Drowning In Waves
August 13, 2008 5:47 PM   Subscribe

How densely is the air in populated places packed with invisible waves? How harmful is all that?

So this question on AskMe, about places where you can't get a radio signal, got me thinking.

On the other end of the scale, say a city of 100,000 or more, how dense is the air with invisible manmade waves? Of course it would depend on exactly how big the population was, and how much wave-transmitting devices were in use there, but I can't help but imagine I'm cutting a path through a wall of micro-, sound- and other waves every time I walk around town.

Between analog and satelite radio and TV, cell phones, wireless computer signals, and all the rest, jeez, that's gotta be a lot of tiny waves. Are there any study results or theories (preferably geared toward the layperson) that discuss the harm all this invisible "pollution" might be doing to humans or other species? Could this sort of thing be part of the big bee disappearances, screwy bird migrations, etc.? What are some vocabulary words I need to know to even do a search on this sort of thing ("transmission pollution?")?

Not paranoid-- just curious.
posted by Rykey to Science & Nature (13 answers total) 4 users marked this as a favorite
Very, and not at all.

(Just as a point of physics, electromagnetic waves don't have mass so using density is not the right word.)
posted by gjc at 5:54 PM on August 13, 2008

What are some vocabulary words I need to know to even do a search on this sort of thing ("transmission pollution?")?

Radio waves and microwaves (which are used by radio, TV, cell phones, and wifi) are all part of the electromagnetic spectrum and are called "electromagnetic waves". So the phrase you'd want to look for is "electromagnetic pollution".

However, Googling this term leads to lots of websites of questionable scientific merit, e.g.:

Using an electric iron or an electric keyboard or working with handheld power tools can quickly drain our energies. When working with electric equipment we can reduce harmful effects by holding our hands under running water from time to time in addition to having a shower in the evening or walking barefoot on grass.

I guess washing your hands cleans off the electromagnetic waves? So yeah, be critical of these sites.
posted by EndsOfInvention at 6:10 PM on August 13, 2008

density is not the right word

don't be silly, of course it is!
posted by sergeant sandwich at 6:17 PM on August 13, 2008 [1 favorite]

There's lots of them, because there are so many sources, but they don't harm you at all because they're so weak. Just you stay away from a powerful broadcasting antenna (tv, radio) or the radar at the airport. That's where the waves are strong.
posted by exphysicist345 at 6:19 PM on August 13, 2008

fwiw, the search term you'll want to use is "non-ionizing radiation" if you're talking about electromagnetic waves. (the health effects of ionizing radiation are pretty well understood.)

there have been a lot of studies done, see for instance here, but the problem is that different frequencies do different things to tissues, so there's no one answer.

as far as effects on wildlife - there is some information here on the effects on migratory birds.
posted by sergeant sandwich at 6:29 PM on August 13, 2008

I guess washing your hands cleans off the electromagnetic waves? So yeah, be critical of these sites.

Agreed... a red flag would be seeing products for sale on said site.
posted by crapmatic at 6:41 PM on August 13, 2008

How densely is the air in populated places packed with invisible waves?

It's a little difficult to answer this in a meaningful manner, but assuming you're talking about the power density in the electromagnetic spectrum, the vast majority will be natural. The power density, or intensity, of electromagnetic waves can be mesured as power per unit of area (e.g. in watts per square meter (W/m2)).

At the Earth's surface the intensity of Solar electromagnetic radiation is approximately 1000 W/m2, almost all of this in the visible portion of the electromagnetic spectrum. Similarly, at the Earth's surface the intensity of Earth-emitted electromagnetic radiation is approximately 300 W/m2, almost exclusively in the infrared portion of the electromagnetic spectrum. For comparison, in the immediate vicinity of a radio or cell-phone tower the intensity of the man-made electromagnetic radiation will be less than 0.1 W/m2.

How harmful is all that?

