Light is one of the most fascinating and mysterious phenomena in nature. We use it for illumination, communication, exploration, and medicine. We know that light is an electromagnetic wave, as James Clerk Maxwell showed in 1865; and that it also behaves like quantum particles called photons, as Albert Einstein discovered in 1905. But the more we study light, the more we discover and the more we learn.

The classical view of light as a wave still reveals new science as light waves interact with artificial “metamaterials”; and we are still exploring light as a quantum particle. Both approaches provide ways to manipulate light that were once only science fiction. Here are five recent wonders.

Making Things Invisible with Light :

The magical invisibility rings and cloaks in fantasy stories reflect the ancient human dream of hiding things and people from sight. Invisibility also appears in science fiction, like Star Trek, where hostile Romulan spacecraft hide themselves with a cloaking device. This uses an idea from relativity, that strongly distorted spacetime makes light curve around the spacecraft as if it didn’t exist. Physicists don’t know how to do that yet, but the classical optics of light waves and light rays suggests another solution. We see an object as it interacts with incoming light. In principle, an invisibility cloak could intercept those incoming rays and bend or refract them into itself so they travel inside the cloak and emerge along their original paths.

An observer, seeing what looks like undisturbed light, would think nothing is there, just as flowing water smoothly splitting around a rock and then recombining gives no downstream indication of the rock. But to make light follow this complex path, the cloak needs to be made from a metamaterial.

INVISIBILITY CLOAK:

We see an object as it interacts with incoming light. In principle, an invisibility cloak could intercept those incoming rays and the observer, seeing what looks like undisturbed light, would think nothing is there. Commons. Researchers first tested this idea in 2006 with a rigid metamaterial cloak, a hollow cylinder whose wall held thousands of small structures that made microwaves traverse suitable paths within the wall. Placed around an opaque metal object, the cloak made the object nearly completely vanish under microwave radiation. Since then, researchers have made small inanimate objects and a fish, a cat, and a hand vanish under ordinary visible light, but only as seen over a narrow angle of view. Others have developed a flexible cloak that wraps around a small object to make it vanish, but only at one wavelength. Science can’t yet make a cloak that completely hides a person in ordinary light; but invisibility research is thriving and we’re approaching Harry Potter’s wondrous cloak. Moving Things with Light Like thrown rocks, photons carry momentum that they transfer to an object on impact.

This radiation pressure is why sunlight pushes comet tails away from the sun, and why it can propel a spacecraft. In 2010, the Japan Aerospace Exploration Agency (JAXA) launched IKAROS (Interplanetary Kite-craft Accelerated by Radiation of the Sun, honoring Icarus who flew near the sun in myth). Its thin, tennis court-sized polymer sail gathered solar photons, which collectively exerted a small force that steadily accelerated IKAROS. Six months and 300 million miles later, it arrived on target near Venus without using any fuel for propulsion.

Now JAXA and other space agencies are considering longer missions using bigger, more effective solar sails. We’re approaching Harry Potter’s wondrous cloak. Surprisingly, a light source can also pull an object toward itself, against the direction that the light propagates. Physicists have shown that within a specially shaped laser beam, the forward push of photons on a particle is dominated by a backward force due to the particle’s own electromagnetic response. The effect is strong enough to pull a microscopic object like a biological cell backward toward the laser. In 2023, however, a related experiment showed that a low-power laser could pull a comparatively big macroscopic object, 0.2 inch x 0.1 inch.

In the experiment, the researchers shot infrared light at the ITO. When the ITO became a mirror for a short time, the reflected infrared light remained in its original form. But when the ITO mirror was very briefly turned on and off twice in rapid succession, the reflected infrared light showed definitively that it had interfered with itself as a result of passing through not one but two time portals or slits. One observer has commented that this work could become a classic like the original double-slit experiment.

By extending that into time rather than space, the research offers a new way to explore “the only mystery.” The work also shows the feasibility of using metamaterials like ITO to control light in optical systems and quantum computers at ultrafast speeds. Catching Up with Light on a Bike If there is one physics fact that people know, it’s that light is the fastest thing in the universe, traveling at 186,000 miles/sec in vacuum.

Later, Hau topped this achievement by bringing light to a screeching halt, then later recovering it and sending it on its way. These results are breakthroughs in fundamental physics and could be useful as well, except for the need to work at temperatures near absolute zero. But since the original work, other researchers have slowed light in gases and solids at room temperature, making it possible to use slowed and stopped light in practical devices.

These are currently being developed, for example, to synchronize signals in fiber optic networks and to store digital data in computers. Both applications are important steps toward developing advanced telecommunications networks and quantum computers based entirely on light rather than conventional electronic chips.

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