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CHAPTER 1
Of Turtles, Cows, Mice, and Men
The electromagnetic spectrum
What we perceive with our eyes is but a tiny fraction of reality. This tiny fraction of reality — what's known as visible light — occupies less than one percent of the EM spectrum. The EM spectrum is the range of wavelengths over which EM radiation extends. What we refer to as "light" is simply that portion of the EM spectrum that the human eye can detect, ranging from violet (with a wavelength of 400 nanometers [nm]) at one end to red (with a wavelength of 700 nm) at the other end. We only have to look at a rainbow in the sky, or see light pass through a prism, to know that the colors between violet and red consist of indigo, blue, green, yellow, and orange. This gives us a total of seven colors, each with its own wavelength.
The Electromagnetic Spectrum. Image courtesy of NASA.
Often we use the terms "ultraviolet" and "infrared" without truly knowing what they mean. Of course, the human eye cannot perceive either, since they lie outside the visible spectrum. "Ultra" means "beyond the range of," while "infra" means "below." Ultraviolet radiation is that portion of the EM spectrum beyond violet — namely, between violet and X-rays (ranging from 400 nm to 10 nm). Infrared radiation, which is synonymous with heat, exists below the red end of the spectrum — namely, between red and microwaves (ranging from 700 nm to 1 mm). The EM spectrum extends even further in both directions, encompassing, in addition to the above, radio waves, microwaves, extremely low frequency (ELF) waves, and gamma rays.
Wavelength and frequency are inversely proportional: the bigger the wavelength, the lower the frequency; the smaller the wavelength, the higher the frequency. If EM waves were animals, ELF waves would be the dinosaurs of the EM spectrum, with wavelengths up to thousands of kilometers. One natural source of ELF waves is lightning. Because they can penetrate sea water to depths of hundreds of kilometers, ELF waves are used by the military for radio communication with submerged submarines. Shorter waves lack this ability — they are absorbed by the conductive sea water. ELF waves can travel long distances without appreciable attenuation, in the same way a charging Triceratops can bust through your house, and then through your neighbor's house, and still keep going.
The difference between ionizing and non-ionizing radiation
The EM spectrum is divided into ionizing radiation and nonionizing radiation, a division that occurs in the ultraviolet range. Basically, the non-ionizing part of the spectrum encompasses ELF waves, radio waves, microwaves, infrared, the visible spectrum, and part of the ultraviolet portion, while the ionizing part of the spectrum encompasses the rest of the ultraviolet portion, X-rays, and gamma rays. As a rule of thumb, EM energy of large wavelength (low frequency) is non-ionizing; EM energy of small wavelength (high frequency) is ionizing.
The difference between ionizing and non-ionizing radiation comes down to energy. Given that the energy of EM radiation is inversely proportional to wavelength, it follows that shorter (higher frequency) waves carry more energy than longer (lower frequency) waves. Let's imagine there are two children holding a skip rope between them, each pulling their end up and down so as to create waves in the rope. The more energy applied by the children, the more waves there will be in the rope. Hence, too, the wavelength will be shorter and thus the frequency higher. (Frequency is measured in Hertz (Hz), which means cycles per second, with 1 Hz equaling 1 cycle per second.)
We've already taken a brief look at ELF waves, which lie at the far end of the non-ionizing section of the EM spectrum. At the other far end of the spectrum, within the ionizing section, we find gamma rays. Gamma rays come right after X-rays; therefore they carry more energy than X-rays. They are in fact the most energetic form of EM radiation, and can penetrate matter with ease. Even a thick sheet of lead will fail to block them entirely. They are emitted during radioactive decay, such as that of uranium, an important nuclear fuel. Ionizing radiation is harmful to living cells, so we're fortunate that the atmosphere of the Earth blocks out gamma rays, X-rays, and other forms of ionizing radiation. Intense or prolonged exposure to gamma rays can result in serious illness (radiation poisoning) or death.
Simply put, ionization is the process whereby one or more electrons are removed from an atom. Ionizing forms of radiation, such as gamma rays, ionize the matter through which they come in contact, stripping electrons from atoms. "When the body's cells are exposed to [ionizing] radiation," explains Dr. Carolyn Dean, "the DNA and proteins inside the cell become 'ionized,' which means that the electrons inside the atoms that make up the cell's components are 'knocked out,' and the DNA and proteins become damaged and lose proper function." Cells that have been damaged in this fashion usually die, although some manage to repair their DNA. If the repair is incorrect, however, it can lead to mutation and possibly cancer.
