The reason that a fly is difficult to swat, I discovered recently, has to do with its vision. The fly's compound eye means that it can see a light flickering at a rate seven times faster than a human. Because the fly's system is processing seven times as much information per second, that second, to the fly, appears to last longer. Dr David McNally, a scientist from Edinburgh University, described the fly's perception of a hand or rolled-up newspaper moving towards it as being like "the slow-motion bullets in The Matrix". The same principle applies to the feeling of time appearing to slow down during the sudden trauma of something like a car accident: the eye and mind are processing more information, more quickly.

The passing of the Typhoon, Frank Tyson, reopened one of cricket's great and unanswerable questions: who was the fastest bowler of the last century? To even begin to find out would require a journey through myth, imagination, memory and technology. And even if the hardcore, empirical evidence of the speed gun were available, it would not be able to factor in the perception of the batsman facing the bewildering variety of thunderbolts that the contenders sent down. Speed is, to a degree, in the eye of the beholder.

Here is the late Bob Woolmer on the experience of facing Michael Holding during one of his most famous spells, at The Oval in 1976:

"Holding was bowling with only one fielder in front of wicket at cover-point. He bowled, and I moved back and across. I saw that the ball was pitched up, so I moved forward, feet first, and then into the shot. Before I knew it, the ball had smashed into my pad. Even though I was wearing state-of-the-art buckskin pads, the pain was so incredible that I thought I had been shot. A small explosion of whitening emanated from my pad and a loud appeal from the bowler and the fielders. Dickie Bird was not known to give too many lbws. But this time he had no choice: the ball would have broken the middle stump."
And this is from Christian Ryan's wonderful piece on Jeff Thomson's fastest spell, terrifyingly enough in a Grade match, Bankstown v Mosman in 1973, when a Mosman player called Barry Knight was able to compare the experience of facing peak Thomson to Tyson, whom he had encountered as a teenager:

"On a drab day in Peterborough, 1956, a teenaged Knight passed Essex team-mate Geoff Smith on his way to the wicket. Smith was whimpering, on a stretcher. The ball had struck him under his pad's knee-roll, the jolt shifting the knee out of alignment: Smith lbw b Tyson 0. Knight faced five Tyson balls, none straight. Two bumpers, a beamer, one pitched up outside off, another pitched up and scudding leg side - Knight knows this because he turned and looked, afterwards. When the five balls were flying at him he could make out only the faintest shadow, or no shadow. Exact same thing facing Thomson."

"Tyson, Thomson, Holding, Shoaib, Lee, Johnson, Clarke - they were fast. Faster on some days than others, on some wickets than others, affected, like the rest of humanity, by their bodies, biorhythms, moods and circumstances"

Geoffrey Boycott faced Thomson and Holding and every other fast man of his generation, and rated Thomson as marginally the quicker but Holding more able to sustain his pace.

Professionals tend to talk in terms of spells when asked about the very fastest bowling. Ricky Ponting recalled one such brutal encounter with Shoaib Akhtar in 1999. Ponting had made three successive ducks, falling to Shoaib, Waqar and then Wasim, and was under severe pressure as the teams arrived in Perth. He went in at No. 6, with Australia at 54 for 4:

"It seemed to last hours and with me on strike the whole time, because even when I did eventually hit one and tried to run, Justin Langer would immediately have his hand up, 'No.' I quickly realised he wasn't coming down to my end if he could help it."

Ponting made 197.

"Until stumps that night, it was seriously quick bowling. I was in my prime then and was trying to take him on with hooks and pulls but, I admit, I couldn't get anywhere near. It was pretty hard work. He was just too quick."

As a young player at the Australian academy, Ponting had astonished Rod Marsh when, during a drill designed for bouncer avoidance, Ponting had been able to pull extremely fast deliveries that the other players had trouble just ducking.

Nick Knight, an accomplished one-day player but not in Ponting's league, faced what became officially the fastest timed delivery, Shoaib's 161kph ball in the 2003 World Cup, and pushed it nonchalantly to square leg.

Players speak of bowlers with "pure" actions - Brett Lee, for example - who bowl at high pace but offer a clear view of the ball, and those with nightmare actions, where the ball disappears until the moment of release. Mitchell Johnson is said to be one of those. The fearsome Sylvester Clarke was another. When Steve Waugh was at Somerset as a young man, he recalled the atmosphere in the dressing room changing a full week before their appointment with Mr Clarke. Waugh then faced what he called "the most awkward and nastiest" spell of his career. "It was something you can't prepare for."

Tyson, Thomson, Holding, Shoaib, Lee, Johnson, Clarke and more… what we know is that they were fast. Faster on some days than others, on some wickets than others, affected, like the rest of humanity, by their bodies and their biorhythms, their moods and their circumstances.

At the other end were men similarly affected. On some days, when the air was clear and the eye keen and everything in harmony, the quickest spell could be overcome. On others, the ball was a blur, a shadow, like Frank Tyson to Barry Knight, visible only once it had passed the bat.

Perception plays its role. Speed matters most to whoever happens to be unlucky enough to be at the receiving end. Long may the debate rage, and long may the answers remain ambiguous.