The World Health Organization has a pretty comprehensive overview, intended for the layman, describing what electromagnetic fields are, their impact on health, as well as the current exposure standards and recommended precautions. You can find it here.
posted by RichardP at 7:21 PM on August 13, 2008 [3 favorites]

Everyone is generally aware of quantum physics and 'photons', and as a result people generally tend to think of waves as discrete particles shooting through the air. But really the best way to think about your question is as waves in the classical sense, and your question is somewhat akin to looking at the surface of a lake on a windy day and asking how many waves are there.

The medical effects of electromagnetic energy on humans is basically limited to thermal effects. Meaning that unlike nuclear radiation, the waves themselves are not at all harmful, but will be absorbed at some rate by human flesh, with the energy converted to heat. This is how a microwave works. There are a lot of rules ensuring that devices such as cell phones don't exceed safe limits, but of course there's controversy about what those limits ought to be. However, these issues really only pertain to the use of a transmitter close to your body. Energy density of a radiator drops with 1/r^2, so if you are 10m away from a cell phone, you absorb 10,000 times less energy than the guy holding it 10cm away from his body. If you are worried about the effects of ambient radiation, don't ever get anywhere near a cell phone!

That being said, I did hear a story about some WWII sailors that were standing in front of a very powerful early radar antenna. Whenever the radar would turn on, they heard a distinct clicking noise. It was later determined that the noise they heard was the sound of their brain slapping against the skull as rapidly expanded and contracted from being heated by the pulsed radar signal.
posted by jpdoane at 7:44 PM on August 13, 2008 [1 favorite]

also, a while ago in victoria BC a couple of guys broke into a navigation transmitter while it was running and stole some tools. supposedly they would have felt some heat in the "boys" and may even have been rendered infertile... but that's basically like standing inside a giant microwave oven.
posted by klanawa at 9:16 PM on August 13, 2008

Neat question.

I was going to talk about RF field strength, though jpdoane has done so quite eloquently. In layman's terms, it's basically a measure of how strong a signal is at a given point, and it's largely dependent on distance. This description (past the product overview) may actually be better than Wikipedia's terse mention of the concept.

Using this not-beginner-friendly calculator online, I plugged in the effects of a 100,000 Watt transmitter, 1 kilometer away, as you may find on a very powerful FM transmitter, and got ~1.75 V/m. (Despite everything talking about how field strength is in Watts/centimeter, this one gives us Volts/meter. But bear with me.) 500 mW (half of 1 Watt), my approximation of what a cell phone puts out, at a distance of 2 inches (~5x10-5 kilometers), shows ~75.25 V/m.

The actual meaning of these numbers can be left as pretty meaningless. (And they certainly shouldn't be taken as all that accurate anyway.) But the point is that a cell phone (or WiFi setup, which uses comparable power at comparable frequencies, actually) held 2" from your head, putting out 1/200,000th of the power as an FM transmitter at 1km distance, is exposing you to much, much stronger electromagnetic waves. And really, no one's been able to conclusively show much of a danger from cell phones. (That said, don't go standing next to 100kW transmitters.)

EndsOfInvention: You owe me a new keyboard after pasting that quote.
posted by fogster at 9:32 PM on August 13, 2008 [1 favorite]

Field strength is a measure of electric field and has units V/m. Intensity is a measure of power incident on (or through) a surface, and has units of W/m^2. Intensity is proportional to the square of the field strength. Also, field strength (of a spherically propagating wave) attenuates at 1/r, and intensity attenuates at 1/r^2

I'm not sure what W/cm (or W/m) would be a measure of.
posted by jpdoane at 10:38 PM on August 13, 2008

Hmmm, apparently the microwave auditory effect is discussed in several places.

Bob Park, who wrote about electromagnetic fields as environmental contaminants in his "Voodoo Science," recently commented that Einstein showed in 1905 that cell phones can't cause cancer. (He flubbed the delivery, though.)
posted by fantabulous timewaster at 1:38 AM on August 17, 2008

See #10

(Although unrelated, #1 is pretty interesting too)
posted by jpdoane at 2:11 PM on August 19, 2008

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