A man wearing a Mickey Mouse T-shirt is pedalling a bike furiously inside a large fibreglass track. Success is defined as a full-circle upside-down loop. An attendant in a white lab coat eggs on the crowd. At last, to hoots and applause, the rider whirrs up the side wall and over-then again and again. A giant g-force "scale" lights up: the gravitational pull the man is experiencing is five. The gravity we usually feel is one.

"What's the wait time?" says Andrew Warby. That's clue number one that Warby is no casual visitor to Scream Machines: The Science of Roller Coasters, an exhibition appearing at Toronto's Ontario Science Centre until September 5. A few minutes later, he's on the bike himself. I stand outside the railing, holding his glasses and jacket, feeling like a nerve-racked parent waiting by the merry-go-round. Warby pedals effortlessly through several 360-degree loops, then brakes unexpectedly at the top, head dangling. The stunt elicits gasps from the audience and top marks for "style" from the attendant.

Ten minutes later, Warby finally steps off and is stumbling toward me. I hold out his stuff. By day, Warby is a computer-network technician, but with his chiselled face, cropped hair, impeccable posture and shades that clip onto his wire-rimmed glasses, he looks like he's walked right out of the flight school in Top Gun. My interest in Warby lies in one fact: he is a roller-coaster junkie.

Warby has ridden almost sixty coasters. That's nothing compared to the 246 sampled thus far by David Bowers, whose "track record" is proudly displayed on his website, Coasterville.com. But it's enough to give Warby serious cred.

Apart from being a coaster enthusiast, Warby is also a connoisseur of the latest coaster-launch technology. He tells me about the new linear-induction motors that use a magnetic field to launch rides to speeds of up to 188 kilometres per hour in just 1.8 seconds. "The kick that this produces is fantastic," he says. He goes on to name his favourite linear-induction specimens: Incredible Hulk at Universal's Islands of Adventure in Orlando, Florida; the Aerosmith coaster at Disney-MGM Studios, also in Orlando; and Top Thrill Dragster at Cedar Point Amusement Park in Sandusky, Ohio.

According to Warby, Cedar Point is "the champion of coaster parks in North America," and to celebrate his birthday a few years ago, he drove the six hours from Toronto to Cedar Point on a Saturday, squeezed in fifteen rides on Sunday, and motored home on Monday. He hopes to travel to Japan this summer, ostensibly for Expo 2005 but really to sample the coasters there-such as the us$51 million Steel Dragon 2000. "There's this one-upmanship thing between the US and Japan," he says. "Cedar Point will have the biggest and best, the following year Japan will have something new."

Warby's the kind of guy who thinks it would be fun to join a group such as American Coaster Enthusiasts (with its 8,000 members) on its field trips to the latest rides, which often include exclusive time for ACE members. Also on his 2005 wish list is the latest addition to Six Flags Great Adventure in Jackson, New Jersey. Dubbed Kingda Ka, the ride rockets riders horizontally at 206 kilometres per hour then vertically up a 139-metre rise and plunges them down into a three-quarter turn, making it the tallest and fastest coaster in the world (for now, that is). In fact, Warby confesses to bidding cdn$1,200 in an eBay auction for the privilege of being Kingda Ka's first official rider. Lucky for his bank balance, he was outdone by ACE member Jeremy Delong, who coughed up us$1,691.66. Delong took his spin on May 19 and crowed afterward that the launch alone was "well worth it, worth every penny."

I learned about people like Warby and Delong from a 2003 article about the vintage Wooden Roller Coaster at Vancouver's Pacific National Exhibition. A Louisiana couple got married on the ageing ride that summer, and hundreds converged on the West Coast, some from thousands of kilometres away, to pay homage to the rickety old reliable, then in its forty-fifth year. While the US-Japan coaster-technology war rages, old fogeys like the Coaster remain popular based on their retro appeal: no shoulder straps means generous helpings of "air time" (bouncing butt or negative g-force); bench seats allow you to slide from side to side without mercy; and a lack of headrests makes for a clear view of the drops and turns toward which you are hurtling.

Old coaster or new, Warby is an equal-opportunity fanatic. "I think it would be excellent if the world was more coaster-oriented." he says. "Can you imagine the buzz from taking the TTC [Toronto subway] downtown if it used linear acceleration to rocket out of tunnels at one hundred kilometres per hour, and the turn into Union Station was done at a forty-five-degree bank? You'd definitely arrive juiced for work."

