The next day the Dow plummets so fast it pulls negative gees, while the NASDAQ jolts back up to another record-breaking close. The previous evening's market wisdom is instantly forgotten. The tech sector is once again the wave of the future, to hell with technicalities like price-earnings ratios, while the moral virtues of the brick-and-mortar economy are exposed as an archaic sentiment, soon to be swept away altogether. Till the next time the NASDAQ goes down while the Dow goes up.

Most serious observers agree, in fact, that daily market movements signify next to nothing.  Trying to get rich by following them is like trying to get home faster by changing lanes on the freeway every time the next lane pulls two cars ahead of you. (Thus, most day-traders have managed to lose money in a spectacular bull market.)

That said, the sheer size of recent market swings does command a certain attention. Just last week the Dow closed on an all-time one-day gain of something like 499 points. Granted that this has to be viewed against a total of some 10,000 points, it is still five percent of the market value, or God only knows how many tens of billions of paper income. Volatility, as they say, is at a high level.

And behind volatility -- let's just admit it -- is the specter that hangs over the stock market: the specter of a crash.

Stock market bubbles and crashes are as old as stock markets. In fact, the first great crash of popular economic lore, the Dutch tulip mania of the 17th century, happened somewhat before stock markets as we know them were invented. Since that time there has been the South Seas Bubble of 1720, which suckered in even Sir Isaac Newton, and a succession of panics and crashes extending through three hundred years. As a small girl in Mississippi at the turn of the 20th century, my grandmother heard the grownups talking about "the Panic," and assumed it was some sort of monster.

Above all there is 1929. Three score and ten years, plus change, have passed since that infamous October, but it hasn't been quite long enough to efface all memories of the Great Crash. Just naming the year is enough to evoke the image of wiped-out tycoons jumping out of skyscrapers ... and the succeeding image of bread lines. A number of experts, mainly of the Chicago School ilk, assure us that the Great Crash really had little to do with the Great Depression, but like assurances about the safety of nuclear power plants they somehow fail to assure. Even the non-catastrophic stock crash of 1987 -- which at the time looked like an eerie replay of 1929 -- has not persuaded us that crashes are either safely domesticated or a thing of the past.

Market crashes are nature's way of telling you you aren't as rich as you thought. The basic mechanism is familiar and well-understood, though not (alas) predictable. A market starts going up, for any number of sound, well-justified reasons. (Over the long run, after all, markets generally do go up.) But after a while people discover that they can make money without knowing or caring about The Fundamentals -- or "technical analysis," or much of any thing else. All you have to know is that the market is going up because it is going up. And so long as people keep chasing stocks with money the market will indeed go up, no matter what the underlying values, or even if there aren't any.

If nothing else, Alan Greenspan ensured his immortality in market lore when he coined the phrase irrational exuberance for markets that keep going up even when there's no real-world reason why they should.

Nothing is easier than finding reasons to suspect that this is exactly the case. The idea that a company's stock will soar even as it reports ever-increasing losses, with no foreseeable expectation of a profit, not only has ceased to raise eyebrows: a whole school of thought now regards expecting a profit as vaguely retrograde. (So long as your stock option value keeps going up, who needs a profit?)

The sheer magnitude of the market's rise is also vaguely alarming. Never mind the Dow, which has roughly quadrupled in the last decade; the NASDAQ has doubled since last fall. Something in human nature says that's too fast and too easy. Then there's the pop-culture angle. Stocks have become a fad, like Beanie Babies were, or pet rocks, or hula hoops for those of us who lived in the neolithic era. Just the week before last I wrote about a plan to let people check their stocks on the Internet while they pump gas at convenience stores. (Read it here.) When such things are proposed with a straight face, decline and fall is surely at hand; the Visigoths can't be far behind.

Prophesizing the collapse of the stock market, and by extension that of market capitalism, ought to be a leftie enterprise, complete with explanations of how it was all foreseen by Engels. But the Left -- the real, Stakhanovite Left, that not only believed in dialectical materialism but knew what it meant -- vanished eons ago. Thus the modern market-doom industry has been pioneered by rightie cranks, the sort of people who believe that the only real money is made of gold.

I have to digress for a moment on the subject of gold, because it is so fascinating. To true believers, gold is the one sure repository of value. In early 1980, so strong was their faith that its price rose to $850 per ounce. Currently it is selling for just about $285 per ounce. Gold itself thus turned out to be a spectacular bubble, and one that has never yet recovered.

A classic sign of a speculative bubble is universal, hysterical optimism, the kind that sucked in old Sir Isaac in 1720. Warnings that the market is overbought are lonely cries in the wilderness. Those cries are anything but lonely now; the wilderness fairly rings with them. Moreover, it has been ringing with them for a surprisingly long time. Never mind the doomsday fringe: Greenspan made his celebrated bon mot about irrational exuberance in December of 1996 -- more than three years and thousands of points ago. In the speeded-up Internet age, the crash has been amazingly long in coming.

There are, to be sure, plenty of hysterical optimists out there. But the overall tone of the market is more nearly one of somewhat anxious fascination. No one quite knows what the real underlying worth of the market is, but even if sharply overvalued now discounted it must have a value that would have been considered wildly extravagant a few years ago.

In this odd atmosphere, the dominant impulse during a market plunge seems to be not a panicky rush for the exits -- the trigger of a crash -- but wry smiles and a tightening of seatbelts. Anxiety, yes, but nearly the opposite of panic.

Undoubtedly the market will at some point decide that the prospects of both the new and old economies have been fully discounted and then some. The bull market will falter, stagnate, and give way to a bear market. This is the way of the world, at any rate the capitalist world. But a bear market is not the end of the world. The prospect of one, somewhere down the road, is nothing to get in a panic about now.

Okay, there, I've admitted it: I'm guardedly optimistic. If the market crashes next week, I'll look like an idiot, won't I?