Name: Light
Rating: 3.7 (21 reviews)
Author: Bruce Watson

What’s in it for me? Be enlightened by the wondrous world of light.

From the dawn of humankind, light has been a source of wonder, appearing in stories of creation and even being worshipped like a god. Light also developed into a source of philosophical inquiry, creative fuel, and scientific struggle – resulting in brilliant art and significant discoveries.

In these blinks you’ll be guided through the fascinating story of figuring out what light is and what light can be used for, from illuminating cathedrals to forming one of the centerpieces of the scientific revolution.

You’ll also learn

what vomit, egg and the Book of Genesis have to do with light;
why ordinary mirrors have been viewed as divine; and
how light is at the center of the most influential experiment in modern physics.

Light has been an essential and influential phenomenon since the beginnings of humanity.

The early humans didn’t study light – they worshiped it. In fact, as light crept across a continent each day, it was invariably met with reverence and awe.

So, it’s not surprising that light is a key player in lots of creation myths. In the Finnish creation story, The Kalevala, an egg cracks open, its yolk becoming the sun and its white the moon.

Or consider the Zuni Native American myth in which earth’s first people emerged from a dark underworld into glorious light. Then there are the Bushongo tribesmen of the Congo, who describe the god Bumba, a deity who vomited up the sun. As the sunlight spread, the earth’s primordial waters dried up and land began to surface.

And finally, there’s the Book of Genesis, in which God says “let there be light.”

So, light is essential to people all over the world and it was one of the first topics studied by ancient philosophers. Greek philosophers like Empedocles asked whether light came from an object or the eye that was seeing it. And in the fifth century BC, the philosopher Leucippus asserted that all objects emitted razor-thin light particles.

Following this claim, Euclid and Ptolemy were some of the first people to study light in a laboratory setting, observing its reflection in flat and bent mirrors. From these studies, Euclid discovered that the angle at which light entered a mirrored plane was equal to the angle at which it was reflected. And Ptolemy figured out how curved mirrors interacted with light.

But despite these experiments, nobody knew what light actually was.

Because light remained a complete mystery, it became for many religions a symbol of all that is holy. For example, the Old Testament used light as a metaphor for God in a couple of ways:

On Mount Sinai, Moses encountered the brightly burning bush from which God spoke to him. Not only that, but every sacred person in the biblical story is depicted with an aura of light that makes them glow.

Light became a divine religious force, as well as the site of artistic mastery.

If you know some Arabic, you might know that the word manara means lighthouse or “place of light." It’s from this word that the minaret, the tower from which a muezzin calls Muslims to prayer, gets its name.

That’s because light is a divine force in Islam. The Qur’an says that God will lead the faithful “from darkness to the light.” It also says that “He will bestow on you a light to walk in,” and “the man from whom God withholds His light shall find no light at all.”

Light was explored in the laboratory and then served as inspiration for artists of all kinds.

As the Renaissance came to a close, European countries began making significant developments in the natural sciences. It was during this period that followed in the seventeenth and eighteenth centuries, now known as the scientific revolution, that the empirical investigation of light began in earnest.

One of the first people to study light scientifically at this time was Johannes Kepler. In 1604 he published a treatise on optics in which he described a fundamental law of light. He said that the intensity of light weakened with the square of the distance from which it was observed. So if you move a candle ten feet away, you perceive its light to be one-hundredth as bright as it was when you were standing right next to it.

The wave theory of light was widely adopted in the nineteenth century and the first electric light was generated.

So, light was garnering scientific attention and inspiring great works of art, but at the beginning of the nineteenth century, it was still poorly understood. In fact, all that was really known was how to calculate the angle at which light deflected as well as its approximate speed, that it broke down into colors and was composed of particles – or was it waves?

Luckily, a new generation of students emerged to investigate further. In the early nineteenth century, evidence was found to support the wave theory of light. It was all thanks to the English scientist Thomas Young, who, in 1802, devised what’s now known as “Young’s experiment," a test that’s been called the single most influential experiment in modern physics.

Einstein transformed the theory of light and used it to make a profound conclusion.

At the end of the nineteenth century, the German physicist Albert A. Michelson made the foolhardy claim that the potential for new discoveries in the physical sciences was extremely slim. But we all know that great discoveries continued to be made and many of them led to Einstein’s description of light as quanta.

In the early twentieth century, scientists were still trying to confirm if light was made of particles or waves, when, in 1905, Albert Einstein offered another description – quanta, or packets of energy.

Key ideas in Light