There is, once again, a massive mail backup at the Why Things Are strategic command bunker. The mail problem is the result of our promise to send a fabulous prize to anyone who sent in a question that made it into print before summer's end (let's all agree that it has now ended). Why do people go nuts to get something free? Here are some more winning queries:
- Roland M. of Alexandria, Va., asks "Why is B.C. an abbreviation for an English term while A.D. is an abbreviation for a Latin term?"As kids we thought A.D. meant After Death, meaning, after the crucifixion. But since B.C. meant Before Christ, there was this annoying, implicit 33-year period that was neither B.C. nor A.D. But this was the lesson of life for a child: To survive, you have to suspend logic.
Now we know that A.D. stands for Anno Domini, Latin for "the year of the Lord." It was first used in the sixth century by an abbott named Dionysius Exiguus (which, come to think of it, is a much better baby name than Jason or Kyle). Before he came along, the year was figured in many different ways: The Greeks made reference to Olympiads, the Egyptians and Chinese used dynasties and the Romans dated everything to the founding of the city of Rome.
Dionysius Exiguus came up with a new calendar based on Jesus Christ's birth. Unfortunately he miscalculated by about four years. That's why Jesus was born, according to modern calculations, about four years Before Christ.
The concept of dating years B.C. is fairly recent. The English abbreviation began during the Renaissance. Before that, medieval historians dealing with pre-Christ history usually referred to the reign of various kings and emperors.
- Vernon F. of Lake Mary, Fla., asks, "If the pilot of a military airplane flying at 500 miles an hour fires his gun's bullets at 500 miles an hour velocity, would the bullets just drop out of the barrel? If he fires them from a turret backward would the bullets just drop out?"
Vern, in your first example, the bullets would travel at 1,000 miles an hour relative to the ground, and 500 miles an hour relative to the plane. Your second guess is correct, insofar as the bullet would appear, from the ground, to fall out of the barrel. But most bullets go faster than 500 miles an hour, so you're not likely to see this happen.
- Len D. of Wheaton, Md., asks, "What shape would a match flame be on the space shuttle?"
He made a guess: Spherical. He was right. A match flame only points upward in the presence of gravity. The flame heats the air, which expands and rises, creating an updraft that stretches the flame. Without gravity, there's no such air flow.
It's not something that you'd actually want to do on the shuttle, said Brad Carpenter, a scientist at NASA who specializes in microgravity. Although the match wouldn't burn with much intensity, because the lack of air flow inhibits the amount of oxygen getting to the flame, the soot might damage instruments, and if anything went wrong, "there's no fire escape," he said.
- Russell F. of Mount Clemens, Mich., writes, "Considering the total amount of drinkable water on Earth and the number of animals and humans that have inhabited it, is it likely that there is any water left that hasn't at one time been urine?"
Russ, we strongly suspect there's something in your drinking water. You seem to be asking whether every H2O molecule on the planet has, at one time, been processed through a living creature's bladder. We can assure you that this is not so, both because new water molecules can form from free hydrogen and oxygen and because even the oldest water molecule on the planet could easily have sloshed around the oceans and occasionally evaporated into the sky without detouring through the bladder of some living creature.
That said, we'd guess that a typical glass of water contains numerous molecules that once were part of a urine solution. We base that solely on the parallel truism (supported by real scientists) that in every breath we are likely to inhale at least one atom that was exhaled by Julius Caesar when he said "Et tu, Brute." This might sound absurd, but it is merely a function of statistics, of the enormous number of atoms that Caesar exhaled in that breath and their ability to get mixed up in the rest of the atmospheric soup.
Let's do some rough math. There are 36.2 quadrillion gallons of water in the oceans, the encyclopedia says. There are roughly 5 billion humans and 3 billion cattle on the planet. Figure there's another 2 billion ruminants of some type, and you've got 10 billion bladders. Now let's say the average bladder processes a gallon a day. That's 3.65 trillion gallons of urine produced on Earth in a year. There have been mammals around for millions of years, but not nearly so many as there are today. So let's just arbitrarily multiply our one-year total by 10,000, and we come up with a total of 36.5 quadrillion gallons of urine produced throughout history.
Which is almost precisely the amount of water in all the seas on Earth.
Coincidence? Perhaps . . .
Washington Post Writers Group