Soon after Mr. Jones posted his paper online, the physics department at Brigham Young moved to distance itself from his work. The department released a statement saying that it was "not convinced that his analyses and hypotheses have been submitted to relevant scientific venues that would ensure rigorous technical peer review." (Mr. Jones's paper has been peer-reviewed by two physicists and two other scholars for publication in a book called 9/11 and American Empire: Intellectuals Speak Out, from Olive Branch Press.)

The Brigham Young college of engineering issued an even stronger statement on its Web site. "The structural engineering faculty," it read, "do not support the hypotheses of Professor Jones." However, his supporters complain, none of Mr. Jones's critics at Brigham Young have dealt with his points directly.

While there are a handful of Web sites that seek to debunk the claims of Mr. Jones and others in the movement, most mainstream scientists, in fact, have not seen fit to engage them.

"There's nothing to debunk," says Zdenek P. Bazant, a professor of civil and environmental engineering at Northwestern University and the author of the first peer-reviewed paper on the World Trade Center collapses.

"It's a non-issue," says Sivaraj Shyam-Sunder, a lead investigator for the National Institute of Standards and Technology's study of the collapses.

Ross B. Corotis, a professor of civil engineering at the University of Colorado at Boulder and a member of the editorial board at the journal Structural Safety, says that most engineers are pretty settled on what happened at the World Trade Center. "There's not really disagreement as to what happened for 99 percent of the details," he says.

Thomas W. Eagar is one scientist who has paid some attention to the demolition hypothesis — albeit grudgingly. A materials engineer at the Massachusetts Institute of Technology, Mr. Eagar wrote one of the early papers on the buildings' collapses, which later became the basis for a documentary on PBS. That marked him for scrutiny and attack from conspiracy theorists. For a time, he says, he was receiving one or two angry e-mail messages each week, many accusing him of being a government shill. When Mr. Jones's paper came out, the nasty messages increased to one or two per day.

So Mr. Eagar has become reluctantly familiar with Mr. Jones's hypothesis, and he is not impressed. For example, he says, the cascade of yellow-hot particles coming out of the south tower could be any number of things: a butane can igniting, sparks from an electrical arc, molten aluminum and water forming a hydrogen reaction — or, perhaps most likely, a spontaneous, completely accidental thermite reaction.

Occasionally, he says, given enough mingled surface area, molten aluminum and rust can react violently, Ã^ la thermite. Given that there probably was plenty of molten aluminum from the plane wreckage in that building, Mr. Eagar says, it is entirely possible that this is what happened.

Others have brought up this notion as well, so Mr. Jones has carried out experiments in his lab trying to get small quantities of molten aluminum to react with rust. He has not witnessed the reaction and so rules it out. But Mr. Eagar says this is just a red herring: Accidental thermite reactions are a well-known phenomenon, he says. It just takes a lot of exposed surface area for the reaction to start.

Still, Mr. Eagar does not care to respond formally to Mr. Jones or the conspiracy movement. "I don't see any point in engaging them," he says.

Hence, in the world of mainstream science, Mr. Jones's hypothesis is more or less dead on the vine. But in the world of 9/11 Truth, it has seeded a whole garden of theories.

***

"Steven Jones! Who'd like Steven Jones!" hollered a man outside the main convention room as people exited Mr. Jones's speech. "Dripping metal! Steven Jones!"

He was selling DVD's of a speech Mr. Jones gave a few months earlier in Utah.

Another man walked by on the conference floor and pointed to a picture of the yellow-hot spew from the south tower. "There's your smoking gun," he said, to another conferencegoer.

The evening ended just after midnight, with the 9/11 Truthers chanting en masse in the conference hall, "We're mad as hell, and we're not gonna take it anymore."

"We have all kinds of weird conferences," said the concierge the next morning. "I mean, not to say this is weird. Last year we had one that was all tall people."

***

"For a while there, people who wanted to dismiss us could say, 'Well, it's just a bunch of crazies on the Internet,'" says David Ray Griffin, a well-known theologian and philosopher and a prominent member of Scholars for 9/11 Truth. "The very existence of the organization has added credibility," he said.

By many accounts, scholarly contributions to the movement began with Mr. Griffin, who retired from the Claremont School of Theology in 2004. About a year and a half after September 11, Mr. Griffin began reading books and Web sites arguing that the U.S. government was complicit in the attacks. Eventually, they won him over.

