STATE COLLEGE, Pa. -- The field rumbles as if a locomotive is approaching from the south tunnel. The stadium shakes once the first note of "Zombie Nation" hits. Players' ears ring, their helmets sometimes vibrating, from a wall of noise.

Welcome to Beaver Stadium during a White Out, an annual Penn State tradition where more than 100,000 fans dress in white and scream until they go hoarse.

"You couldn't hear the guy six inches next to you," remembered former Michigan center Jack Miller, who was on the sideline for the 2013 White Out. "It was piercing loud, I think that's the best way to describe it."

Added former Penn State linebacker Dan Connor, who spent six seasons in the NFL: "It's really nothing I've ever experienced before. You don't get that anywhere else. You can't emulate that environment, that type of noise and that type of energy. It's the loudest thing I've ever heard."

The Nittany Lions' White Out has fast become one of the great spectacles in college football, an event that has inspired as many Penn State fans as it has copycats. Even Ohio State coach Urban Meyer named it one of the game's top-five atmospheres -- and he should know. He twice has witnessed the White Out, in 2012 and 2014, and he'll see it again Saturday night when the second-ranked Buckeyes visit Penn State (8 p.m. ET, ABC).

"It's a different kind of atmosphere. The White Out, it changes for the players -- the players can really see what kind of support they have behind them," Connor said. "And I can only imagine a visiting team's player seeing 100,000 in all white filling up the stadium. Especially at night."

This isn't a tradition steeped in years of planning and focus groups. Penn State's White Out boasts humble beginnings, the spontaneous idea of an official who -- 12 years ago -- had no inkling this would grow into a Penn State phenomenon.

Here's how it all happened:

The Beginning

Guido D'Elia can still remember staring up at a quiet student section in early September 2004, turning toward a marketing employee and asking aloud, "You think we could get them to wear one color?"

His colleague, Loren Crispell, nodded.

Penn State's White Out has been called one of the top five game atmospheres in the country by Ohio State's Urban Meyer. He and the Buckeyes will see a White Out for the third time when they visit Penn State on Saturday night. Randy Litzinger/Icon Sportswire

"I just thought, how do you get people to act as one?" said D'Elia, Penn State football's former director of communications and branding. "You put them in a uniform. We figured everyone's got a white T-shirt -- so let's make it white."

Those were the simple roots of the White Out, born away from offices and meeting rooms. But there was no time to waste. Penn State had only one remaining home game before late October -- on Oct. 9 against Purdue -- and the color-coded experiment might not work if students were forced to wear sweatshirts or winter jackets.

This was a White Out involving only the students, but the marketing department had only two weeks to plan. Student email addresses were off-limits, and social media didn't really exist yet. Facebook remained in its infancy, and Twitter wouldn't even launch for another two years. Worse yet, D'Elia knew, if the White Out didn't succeed this time -- then it was probably dead forever. It was now or never.

So the marketing department turned to essentially its only option -- guerilla marketing.

"I remember stuff on the White Out was all over the place," said Zack Mills, Penn State's quarterback during the 2004 season. "I remember there being a hype around it. Everything they promoted that game week was all about the White Out. We had a pep rally that was all about the White Out. It was just over and over and over again."

Some students would stand on street corners and shout about the White Out through megaphones. Others would paint their faces white and parade through the HUB-Robeson Center, a popular student hangout. Signs went up, chants were started and campus cafeterias were flooded with ads.

It worked. Penn State fell to Purdue, 20-13, but the first White Out was a success. Mills called it a "special atmosphere ... that was a little crazier than usual." Now, at least, there'd be a second one.

The Evolution

Connor played in 62 career NFL games and 44 college games. He was the nation's top linebacker as a high schooler, a Bednarik Award-winner in college -- and he coaches high school ball now.

But Connor still can't forget the student-only White Out in 2005.

Deep in Ohio State territory, near the student section, he could feel his head buzzing. It wasn't a sensation with which he was familiar. He tried to pinch his helmet near the ear for relief.