The genius of the roller coaster lies in how firmly it takes hold of the senses and throttles them into submission. The tracks aren't jammed together just to save space: their makers are messing with your eyes. Racing forward, you see a jumble of rails and scaffolding in front of you-and sometimes another train hurtling past. You see trees, fences, water, ground. You don't know what's going to hit you, but something surely will. Having no other recourse, you scream-thus adding nicely to the sensory effect. The groans and cracks associated with wooden coasters, the industrial clank of the steel models-all this din does a fine job of freaking you out.

A coaster's most powerful trick, says Kiran Sachdev, until recently a researcher and programmer with the Ontario Science Centre, is the unpredictable nature of the ride: it scares you silly, then scares you in a different way. It hurls you around a hairpin turn, shoots into a tunnel, dips into a corkscrew, races over back-to-back camel humps and twists into a rising helix. "You don't habituate the fear," says Sachdev. "The second you drop, you do something else: you veer off to the side, you do a loop. It's continually changing the stimulus. It's one of the most frightening things you can do, because nothing in the natural world will do that in the same way."

Of course, there are those who "habituate the fear" more successfully then others. And as if to underline the point, Warby, after his triumphant turn on the bicycle, is eager to visit the vomit display. A fluid in your ear, we read, informs your brain that you're in motion, along with signals collected by your eyes. When the messages from these two sources disagree-that is, when a fast ride jolts you more quickly than the fluid can react-the confusion tells your brain that you are being poisoned. Apparently, ingesting poison has a similar effect on the ear. The body, eager to rid itself of the offending substance, embarks on an emergency "purge moment."

"Purge moment," Warby repeats. "That's great." We press and re-press the button that forces a simulated vomit of the chunky variety to rise from a clear plastic stomach up through an esophagus. The demonstration comes complete with the puker's belch.

By now, my research has made me aware that people have willingly risked the purge moment since 1650, when the trendiest thrill in St. Petersburg, Russia, involved tucking oneself into a sled with iron runners and hurtling down a giant ice slide supported by hefty timbers. Some two hundred years later, in 1846, the Chemin de fer centrifuge, inspired by mineshaft railways and described as a "looping gravity railway," debuted at a park in Paris. Then came New York's infamous Coney Island, home of the first true roller coaster on this side of the Atlantic: the Switch Back Railway, built in 1884 (although a Pennsylvania gravity railroad used to transport coal had been turned into a ride in 1872). By 1910, the United States was home to more than 2,000 amusement parks, with plenty more to come. The National Amusement Park Historical Association pegs the nineteen-twenties as the industry's golden age, when "many of the best roller coasters of all time were built."

One of these was the Cyclone built in 1927 at Crystal Beach Amusement Park, a twenty-seven-acre park in Fort Erie, Ontario. The park had begun life in 1888 as a site for religious revivals, then gradually shifted to less heavenly pursuits (according to one report, this evolution began with the revivalists' need to entertain their children while they were communing with God). According to lore, the Cyclone had a full-time nurse on duty-for good reason. "It swerved eighty-five degrees after the first drop, causing cracked ribs and fainting incidents," says Sachdev, reading to me over the phone from his file on the attraction. It was dismantled in 1946, reportedly due to its habit of inflicting injuries on riders (but mostly because of declining numbers of riders and astronomical maintenance costs).

As it happens, Crystal Beach later became the place I cut my own coaster teeth on two renowned circuits. First was the tame but charming Giant: yellow and creaking, it was already the second-oldest coaster in North America (after Lakemont Park's Leap-the-Dips in Pennsylvania) when my brother and I were riding it in the early eighties. Next, the Comet: a grey, fierce, 114-second ride with a ten-storey drop and speeds of up to one hundred kilometres per hour-and a consistent rating among the top ten coasters in the world. In 1989, the year the park closed, Michael Tenszen wrote a eulogy in the Toronto Star that lovingly recalled how the last car on the "Vomit Comet," as it had been dubbed, would literally lift off the tracks during the ride-news to me-and included this boast from forty-two-year-old Jay Wopperer: "I like to say that the day I first rode the Comet I became a man."

