Martin Hellman
Professor Emeritus of Electrical Engineering
Stanford University
October 21, 2008
Hellman is a co-inventor of public key cryptography, the technology that secures communication of credit card and other sensitive information over the Internet. He has worked for over twenty-five years to reduce the threat posed by nuclear weapons and his current project is described at NuclearRisk.org. He is a glider pilot with over 2,600 hours in the air.
Section 1: 99.9% Safe ManeuversLet's face it, nuclear weapons are the elephant in the room that no one likes to talk about. So let's approach the issue from the less threatening perspective of the awesome picture below.
Figure 1: A glider executing a high speed low pass.
The glider looks like it's suspended above the runway, but in reality it's screaming toward the photographer at 150 mph in a maneuver known as a high speed low pass. The pilot starts about 2000 feet high and a mile from the runway. He then dives to convert altitude into speed and skims the runway. Next, he does a steep climb to reconvert some of that speed into altitude so he can turn and land.
Given that the glider has no engine, you might wonder how the pilot can be sure he'll gain enough altitude in the climb to safely turn and land. The laws of physics tell us exactly how altitude is traded for speed and vice versa. While there is a loss due to the air resistance of the glider, that is a known quantity which the pilot takes it into account by starting from a higher altitude than needed for the landing phase.
But it's important to read the fine print in that guarantee provided by the laws of physics. It only applies if the air is stationary. If there's a slight wind the difference is negligible, but if the air movement is unusually strong all bets are off – which is what happened to a friend of mine who had safely executed the maneuver many times before. But this time he hit an unusually strong, continuous downdraft. The laws of physics still applied, but the model of stationary air was no longer applicable and he had no way of knowing his predicament until he approached the runway with much less speed than needed for a safe landing. He managed to land without damage to himself or his glider, but was so shaken that he no longer does that maneuver.
While most experienced glider pilots sometimes do low passes (and some race finishes require them), I've opted not to because I regard them as a 99.9% safe maneuver – which is not as safe as it sounds. A 99.9% safe maneuver is one you can execute safely 999 times out of a thousand, but one time in a thousand it can kill you.
Even though they are clearly equivalent, one chance in a thousand of dying sounds a lot riskier than 99.9% safe. The perspective gets worse when it's recognized that the fatality rate is one in a thousand per execution of the maneuver. If a pilot does a 99.9% safe maneuver 100 times, he stands roughly a 10% chance of being killed. Worse, the fear that he feels the first few times dissipates as he gains confidence in his skill. But that confidence is really complacency, which pilots know is our worst enemy.
A similar situation exists with nuclear weapons. Many people point to the absence of global war since the dawn of the nuclear era as proof that these weapons ensure peace. The MX missile was even christened the Peacekeeper. Just as the laws of physics are used to ensure that a pilot executing a low pass will gain enough altitude to make a safe landing, a law of nuclear deterrence is invoked to quiet any concern over possibly killing billions of innocent people: Since World War III would mean the end of civilization, no one would dare start it. Each side is deterred from attacking the other by the prospect of certain destruction. That's why our current strategy is called nuclear deterrence or mutually assured destruction (MAD).
But again, it's important to read the fine print. It is true that no one in his right mind would start a nuclear war, but when people are highly stressed they often behave irrationally and even seemingly rational decisions can lead to places that no one wants to visit. Neither Kennedy nor Khrushchev wanted to teeter on the edge of the nuclear abyss during the 1962 Cuban Missile Crisis, but that is exactly what they did. Less well known nuclear near misses occurred during the Berlin crisis of 1961, the Yom Kippur War of 1973 and NATO's Able Archer exercise of 1983. In each of those episodes, the law of unintended consequences combined with the danger of irrational decision making under stress created an extremely hazardous situation.
