The following, posted on many websites each year, first appeared in the January 1990 edition of the defunct Spy Magazine under the title “Is there a Santa Claus?” by Richard Waller.

No known species of reindeer can fly. BUT there are 300,000 species of living organisms yet to be classified, and while most of these are insects and germs, this does not COMPLETELY rule out flying reindeer, which only Santa has ever seen.

There are 2 billion children (persons under 18) in the world. BUT since Santa doesn’t (appear) to handle the Muslim, Hindu, Jewish and Buddhist children, that reduces the workload to 15 percent of the total — 378 million according to Population Reference Bureau. At an average (census) rate of 3.5 children per household, that’s 91.8 million homes. One presumes there’s at least one good child in each.

Santa has 31 hours of Christmas to work with, thanks to the different time zones and the rotation of Earth, assuming he travels east to west (which seems logical). This works out to 822.6 visits per second. ... This means Santa’s sleigh is moving at 650 miles per second, 3,000 times the speed of sound. For purposes of comparison, the fastest manmade vehicle on earth, the Ulysses space probe, moves at a poky 27.4 miles per second — a conventional reindeer can run, tops, 15 mph.

The payload on the sleigh adds another interesting element. Assuming that each child gets nothing more than a mediumsized Lego set (2 pounds), the sleigh is carrying 321,300 tons, not counting Santa, who is invariably described as overweight. On land, conventional reindeer can pull no more than 300 pounds. Even granting that “flying reindeer” (see point No. 1) could pull TEN TIMES the normal amount, we cannot do the job with eight, or even nine. We need 214,200 reindeer. This increases the payload — not even counting the weight of the sleigh — to 353,430 tons. ...

353,000 tons traveling at 650 miles per second creates enormous air resistance — this will heat the reindeer up in the same fashion as spacecraft reentering Earth’s atmosphere. The lead pair of reindeer will absorb 14.3 QUINTILLION joules of energy. Per second. Each. In short, they will burst into flame almost instantaneously, exposing the reindeer behind them, and create deafening sonic booms in their wake. The entire reindeer team will be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will be subjected to centrifugal forces 17,500 times greater than gravity. A 250pound Santa (which seems ludicrously slim) would be pinned to the back of his sleigh by 4,315,015 pounds of force.
In conclusion — If Santa ever DID deliver presents on Christmas Eve, he’s dead now.