Waves in Nothing

The sun is coming back north, and northerners starved for light and heat should be cheering for electromagnetic radiation. Yet "radiation" has become a kind of high-tech dirty word, calling up images of Chernobyl or fallout from bomb tests. In fact radiation, like fire, confers benefits far greater than its undeniable dangers.

Electromagnetic radiation includes X-rays and the dangerous gamma rays released by atomic reactions, but radio waves, television broadcasts, microwaves in and out of ovens, heat radiation and sunlight are also examples. This type of radiation is the only possible way of transmitting energy through a vacuum, and life as we know it could not exist without it. If the Earth could not radiate energy away into the near-vacuum of space, heat from radioactive elements would build up until the planet melted. Since the Earth can radiate surplus energy, its temperature would drop to absolute zero ( -460 degrees F) if it were not also receiving energy through space in the form of electromagnetic radiation from the sun.

Electromagnetic energy exists as waves, with an extremely wide range of wavelengths. Gamma rays, which are produced by atomic decay, have the shortest wavelengths. Next are X-rays, with wavelengths of around 1/250,000,000,000 inch to 1/25,000,000 inch. The wavelengths between X-rays and about 1/64,000 inch are called ultraviolet radiation. The longer wavelengths of ultraviolet radiation are responsible for suntans, sunburns, and skin cancer; the shorter wavelengths would be even more damaging. Fortunately, the atmosphere does a good job of protecting us from the small amounts of short ultraviolet and X-ray energy put out by the sun. (Added July 1996: It is, of course, the ozone in the atmosphere that is most important in filtering out the longer ultraviolet radiation; hence the concern about the ozone hole. Ordinary oxygen takes out much of the shortest ultraviolet.)

Of the longer wavelengths, those with wavelengths from 1/25 inch to several miles can be grouped as radio waves. The longest wavelengths in this range are used for long-range communications and navigation aids. Intermediate wavelengths are used for radio and television broadcasts, two-way radio communications, and some radars. The shortest wavelengths (microwaves) are used for radar, line-of sight communications, passive and active remote sensing, and microwave ovens.

Wavelengths shorter than microwaves but too long for our eyes to see (1/25 inch to 1/30,000 inch) are grouped as infrared. Objects at ordinary Earth temperatures emit infrared, and this is how the earth radiates surplus energy to space.

Finally, our eyes respond to the narrow band from 1/30,000 inch to 1/64,000 inch, which we call light. The wavelengths in this band are perceived as different colors, with 1/30,000 inch being red and 1/64,000 inch being violet. The sun's energy peaks in the visible light range, with some energy spilling over into the short infrared and long ultraviolet wavelengths. This solar energy is transformed by plants into food and fuel. (Oil, coal, and gas store energy captured from the sun by plants that lived millions of years ago.)

By the time you consider the usefulness of the short wave lengths in medicine and industry, electromagnetic radiation's benefits far outweigh the occasional problems it causes. So once again, as the wavelengths from 1/6,000 to 1/100,000 of an inch return to Alaska with the sun, three cheers for electromagnetic radiation!