Why didn't the Vikings populate America?

It got cold. That was a big part of it.

But first you have to realize that the Vikings didn't have royal backing the way Columbus did. They were wildcatters, freelance plunderers, show-up-without-calling-first houseguests. As marauders go they weren't terribly ambitious: They tended to invade sparsely populated islands and set up some Viking farms. Populating America would have been a big order for a few entrepreneurs looking for pelts and grazing land.

If you look at a map of the Northern Atlantic, you see how it is possible to reach North America from Europe though a series of jumps, starting at Norway, moving on to the Faeroes, then to Iceland, then Greenland and finally Newfoundland. That's exactly how the Vikings did it.

A Viking ship headed for Iceland was blown off course and found Greenland in the 10th century. Greenland was pretty green back then, because temperatures in the Northern Hemisphere were warmer than they are now. Just before the turn of the millennium, another sailor got blown off course and hit North America. He went home and told his Viking friends, and soon Leif Ericson paid a visit to Newfoundland with a few dozen hardy colonizers.

They figured they had merely found some more islands. As Daniel Boorstin notes in "The Discoverers," the Vikings didn't really discover North America. "Was there ever so long a voyage ... that made so little difference?" They missed the point, just like that record-company guy who turned down the Beatles in the early '60s. (In fairness, even Columbus missed the point; he insisted to his death that Cuba was the Asian mainland and the Earth itself was pear-shaped.)

Why didn't the Vikings eventually drift down to Daytona Beach and hit the bars during Spring Break? To this day there are goofballs who insist the Vikings went all over the place ("Even in Oklahoma?" is a chapter title of one book). One piece of pseudo-evidence is the Kensington Rune Stone, a rock dug up in the late 1800s with Norwegian writing and the date 1323 on it. It was a hoax. Nonetheless the Viking myths persist among some of the Scandinavians who settled in large numbers in the northern Midwest (which is one reason they call their football team the Minnesota Vikings).

In truth, the Vikings only explored a little bit of the East Coast, possibly getting as far down as what is now Massachusetts. The one settlement lasted only about two decades, because the Europeans didn't get along with the locals. In fact the Skraelings, as the Vikings called the native inhabitants, attacked the Vikings with moose-bladder buzz bombs. Our sources don't explain how these things were made or what they were filled with (water? codfish oil? moose pee?), but no doubt these weapons are currently being developed by Saddam Hussein.

The Norsemen, who were never much more than a couple dozen strong in the New World and didn't even have guns, eventually packed it in and shipped home. Greenland, meanwhile, was becoming more inhospitable as the climate grew colder, and eventually all the Scandinavians left or died. The Viking era essentially ended in the mid-11th century as sailors drifted back to the homeland, became integrated into Western European culture, abandoned Thor and Odin for mainstream Christian beliefs, and presumably threw away those helmets with the horns.

Let's face it, Scandinavians have been a little dull ever since.

Why are there only four dimensions?

Most of what we know about dimensions is limited to what we learned from Rod Serling:

"There is a fifth dimension, beyond that which is known to man. It is the middle ground between light and shadow, between science and superstition, and it lies between the pit of man's fears and the summit of his knowledge. This is the dimension of the imagination. It is an area which we call ... The Twilight Zone."

What Serling didn't say is that there may be as many as 10 or even 26 dimensions. That's the word from theoretical physicists. A theoretical physicist is paid to think up dumb stuff like that. If you corner one of these geniuses and ask the obvious question about the phantom dimensions -- where are they? -- you'll probably be told that they are very small and curled-up and aren't "flat" like the dimensions we experience. (That old excuse.) Essentially these extra dimensions are just mathematical inventions.

Of the four dimensions that definitely exist, we see three, and experience the fourth (time). Einstein realized that space and time are inseparable, that time does not have some independent reality but rather is merely a dimension by which we can describe the coordinates of an object (i.e., we can say that Michael Jordan is 10 feet off the ground at longitude 88 west and latitude 42 north at 8:30 p.m. -- four coordinates).

Why just four? Well, what we do know is that for us to exist, we need four. Stephen Hawking, in "A Brief History of Time," gives a terrific summary of why living creatures can't exist in two spatial dimensions. Among other problems, a two-dimensional person couldn't consume food at one end and excrete wastes at the other, the way we three-D people do, because the gastrointestinal passageway would sever him or her into two unconnected parts. Hawking also explains why life can't exist in a universe with more than three spatial dimensions. It has something to do with gravity. Gravity wouldn't work right. Life would be impossible. We'll just take his word for it.

Hawking leaves open the possibility that universes beyond our own (assuming our universe is just one bubble in some larger brew) could have one or two or 10 dimensions but not support life. Indeed, a four-dimensional universe might even be rare. It's just that those are the only kind of universes in which there are living creatures who count dimensions.

The Mailbag

Recently, explaining the high death rate among the parents of comic book and TV adolescents, we wrote that Spiderman's parents were killed by a burglar. A couple of readers refreshed our memory: The burglar killed Spiderman's Uncle Ben. The superhero had already been living with his aunt and uncle. Another reader told us that Spiderman's parents were CIA agents who were killed on the job. It's impossible to keep track of all the carnage.

What really mystifies us is that some readers refuse to accept the solution we offered last week for the Monty Hall puzzle. For example, Larry W. of Kensington accuses us of "creative mathematics and elastic logic." We, in turn, accuse Larry of being a retrograde fungus. As for Mr. Jim F. of NASA who says he's an expert in logic and knows we are wrong, all we can say is, "O-rings."

A quick summary: There is a car behind one of three curtains, and goats behind the other two. You pick Curtain 1, and Monty Hall, sticking to a game show formula designed to heighten drama, shows you what's behind Curtain 2: A goat. Monty asks if you'd like to stick to your first choice or switch to Curtain 3. We advised you to switch to Curtain 3, because there will be a car behind it 67 percent of the time. The reason is fairly simple: Two times out of three you'll pick a goat curtain, and Monty Hall, imprisoned by formula, will then show you the OTHER goat curtain. That means that, two times out of three, the car will be behind the curtain Monty doesn't show you.

For some unfathomable reason this answer really ticks people off. Notwithstanding our tortuous explanation of game-show theory, they think the odds are 50-50 of the car being behind Curtain 1 or Curtain 3, and to hear otherwise puts them in a spittle-spewing rage. Why? The anger we understand: Smart folks consider their logic skills to be the last, unassailable bastion of their intellect. But why do they get it wrong? Maybe a 50-50 split of the odds seems fairer, more democratic, more American. They figure if you've got two choices, and it's one or the other, the odds must be even.

The funniest part is that it's easy for these people to "prove" that it's a 50-50 choice. They simply play the scenario over and over, using cards or napkins or whatnot, and sometimes they stick to the first curtain and other times they switch to the third. If they do this 30 times, chances are they'll end up with 15 cars. That's 50 percent. They beam with righteousness. But in fact, all they've proven is that if you alternate between a choice that has a 33 percent chance of being correct and one that has a 67 chance of being correct you'll be right half the time. The only way to do this experiment meaningfully is to switch every time. Then you'd be right, on the average, two times out of three.

Sincere apologies to those for whom this puzzle was, and remains, incomprehensible.