Even before scientists discovered distant and mysterious planets such as Neptune and Pluto, they knew they were there because something seemed to be bending the orbit of the planets around them. It's the same with that much-discussed but irritatingly elusive earthbound quality known as "social capital". It may be impossible to define or to bottle - but it still seems to have an effect.
The American journal Science recently carried the results of an exhaustive study of 343 different neighbourhoods in Chicago. Researchers from Harvard University's School of Public Health interviewed nearly 9,000 people about local violence and found that it seemed to be unrelated to the usual measures of deprivation. Equally poor districts had very different levels of violence.
What made the difference? The researchers defined it as " informal social control and cohesion and trust". The least violent neighbourhoods were places where local people were prepared to "intervene for the common good".
Call it "community", like Amitai Etzioni, "duty", like David Selbourne, "trust", like Francis Fukuyama or "social capital", like Robert Putnam - who discovered it wandering around the medieval towns of Italy - but it is the quality described by Tony Blair as the "magical ingredient" that decides between social breakdown and cohesion.
Social capital is not just difficult to define, it also seems impossible to create. Blair's Fabian pamphlet The Third Way offers little help. "The politics of 'us' rather than 'me' demands an ethic of responsibility as well as rights," he wrote. Then suddenly he plunged into how society can enforce this - discipline, responsibility, curfews and so on. It's as if he had given up at the first hurdle and had already begun planning the consequences of failure.
So how do we recreate this local trust that the Harvard researchers found? As in the case of the metaphorical blind people describing an elephant, parts of an answer have emerged in different aspects of community development, many of them pulled together in the recent report from the Social Exclusion Unit. Yet still the government seems to fall back on Singapore-style authoritarianism, in the absence of any other idea about how to change people's attitudes to their responsibilities.
Yet there is one emerging idea that could fit the bill and has won praise from the inventor of the Third Way himself, Anthony Giddens, the director of the London School of Economics. This is a technique that boosts civic involvement by using people's time as a kind of money - borrowing as much from the idea of Air Miles and supermarket loyalty points as it does from old-fashioned volunteering.
There are now more than 200 projects using the idea across the USA and Japan. Yet it has received remarkably little coverage in the UK - where it originated.
"Volunteers who take part in charitable work are 'paid' in time donated by other volunteer workers," explains Giddens. "A computer system registers every 'time dollar' earned and spent and provides participants with regular accounts. Time dollars are tax-free and can be accumulated to pay for health care as well as other health services."
It sounds too simple. Yet time dollars are more radical than they seem at first sight, particularly when, in addition to health, they can be spent on a wide range of items, from food and clothing to computers and literacy training.
Building a local economy in time is also egalitarian, since everyone gets paid the same - an hour is worth an hour whether you are a wealthy lawyer, an elderly housebound woman making supportive phone calls to neighbours or a disaffected 16 year old tutoring 14 year olds after school. And the relationship of donor and recipient gets turned upside down. It sounds like volunteering, but its reciprocal nature makes it in some ways the opposite: people who were once labelled "recipients" or "clients" become participants. They are no longer receiving charity; they are taking part.
Making people feel useful - when the whole resources of government used to be dedicated to making them feel like a burden - has also proved to be transformational. Problem people turn out to be assets after all.
"This new money can enlist the people the market had already discarded or rejected," says one driving force behind time-dollar schemes, the US civil rights lawyer Edgar Cahn, who cut his political teeth writing speeches for Bobby Kennedy. "It puts them to work on problems generated by the very economy that had thrown them away. Creating a new form of money that could do this was driven by a simple moral imperative: no more throwaway people."
The first time-dollar projects were launched in six cities in 1987 amid widespread publicity, and many health centres and hospitals now have their own schemes attached. Research shows that about a third of the people taking part in time dollars have never volunteered for anything before. They also tend to stay volunteering longer than average volunteer schemes, many of which have a serious "burn-out" problem.
The first projects - in Brooklyn, Dorchester in Massachusetts, Jefferson City, Miami, St Louis and San Francisco - proved within a year or so that they were effecting real budget savings. Services were being provided that allowed older people to stay in their own homes, and taking part in the programme as volunteers and recipients - or both - was giving people human contact and a sense of purpose, which also kept them healthier.
Time-money is an explicit attempt to reward altruism. "Market economics values what is scarce - not the real work of society, which is caring, loving, being a citizen, a neighbour and a human being," says Cahn. "That work will, I hope, never be so scarce that the market value goes high, so we have to find a way of rewarding contributions to it."
The idea can be developed in other areas apart from health - anywhere, in fact, where we need to transform neighbourhoods or set up a new kind of relationship between institutions and clients.
The notorious Benning Terrace housing complex in Washington DC is a prime example. Here residents earn time dollars for volunteer work, which has transformed the estate, and they use these to buy four tons of food per month at the local food bank.
Perhaps the most impressive story comes from the Washington law firm Holland & Knight, which won the 1997 American Bar Association award for its time-dollar project, organised under the company's pro bono programme.
It could have done the work for the community group for nothing, of course. But it was a big job, which meant closing crack houses in the Shaw neighbourhood, unfreezing the grant money allocated for refurbishing a local playground, cleaning up local police corruption and keeping the neighbourhood school open - and Holland & Knight needed local involvement for it to work. So it charged the community a retainer in time-money.
