What should you say to a parent scared of Wi-Fi?

This situation can hopefully be improved by educating parents about reality.

I've observed some of these classrooms where every child is using a laptop. About the only benefit is the occasional need to carry less books on their back -- the rest just provides a neat factor and gives the kids an increased familiarity with technology. Education isn't suffering from a lack of laptops and technology.

It's fearsome compared to not-wifi. :(

Wi-Fi is technological magic, and some people are afraid of that.

Also: unfortunately, a lot of the approaches here aimed at educating people about wifi won't work. Not that the approaches are wrong -- they're the best approach -- but they still won't work in too many cases, because people sense that they have no reason to trust you, and if you're trying to change their opinion, it's only because you're trying to push your own agenda forward at the expense of their health.

People in that mindset then treat facts as scary things that confuse them, so they avoid them altogether.

I live in an area with a higher-than-average ratio of such people, and we also happen to have a fairly thriving tech community. The wifi "debate" comes up often, there have been town meetings about it, it's interfered with city-wide wifi rollouts, etc.

I've made similar comparative harm arguments on a number of occasions. For example: the higher fat content in the organic milk [1] will kill you long before trace amounts of evil scary chemicals in inorganic milk will.

Strangely, arguments like that never seem to convince anyone. Anyone susceptible to the power of reason is already convinced.

[1] 1%/2%/3% milk has a wide range of acceptable values. I.e., 3% means "between 2.8% and 3.5%" or something like that. Organic milk is always at the top of the range, which makes it taste better. (It's also pasteurized at a lower temperature.)

Well, that could backfire. I would imagine that the parents complaining about the WiFi radiations are very probable to be non-smokers.

Indeed.

The problem is, so often, that both proponents and opposers of something, whether it is Health Effects of EM Radiation or Global Warming, either approach those problems with unscientific religiosity, or take some narrow scientific evidence that exists to further their view and discard any criticism.

For our own survival we need more and better research in those issues, not the kind of political and religious pissing contests that we mostly have now.

The amount of energy put out by Wi-Fi is absolutely dwarfed by the radio, television, and cell phone EM signals that we are swamped in at all times. And none of them put out enough energy to do anything but raise our temperature an immeasurably small amount.

See here: http://scienceblogs.com/builtonfacts/2009/09/wifi_and_radiat...

Well, this is called argument-from-ignorance; as others have pointed out, science is pretty bad at proving negatives. So, no, there are no guarantees.

So what we do is we compile the information that we do have, and we try to study effects, establish correlations, and then -- if we're somewhat lucky -- we can reach a conclusion about causation. In the case of the question, "is X dangerous", mostly all we can do is rate it on a relative scale compared to other common things.

(I might get some of the following wrong, but hopefully only in detail. The gist should be correct.)

We know for example that most of the causes of, let's call it spontaneous illness -- tumors and certain diseases and the like -- in healthy adults is the result of damage to nuclear DNA. We also know that most such damaged cells, or cells that are the result of damage during recombination, are attacked and consumed by a person's own immune system. Most of the rest are never viable to begin with -- think of it as a computer program with a serious bug -- and many of the remaining don't produce any viable damaged cells during mitosis.

But, still, we should be cautious about things that do damage to DNA. So, what kinds of radiation do damage to DNA? Well, ionizing radiation does, and as far as we know, it's the only kind that does.

Factors like amplitude, total power, and phase are actually well understood. Scientists shy away from saying with absolute certainty that a particular wavelength is non-ionizing, because they have to take into account other factors, like total power involved. However, microwave radiation -- the 2.4 ghz part of the electromagnetic spectrum -- is pretty safely in the non-ionizing range.

Now, at sufficient power levels, microwaves might cause some minor amount of radiation damage to tissue, but it would have to be an enormous amount of power. Home wifi routers measure their radiation output in milliwatts. You're more susceptible to greater doses of radiation from standing too close to your microwave, and you could probably do that your entire life with no adverse effect.

(In case you're curious: microwaves heat things due to frequency resonance in molecules; i.e., they get certain kinds of molecules -- those containing water -- really excited without stripping their electrons. See also http://www.gallawa.com/microtech/howcook.html)

And all of this is of course aside from the numerous studies which have failed to produce any evidence so far of actual physiological sensitivity to cell phones and wifi and the like -- we're just visiting theory here.

So, how dangerous is it comparatively then?

You are at far more specific danger from walking around outside in the sunshine for just a few minutes than you are from wifi, in terms of ionizing radiation. Although much of the ultraviolet spectrum is non-ionizing, some of it is not, and a small portion of the heat from the sun is ionizing radiation.

And this is where the inconsistency in wifi paranoia comes out, because if you're really, truly that concerned about very very small amounts of radiation, then you shouldn't be venturing around outside wearing anything less than full clothing.

We know plenty about it. The mechanism for causing cancer is ionizing radiation. The ionization rate for radiation is proportional to (I'll ignore boring constants) Amplitude^N, where N is the least integer such that N omega > - E_0.

Here, E_0 is the energy of the bond the radiation breaks, and omega is the frequency of the radiation. Amplitude is small (you'll be thermally cooked long before Amplitude > 1), so the ionization rate is a small number to the power of large N.

It's virtually unmeasurable for small amplitude and large N. Typically to measure ionization in the microwave regime, one needs to use a microwave resonating cavity.

(I have a paper doing some rigorous math on this topic. The paper itself is not so interesting, but the references might be useful to you. Many of them go into the basic physics of radiation interacting with matter. http://cims.nyu.edu/~stucchio/pubs/dipole_delta.pdf )