That left him feeling a peculiar sense of obligation, he says. The official story had all the voices of authority on its side, and the case for government complicity in the attacks had no real standing. "It was not reaching a really wide audience," he says.

So Mr. Griffin wrote his own book, trading on his authority as an academic. He called it The New Pearl Harbor. It was mostly just a synthesis of all the material he had read, tidied up by a philosopher's rhetorical skills.

When it was finished, he aggressively pursued blurbs for the book jacket — and eventually scored one from Howard Zinn, the radical professor emeritus of political science at Boston University. Mr. Zinn said the book was "the most persuasive argument I have seen for further investigation on the Bush administration's relationship to that historic and troubling event."

It went on to become one of the most successful books on the purported conspiracy.

"There's a big chasm between those who are even willing to entertain the hypothesis enough to look at the evidence and those who aren't," Mr. Griffin says. "The only way to overcome that is by appeal to authority."

"You can't just appeal in terms of straight argument," he says. "You've got to do something to break through, to get people to look at the evidence."

Now that the movement has progressed, and more voices of authority have joined, Mr. Griffin is more convinced than ever.

"I think now it's just irrefutable," he says. People who don't question the official story, he says, are "just whistling in the dark."

***

James H. Fetzer, the co-chairman of Scholars for 9/11 Truth, retired last month from his post as a distinguished McKnight university professor of philosophy at the University of Minnesota at Duluth. He wanted to focus more on the movement. "Whether there's another critical-thinking course being taught at the University of Minnesota is relatively trivial," he says, "compared to this."

Mr. Fetzer, a voluble, impassioned man who often speaks in long paragraphs, is no stranger to conspiracy theory. Before September 11, he had a side career investigating the assassination of President John F. Kennedy. But the issues surrounding the Scholars for 9/11 Truth are far more acute, he thinks. In Mr. Fetzer's mind, the country is in a state of dire emergency.

Hence, it does not much bother Mr. Fetzer that outside scientists have largely refrained from tackling the group's arguments. "I don't think it's a problem," he says, "because we have so much competence and expertise among ourselves."

911myths.com, a Web site run by a software developer in England, is one of the few venues that offers a running scrutiny of the various claims and arguments coming out of the 9/11 Truth movement. Mr. Fetzer has heard of 911myths .com, but he has never visited the site.

"I have been dealing with disinformation and phony stories about the death of JFK for all these years. There's a huge amount of phoniness out there," he says. "You have to be very selective in how you approach these things."

"I can assure you the things I'm telling you about 9/11 have objective scientific status," he says. 911myths.com, he says, "is going to be built on either fabricated evidence, or disregard of the real evidence, or violations of the principles of scientific reasoning."

"They cannot be right," he says.

***

On the second afternoon of the conference, Mr. Fetzer gave a speech in one of the hotel salons to a standing-room-only crowd. It began like an introductory lecture in moral philosophy he might have given at the University of Minnesota. He discussed different theories for the origins of right and wrong — moral egoism, utilitarianism, deontological moral rights. Then he came to the emergency.

"The threat we face," he said, is "imminent and ominous." He recommended arming the citizenry.

During the question-and-answer session, an audience member asked whether there might be a way to capture a TV station, to get the word out about September 11. Mr. Fetzer upped the ante on the idea.

"Let me tell you, for years, I've been waiting for there to be a military coup to depose these traitors," he said from the podium.

"Yeah!" shouted some men in the audience.

"There actually was one weekend," Mr. Fetzer went on, "where I said to myself, my God, it's going to happen this weekend, and I'm going to wake up and they will have taken these guys off in chains."

His voice was building. "Listen to me," he said. "The degree of perfidy involved here is so great, that in the time of Aeschylus, Sophocles, and Euripides, frenzied mobs would have dragged these men out of their beds in the middle of the night and ripped them to shreds!"

"Yeah!" cried a chorus of voices in the audience. "Yeah!"

Amid the cheers and applause that swept the room, there was Steven Jones, sitting quietly in a chair against the wall. He had one leg crossed over the other, and he was looking around at the cheering audience with a vaguely uncomfortable smile on his face, holding his foot in his hands.

End