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Each morning I wake and open my eyes to a new day filled with things I can’t see. I’ve even grown to appreciate how much the unseen makes its presence felt throughout our daily lives. It has been this way since the dawn of time, but modern science has opened the doors to understanding the unseen worlds that crowd into our own and even allows us to manipulate some of them for our own ends. An endless silent babble of radio waves, massed armies of insects, long-gone planet-girdling ice sheets, endemic microbes, rivers of wind, and more all leave their stamp on the shape of my life in the course of 24 hours. Determined, I set off to unravel the mystery of my invisible day.

The Demons Within
8 a.m. I could pretend that I shoot out of bed bright-eyed and bushy-tailed, ready for another day at DISCOVER. But the truth is much blearier, an important part of which is the eradication of the first invisible presence of the day: morning breath. My mouth feels less than fresh as I yawn my way to the bathroom.

Morning breath comes mostly from bacteria that live in the mouth. More than 500 types of oral bacteria have been identified in people so far, and “we keep on identifying more,” says Patricia Lenton, an oral malodor researcher at the University of Minnesota School of Dentistry and a “calibrated breath odor judge.” While we are sleeping, the flow of saliva in our mouths decreases, leaving the bacteria alone “back there, just producing things, lots of sulfur gases,” Lenton says. These orally produced sulfur gases—with names like hydrogen sulfide, methylmercaptan, and dimethyl sulfide—plus some other miscellaneous by-products of bacterial metabolism, account for 90 percent of bad breath that can’t be traced to an outside cause. Meanwhile, foods such as garlic and onions release sulfur compounds as they are digested in our intestines. Some of these compounds are absorbed into the bloodstream and pass into the air in our lungs. As we exhale, we breathe them out.

It’s also through the lungs that changes in blood chemistry caused by disease can affect the odor of our breath. “Diabetes is a good example. When people have uncontrolled diabetes, they can have a really sweet, fruity smell in their breath,” Lenton says. Researchers are even working to develop tests for breast cancer and organ transplant rejection based on the bouquet of a patient’s breath.

Most odor-producing bacteria live on the tongue, not the teeth, so I give my tongue a few good scrubs with my toothbrush before continuing my morning routine.

Scrutinizing the Jet Stream
9 a.m. I’m ready to leave, checking out the window for the effects of that all-time-classic invisible entity, the wind. I’m not looking for the effects of just any old gust of air. The specific wind that is going to determine whether I’ll have to put on a jacket is one that weather watchers didn’t even know existed a century ago.

It’s called the polar jet stream, and as it writhes eastward across the North American continent, it can bring storms in its wake or herald an unseasonable change in temperature—north of the jet stream lies cold, Arctic air, while to its south are warmer conditions। In summer months the polar jet stream flows mostly across Canada. During the winter it dips as far south as the U.S. Gulf states. http://louis-j-sheehan.com

Jet streams occur at very high altitudes—30,000 to 40,000 feet—which is why they were not definitively identified until World War II, when pilots noticed intense headwinds during long-distance military missions. The heart of a jet stream is a relatively narrow band of strong wind a few hundred miles wide that can reach speeds of more than 200 miles per hour. Jet streams draw their energy from the rotation of the earth and the difference in temperature between the equator and higher latitudes. Without jet streams, “it would be a pretty boring place,” weatherwise, says Klaus Weickmann, a meteorologist at the Earth System Research Laboratory of the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado.

Small changes in the jet stream as it passes overhead can create stormy weather at low altitudes. For example, “if you have a low-pressure area aloft, then you will tend to produce low pressure at the surface ahead of it,” Weickmann explains. “That particular [atmospheric] structure is very efficient at extracting available potential energy and converting it into kinetic energy.” This kinetic energy manifests itself in the kind of high winds and rains that can turn a day into a washout. From what I can see out my window though, the weather appears to be pretty calm, so I decide to leave my jacket at home and gather my things. I open my building’s front door and look up at the slight hill I have to climb to my subway stop.

Glacial Moment
It’s not much of a slope, but this hill, and others like it, are evidence of the ancient forces that ultimately brought me and more than 8 million other people to live in New York City. At the peak of the last ice age, some 20,000 years ago, right outside my front door was a frozen glacier wall that rose as high as 300 feet, the southern edge of a vast ice sheet that covered Canada and the northern part of the United States. “Glaciers act as a plow, pushing stuff ahead,” says Sidney Horenstein, a geologist at the American Museum of Natural History in New York City. The edge of America’s ice sheet—marked by a line of rubble called the terminal moraine—ran along Long Island. When the earth warmed and the glacier receded, the rubble was left behind as a series of low hills. Look at a map of New York City and in the boroughs of Brooklyn and Queens (located on the west end of Long Island) you can see that chilly history encoded in the names of today’s neighborhoods: Cobble Hill, Brooklyn Heights, Park Slope, Forest Hills. Southeast of where I live, water from the melting edge of the glacier flowed over the landscape, depositing layers of sand and silt and leaving behind areas with names such as Flatbush and Flatlands. “The community names have meaning,” Horenstein says.