There's something different about the crowd at a White Out. "My helmet was shaking," former PSU LB Dan Connor said. "When you play at Penn State, it's always loud -- but any of those White Out games, especially the night ones, it was a different level." Patrick Smith/Getty Images

"The noise was actually vibrating through the facemask," Connor recalled earlier this week. "My helmet was shaking. When you play at Penn State, it's always loud -- but any of those White Out games, especially the night ones, it was a different level."

Two miles away, in the campus' West dorms, students who eschewed football for naps were forced to close their windows because of the noise. Ohio State center Doug Datish recalled, in 2006, how his ears were ringing from the all-white student section. Another Buckeyes offensive lineman, T.J. Downing, later told Penn State's student newspaper that he couldn't hear Nick Mangold from two feet away.

It's not fair to say the White Out was the sole reason for that noise level in 2005. Penn State was surging after several down years, and the Buckeyes arrived late in Happy Valley with a No. 6 national ranking. But it's no stretch to say the White Out contributed to that environment, one in which ESPN analyst and Ohio State alum Kirk Herbstreit referred to Penn State as "the best student section in the country -- they're crazy."

Penn State won that game, 17-10, as fans rushed the field and celebrated in the streets downtown. The White Out was a huge success -- and the athletic department clamored for a stadium-wide White Out the next season. D'Elia talked them out of it.

"We didn't have a game with the right weather and the right opponent," D'Elia said. "I thought we had to wait -- and I fought a heck of a battle to hold off on it in '06. I thought it needed to be a big game, nationally televised, with a full stadium to lock that in."

In 2007, the perfect game emerged: Sept. 8 against Notre Dame. The marketing department tapped into extra resources by printing out reminders on tickets, running commercials featuring an all-white bus driven by a man wearing an all-white uniform, and stationing white-clad employees -- armed with cowbells and bullhorns -- at each stadium exit the week before.

Hours before kickoff against Notre Dame, D'Elia stood atop the press box with field glasses on that 70-degree day, wondering and hoping if his plan would pay off. But as fans left their cars and streamed down Curtin Road, D'Elia could see only white.

The White Out was here to stay.

"It was incredible," said Anthony Morelli, the quarterback in 2007. "I tell young kids all the time that if they can ever get out to a Penn State football game, get to a White Out.

"It's so loud, you can almost feel it."

The Now

Not much has changed from those early days.

Players still need to crane their necks to hear their teammates, the crowd still dresses from head-to-toe in white, sometimes waving white pom-poms, and the atmosphere remains electric. But, as the White Out has grown, the marketing department has no longer needed to rely on commercials or guerilla tactics. Last season's White Out even took place in late November.

In some ways, Penn State's White Out has grown as synonymous with Penn State as the Nittany Lion. It's evident every season, and it's a tradition that's inextricably linked with the university.

"The White Out is one of the reasons why you come to Penn State," said cornerback Grant Haley, who's from Georgia. "You can feel the ground shaking. ... When you see it, it's just something like, it just catches the eye. It's unexplainable. It's unreal."

Added running back Saquon Barkley: "I lost my mind. It was amazing; I never had seen anything like that."

The White Out has become one of Penn State's biggest recruiting draws of the year. For fans, it routinely highlights the most exciting home game of the season. And, with the crowds, at least 107,418 have shown up for the last five such contests.

That's what makes Saturday night's White Out a little bit more different than the road venues Ohio State has faced before. A record-breaking 87,037 fans showed up in Oklahoma, and 81,541 packed Camp Randall. But Penn State will have at least 20,000 more on hand.

"I think Penn State has more people," Ohio State quarterback J.T. Barrett acknowledged earlier this week, "and that can make it louder."

In 2014, PennLive photographer Joe Hermitt measured the crowd volume at 111 decibels on his iPhone app. That's just 14 decibels away from when noise begins to cause literal pain.

Whether it's the loudest stadium or not, Penn State and its White Out have come a long way in the last 12 years -- from an on-field idea into an annual practice the school takes immense pride in.

It was essentially an experiment in 2004 and, again, in 2007. Now?

It's one of the most eye-catching traditions in all of college sports.