By the end, the firm had billed the equivalent of $230,000 in time dollars. This was paid off by the local community by helping with the clean-up, providing a night escort service for old people, campaigning for better street lighting, taking down the car numbers of drug dealers, school tutoring and much else besides.
Lawyers were motivated to organise this innovative scheme because they knew that every hour they put in would generate another hour of self-help in the community. And all the activity from this reciprocal relationship made Shaw a better place to live.
As Cahn develops the idea to bring in young people and encourage training - in the time economy people earn by doing training - the systems look for wasted resources that can be made available for time earnings. And increasingly the wasted asset underpinning the time-dollar economy is old computers, about 15 million of which are put into landfill every year in the USA - with many more pending, thanks to the millennium bug.
So in 17 Chicago problem schools, pupils have been earning time dollars by taking part in a peer-tutoring programme, earning the 100 or so time dollars necessary to buy their own refurbished computer. Their parents also have to chip in four time dollars for their children to make the purchase.
The schools found that attendance went up when the tutoring was happening. Less predictable was the big reduction in bullying, because it was considered bad form to bully a person you were tutoring - or to let anybody else do so either.
"We will never know the positive impact of this programme on these young people," the director of the project, Calvin Pearce, told the Chicago Tribune. "Most of the families involved in this programme would never have been able to afford a computer."
Cahn himself has taken over part of the youth court from the District of Columbia, which - like the Chicago public school system - has been groaning under a surfeit of violence and a shortage of money and ideas. Now, defendants are tried for minor offences by other teenagers, who are paid for their participation in time dollars - also used for buying refurbished computers.
A similar idea has been tried, much more controversially, in Baltimore public housing. Families in this system pay up to eight hours a month in time-money in addition to paying rent. This is a difficult idea - especially if the hours worked are perceived as providing replacements for services that the landlords should be providing anyway.
Cahn believes it is defensible provided the participants of the system are in charge, rather than making landlords responsible for enforcing the time debt. He also points out that this kind of scheme can tackle depression and isolation and revitalise an estate.
Giddens praises the idea of time dollars in the context of "building civil society" and as part of a growing alternative to mainstream work. Time-money is a helpful way of redefining work, going beyond conventional paid jobs and including in its definition anything that communities need doing in order to thrive.
That includes all those tasks that get downgraded by a society impoverished by market economics, such as parenting, caring or tending local parks. Ironically, these are tasks that prop up the money economy.
According to one study, volunteering is already putting £41 billion a year into the social economy in the UK, levered by public support worth £300 million. That's £40 of volunteer effort for every £1 spent by government. Encouraging the time-money idea in the UK could have a major impact.
First, it is affordable. Time-money can radically cut the cost of programmes for the socially excluded, enabling public bodies to offer services that only the better-off could pay for in cash. For example, because involvement with time-dollar programmes keeps people healthy, a Brooklyn health insurance company, Elderplan, found it was able to accept time-money for 25 per cent of its insurance charges. That is also how the US housing charity Habitat is able to reduce the price of homes for people on low incomes. They require people to give 500 hours' help in building homes as part of the price. This could equally be applied to rents.
It could have a significant impact on education, too, in particular on the UK student loans system. People on low incomes could repay loans partly in time. In the US, AmeriCorps now has an education grants programme that allows students to pay tuition fees or student loan payments in this way. Berea College in Kentucky, for example, has always required students to pay part of their fees in community service.
It is not just Third Way politics that is stuck between the devil of demanding people's responsibility and the deep blue sea of prosecuting them if they fail. What can authorities do if property taxes, fines or family maintenance payments remain unpaid and the debtors simply do not have the money? The expense of taking them to court is often greater than the debt, and a jail sentence risks turning someone who is merely unfortunate into a hardened criminal.
Allowing payment in time-money could be a less authoritarian option. In one Colorado town, for example, the authorities have allowed older residents who risk losing their homes to pay property taxes by volunteering time.
One of the difficulties of the US Workfare scheme has been the lack of transport and social facilities such as childcare provision in the worst unemployment black spots, making it even harder to wean people from welfare to work. The extended families of days gone by are no longer there. How can single mothers commute to work without child-minders or buses? Where they find a way, all the informal work that unemployed people have done for each other is left undone. A scheme currently under discussion for the Marshall Heights neighbourhood of Washington proposes that some of this vital community work - care for the elderly, child-minding and so on - should earn time-money, which in turn can be exchanged for benefits.
There is an echo of this in the government's new concept of citizenship pensions, floated in the green paper on welfare reform, which proposes giving carers pension credits to make up for the National Insurance they never paid because they were looking after elderly relatives.
If people are prepared to make a contribution to society in this way - earning time-money because there are no paid jobs - then even the most enthusiastic devotee of the work ethic would probably accept that they deserve the basic necessities of life.
The first major time-money scheme in the UK has already been launched by the charity Fair Shares in Stonehouse, a forerunner to nine linked time-money projects in Gloucestershire. Other schemes by the New Economics Foundation will follow in Newcastle and Lewisham, London, later this year.
Time-money could soon be playing an increasingly significant role in all our lives.
David Boyle is the author of "Funny Money: in search of alternative cash" (HarperCollins, £14.99)