Home is where the heart is

Originally published 24 December 1990

Remem­ber this old rid­dle? A man leaves his house for a walk. He walks a mile due south, a mile due east, and a mile due north, and finds he is back at his house. What is the man’s name?

Yes, Vir­ginia, his name is San­ta Claus. And his house, accord­ing to the rid­dle, is at the North Pole.

But don’t go look­ing for him there. These are the sci­ence pages, Vir­ginia. We enjoy a good rid­dle but we don’t deal in myths. Here’s the cold fact: San­ta Claus does­n’t live at the North Pole.

I always knew there was some­thing fishy about San­ta’s address. At the age of six or sev­en I dis­cov­ered that the North Pole is in the mid­dle of the Arc­tic Ocean. I asked my moth­er about this and she said that the ocean is frozen. San­ta’s work­shop, she said, is built on the ice.

It sound­ed rea­son­able, and a lit­tle research in the geog­ra­phy book seemed to con­firm her sto­ry. The Arc­tic Ocean is indeed most­ly frozen, and the ice is typ­i­cal­ly 10 feet thick. Plen­ty thick enough to sup­port a work­shop and an army of elves.

But, alas, Vir­ginia, it’s not that sim­ple. For one thing, the sea ice is drift­ing all the time, in a direc­tion that takes it away from Siberia toward Green­land. Sovi­et and Amer­i­can sci­en­tists some­times set up research sta­tions on the thick­er parts of the ice and go with the flow. A sta­tion might drift a thou­sand miles or more dur­ing its lifetime.

If San­ta built his work­shop on the ice at the North Pole, it would­n’t stay there. It would sim­ply drift away. Next thing you know, elves, toys, rein­deers and sleigh would be float­ing into the North Atlantic on a rapid­ly melt­ing ice floe.

A case of the wobbles

What’s that you say, Vir­ginia? Maybe San­ta’s work­shop is built on the floor of the sea, right smack at the North Pole? An under­wa­ter fac­to­ry that San­ta enters and exits by submarine?

Hmmm, a clever notion. But even that does­n’t quite work. It turns out that the floor of the Arc­tic Ocean has a tricky way of mov­ing around with respect to the pole.

You see, the geo­graph­i­cal North Pole is the place where the Earth­’s spin axis (if Earth were a wheel, the spin axis would be its axle) inter­sects the crust. But the body of the Earth wob­bles with respect to the rota­tion axis, some­thing an astronomer named Chan­dler dis­cov­ered back in 1891. No one is quite sure what caus­es the Chan­dler wob­ble—prob­a­bly a shift of mass in the body of the Earth, or in the oceans, or in the atmos­phere. Appar­ent­ly, the Earth wob­bles like the wheel of a car when a tire gets out of balance.

I’ll grant you it’s not much of a wob­ble, Vir­ginia. The Earth­’s crust wob­bles about the pole in a cir­cle about 50 feet in diam­e­ter every 14 months. Still, if San­ta had a work­shop on the floor of the sea, it would wob­ble too.

And then there are a few oth­er things we need to think about, espe­cial­ly since San­ta will be around for a long time to come.

For exam­ple, there’s plate tec­ton­ics. The Earth­’s sol­id crust is like a bro­ken eggshell. The pieces of the eggshell, or plates, move this way and that at the rate of an inch or two a year. In a mil­lion years or so that can add up to a real change in San­ta’s address.

And recent­ly sci­en­tists have begun to sus­pect that some­times the Earth gets real­ly out of bal­ance. The ten­den­cy is for the heav­i­est part of the plan­et to move toward the equa­tor, in response to cen­trifu­gal force. Over mil­lions of years, the entire crust and man­tle can slip by hun­dreds of miles with respect to the pole.

And then there are the quasars

The amaz­ing thing, Vir­ginia, is that sci­en­tists can now pin­point the posi­tion of the North Pole with an accu­ra­cy of a few inch­es, and they do it by bounc­ing laser beams off of the moon or arti­fi­cial satel­lites, or by com­par­ing the dif­fer­ence in arrival times at sev­er­al radio tele­scopes of sig­nals from quasars bil­lions of light years away.

If we even­tu­al­ly con­firm that all of these wob­bles and shifts in the loca­tion of the North Pole are due to redis­tri­b­u­tions of mass deep inside the Earth, then we have dis­cov­ered some­thing about the inside of our plan­et by observ­ing the most far­away things we can see in the uni­verse — the quasars.

So you see, with all this drift­ing and slip­ping it’s sim­ply not prac­ti­cal for San­ta Claus to locate his work­shop at the geo­graph­ic North Pole. Not unless he wants to mount his entire oper­a­tion on a giant sleigh and con­tin­u­al­ly go mov­ing about on the ice just to stay put.

But no need for that, San­ta has found a firmer address.

The real North Pole, Vir­ginia, is in your heart.