Smart News | June 22, 2023

This Physicist Uses Drones to Create Giant Light Cones in the Desert

Evoking a key concept in relativity, Elliot McGucken traces out hourglass-like shapes in the sky that stretch as high as a seven-story building

A light cone above the coast of California

A three-to-four-minute exposure captures the light of a drone as it traces the shape of two cones in the sky along California's coast. Elliot McGucken Fine Art Photography

Will Sullivan

Daily Correspondent

Over the last couple of months, Elliot McGucken has traveled into the southern California wilderness late at night with a camera and a drone. He’s visited places like the Trona Pinnacles in the California Desert Conservation Area, where rocky spires tower as high as 140 feet above the ground. He’s also trekked to the Mobius Arch formation in the Alabama Hills at the base of the Sierra Nevada, surrounded by eroded peaks and rounded rocks.

McGucken, a photographer and trained physicist, hasn’t ventured to these sites to merely capture the landscape or image the moon and stars. He uses his drone to add something more to his photographs: giant cones of spiraling light. The bright, hourglass-like shapes, captured through three-to-four-minute long exposures, are artistic representations of a physics concept called a light cone.

“I’ve been fascinated by the light cone, because I don’t think it gets enough credit,” McGucken tells Smithsonian magazine. He hopes his project can evoke a sense of wonder in people and spark their curiosity.

“People don’t spend enough time looking at this and pondering this and kind of marveling at it,” he says.

A light cone in the night sky above a rock formation — A giant, spiraling double cone above the Alabama Hills rock formation in California. Elliot McGucken Fine Art Photography

Light cones, in short, represent how light moves through space over time. More specifically, they visualize the motion of light that radiates in all directions from a single point. The concept was first modeled by the German mathematician Hermann Minkowski in the early 20th century, and Albert Einstein later used the idea in his work with relativity.

Here’s how it works. Imagine turning on a light bulb that can shine infinitely in every direction. At the instant the bulb turns on, the light is only a small dot. But as time passes, the light shines outward, illuminating increasingly larger areas as it moves. A fraction of a second after the bulb has turned on, the light will encompass a small sphere around the light bulb. After another fraction of a second passes, the light has traveled farther, and it forms a larger sphere.

Light cones track the spread of light in two-dimensional space, emanating out in wider and wider circles around a central point. You could think of it like dropping a stone in pond. As time passes, ripples spread farther and farther across the surface of the water. In two dimensions, light from a bulb will fill increasingly larger circles as time goes by.

If you took each of these two-dimensional circles and stacked them on top of each other, with the smallest circle at the bottom and largest at the top, it would form a shape like an ice cream cone. In this way, the cone represents both space and time—at locations farther from the cone’s point, more time has passed since the bulb was lit.

A diagram of a light cone — A diagram of light cone from Albert Einstein's *The Meaning of Relativity*. 1922 Princeton University Press

But that’s only half of the light cone idea. A mirror image of a cone beneath the first one represents locations in the past, where light can travel from and reach you and your light bulb in the present. The narrow part of this upside-down cone represents moments in the more recent past that are located close to you—that’s because in order for light to reach you in a short amount of time, it must come from relatively nearby. The wider parts of that cone represent the more distant past—and for light to have reached you from those times, it would have had to originate farther away.

Minkowksi’s work with light cones and the relationship between time and space helped Albert Einstein develop the theory of general relativity, or the ideas surrounding how gravity influences both space and time.

While the concept of relativity might seem abstract, it actually matters in everyday life. If satellite clocks weren’t adjusted for relativity, our GPS systems couldn’t be accurate enough to be useful, McGucken says. Since satellites are far from Earth, they don’t feel as strong a tug from the planet’s gravity. As a result, time moves slightly faster for them than for a clock on the ground. They’re also orbiting the Earth at high speeds, which actually slows down time for them ever so slightly.

Even operating McGucken’s drone requires knowledge of relativity—its position is determined by GPS. In this way, the art project sets up a sort of meta premise: The drone’s traced-out light cone honors the theory of relativity, and it wouldn’t be possible to make without relativity existing in the first place.

“That’s kind of a fun thing that I didn’t really think about until after I was doing it,” McGucken says.

McGucken’s light cone artwork started with some 3D printing of the cones. But then, a few months ago, he got the idea of representing them with a drone—or, as he says, “painting with light.” His drone is pre-programmed to trace the shape of two, mirror-image cones on top of each other. It starts with the wide bottom of the lower cone before arriving in the middle and continuing upward to create the top spiral.

His cones are around 40 feet wide on average, and the two halves together span an average height of roughly 70 feet—about the size of a seven-story building. They look slightly different from the true, theorized light cones, which don’t spiral like McGucken’s do.

From the ground, the camera uses a long exposure to capture the traced-out light. Each shot takes around ten minutes in total, and McGucken says he’ll do a couple of takes in a row to make sure he’s gotten a good picture. He’ll also return to a site on several different nights to adjust his setup and improve his images.

On occasion, wind will push the drone slightly off its planned path. “The most perfect spirals are on the windless nights. And those are actually hard to find in the desert,” he says.

Beyond the ethereal cones, the images also capture the beauty of the surrounding landscape. In some shots, McGucken tries to align the diagonal edges of the cone with the diagonals on the rock formations below. And in many of his images, the stars appear as streaks in the night sky—an effect of the long-exposure technique.

He doesn’t necessarily have a single physics lesson that he wants to impart with his photographs. But he does hope they will make someone interested in learning more.

“The first thing you have to accomplish is a sense of beauty. You owe that to the viewer before you start giving them any sort of physics lecture,” he says. “I want people to see the desert landscape at night, and then see the light cone, and then start wondering, ‘What is that? What does it mean?’”