(CNN) -- It is the question that has followed Usain Bolt for the past four years, the answer to which will not truly be known until the final for the men's 100 meters sprint in London has been done and dusted.
Just how fast could he have run on that night in Beijing?
It seems a crazy thing to ask. After all, the Jamaican smashed the world record with a time of 9.69 seconds, wining gold and saving the Olympics' marquee sport from itself after successive drug scandals.
And he has run faster since, setting a new record a year later at the World Championships with a time of 9.58 seconds.
But Beijing was much more than a world record. It was the manner of his victory that catapulted him into the kind of international fame not seen in track and field since the U.S. Olympic legend Carl Lewis.
Not only did he blow the rest of the field away, he cantered across the line with 20 meters to go, chest turned to the cameras, arms wide open.
A new hero
Other athletes past and present, not to mention the International Olympic Committee president, derided his showmanship. But the public had made their mind up. They had a new hero.
"My one aim was just to be a champion. That is what I came here to do," Bolt, then 21, said after the race.
"I told you I was going to be number one and I did just that ... It was crazy, phenomenal."
Ever since he has rightly been heralded as the greatest sprinter of all time. But the celebration and the criticism left that one question hanging in the air. Just how fast could he have run? The press, coaches and fellow athletes all speculated. The trainer credited with Bolt's rise, Glen Mills, suggested that he could have run under 9.6 seconds.
Academia even got involved. The University of Oslo's Institute of Theoretical Astrophysics, which deemed the issue of such importance that it dedicated some of the finest minds on the planet to the quandary, predicted that he would have run 9.55 seconds.
Now all the talk is of this Sunday's 100m final at London 2012.
Is 9.4 possible?
Photo by Julian Finney/Getty Images
Bolt could become the first sprinter since Carl Lewis to defend an Olympic 100m title. But no one is talking about 9.69, 9.58 or 9.55. Now Bolt is looking at breaking the record again and seeing if the human body can be pushed further, through the 9.4 second barrier.
"Everyone has been talking about 9.4 all season," Bolt explained in an interview with CNN in July, when asked whether he could run that time at London 2012.
"If it's possible I am the one."
One study by Dutch mathematicians at Tilburg University concluded that, theoretically, Bolt's dream could be realized.
"According to our results this is achievable," the co-author of the report Sander Smeets said in an interview with AFP.
"The absolute limit for a world record at the moment is 9.36 seconds," he added.
The theory, along with Bolt's rhetoric, sounds fine.
But the reality is that Bolt comes into the Olympics having struggled with injuries this season and seen a genuine threat to his title emerge in the shape of training partner Yohan Blake.
"He [Bolt] has had some problems this year," 200m Olympic champion Michael Johnson told CNN's Piers Morgan this month.
"But he can still run two tenths (of a second) quicker than anyone else... he doesn't need to be 100 per cent."
Winning would be enough of an achievement, one that would bookend and incredible four years since his record run in Beijing. That run transformed Usain Bolt's life.
He is now mobbed wherever he goes, adorns billboards from Tokyo to Mexico City and has written his first autobiography. As former Olympic gold medalist Linford Christie remarked during a recent interview with Bolt for CNN, the Jamaican is the most famous athlete, not just in the world, but of all time.
Where it began
Bolt's journey began, like many other world record sprinters, in the Jamaican district of Trelawny where other greats such as current Olympic women's 200m champion Veronica Campbell-Brown also have roots. Although he was Canadian, Ben Johnson was also born here.
It is an area famed for breeding sprint stars thanks largely to a fiercely contested four-day race championships where crowds of up to 30,000 fill the national stadium in Kingston. Over a million people watch the young sprint hopefuls live on TV for what is often the springboard towards the Olympics.
"I feel we push our young athletes," Bolt told CNN when asked why Jamaica produces so much sprinting talent earlier this year.
"There is this thing called the Boys and Girls Championships in Jamaica, which showcases the talent. The level of competition is really high because it pushes you every day to be the best in your event, in your class."
Bolt came on to the sprint world's radar at the 2003 Boys and Girls Championship when, at just 16, he posted times in the 200 and 400m good enough for the Olympic finals in Sydney three years earlier.
He went pro a year later but his failure in the 200m