Given its ability to alter atoms by stripping them of their electrons, thereby causing damage to cells, ionizing radiation is obviously nasty stuff. But even though non-ionizing radiation lacks the energy required to affect atoms in this fashion, it too can be harmful to living things. When it comes to the issue of biological effects resulting from exposure to non-ionizing radiation, much is known from a thermal perspective, though little is known from a non-thermal perspective. We'll explore the possibility of non-thermal effects in a later chapter, but for now let's take a look at the thermal effects.
These days just about everyone has a microwave oven in his or her home. A microwave oven generates microwaves (of around 2,450 megahertz) by means of a kind of electron tube, called a magnetron. The radiation is absorbed by the food placed inside the oven, exciting the atoms that make up the food and thereby causing the food to be heated from within. Only those substances that absorb microwaves can be heated by them, such as the water, fats, and sugars. Microwaves pass quite easily through glass and polyethylene — hence the reason microwave containers are generally made from these substances. Metallic substances such as aluminum foil, on the other hand, deflect microwaves, and so aren't "microwave friendly."
Just as a piece of chicken would get cooked if placed inside a microwave oven for a sufficient period of time, so too would a human hand. The microwaves would heat your tissue to the point where it would be irreversibly damaged. This example illustrates the fact that non-ionizing radiation, though generally considered harmless, has the potential to be just as dangerous as ionizing radiation.
Infrared and ultraviolet vision
I live in Darwin, Australia, which is known for its abundance of crocodiles, snakes, and other reptiles. Though none exist in Australia, there is a family of snakes known as pit vipers, named as such because of their heat-sensitive pit organs, located between each eye and nostril. These organs constitute a "sixth sense," enabling the snake to detect infrared radiation. Most species of pit viper are nocturnal; they hunt at night, when temperatures have cooled down, making use of their special organs to locate warm-blooded prey such as rodents.
Mosquitoes, too, have infrared vision. You could be standing perfectly still on a pitch black night yet mosquitoes will still manage to find you, as they are attracted to the heat emitted by your body.
Some animals can see into the ultraviolet portion of the spectrum. In fact, many species of bird have UV-sensitive vision, only it doesn't extend very far into the UV realm; they can see only one of the three bands of UV radiation — that which lies nearest to visible light, known as UVA (400–315 nm). The two remaining bands are UVB (315–280 nm) and UVC (280–100 nm), these being shorter in wavelength to UVA.
UVB can have a harmful effect on humans and other living things, causing skin cancer and eye damage. For this reason scientists were inclined to assume that no creature had the ability to perceive UVB. This assumption was disproven in 2007, when it was discovered that the species of jumping spider Phintella vittata can indeed sense UVB. These strikingly patterned spiders have specialized surfaces on their bodies that reflect UVB. They use these reflective surfaces to communicate with each other privately. Experiments have shown that during courtship, the female of the species shows significantly less interest in the male when the spiders are placed in an environment with a UVB-blocking filter, compared to normal conditions.
Given that snow is extremely reflective of sunlight, with an albedo that can reach as high as 90 percent, you'd be foolish not to wear a pair of sunglasses if you're planning to spend a lot of time in the snow. Anyone who has suffered from "snow blindness" (photokeratitis), caused by overexposure of UV to the eyes, would know how painful it is. Sufferers liken the sensation to having sand in their eyes. The Inuit took measures to prevent the occurrence of snow blindness by wearing "snow goggles" fashioned from caribou antler. The goggles have a thin slit down the middle, through which the wearer peers out, greatly limiting the amount of UV that is able to reach the eyes.
Unlike humans, arctic reindeer don't have to worry about snow blindness: their eyes are perfectly adapted to the UV-rich environment of the arctic, such that they have perfect access to the UVA portion of the spectrum. Whereas humans can see very little in the all-encompassing whiteness of the arctic, the reindeer that live there can see virtually everything. Things that absorb UV, such as the lichen on which they feed and predators like wolves, would to them appear dark against the snow. Clearly, were it not for their UV-sensitive vision, the arctic reindeer would be unable to survive. It is now believed that many arctic animals, not only reindeer, possess UV sensitivity.
Scientists are discovering more and more all the time about the remarkable sensory capabilities possessed by different animals. Gradually we are beginning to realize that our precious visible spectrum is narrow in the extreme. In fact, when compared to other animals, humans are rather exceptional in not being able to perceive either infrared or ultraviolet. For a reindeer grazing in the snow, or for a rattlesnake hunting its prey in the cool night of the desert, there is a whole other dimension of reality to which we humans are blind.
Earth's magnetic field
Every creature on Earth is immersed in a "sea" of EM energy from both natural and artificial sources. It's easy to forget that the Earth is more or less a giant magnet, and that we spend each moment of our lives wrapped up within its constantly fluctuating magnetic field, also known as the geomagnetic field.
