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AT THE climax of “The Day the Earth Caught Fire”, a science-fiction film made in 1961, the fate of the planet hangs in the balance. The world's great powers decide to detonate nuclear bombs, hoping to push the Earth off a collision course with the sun. Do they succeed? The final scene shows two versions of the next day's Daily Express: the headline on the first reads “World Saved”; the other, “World Doomed”.

In the 2007 sequel, “The Day the Credit Markets Seized Up”, Wall Street seemed this week almost to have made up its mind about the ending: World Saved, Probably. Financial markets had expected the Federal Reserve to cut interest rates by a quarter of a percentage point on September 18th, but prayed fervently for a half. When the half came, America's markets rejoiced: the S&P 500 index enjoyed its largest rise on a single day since January 2003; the next day share prices elsewhere jumped for joy and junk-bond markets sprang back to life.

But on sober appraisal, there is less cause for celebration. Global money markets are still bedevilled by banks' need for cash and mistrust of one another: witness the thousands of Britons who queued this week to take their money out of Northern Rock, a mortgage lender. The longer that money-market rates stay high, the greater the danger that expensive credit will start to hurt real economies. Central bankers still have work to do and reputations to make and lose—chief among them Ben Bernanke, the chairman of the Fed. Mr Bernanke may have been feted this week. But it will take more than one rate cut, with Wall Street and Congress screaming for it, to make his name. In the past the Fed has been too eager to cut rates repeatedly when markets gripe. Mr Bernanke has yet to show he is not making the same mistake.

The size of the Fed's cut and the statement that accompanied it signified fear more than hope (see article). The central bank hopes to “forestall some of the adverse effects” of the credit crunch on the economy. But trouble may be coming anyway. The housing market's malaise is deepening all the while. This week's symptoms were a 12-year low in housing starts and a doubling of foreclosures in a year. No wonder housebuilders are their gloomiest since the 1991 recession.

If America is set for a sharp slowdown, or even a recession, it is sure to import less from other countries. That, however, is not the main danger to the rest of the world. Both Europe and Asia are less dependent on American growth than they used to be. Europe is now on a par with America as a market for Chinese exports. Sales to America account for less than 3% of euro-zone GDP. And some rebalancing of the world economy—a smaller American current-account deficit, a weaker dollar—is no bad thing.

The real source of pain is the rise in borrowing costs in both America and Europe. Granted, things are a little better than they were. The gap between three-month interbank rates and Treasury bills, a measure of the risk of lending to other banks rather than Uncle Sam, has narrowed in recent days, helped by the Fed's cut. Sterling interbank rates also fell, notably after the Bank of England abandoned its refusal to intervene in the three-month money market. But the about-turn came only after the panic at Northern Rock—and has heightened criticism of the governor, Mervyn King. Central banks must hope that a turning point has been reached, but interbank rates are still high. There is a long way to go.

A lot of this pain, alas, is necessary. Central banks have been saying for months that risk had become underpriced. Well, now the repricing is at hand, and it is not going to be fun. Banks have to work out the cost of the damage done by years of easy credit and gorging on complicated financial products (see article). It could take months to put prices on the complicated mix of assets for which they are ultimately liable. Meanwhile, they will want to keep cash to themselves rather than lend to others. And in future they may be choosier about who they lend to, directly or indirectly.

This is not to say that securitisation is about to be uninvented. It cannot be and should not be. In recent weeks the dangers of financial innovation—the divorce of originator from ultimate lender; the sheer complexity of some derivatives—have become plain. The benefits remain, not least the increased ability of households to smooth spending over their lifetimes and of markets to allocate risks to those most willing to bear them (see article). But there are cycles in all things: underpricing begets excess, which begets a reckoning. For a while at least, many people and businesses will have to pay more to borrow, or will not be able to borrow at all. The results will be felt in markets for housing—America's was far from the frothiest—as well as junk bonds and corporate buy-outs.

To some extent, easier monetary policy may soothe the transition. Already some central banks have held off interest-rate increases that looked certain a few weeks ago. But even if some of these eventually cut rates, they are unlikely wholly to reverse the tightening of conditions just yet. The markets are in effect raising rates on the central banks' behalf. These monetary policymakers are unlikely to forget inflation in a hurry.

But might the Fed? It says not. And given the recent run of economic data, inflation hardly seems an imminent threat. That ought to help to protect Mr Bernanke from the charge levelled at Alan Greenspan, his predecessor. Under Mr Greenspan, whose memoirs came out this week (see article), the Fed won a name for being quick to cut rates when markets squealed but slow to raise them when the economy picked up. The housing boom—and today's mess—are the result.

Having delivered a half-point cut rather than a quarter, Mr Bernanke is not yet free of the suspicion that he will follow Mr Greenspan's path. Nor is he surely guilty. His Fed has cut rates with the economy looking ropy—but also with bankers and politicians trying to bully him. The hope is that he acted because he saw a gloomy outlook. The fear is that he did so because it is hard for central bankers to say no.