What is momentum anyway?

Have England found a captain who doesn't believe in momentum - and a winning captain at that? Such a man might be a rarity in a soundbyte culture, where the idea has become, like the existence of God, inescapable but impossible to disprove.

Alastair Cook, who has guided England to their first series victory in India for 28 years, failed to offer such comforting platitudes when a win in Mumbai had tied the series at 1-1 with two to play, but even though he dared to dismiss the suggestion that momentum was on his side, he guided England home anyway.

"After the first game momentum was with India," Cook said before the Kolkata Test, "but we managed to bounce back. The Mumbai win has certainly left us a little more confident, and with a belief that what we are doing is fine. That doesn't mean it is going to count for anything in this match."

The notion of momentum has exerted a momentum all of its own upon the modern era. Cricket, especially in its longer forms, is such a nuanced game, it is often difficult to tell who, if anyone, holds an advantage, and into that vacuum must come something. Coaches like the idea of momentum because it is a positive thought to give to players. Commentators, especially ex-players, love it because it appeals to powers of insight that the layman may not have.

A little while ago, Michael Lewis, the author of Moneyball, a book about an impoverished MLB franchise that prospered when they realised that baseball coaches often misjudged the value of players, saw that he had left a question hanging: why, if those coaches had spent their entire lives watching baseball, had they got player selection wrong so often?

The answer led him to the door of Daniel Kahneman, a man who won the Nobel Prize for Economics in 2002, even though he wasn't an economist but a psychologist. ("Ah don't take that Nobel stuff too seriously," he rather charmingly told Lewis when he arrived to have coffee.) Together with the late Amos Tversky, Kahneman had, between the years of 1971 and 1984, researched an area known broadly as "the availability heuristic", which showed that human judgement is often based on the most easily recalled information. He explained this by means of a simple experiment: a roulette wheel was rigged to stop on one of two numbers, 10 or 65. Kahneman asked the groups he assembled in front of the wheel to write down the number they saw. He then asked them an unrelated question: "What is your best guess of the percentage of African nations in the UN?"

The average answer of the groups whose wheel landed on 10 was 25%, and that of the groups for whom it landed on 65 was 45%. Clearly the unrelated roulette number affected their guess.

Kahneman called this "the anchoring effect". There are thousands of examples of it in cricket, many coming from players who have been inconsistent but whose best moments are deeply memorable: Steve Harmison's 7 for 12 is worth considering in this light, a performance that came 18 months into a Test career and resounded for the next seven years ("We all know what Steve's capable of" became a much-uttered phrase).

Kahneman's work also seemed to offer a response as to why coaches, commentators and observers often based their judgement on nebulous concepts and "instincts" rather than empirical evidence of statistical performance. Momentum is the king of the nebulous concepts affected by the availability heuristic.

Yet can it exist as anything other than a concept? During one of the craziest Test matches of the modern era, at Newlands in November 2011, Australia were dismissed for 284, South Africa were bowled out for 96, and before the end of day two, Australia's second-innings score stood at 21 for 9.

On commentary, Robin Jackman asserted, "South Africa have the momentum here." How did he make that judgement? Probably because, to his mind, South Africa taking 9 for 21 was more readily available than the knowledge that Australia were 209 runs ahead on a day when 20 wickets had fallen for 128 runs.

As it turned out, Jackman was right. South Africa went on to win by eight wickets, with centuries from Smith and Amla. Yet the game makes the case for Kahneman as well. The batting collapses of both teams in a single day exerted a tremendous internal force, even though the scores either side of them, 284 in Australia's first knock and 236 for 2 in South Africa's second, were far less panic-stricken and fell within the normal range. It's easy to conclude that those collapses had "momentum" too: in the minds of both batsmen and bowlers, tumbling wickets were the most easily available thought and thus became a destructive and self-fulfilling notion.

On the third morning of the game, Amla and Smith batted quietly for the first hour, scoring 31 runs, before taking the Australian bowling apart, Amla's century coming from 126 deliveries. That initial hour of calm helped the batsmen restore some mental equilibrium to the game, and as the runs began to come, the psychological reference points of both batters and bowlers changed once more. Smith and Amla's play "highlighted the ridiculous nature of the second day", according to ESPNcricinfo's report.

Most Test matches are far less extreme, and yet their nature is often fickle and contrary. A week after Newlands, with the "momentum" of their epic win behind them, South Africa duly lost the second Test to Australia.

Momentum may be nothing more than a balance of probabilities that shifts as the game does, with each movement encouraging a different memory with which to compare it. If it exists, it exists in this fluid and individual state, and unless a team has a collective psyche, it could be convincingly argued that it doesn't exist at all.