But the biggest impact on New York’s destiny came from the glaciers’ ability to erode, not build, landforms. A glacier “acts as sandpaper because it has rocks embedded in its base…so as the glacier moves, it’s deepening valleys and smoothing off the tops of hills,” Horenstein says. As the glacier moved south toward the future location of New York City, it widened and deepened the Hudson River valley. “The Hudson is the southernmost fjord in North America,” Horenstein says. When the first Europeans explored the river in 1609, they found in it an ideal trade route that penetrated into the continent. The glacier’s deepening of the Hudson also made New York Harbor a snap for trans-Atlantic shipping to navigate.

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These geologic advantages—a terrific natural harbor and an easy transportation route into the interior—allowed an active trading outpost to be established on Manhattan Island by 1625. Over the next four centuries, this blossomed into the international financial and cultural powerhouse that is New York City today—one that still draws people from all over the world to settle here.

Magnetic Attraction

There’s a lot of worry about what we might be breathing while commuting, so I borrowed an air sampling pump to find out.

It’s only a few minutes’ walk up the hill to the subway, and I descend the steps and enter the realm of magnetism. Magnetism is what gets 5.4 million passengers around New York City’s subway system every day, starting with the MetroCard I swipe at the turnstile to enter the system. My MetroCard has a stripe made from a slurry of barium ferrite particles painted onto the card. The stripe encodes a couple hundred bytes of data in magnetized patterns. The data are read by the subway turnstile, which decides whether I have paid for the trip. The turnstile also keeps a record of the card’s unique identification number and the time and date the card was used, regularly uploading this information to the New York City Transit Authority’s central computers. (The local police have found this inconspicuous record-keeping handy in implicating or exonerating suspects in criminal cases and have even used it to trace notorious fugitives such as Peter Braunstein, who sexually assaulted a woman after pretending to be a fireman checking for smoke damage in her building, according to newspaper accounts.)

But where magnetism really reigns supreme is in the motors that drive the subway trains. The New York City subway system supplies power to its trains via a third rail charged with about 625 volts of direct electric current (DC). A device called an inverter turns this into alternating current (AC), which is fed to the motors underneath each car. Inside the motor, the AC electricity flows through coils that surround the rotating core of the motor. The alternating current creates a constantly changing magnetic field and, through some clever engineering, magnetizes the core of the motor as well. Magnetic attraction pulls the rotor toward one coil and then to the next. The changing magnetic field ensures that the rotor will never come to rest, and its strength—thousands of times more powerful than a typical refrigerator magnet—provides the necessary push to keep the train moving.

Iron Lungs
Driven by its motors, my train rumbles into the station, clattering along the tracks. It’s about a 35-minute commute to my stop at 14th Street and Sixth Avenue in Manhattan, and from there a five-minute walk to DISCOVER’s offices. There’s often a lot of worry in New York City about what we might be breathing into our lungs while we’re commuting and otherwise out and about. As is common around the country, New York State’s Department of Environmental Conservation routinely monitors the levels of ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, and particulates in the air. Together these measurements give a pretty good snapshot of the health of the air, known as the Air Quality Index (AQI). Anyone can get a real-time report on the AQI in his or her area by visiting airnow.gov. But I was interested in finding out what else I might be breathing, so I borrowed an air sampling pump from Jennifer Richmond-Bryant, an assistant professor of environmental and occupational health sciences at Hunter College in New York City.

Fortunately for me, I’m in no danger of metal poisoning—nearly all the elements we tested for, including lead, arsenic, and chromium, weren’t present at detectable levels. But two were detectable—iron and calcium. The iron comes from my time in the subway, generated from “wear and tear on the wheels and on the tracks,” which produces tiny iron particles in the air, Richmond-Bryant explains. The calcium comes from aboveground: There is “a decent amount of calcium in concrete,” she says. The concrete gets ground up “when people drive over it or when construction is going on,” and small amounts of it are released into the air. But New Yorkers needn’t worry—iron and calcium are not considered hazardous air pollutants by the EPA.

