Economists are watching the wrong bubble for signs of an impending Big Bang. It isn't real estate that's ripe for the popping; it's the overheated market in another commodity that has become as precious as a perfect diamond the size of a hazelnut, gracing the ring finger of a perfectly manicured left hand: celebrity.

I'm talking about manufactured celebrity, as opposed to the naturally occurring kind. The whole celebrity-industrial complex looks to be on the verge of a nervous breakdown.

The surest danger sign has to be the unintentionally hilarious Tom Cruise-Katie Holmes "romance," which, to say the least, isn't playing quite the way their publicists wanted.

It's not just that the whole world suspects this whirlwind courtship is about true publicity, not true love. That would make sense. Cruise is a matinee idol entering that mid-forties transition zone, the point at which producers start pitching him fewer leading roles and more character parts. In his recent outing, "Collateral," he was upstaged by the younger Jamie Foxx; one wonders how credible he will be as an action hero in the next "Mission: Impossible" installment. His fiancee, Holmes, meanwhile, is still at the ingenue stage.

Both are featured in big-budget summer movies -- Cruise in Steven Spielberg's "War of the Worlds" and Holmes in "Batman Begins" -- when all of Hollywood is frantic over a decline at the box office that seems to have no bottom. Any attentive celebritologist (and we're all celebritologists these days, like it or not) knows a high-profile romance might brighten the prospects of both movies and both actors.

No, it's not the idea but the execution -- the frantic, naked desperation -- that makes me want to call my broker with a "sell" order for celebrity futures.

Here we have Cruise playing the besotted swain, leaping insanely around Oprah's couch, as if Holmes's fairy-tale kiss never quite completed his transition from frog to prince. Here we have him proposing marriage at the Eiffel Tower, so we all get the point that this is a romance, a big, fat, capital-h, capital-r, Hollywood Romance. Here, the minute he crams the ring onto her finger, we have him dragging his betrothed to a news conference to show off his unbridled joy, expressed with a smile that must have fried the light meters of the paparazzi, so vast was its extent and so blindingly intense its ultra-white gleam.

Teeth, don't fail me now.

Granted, all of Hollywood has a lot riding on the new Spielberg flick. Even the final "Star Wars" episode, a genuine blockbuster, wasn't enough to pull the movies out of their worst slump in two decades. Both the number of movie tickets sold and overall box-office revenue are substantially down from last year.

Still, it's a sign of the celebrity-market bubble that a bona fide, top-gun movie star has to make such a spectacle of himself just to stand out from the crowd. There's such a glut of celebrities that they'll soon have to begin storing the surplus in silos in Iowa.

I'm not talking about people like Paris Hilton, a young woman with no discernible talent who has become a mega-celebrity. The Naughty Heiress is a stock celebrity character dating back, well, as far as there have been heiresses. I'm talking about pseudo-celebrities like Fabian Basabe, the New York lounge lizard famous for being a New York lounge lizard who has Paris Hilton on speed dial and for staying out late at nightclubs (sorry, if you have to ask which nightclubs, you don't have a prayer of getting past the bouncers) where table-dancing reportedly takes place.

I'm talking about how anybody who's ever been on a "reality" TV show is a celebrity. About how anybody who's ever been on "American Idol" is a major celebrity. About how anybody who styles the hair of, chooses clothing for, or otherwise performs grooming services for a certified celebrity is now a minor celebrity in his or her own right. About how star publicists are such celebrities that they need their own publicists.

Celebrity "journalism" is in overdrive -- more magazines, more pictures, more everything. I defy anyone, no matter how young and/or hip, to pick up the latest issue of Star or US Weekly or People and, without reading the captions, recognize every celebrity in every photograph. You can't, because you're not supposed to. We need to mint a batch of brand-new celebrities every week to throw into the maw.

This is irrational exuberance. Sell your stock in Justin Guarini, Trista Rehn and Farnsworth Bentley, the guy who used to be P. Diddy's valet. Someday the bubble will pop. And poor Tom Cruise will be able to give it a rest.