The Blair Government, like all others before it, conforms to the entropy theory of politics; entropy being, in case it comes up in your Christmas charity quiz night, "the degradation of the matter and energy in the universe to an ultimate state of inert uniformity". The Blair universe started in 1997 with a big bang in which combustible parts of euphoria, idealism and intense hype exploded, generating huge quantities of energy and high expectations. Since then the energy has gradually dissipated and the expectations have fizzled into a dull grey goo.
However, it is important to distinguish between two entropic processes. One is real, and consists of the inevitable alienation over time of supporters from any once-popular venture. In the past, political movements have been able to counter this effect by recruiting new supporters, usually to defend some group interest.
Since the rise of the Labour Party as the party of the organised working class, however, British politics has become increasingly atomised. Margaret Thatcher tried to create new interest groups by selling them council houses and privatised-industry shares at a discount, but won a gently declining share of the vote at her three successive elections. In the absence of such interest groups, or great national challenges, politics becomes essentially a defensive activity, one of husbanding political capital and trying to make it last for as long as possible.
The other kind of entropy has been the staple of political commentary over the past few weeks, but it is largely imaginary, the product of wishful thinking by people who have been overly affected by the first kind of entropy and who have fallen out of love with New Labour. It assumes that governments become exhausted if they stay in power for too long, that ministers gradually lose the will to live and become unconscious collaborators in pushing the pendulum to the other side.
It is a theme that lies behind much of the commentary on David Blunkett, but also on the Blair-Brown rivalry which the Home Secretary managed to push off the front pages. Had it not been for Blunkett's drama, it is easy to imagine the endless analysis that would have been devoted to the body language of the Chancellor's refusal to play ball with the Prime Minister, literally, at their photo opportunity with children doing rugby training, an event designed to advertise their unity behind the Pre-Budget Report.
Time and again, the Home Secretary has been described as "pivotal" to Tony Blair's Government, as if it were only the lack of suitable candidates to replace him that explained the Prime Minister's determination to keep him on. True, Blair did once exclaim with delighted approval, after a meeting with Blunkett in opposition when Blunkett was Education spokesman: "He's even more right-wing than I am!" And Blunkett's obvious successor at the Home Office, Charles Clarke, who also succeeded him at Education, is more of an instinctive liberal.
But John Reid, the Health Secretary, is equally well qualified to be Home Secretary and he yields to no one in his robust social conservatism. The only argument against Reid, should Blunkett be forced out in the next week, is that he has held five Cabinet posts in five years and has only been in his present job for 18 months.
The idea that the Government's cosmic clockwork is running down because the supply of true Blairite believers has dried up is, therefore, mistaken. Just as mistaken as the view that, because personal relations between Blair and Brown are tense to the point of non-existent, the foundations of the Government are about to collapse. I have fallen victim to this fallacy myself. I thought in 1998, when Paul Routledge's biography of the Chancellor revealed the depth of his resentment against Blair for stealing his crown, that this could not go on, echoes of Thatcher and Lawson, fatal fracture in central axle of government, and so on and so on.
Six years later, it has gone on. Relations between the two men have always "never been worse", yet public differences of policy remain surprisingly hard to discern. Talk about psychologically flawed - but as a political relationship it endures.
There is a journalistic self-importance, too, in the assumption that headlines in large point sizes about ministerial impropriety have a cumulative effect on a government. It was widely said at the time by journalists - possibly including me - that if the Ecclestone business had happened later on in Blair's Government, instead of when the ardour of the honeymoon was still undimmed, it might have brought him down. I doubt that now. There is a hidden assumption about the coverage of Blunkett's misuse of free rail travel (admitted) and influence of immigration procedures (contested) that, after Hinduja, Mittal and all those other teacup-tornadoes that not even most journalists can remember, his head cannot long remain off the pointed stick outside the encampment.
We are perhaps too influenced by memories of the dying years of the Major administration, when the government did indeed seem exhausted and the cumulative and largely unfair impression of ministerial venality did take its toll. This Government has its problems all right, but they are not terminal yet. After all, Labour has only been in power for seven and a half years: the Tories managed 13 years after 1951 and 18 after 1979.
Blair's grasp of this seems astute. He has recognised that three parliamentary terms is probably the normal limit for a prime minister. Not even Thatcher, the longest-serving one of the 20th century, quite managed that. Yet it should be perfectly possible for one political party to remain in power for longer than three terms, provided it can renew itself in office. That is the deep question of politics today, not whether the Government is so weakened that Blunkett's fall is inevitable. My guess is that Blunkett will only go if he's discovered to have done something more unambiguously contrary to the ministerial code than anything so far alleged.
This is, as it has been almost since 1 May 1997, a government in decline. It is succumbing to the law of entropy, but rather more slowly than its virulent critics in the biased metropolitan media hope. They should not confuse the inevitable and gradual erosion of support for it, as clumps of students, hunters and anti-war activists peel away, with a loss of drive and ambition among ministers, from the Prime Minister down. Yes, Iraq has taken a heavy toll of Labour's support, and it has demoralised the Labour Party. But London-based journalists, who tell each other "I don't know anyone who says they will vote Labour", tend to exaggerate it.
The Blunkett furore does not, therefore, signify a government in trouble. The more important question over the coming year is whether Gordon Brown would be more successful than John Major in renewing his government without changing the party in power.
The writer is the chief political commentator for 'The Independent on Sunday'