WALNUT CREEK -- Proving the absence of something, philosophers and physicists have observed, is among humankind's most difficult feats.

Movie star Arnold Schwarzenegger's absence from the first debate of California's historic recall election, however, was impossible to ignore. Just as his larger-than-life persona seems to fill whatever space he occupies, Schwarzenegger's absence dominated the consciousness of those on and off stage Wednesday in Walnut Creek's downtown arts center.

Gov. Gray Davis, the target of the recall, didn't mention Schwarzenegger, the leading Republican candidate, during his half-hour of questioning by a panel of journalists and voters. The governor concentrated, instead, on reinforcing his latest plea to voters -- that he's "gotten the message" of their anger and will be attentive to them if they reject the recall.

And without Schwarzenegger's participation, the 1 1/2-hour debate among five of his rivals to succeed Davis -- should the governor be recalled -- was little more than a low-key exchange of sharply divergent ideological views. Lt. Gov. Cruz Bustamante, Green Party candidate Peter Camejo and media gadfly Arianna Huffington paddled on the ideological left -- in calling for higher taxes, particularly -- while state Sen. Tom McClintock championed unleavened, anti-tax, budget-cutting conservatism and businessman Peter Ueberroth plowed the middle.

It was interesting in its own way, albeit somewhat repetitious. But without Schwarzenegger's participation, the event took on an air of irrelevance.

Schwarzenegger, of course, was invited to the debate. But he refused to attend and spent the day campaigning in Southern California. "Up to today, we even kept a seat open for him," moderator Randy Shandobil said as the debate began.

Schwarzenegger's campaign has said he will participate in the second recall campaign debate, two weeks hence, in Sacramento. But his refusal to appear in Walnut Creek adds fuel to an increasing level of criticism from opponents and the media about his personality-centered campaign and his lack of specifics.

McClintock, Schwarzenegger's chief Republican rival, said Schwarzenegger's non-appearance here was "an insult to voters." Although Schwarzenegger made a gesture toward adding substance to his campaign two weeks ago by convening an "economic recovery" meeting in Los Angeles, he has concentrated since then on content-free public appearances and slogan-filled television ads.

The question, of course, is whether Schwarzenegger can continue promising to clean house in Sacramento without providing at least a modicum of specificity. The bodybuilder-turned-actor's entry into the gubernatorial sweepstakes spawned a bumper crop of media and public interest, reflecting not only his celebrity but his pledge to apply his take-charge persona to a troubled state government.

The initial excitement seems to have cooled, however, and everyone is now waiting for Schwarzenegger to demonstrate that he has not only the desire to govern the nation's most populous state but the capability. The more he ducks questions from the political media and continues to deliver platitudinous speeches, the more doubts about his capabilities arise.

The oddest aspect is that Schwarzenegger had demonstrated on many previous occasions that he's very capable of holding his own with the media. One suspects that he has succumbed to an affliction common among political novices that one might call "consultantitis." Lacking direct experience in politics, they often put themselves in the hands of professional political managers who then advise them not to do or say anything that's not been predigested by the consultants.

The novices come into politics promising to bring a fresh perspective to government -- but with hired managers pulling their strings, they often start sounding like the politicians they want to replace. And these days, what Schwarzenegger is saying is as vapid as anything being uttered by Davis and the other professional politicians.

Schwarzenegger is spinning his wheels, and his absence from Wednesday's debate indicates that if he wants to regain traction, he's going to have to do more than grin, utter lines from his movies and flex his muscles.