Actress Jenny McCarthy’s favorite line is, “My son is my science.” She’s an autism activist who insists that vaccines caused her son’s neurological disorder, a claim that has near-zero support in scientific literature. Years ago, she might have been dismissed as another irrational celebrity or passionate crank. But in the brave new world of “experts” online, McCarthy is more than that. In some corners of the world, she defines a debate, blotting out scientists who completely debunk her claims.

And then there’s Orac, McCarthy’s opposite number. Orac is the nom de blog of someone who writes that he is a “surgeon/scientist.” He’s another self-appointed autism expert but, unlike McCarthy, Orac attacks the vaccines-cause-autism set. He recently delighted in the downfall of a telegenic anti-vaccine doctor in England, for example, who finally lost his license. We, the audience, don’t know who Orac really is, although he has taken on a leading role as a debunker of the autism-vaccine link.

As long as I can remember, “the expert” arrived through news articles, inevitably a guy at that smart-sounding think tank, a famed professor of social science, a renowned author. The expert quote arrived toward the second half of most pieces, wafting out of some glorified institution, as iconic and predictable as Colonel Mustard in the board game Clue.

Structurally, the expert quote is supposed to act as the inarguable voice of reason, getting rid of any doubt left in our minds or splitting the difference between extremes. As the poet Philip Larkin writes of such voices, “Ah, solving that question / Brings the priest and the doctor / In their long coats / Running over the fields.”

But the mystique around expertise has always troubled those who bothered to think about it. The philosopher John Dewey expressed irritation over the unquestioned expert a long time ago, chiding that experts were but “a class” with “private interests and private knowledge.” As the British critic Adam Phillips writes in his book on the nature of expertise, Terrors and Experts, expertise carries with it some troubled assumptions—that “because a person has done a recognizable or legitimated official training they are then qualified to claim something more than that they have done the training.” Phillips points out that it is almost always a feeling of uncertainty that drives the non-specialist—the reader, the patient, the investor—into the arms of experts.

For journalists, this uncertainty is at the center of every traditional news story. Journalists have long gathered expert quotes, secretly hoping to have our angles confirmed and our fears of imposture put to rest. But also because many journalists believe there’s a Platonic truth out there, a definable explanation for everything under the sun—and the experts can tell us what that is.

But with the rise of the Web, as well as changing ideas of authority in general, “the expert” has come to mean something different from what it once did. There’s the rise of what the Brits call “experts by experience”—people like Jenny McCarthy, and also like Orac—who have emerged online because they write well and/or frequently on their subjects, rather than becoming an expert by acclamation of other experts or because of an affiliation with a venerated institution. The worst part of all of this is the thicket of false expertise available on the Web, mistaken by Google-search enthusiasts or, sometimes, naïve reporters, as real expertise. These fauxperts are not entirely new, but not many years ago they had a somewhat harder time getting their point of view presented as coming from an “expert.”

This change in the way we think about expertise stems from a few sources. The first is a weakened trust in institutions or companies or government. Some contend this started in the 1980s and 90s, though, as measured by the Edelman Trust Barometer, trust took a serious dip in 2007. The second is due to what Net brainiacs call “disintermediation,” or the disappearance, due to the Web, of the grinning middlemen who previously connected one institution to another. In the case of journalism, a perfect example of “disintermediation” is that experts used to be mediated and selected by journalists, but now experts themselves may well present their expertise online, like Orac, or the twenty-three-year-old hurricane blogger Brendan Loy, a self-described “weather nerd” in Indiana who predicted Hurricane Katrina days before it occurred, yet another “expert” emerging from the crowd without the usual vetting or filtering.

This is a two-sided thing. On one hand, it’s great that an expert can go straight to the people. On the other, if that expert is an autism-vaccine connector or a climate-skeptic blogger like Anthony Watts, whose claims have been disputed by scientists, it’s pretty clear that mediation is needed. But who should the mediator be?

Alissa Quart is a CJR columnist and contributing editor. She is the author of two books, Branded and Hothouse Kids. Her third, about American outsiders, comes out in 2013. She is also senior editor of The Atavist and an adjunct professor at Columbia Journalism School.