I can hear you thinking, "Bullshit." Surely the achievement of so-called manhood must involve something more challenging than going on an amusement-park ride. Netting a giant squid perhaps? Staring into the mouth of an active volcano? Sleeping alone in the Amazon jungle? Surely, at the very least, getting a campfire going-sans matches.

But what do I know?

Dr. Thrill is a Philadelphia-based sociologist otherwise known as Margaret King. She conducts research on social behaviour for clients like amusement-park giant Six Flags and writes reports with titles such as "The Deeper Meanings of Screaming." King argues that riding a roller coaster falls into the same risk category as mountain climbing, bungee jumping and skydiving. She also believes thrill rides do a passable job of standing in for coming-of-age rites that are in increasingly short supply.

Not a coaster person herself-"For me, the anxiety it produces is higher than the reward"-King is especially keen on comparing a turn on a coaster to an Australian Aboriginal walkabout. The walkabout is a journey carried out by Aboriginal boys, age thirteen or fourteen, who travel around desert water holes entirely alone. The trip can take eight months. If they survive, they're "promoted" to manhood. People beyond adolescence who enjoy rides are revisiting a similar testing-of-the-mettle experience. "Your rational self knows that you're going to walk off that ride," King says, "but the body is reacting as if it's on the front lines. Your fight-or-flight response goes into full gear. But you can't get off and you can't stop it. Your heart rate speeds up and your digestive system shuts down."

Adrenaline kicks in, endorphins too, just as they would if you were on a plane you thought was about to crash. People coming off a roller coaster are overcome by the same "triumphal flash" as people who truly have escaped their death by a hair's breadth. "It's a euphoric, hedonistic, elevating experience," says King. Her analysis eerily echoes Warby's take on the allure of a coaster: "It's 'If I go on this, I'm definitely going to die. I've got no control over what's going on.' That's the most terrifying thing around."

But is it really walkabout material? Warby, who may not be a sociologist but happens to be Australian, is skeptical. "The walkabout is more of a trial," he says, "not an adrenaline-based thrill. I think at the end of a coaster ride, you are in a more euphoric state rather than a wiser state. You run off to do it again. What's so wise about that?"

Warby raises a cogent question. According to the International Association of Amusement Parks and Attractions, which quotes statistics from the US Consumer Product Safety Commission on its website, an amusement-park ride is far less likely to cause you harm than riding a bike, driving a car, or a host of other everyday activities. In 2002, for example, 3,800 people visited US emergency rooms as a result of injuries on rides, while an estimated 20,000 battered concert-goers turned up. But statistical comparisons are tricky; a 2004 New Yorker article interpreted the hazards differently, stating that, based on a "standard-deaths-per-rider-miles formula," amusement-park rides are way more likely to do you in than a trip on a plane, train or bus. One thing is obvious: if a roller coaster does go awry, there is little doubt the results will be ugly. The ThemeParkInsider.com website, run by coaster aficionado and former journalist Robert Niles, keeps a running tally of coaster accidents. Its list of verified incidents from 2004 includes a collision on Big Thunder Mountain Railroad at Disneyland that resulted in injuries to three people. The site also reports the death of a man who fell out of a car on the Superman Ride of Steel at Six Flags New England. Another gruesome incident involved riders being struck by metal fragments sent flying when their coaster ran over a frayed cable.

Moreover, the increasing pick-up speeds of roller coasters and their ever-higher drops are pushing the limits of what the body can endure. "If you accelerate too fast, the forces become too high," says Sachdev. "At 8.5 g's, a jet pilot will brown out [lose his vision]. At 10, he'll black out. You don't want to exceed 5 g's. Though I think there's a ride in Japan that approaches 6." Ride designers are well aware of the g-force constraints under which they work and are increasingly using illusions and visual tricks-and heavily themed attractions-to heighten the experience without further heightening the danger.

The dangers are real enough as it is. "On coasters like Top Thrill Dragster," Warby says, "you sit up high and your body is much like the windshield on a car. You are the first point of contact for anything airborne as you speed forward. I remember when I first looked at it, I thought that you would be in a world of hurt if you hit a bug, especially in your eye at 200 kilometres per hour."

