Wi-Fi in Schools

A friend of mine asks :


Question : What's the effect on the human body, of 20 children in a classroom, each downloading a 3 minute youtube video over Wi-Fi?

An excellent question!

As with all good science, let's start with an experiment.  I happen to have a 3 minute HD video on my network, so I can time how long it takes to copy across to my laptop:

missingbytes:$ time copy /NetworkDrive/HDVideo.mp4 .
real   0m6.550s
user   0m0.001s
sys    0m0.116s

So a single 3 minute video (3:19 to be precise) will use about 6.5 seconds of Wi-Fi time to copy.

With 20 students, and rounding up a little to account for congestion..

... lets call it 200 seconds of Wi-Fi activity total.

Transmit power

The transmission power for Wi-Fi signals is heavily regulated in the EU, the US and also in New Zealand where I'm performing the test.

The maximum 2.4-GHz transmission power is regulated by law, so lets assume it's 20dBm = 100mW = 0.1W ( source )

As we all learnt when we were in school, a watt is a joule per second, so 200 seconds at 0.1W is 20J.

Now we know that a class room of children downloading a youtube video results in 20 joules of microwave energy being emitted from the Wi-Fi router's antenna.

A brief diversion : Ionizing and Non-Ionizing radiation

Electromagnetic radiation forms a spectrum, from low frequency and radio waves, up through the microwaves, visible light, X-rays and on to gamma rays which have very high frequencies indeed.

Those high frequencies are characterized as ionizing, they're very dangerous to humans and their ability to cause DNA damage and ultimately cancer is well known. This is the reason why we need to be so careful around medical/dental imaging devices, and need to take precautions such as wearing sunscreen and polarized sunglasses when we're outdoors on a sunny day.

It's not necessarily the amount of energy, it's more the frequency that's the problem.  This high frequency ionizing radiation quite literally has the ability to rip electrons off their atoms.  It's these "ions" which go on to cause damage to biological systems.

By contrast, the lower frequency non-ionizing radiation (such as used in Wi-Fi, or FM radio) doesn't have the same ability to affect us in this way.

By itself, non-ionizing radiation can only cause heating in biological systems. Indirectly, it's this heating which slows down or speeds up chemical reactions and/or signalling within the cell, and it's these secondary effects which has the potential to cause problems.

Intuitively, this is why the 1000 watt microwave oven in your kitchen makes food super hot in a few minutes using microwave energy, but it doesn't actually make your food radioactive.  (You'd need an X-Ray oven for that!)

Anyway, lets continue, we've got 20 joules remember?

Absorption

Now we need to make a pretty unrealistic assumption. Suppose that the entirety of those 20 joules of energy was somehow absorbed by one child.  Of course, this can't happen in the real world for two fairly obvious reasons:

• A router transmits energy in all directions.  For all the energy to be absorbed by the child, the router would somehow need to be inside the child.
• Microwave energy interacts only weakly with the human body.  That's one of the great benefits of Wi-Fi, it can pass right through walls and ceilings and straight through you and me.

But just for fun, lets continue on anyway and figure out what would happen if all of those 20 joules were absorbed by one child.

An average 6 year old child weighs about 22 kilograms.  (Of course, my 4 year old son also weighs 22 kilograms, but that's a blogpost for another day!)
The human body is about 65% water, so lets consider 14 kilograms of water.

The specific heat capacity of water is 4.18 J / gK

So we have 20 J / (14,000 g) / (4.18 J / gK) = 0.00034 K = 0.0004 °C
(That's 0.4 millikelvin for all you geeks out there.)

Answers!

So there we have it, even with a wildly exaggerated assumption:

Answer : A classroom of children, all downloading a 3 minute youtube clip over Wi-Fi yields a maximum biological heating due to 2.4GHz microwave radiation of 0.0004 °C.

(0.4 millikelvin is about twice as small as it's possible to measure using a precision thermometer.)

Conclusion

We shouldn't really be too surprised.  Wi-Fi signals are incredibly weak. Consider this, those 20 joules of microwave radiation is the same amount of chemical energy contained in one thousandth of a teaspoon of sugar.

There's no way to prove scientifically that microwave radiation from Wi-Fi is safe in the human body. Science doesn't work that way. You can't prove a negative.

But we can try and make smart choices about tiny risks.


For example, the exposure from a banana is about 0.1 μSv of harmful ionizing radiation because of their high quantities of naturally occurring radioactive potassium.

Yet who thinks twice about giving bananas to kids in schools?

Thoughts, questions or especially corrections?  Please feel free to leave a comment down below!

Analytics

If you happen to live in a certain North European Country, in the wee hours of this morning, ScooterBoy went live!!

That's right, you can now download ScooterBoy, for free!!  (with certain geographical restrictions.)

"But why can't I download it??!" I hear you ask.

Well, you see, it works like this :

We want to make the best release possible in the largest market.

 ➡  The best way to do that is to use feedback from real live customers to improve the game.