The first magnetic compasses appeared during the 12th century and were used by mariners in both China and Europe. (It is believed that they invented the compass independently of each other.) These primitive devices consisted of a piece of lodestone — a naturally occurring magnetic ore — attached to a stick. It was noticed that the stick, when floated in water, would align itself in such a way as to point in the direction of the polestar. In place of lodestone, subsequent designs incorporated an iron or steel needle that had been given a magnetic charge through contact with a lodestone. A compass works by aligning itself with the Earth's magnetic field, enabling one to determine which way is north — and hence figure out any direction.
The English scientist William Gilbert (1544–1603) — who served as physician to Queen Elizabeth I during the final years of her reign — conducted pioneer research into magnetism and, to a lesser extent, electricity, experimenting with lodestone and pieces of amber (a good accumulator of static charge). Widely considered the founder of the modern sciences of electricity and magnetism, in 1600 he correctly concluded that a compass behaves the way it does because the Earth is a giant magnet.
If you place a bar magnet beneath a piece of paper and sprinkle the surface of the paper with iron filings, the iron filings align themselves with the dipole magnetic field that is present, rendering visible what was previously invisible. The magnetic field of the Earth is similar to that produced by a bar magnet, its magnetic lines of force having approximately the same pattern. Imagine the Earth from a distance with a large bar magnet buried in its center, the south end of the magnet facing toward the (geographic) North Pole and the north end of the magnet facing toward the South Pole. If the magnetic field lines of the Earth were visible, they would be seen emanating from the South Pole, curling up and crossing the equator, and then curling back around and entering the North Pole.
Of course, there is no permanent magnet buried within the Earth. Nor does this "magnet" line up precisely with the North and South Poles; the Earth's rotational axis is inclined 11.7 degrees with respect to its magnetic axis.
According to the widely accepted dynamo theory, the magnetic field of the Earth is generated deep within the planet, where heat produced by means of radioactive decay in the solid inner core drives convective motion in the liquid iron outer core. This activity produces an electric current, which in turn gives rise to a magnetic field.
The unit of measurement known as the gauss (named after the scientist Carl Friedrick Gauss) pertains to magnetic induction, but is also used in relation to magnetic field strength. Magnetic field intensity drops off rapidly with distance. Thus, the closer you are to the source of the field, the higher the reading will be. Deep underground, in the very core of the Earth, the strength of Earth's magnetic field is approximately 25 gauss. Here on the surface, the field is some 50 times weaker — that is, approximately 0.5 gauss. Considering that a small bar magnet measures approximately 100 gauss (200 times stronger), one gets the impression that Earth's magnetic field is extremely weak. The comparison is a misleading one, however, because Earth is a huge magnet, the volume of its field inconceivably larger than anything an artificial magnet could produce.
The first worldwide survey of the Earth's magnetic field was carried out in the 1830s. The brains behind this work was the brilliant German scientist Carl Friedrich Gauss (1777–1855). It was Gauss's invention of the magnetometer in 1832 — an instrument used for measuring the strength of magnetic fields — that made this accomplishment possible. Records show that since Gauss's time the magnetic field of the Earth has weakened by approximately 10 percent, and that throughout the last century, magnetic north has migrated more than 1,500 kilometers.
Geological evidence confirms that the Earth's magnetic field flips, on average, once every 200,000 years, with the most recent flip having occurred around 780,000 years ago. Scientists predict that the field will continue to weaken for the next 500 years, all but disappearing, at which point it will gradually reverse and build up in strength. That the Earth is overdue for a magnetic pole reversal is well established by scientists; though, as mentioned, this event is unlikely to occur for many hundreds of years. Nor is the event expected to occur suddenly; the evidence suggests that reversals are a gradual process.
A protective cocoon
In the 2003 sci-fi disaster film The Core, the Earth's core suddenly grounds to a halt. The result: the Earth's magnetic field begins to collapse, thereby rendering the planet — and all life on the planet — vulnerable to harmful space radiation. All of a sudden the Earth is ravaged by huge electrical storms, pacemakers cease to function and people die as a result, and birds, no longer able to navigate by means of the geomagnetic field, begin to behave erratically, even falling from the sky. A team of scientists backed by the U.S. Government craft an "ingenious" plan to kick the Earth's core back into action and consequently restore the Earth's magnetic field before it's too late: they will bore into the core itself and deposit a series of nuclear charges.
It's impossible to predict precisely what would happen if the magnetic field of the Earth suddenly collapsed, though no doubt the outcome would be rather less dramatic than what is presented in The Core. So just how important is the geomagnetic field in terms of protecting life on Earth?
(Continues…)
Excerpted from "Strange Electromagnetic Dimensions"
by .
Copyright © 2015 Louis Proud.
Excerpted by permission of Red Wheel/Weiser, LLC.
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