Radio Free New York
As I stroll along 14th Street to work, I’m also wandering through an invisible electromagnetic bedlam. Indeed, if I could see radio waves, the top of the Empire State Building 20 blocks north of me would be lit like a kaleidoscopic flare, illuminating the entire city. The Empire State Building is host to an array of antennas that are taking advantage of the building’s 1,454-foot height—to the top of its lightning rod—to broadcast a bevy of radio and television stations.

But it’s not just radio and TV signals that are in the air. Cell phones, Wi-Fi-enabled laptops, walkie-talkies, and more are all adding to the bedlam. To prevent transmissions from interfering with each other, the Federal Communications Commission and the National Telecommunications and Information Administration tightly regulate the use of every radio frequency on the electromagnetic spectrum. With a device known as a spectrum analyzer, it’s possible to visualize just how the spectrum is being used. I borrowed one that could detect signals from 100 kilohertz (kHz), just below the frequency of long-wave radio stations, up to 3 gigahertz (GHz), somewhat above the 2.4 GHz portion of the spectrum used by Wi-Fi connections (see “Radio Ways,” below). If you have a Wi-Fi-enabled computer, you can create your own poor-man’s version of a spectrum analyzer. You’ll need a piece of software like Kismet or KisMAC, which you can find free online. This software taps into your Wi-Fi card’s radio and displays all the signals from nearby Wi-Fi base stations, along with the frequency, or channel, that they are broadcasting on. This can come in handy if you’ve noticed a slowdown in your wireless connection speed—it might be that neighbors have set up a new Wi-Fi base station that is using the same channel as yours, resulting in interference. If you spot an unused channel with Kismet or KisMAC, you might want to adjust your base station so that you are connecting without interference.

It’s not just radio and TV signals. Cell phones, Wi-Fi laptops, walkie-talkies, and more are adding to the bedlam.

Software Shock
Once I finally reach DISCOVER’s office, around 10 a.m., the first thing I do (after fixing myself a cup of tea) is fire up my computer and check my e-mail accounts. The difference between a computer that is useful and one that is an expensive paperweight is, of course, software. A piece of software is essentially a list of instructions that tell a computer what to do. And these days, computers, along with their software, are everywhere.

If you’ve ever struggled to understand how a piece of software works, you are not alone. In fact, simply checking for new e-mail triggers a cascade of activity so complex that no human being could ever completely understand all of it. Subsystem interacts with subsystem as electrons surge and flow through microchips that operate according to the dictates of semiconductor physics. How is it, then, that every time you log on to the Internet, there’s a cool new Web site that seems to work just fine, despite not being programmed by a crack squad of Nobel laureates?

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The key to making it all work is the concept of layers. The top layer is the application that you’re using at the moment—a word processing application like Microsoft Word, say. The word processing application talks to your operating system, like Vista, a lower layer that handles requests to do things like save a file. In turn, the operating system talks to the hardware, such as your central processing unit, which has the responsibility for actually storing the file. And each one of those layers is composed of many sublayers. “It’s layer upon layer upon layer.…To me, the most marvelous thing about it is that all this stuff is transparent,” says Warren Harrison, a professor of computer science at Portland State University in Oregon. What Harrison means by “transparent” is that each layer makes the messy details of what it’s doing invisible to higher levels. This approach means that your word processor can just say “save this file” without worrying about the low-level details of how to organize the bits on your computer’s hard disk. Transparency also “gives us division of labor. So I can specialize in writing network software, and I don’t have to worry about knowing how to write a good user interface. Or, conversely, I can specialize in writing user interfaces and I don’t have to worry about network software,” Harrison says.

I obtained a measure of bacterial activity from a swab taken at a water fountain near our offices.

This principle of transparency extends to the Internet. Whenever I check the online weather report or my Facebook profile, the request passes from computer to computer until it reaches its destination. Yet as I sit at my computer, all these computers hide their presence as best they can, so it looks as if I have a direct computer-to-computer connection with the Web site of my choice.

Rocky Foundations
1 p.m. Lunchtime. I go out to grab something at a gyro stand down the street. I’m surrounded by buildings that are rather on the short side for Manhattan, rising only 10 or 11 stories. North of 33rd Street and at Manhattan’s southern tip, buildings that are over 40 stories high are common, giving the city’s skyline a saddlebacked appearance, as building heights drop sharply between the two clusters of towers. Another quirk of geology is to blame. The city’s bedrock, formed through a cataclysmic series of tectonic collisions 550 million years ago, rises close to, or even pushes through, the surface in some parts of the city, creating the perfect foundation for very tall buildings. In other parts—such as near 14th Street, where I am standing, waiting for my lunch—the bedrock is covered by up to several hundred feet of dirt and gravel. This looser material can’t support as much weight as the bedrock, resulting in more squat buildings.