 ➡  Where best to get those customers? Yes! From a certain Northern European Country!

Analytics

Now our analytics takes over.  How many downloads will we get? How long will players play? Which level and characters do they play the most? How quickly do they earn currency? What's their favorite IAP (In-App Purchase). What does our retention look like? Where does the game crash?

We can turn all these questions into metrics, then apply those metrics to our game.

We will compare our numbers to our expectations, and then see which numbers we want to improve.

What If?

The next step is to play the "What-if" game.  For example, suppose we make the decision we want to increase player retention:

• What if we had more characters?
• What if we had more levels?
• What if the game were harder? easier?
• What if we gave a bonus for playing every day?
• What if we had daily challenges?
• What if we highlight the leaderboard?

Soft Launch

Exciting times for ScooterBoy!  And lots of geek-out points writing queries in SQL to try and turn a mountain of data into usable information.

We can't wait to make ScooterBoy even bigger and release in more markets!

...watch this space...

Self-Drive Engage

Lately I've been thinking a lot about self-driving cars.

You see, the whole point of a self-driving vehicle is that the occupants of the vehicle are absolved from all the responsibility and all of the joy of operating the motor vehicle.

In such a scenario, which is currently playing out in both California and Nevada, the part that I've been thinking about the most is: Who should be responsible for paying the speeding tickets?

It brings in a number of thorny questions, not the least of which is the difference between driving safely and driving legally.  I hope that we can assume that the car will be authorized to drive safely first, and legally second. (Please let me know in the comments below if this is not the case!!)

It also calls into question the goal of the speeding ticket program in general.  If the goal is to genuinely limit the Kinetic Energy of the vehicle (= mass x sqr(velocity)/2), then lets forget about speeding, and instead record this computed kinetic energy quantity in a continuous manner, along with the GPS co-ordinates, and at the end of the month compare it with the local authority's database of speed kinetic energy limits.

Behavior Modification

In gaming terms, a (speeding) fine is a way of modifying behavior by producing a sharp negative feedback at random intervals.  This is among the most effective ways we know of reducing an undesired player behavior.

Unfortunately this technique simply does not work against computer software.  The only people qualified to change the software are the developers, and it requires active participation on the vehicle owner's part to update the software on a regular basis.

Insurance

I hereby propose an Insurance based licensing scheme for self-drive vehicles.  I propose that in order for a vehicle to (legally) use a self-drive mechanism, the owner of the vehicle must purchase insurance from an organization that is both state licensed, and independently audited.  Eligibility for any given insurance policy will be based on the make and model of the vehicle, plus the software package, version and database of the self-drive mechanism.  At the end of the month, all of the occasions when vehicles with the same policy have exceeded the posted speed kinetic energy limit are summed up, and it's the insurance policy fund which pays out to the state, with no additional per-vehicle owner expenses.

This creates a market for insurance policies.  You can purchase cheaper insurance by buying more conservative software, or pay more in insurance but arrive at your destination sooner with more aggressive software.  As technology and software changes and improves, so too will the market for your self-drive insurance match the current conditions in your state.

And if the price of the insurance is too high for your particular vehicle (e.g. it's too old, or too unsafe, or you're currently out-of-state), you can always opt-out and disable the self-drive feature of your vehicle.

Incentives

This proposal create the right incentives, the software developer must use the best software engineering techniques, the vehicle owner must keep their vehicle updated with the latest software, the insurance socializes the speeding costs amongst all vehicle owners of the same class, and the market ensures an efficient allocation of policies and choice of software programs across all the vehicles in the state's fleet.

The one piece of the puzzle that's missing is the state.  Suppose that a speed kinetic energy limit on a particular stretch of road is changed, but the software developers aren't notified in a timely manner.  In this case, the state itself has been negligent, and it's the state itself which should be fined for putting motorists at risk.  In the same way that the state must adequately signpost the speed limit, so should be it's responsibility to notify the state licensed self-drive software developers.

Speeding?

Of course, I've used speeding as an example of unsafe vehicle behavior, but this regulatory framework extends in a natural way to all vehicle behaviors - stop signs, following distances, red light rules, yielding to buses on residential roads.  Even accident compensation, emission standards, and fuel usage.

The only exceptions I can see are when a vehicle is attempting to drive safely rather than legally.  Without getting all Carl Sagan here, it seems that we could use the black-box data to evaluate all collisions (few) and near-misses (many) to improve the software and improve safety over time.

Failure To Yield

Interestingly, the large majority of vehicle collisions are caused by one simple mechanism, "Failure To Yield".   That's what stop signs and traffic lights and turning circles are all about. A self-drive vehicle, equipped with appropriate sensors, has no reason to stop at stop signs, nor yield at yield signs (if it can negotiate with another self-drive vehicle to yield instead), other than to avoid startling other human drivers.

Reality?

Will it happen?  An insurance based self-drive licensing scheme? I don't know..  If anyone knows of the actual proposed self-drive licensing situation, please post it in the comments below!