Sometimes it is easy to take nature for granted. The air we breathe, the water we drink, and the soil we step upon are so commonplace that we rarely give them much thought. Light seems another one of those things.
Therefore, the United Nations' declaration that 2015 is the International Year of Light might seem at first like raising a glass to cold water. After all, the Earth has been bathed in light since its birth. However, only relatively recently have we developed the ability to tame light in its visible and invisible forms.
This year is the 150th anniversary of a key turning point in the science of light.
In 1865, Scottish physicist James Clerk Maxwell published a remarkable paper showing that light is the radiant offspring of electricity and magnetism. He showed how those two natural forces, once thought independent, were in fact married through a set of four simple mathematical relationships.
Maxwell's equations match the known speed of light and predict that it comes not just in different colors but also in a spectrum of invisible frequencies - now known as radio waves, microwaves, and so forth.
Relaying a radio signal turns out to be as simple as jiggling a charge up and down in a transmitting antenna, generating waves that travel through space and jostle charges in receiving antennas. Attach a microphone at the transmitting end and a radio set and speaker at the receiving end to create light-speed communication.
Consequently it was less than half-a-century after Maxwell's discovery that Guglielmo Marconi sent the first radio transmission across the Atlantic Ocean, developed a means of continuous relay, and the age of wireless communications began.
The International Year of Light commemorates other key anniversaries.
For example, in 1905 Einstein developed his Nobel Prize-winning theory of the photoelectric effect, which later found use in digital cameras. The same year, he demonstrated in his special theory of relativity how the velocity of light serves as the ultimate speed limit. Nothing in nature can move faster.
The scientific community is also celebrating the centenary of Einstein's general theory of relativity, which mainly has to do with gravity but offers a startling prediction that light bends near massive objects such as the sun. When this was confirmed during the 1919 solar eclipse, Einstein became world famous.
Light offers a way of probing the heavens and reaching back into the deep cosmic past. Astronomical observations by Edwin Hubble, coupled with Einstein's theories, indicated that the universe is expanding and was once much smaller. Theorists surmised that it was born in a hot big bang. The clincher was relic radiation, first observed by Arno Penzias and Robert Wilson in the early 1960s with a horn antenna in Holmdel, N.J. The radio hiss they found beautifully matched predictions for light cooled down from the Big Bang due to billions of years of cosmic expansion. A number of satellite missions since then have mapped out the cosmic background radiation with greater and greater precision, opening a window to the state of the early universe.
By sad coincidence, on Jan. 27, Charles H. Townes, the inventor of the laser (originally known as the maser), died at the age of 99. Townes' invention harnessed light in unprecedented ways, leading to an extraordinary range of applications that have improved the quality of life considerably.
Invasive surgery that used to require the sharp blade of a scalpel and led to many weeks of healing and perhaps scarring now takes place precisely and seamlessly through laser techniques. Lasers have improved vision, pulverized kidney stones, removed blemishes, and served a variety of other medical and dental purposes. Through fiber optics they have revolutionized communications. Compact discs are but one example of their use in data storage. And we can thank them for bar-code scanners, which have led (theoretically at least) to speedier checkout lines.
The harnessing of light's power offers much cause for optimism. Theoretical constructs, such as Maxwell's and Einstein's, offer the promise of dramatically improving our lives in unforeseen ways. Light has existed since the dawn of time, but science is only now beginning to realize its true potential.