The Microbial Manifest
Lunch in hand, I return to the office. The rest of the day is spent in meetings and working at my computer. Six o’clock rolls around and I descend again into the subway. The train is usually pretty crowded, so I often have to stand and hold on to a metal railing for the trip. It’s when the railing is still warm and slightly greasy from an earlier passenger’s hand that my thoughts turn to the subway’s microbial population. Vincent LaBombardi, director of microbiology at Mount Sinai Hospital in New York City, is reassuring, though: “Most organisms that you find are not pathogenic; they’re typical environmental bugs that you would not be terribly surprised to find, like corynebacterium species and bacillus species.” LaBombardi does note that also to be found is “the cold virus and other types of the adenovirus and whatnot—but that is no different from anyplace else.”

Just to make sure, I swabbed a subway car handrail and had it checked for two bugs that are often in the news lately, E. coli and staph bacteria, as well as for a general measure of bacterial activity, known as the standard plate count, or SPC. The E. coli and staph test came back negative, and the rail’s SPC count of 480 compared favorably with the SPC of 200,000 that was obtained from a swab taken at a water fountain in a park near DISCOVER’s offices.

On the less reassuring side, LaBombardi says that in New York City tropical diseases are common: “We have a lot of people who travel, and they bring back souvenirs. So we see malaria; we see many parasitic infections.” But his big worry is drug-resistant bacteria. New York has “more strains that are resistant to antibiotics” than do other parts of the United States. For “some of these bugs [such as enterococcus] we have no drugs left,” he says. “They’re totally resistant to everything now.” Hand-sanitizing gels do not get rid of spores such as those belonging to Clostridium difficile, “a big pathogen” that can cause diarrhea and inflammation of the colon. But old-fashioned hygiene makes a good defense—LaBombardi recommends simply washing hands regularly with soap and water.

Picture Platters
Once home, therefore, I make sure to wash my hands before fixing dinner. My wife, Annie, and I settle down to watch a DVD. DVDs—like CDs before them and the Blu-ray discs that will eventually replace them—are a form of optical media. Beneath the plastic surface of the DVD, tiny pits and level spots called lands are arranged in a spiral with a 0.74-micron pitch about the size of an average bacterium. These tiny pits and lands encode digital zeros and ones. The DVD player spins the disc, and as it rotates, the spiral is scanned by a laser beam, which acts much like the needle in an old record player. The laser light used in DVD players operates at a wavelength of 650 nanometers (nm), which means it has a visible red color. Blu-ray discs squeeze more information onto the same size disc as a DVD—up to 50 gigabytes on a typical disc, compared with about 8 gigabytes for many movie DVDs—by using a data spiral with a pitch of just 0.32 micron and a 405-nm laser beam. Although 405 nm corresponds to a violet color, it is referred to as blue—hence the name of the format.

The Arthropod Army
Soon enough it’s midnight and time for my eight hours of shut-eye. I climb into bed, not thinking of the extensive colony of tiny arthropods lurking in my pillow and mattress. These arthropods are dust mites, and unless you’ve taken exceptional measures, they’re in your pillow and mattress too. Dust mites “need places to hide, and they like places with higher humidity,” says Jason Rasgon, an assistant professor of microbiology at the Johns Hopkins Bloomberg School of Public Health। “They’ll definitely be in mattresses and pillows; they’ll be in the carpets. They can be pretty much every­where.” Dust mites feed on organic detritus: “Household dust is made up of dirt and shed skin cells, and they like that kind of stuff,” Rasgon says. Male dust mites live for about a month. The females live about twice that and lay about 30 eggs in their lifetime. Both sexes are less than 420 microns long and look like specks of dirt to the naked eye. There can be as many as 19,000 dust mites in three-hundredths of an ounce of dust (but a few hundred is more likely). http://louis-j-sheehan.com

Dust mites are a subject of increasing health concern because they can be highly allergenic. According to Rasgon, people can react not only to the mites themselves but also to their exoskeletons, which are shed as the mites molt during their life cycles. And then there’s frass, which, Rasgon helpfully explains, is “mite poop.” Dust mite allergens can trigger serious asthma attacks and other allergic reactions. Some severe sufferers have to cover their mattresses and pillows with impermeable material.

For me, though, it’s head down and off into the realm of sleep. Exactly what happens inside our skulls when we are dreaming is still an area of active debate, but my nighttime visions are anything but invisible to me as I slumber, resting and gathering my forces for another day.