send light in the desired direction, information can be delivered to every corner of the world.
Because we understand the nature of light, we can study the composition of the Sun's atmosphere without having to go to the Sun, and we can also study the environments of planets that are too far away to reach.
All of this is the result of photonics using light.
In short, light is the most powerful means by which we understand the world.



An example of utilizing the properties of light: optical communication networks

Can you even imagine a world without cell phones and the internet to search for the unknown? Such a situation would be nothing short of a "disaster."
The optical communication network that uses optical technology has played the most crucial role in sharing and disseminating information.
Today, vast stretches of optical fiber are laid across the Earth's ocean floor, and optical fiber plays a key role in making these networks work.
An optical fiber is a device designed to transmit light in a desired direction by utilizing the reflective property of light, but to allow the light to travel a long distance without being absorbed by the optical fiber.
The light that transmits information at this time is infrared light with a long wavelength.
Using this optical communication network, binary signals are constantly exchanged, allowing information to flow everywhere.
This has allowed the world to overcome many of its physical limitations.
That is why optical communication networks are also called ‘the blood vessels of humanity.’



Two examples of utilizing the properties of light: gravitational wave detection

The Nobel Prize in Physics can be said to be a barometer showing how science using light has developed.
The 2017 Nobel Prize in Physics went to three physicists (Kip Thorne, Rainer Weiss, and Barry Barish) for the detection of gravitational waves.
Gravitational waves are “tremors in spacetime” that occur when unimaginably massive objects, such as black holes, collide and merge (p. 95).
The gravitational waves detected in 2016 were created when two black holes merged 1.3 billion years ago. Their detection means, firstly, that they have proven Einstein's theory of general relativity, which he proposed over 100 years ago. Secondly, it means that we can now obtain accurate information about the space-time of the universe.
The detection of gravitational waves is based on a phenomenon called light interference.



Three examples of the properties of light, almost everything we encounter in everyday life.

The beautiful diffraction patterns created by light waves, the sacred stained glass windows of churches made up of the three primary colors of light, the rainbow that beautifully colors the sky through the refracted light, Wi-Fi and Bluetooth that allow people to communicate anytime and anywhere, GPS that can locate objects, X-rays that save people's lives, lasers used in treatment, and radio telescopes that explore the secrets of the universe - these are all phenomena or results created by the properties of light.
Even without looking for it, we find light by turning on a light on a dark night or by the faint light pouring in through a window at dawn.




Features of this book

The part about light in physics classes is difficult to understand intuitively.
The image of an object reflected in a mirror is formed as an image on the retina by reflecting light from the object, but people feel that the image of an object arrives at the brain in a straight line from the mirror.
The colors that people perceive are the result of the mixing or reflection of light of various wavelengths, but the process is not perceived.
Therefore, to understand light, we must learn a process that we have not actually experienced.
It is bound to be difficult to learn something you cannot experience.
This book faithfully explains the various properties of light—that is, light behaves as both a wave and a particle, travels straight but also bends, and disperses into various wavelengths—while also specifically introducing the intersection of these properties with modern optical technology.

Humanity has been constantly researching efficient artificial light sources, and one of the results is the laser.
Laser amplification technology has advanced to the point where nuclear fusion can be expected.
This is attracting attention as a clue to solving the most serious problems facing the Earth today: environmental pollution and global warming.
When light passes through a specific gas, some light passes through it and others is absorbed by it, depending on the wavelength.
Using this, humans can infer the composition of the atmosphere of the sun or other planets even if they have not visited them directly.
Rather than simply explaining the complex concepts of physics, it specifically describes how they are actually applied in science and technology.
It is also special that the history of the Nobel Prize in Physics is connected to the history of light, and several award cases are explained together with examples of advancements in optical technology.



Einstein's imagination: "If we could travel at the speed of light, what would light look like?"

There were scientists who stood at the starting line in the history of light.
They may have begun to see the light out of pure curiosity.
It is said that Einstein, who left behind the theory of relativity, the most important step in modern physics, used to ask this question.
'If you could travel at the speed of light, what would light look like?' Even scientists themselves might not have known what consequences this question would lead to.
I just clung to it persistently out of curiosity.
It is no exaggeration to say that we live off the fruits of this pure curiosity.

If it had not been for Wilhelm Röntgen's curiosity, we would never have discovered X-rays, which lie outside the ultraviolet region.
It was after this that X-rays began to save countless lives.
Without scientists observing vibrations and studying their properties, we would not be able to measure and communicate the risks when natural disasters like earthquakes or tsunamis strike.
If we hadn't known about the interference effects of light waves meeting each other, we wouldn't have had the amazing experience of measuring gravitational waves, the "tremors in spacetime" caused by a planetary collision 1.3 billion years ago.
The "Teenagers Who Know a Little About Science" series, which covers pure sciences such as physics, chemistry, and earth science, shows how interests that began without a purpose and without any idea of ​​what changes they might bring about can enrich the world and reveal secrets that have yet to be solved.



"Teenagers Who Know a Thing About Science": A Lively Forum for Scientific Debate That Takes Science to the Next Level

The '2015 Revised Curriculum' pursues an image of a human being who is independent, creative, and lives together.
Under this value system, we focus on strengthening basic literacy education in the humanities, social sciences, and science and technology, focusing on core concepts and principles for each subject, while also promoting integrated and convergent education across subjects.
In line with this educational trend of fostering future talent, Poolbit has planned a science series for youth that selects core concepts rather than focusing on the amount of knowledge, and clearly explains the principles behind them and how they can be applied.
A humanistic reflection that encourages questions and discussions on the three pillars of core, principle, and application is what middle school readers, field teachers, and parents want, and is the clear direction that the "Teenagers Who Know a Little About Science" series aims for in science studies.

So far, starting with No. 01, 『10 Things You Know About Artificial Intelligence』, which dissected the reality of artificial intelligence, a cutting-edge science and technology, point by point by combining it with realistic concerns, No. 02, 『10 Things You Know About Materials』, which explored the essence of the world filled with numerous colorful components, No. 03, 『10 Things You Know About Environment and Ecology』, which delved into environmental issues through eight easy consumption practices in daily life, No. 04, 『10 Things You Know About the Big Bang』, which covers cosmology, and No. 05, 『10 Things You Know About Light』, which talks about the various properties of light and the future of optical technology.
Following this, 『10 Things You Need to Know About Gravity』『10 Things You Need to Know About Elements』『10 Things You Need to Know About Electromagnetism』『10 Things You Need to Know About Genes』『10 Things You Need to Know About Future Energy』『10 Things You Need to Know About Climate Change』 etc. will cover the most basic and core areas of natural science, such as physics, chemistry, life science, and earth science.