Here's the letter (dated March 20, 2006):
On last week's "Wait Wait Don't Tell Me!" NPR News quiz, Peter Sagal reported that when Senator Russ Feingold stood up to censure the president, "The Democratic senator from Wisconsin went down to the Senate floor to introduce a resolution censuring President Bush for what he called 'his illegal wiretapping' of American citizens. All of his Democrat colleagues ran away so fast that -- as per Einstein's theory of relativity -- they ceased to age. When the smoke cleared, the only thing behind Senator Feingold was a Ted Kennedy-shaped hole in the wall."
Can you explain the physics behind this joke? And why didn't more Democrats join in to censure the president? And are they continuing to age now that the censure is over?
In the classical mechanics of Galileo and Newton, space and time are understood to be absolutes. This means that observers in different inertial reference frames might disagree on the velocity of an object that they're both observing. If I'm on a train platform and you're on a train, I might observe the train to be moving at 20 meters per second (and I observe you to be moving at 20 meters per second along with it), while you observe the train not to be moving at all. Likewise, I might observe a beam of light to be traveling at 300,000,000 meters per second, but if you're moving toward it at 100,000,000 m/s, then you'll observe the light to be traveling toward you at 400,000,000 m/s.
Einstein's special theory of relativity postulates that the speed of light has the same value for all observers. In order for this to be logically consistent (given the paragraph above), something has to give. Turns out it's space and time. Objects traveling at speeds near the speed of light undergo time dilation and length contraction, meaning that we would observe them to be shorter in the direction of their motion, and aging at a slower rate. (They would make the same observation about us, but they underwent acceleration to get to where they are, and we didn't, so the two situations are not symmetric.) (This happens for objects traveling at any speed, but the effect is sufficiently negligible at low speeds. Something would have to go at 14% of the speed of light, or 42 million m/s, in order for you to notice a 1% difference in its length or its rate of aging.)
Therefore, NPR's news reporting is mostly correct. These senators would in fact age more slowly as a result of their high velocity, and they'd be thinner as well. Length contraction only occurs along the axis of motion, so they would only get thinner from front to back, not from left to right. Therefore, the hole in the wall of the Capitol should indeed be Ted Kennedy-shaped and -sized, and is unaffected by length contraction.
However, in order for them to cease entirely to age, they would have to be traveling at the speed of light. This is impossible, because unlike photons of light, senators have mass, and it would therefore take an infinite amount of energy to accelerate them to the speed of light. The Bush administration may have thought they would obtain an infinite amount of energy by invading Iraq, but their incompetent handling of the war has placed this beyond our grasp.
Perhaps "ceased to age" is an exaggeration. In order to make 3 years (the duration of the Iraq war so far) seem like 6 weeks (the time from the initial invasion until "Mission Accomplished"), one need only be traveling at 99.926% of the speed of light, which is possible with a finite amount of energy, costing only the amount that the federal government has lost by cutting taxes on incomes above the 99.926th percentile.
Yes, the senators should begin aging normally as soon as they come to a stop, but they are traveling so fast that they will be far beyond the Beltway by the time they can finish decelerating. Everyone outside should exercise caution, since the Democratic senators will need very large turn radii at these relativistic speeds. A collision could be fatal, allowing the governor (in many cases, including Ted Kennedy's state, a Republican) to appoint a replacement senator until the midterm election.
Other paradoxes may arise in explaining this anomalous behavior (e.g. "why didn't more Democrats join in to censure the president?"). When paradoxes come up in special relativity, the resolution is often that the object in question ceases to act as a rigid body. And there are few bodies less rigid than the spines of the Democratic senators who fear the political consequences of censuring a president with a 33% approval rating. Sen. Feingold, on the other hand, has a strong spine, thanks in part to all the calcium he has ingested in his home state of Wisconsin, America's dairyland.
Readers, keep the letters coming, and keep planting those carob trees! Your letter will be answered eventually.