According to one theory, people who would read the previous statement and think, "Cool, I've got to try that!" may not be able to help it. They may be driven by low levels of an enzyme that, Kiran Sachdev tells me, is a key regulator of arousal, inhibition and pleasure. "They can tolerate more stimulation before serotonin kicks in to dampen it," he explains. There is also the genetic explanation: a small percentage of people are wired to seek danger-for the benefit of the species, no less. "Say a group of people try exploring new land and want to figure out which plants they can eat," says Sachdev, clearly the teaching scientist. "If there are a couple of people willing to take that risk, that's better than everybody taking that risk."

I can count the roller coasters I've ridden on my fingers. I enjoy it, but I don't feel compelled to get my fix. Nor do I suffer the coaster blues in winter. Is a guy like Warby simply more wired for risk than I am?

Not according to the "Are you a thrill-seeker?" quiz we take at the Scream Machines exhibition: we both come out average. And not according to Warby's own childhood history with "scream machines," which he describes to me over a coffee in the Science Centre's lobby cafª.

He hated roller coasters as a boy. One year, at the Sydney Royal Easter Show, an Australian fair akin to the Canadian National Exhibition, he stood at the top of the giant slide, gripping the sack he was to slide down on. And froze. "I couldn't do it." Henceforth, rides involving massive drops filled him with dread.

As a teenager, fed up with what he considered to be a childish fear, he forced himself to ride the Bush Beast at Wonderland Sydney. "It was this big wooden coaster, the biggest thing I could go on at the time. It rattled and shook a lot." In fact, the track veered above the lineup, sending screaming riders overhead while the nervous Warby waited his turn. "It's moving and shaking above you the whole time," he recalled. "I figured if I could get through this, I can go on everything, anything."

Ultimately, his relationship to the coaster is more than the rush, more than the squelching of fear-rather like the walkabout analogy that King would draw from this tale. But it all goes back to that boy at the top of the slide.

In the summer of 2003, age thirty-one, I spent a day at Paramount Canada's Wonderland, in Toronto, with an old high-school friend. We traipsed around one of the most coaster-diverse parks in North America, lining up for rides with absurd, comic-book names: the Bat, Vortex, Thunder Run, Wild Beast, Dragon Fire, the Mighty Canadian Minebuster. We rode stand-up, backwards, double-looping, suspension and two brain-bruising wooden throwbacks.

I thought I had left such mindless amusement behind, outgrown it. I thought wrong. And was I disappointed in myself? I might have been, if I hadn't been so deeply smitten by Top Gun, a 105-second ride at speeds of up to ninety kilometres per hour. It was built in 1995 based on a design that could simulate dogfight-style flight. The cars are like open cockpits that hang freely from the track above, and the flight pattern is punctuated-according to Wonderland's description-by "barrel rolls," "inverted wing loop-overs," and "snap rollovers."

All I know is this: I was strapped in snugly, my legs left dangling and my feet bare (I'd prudently removed my slip-on sandals). As we whipped around, my naked feet swinging beneath me, cutting through the sky, I felt vulnerable and exhilarated in a way that rivalled all physical sensations I'd previously experienced-sex included, I'm sad to report.

How far would I drive for this rush? How long would I wait? I'm not sure I'm prepared to divulge the answer. But I will tell you what I later thought-at least twenty-four hours later, when I was back in touch with my thinking faculties: the coaster buffs know a good thing when they find it.

As we're gathering up our coffee cups, getting ready to leave the Science Centre, Warby tells me how, several years ago, he dragged some friends on the long drive from New York to Sandusky. This was to be his inaugural visit to Cedar Point and his first time on what was then the tallest and fastest coaster in the world: Millennium Force. It didn't happen; rain prevented the park from opening during their short time in Sandusky. But the group arrived at night, before they knew their plans would be foiled the following morning. Warby stood on the shore of Lake Erie in the darkness, looking toward the peninsula that houses the park. "I saw this lit arch across the bay," he says. "These huge neon arches. It looked really cool. Then I realized it was Millennium Force."

What you hear in his voice when he invokes the scene is something that seems to exist in shorter and shorter supply as people age. It is the sound of a person contemplating something larger than himself. It is the feeling that gripped the boy facing the slide. It is, finally, the thing that cuts right down to the heart of the human condition. The only explanation that matters, the only one we can truly understand. It is awe.

Photographer John Morstad and Staff Writer Alana Coates braved whiplash and long lineups at La Ronde. Flip through their scrapbook of the day at Maisonneuve.org.