In the beginning, God said, “Let there be light!” And there was light.

But what was light?

Perhaps light is the source of all matter in the universe. Medieval philosopher Robert Grosseteste imagined the first pinprick of God’s created light radiating out in all directions until it reached the limits of the universe, then rebounding back upon itself over and over, leaving thick substance in its wake like layers of paint. Though Grosseteste’s De Luce is certainly less numerical and more worshipful than modern cosmology, there are some striking similarities. The zig-zagging motion of light through chloroplasts, moreover, powers the formation of all organic matter.

Perhaps light is the great alchemist, which does not form but transforms matter, as mud to gold. In Sonnet 33, Shakespeare depicts the morning sun

            Kissing with golden face the meadows green,
            Gilding pale streams with heavenly alchemy…

In Sonnet 114, he wonders if the eye’s inner light has power

            To make of monsters and things indigest
            Such cherubins as your sweet self resemble,
            Creating every bad a perfect best
            As fast as objects to his beams assemble?

Though our eyes may not send out beams of light—as Shakespeare and his contemporaries believed—the art of photography uses light to beautify the most common things, sometimes by simply focusing our attention. While film photography involves a kind of chemical transformation, light can also perform “transmutation,” as the alchemists called it: at the right frequency, a ray of light can change the identity of an atomic nucleus.

All this is what light does. In 1873, James Clerk Maxwell translated the magic of electricity and magnetism into mathematical language and revealed a thrilling clue as to what light is.

If it should be found that the velocity of propagation of electromagnetic disturbances is the same as the velocity of light…we shall have strong reasons for believing that light is an electromagnetic phenomenon… (A Treatise on Electricity and Magnetism, Vol. II, 382)

He’s being coy—this is exactly what he found, and he was right. Light travels at a constant speed of 186,000 miles per second, the same as the speed of an electromagnetic field in the form of a wave. Light is electromagnetism.

So, then, what is electromagnetism? My dad says I asked him that question when I was four, crawling onto his lap as if asking for a bedtime story. For the next 16 years, I continued to ask it of one science teacher after another. The more I learned, however, the more the answers baffled me. On the one hand, light must be a wave: in the decades before Maxwell’s discovery, various experiments showed that beams of light diffract and interfere like ripples of water. Since waves have to move through a medium—waves are, by definition, the oscillation of a medium—the wave nature of light meant that there must be some universal medium, imperceptible but ubiquitous from the surface of earth to the edges of space. This “luminiferous ether” was not only essential for Maxwell’s equating light and electromagnetic waves; it was how he believed an infinite Creator could shape and direct the finite material universe. [1] Yet after Maxwell’s death, the ether hypothesis failed over and over in increasingly precise experiments, making its existence less and less plausible. Even worse, further experiments at the turn of the 20^th century revealed cases where light acts much more like particles than waves.

Is light a wave or a particle? Both? Modern physics says it’s neither, which seems worst of all. Contemporary physical theories of light like quantum optics are pure math. These mathematical theories bridge the gap between wave and particle properties, but at the cost of intuitive comprehensibility. Light is now just numbers and that tiny little letter c, celeritas, the speed of light. A constant without content.