A New York police officer leans forward and yells as if attempting, with the sheer force of his anger, to hold back time. His rage is understandable for, in this photograph, you can actually see the world turn upside down and all that was solid melt into air. This truly is a picture of a turning point in the history of the world.

It shows the moment when Occupy Wall Street campaigners reached Times Square, whose giant hoardings glow brightly in broad daylight even as furious protesters confront mounted police. When this photograph was taken, movements were simultaneously starting up around the world in emulation of Occupy Wall Street and its attempt to hold finance capitalists to account. In London and Vancouver, Brussels and – with a violent twist – in Rome, the call went out and the people came. But of all the weekend's photographs of global protest against capitalist excess, this, surely, is the image that will endure.

That is because it captures the surrealism of a moment when the stabilities and certainties of an era suddenly became yesterday's distant memory. Times Square makes a powerful setting for this picture. Shiny walls of towing glass, the citadels of corporate entertainment, dazzle among the giant screens – is that Apu from The Simpsons? – in the bright autumn air.

But no one is entertained. The faces in the crowd are genuinely angry and determined. A man in the foreground has a red star on his T-shirt. Sixty years ago they hunted reds in Times Square, metaphorically at least, as America fought the cold war. Today that red star says it all. These people have not come to protest just against a bad law or a single issue, but the system itself. They are putting capitalism in the dock. The photograph powerfully captures this moment because it so vividly shows the symbols of the order of things that inhabitants of western economies have up to now accepted.

There were "anti-capitalist" protests in the boom years but these were self-evidently marginal to a society lapping up the joys of credit. Today, the world is ready to listen to Occupy Wall Street and its claim to speak for the 99% against the profiteering 1%. Everyone knows what they are talking about and everyone can see some truth in it.

This deserves to be the remembered image of a moment when history assumed a new basic structure, but if you wanted to gauge the significance of these events a cartoon in the Times was also telling: a fat cat capitalist looks down on the marchers from a lofty skyscraper office. He comments that the people down there look small enough to crush with one finger. We've already done it, says his cigar-smoking colleague. When such a cartoon appears in the Times, hardly a Marxist publication, the world has changed.

This is a photograph of a turning point in history, not because the Occupy movement will necessarily succeed (whatever success might be) but because it has revealed the profoundly new possibilities of debate in a world that so recently seemed to agree about economic fundamentals. Occupy Wall Street and the global movement it is inspiring may yet prove to be an effective call for change, or a flash in the pan. That is not the point. Nor does it even matter if the protest is right or wrong. What matters is that unfettered capitalism, a force for economic dynamism that seemed unassailable, beyond reproach or reform, a monster we learned to be grateful for, suddenly finds its ugliness widely commented on, exposed among the lights of Times Square. The emperor of economics has no clothes.

This is an unbelievable moment. Pinch yourself. The global market economy triumphed two decades ago. In the 1980s, it was possible to dispute the Thatcherite cult of "wealth creation", but by the next decade most agreed she seemed to have been right. After the Soviet bloc disintegrated in 1989 the market ruled universally, the communist alternative turned out to have been a grotesque sham, and Bill Clinton and Tony Blair led the left to embrace free finance. This was the way the world worked. The old volumes of Das Kapital might as well go to the secondhand bookshop.

In this photograph we see the end of that consensual age, which turns out to have lasted just 20 years, when the free market was essentially beyond criticism. The very use of the word "capitalism" seemed corny a decade ago. What was the point of applying such a term to a way of life that seemed to have no outside to it? Now it is once again a word to hurl as abuse, as it was in the era of RH Tawney, or for that matter Lenin. Capitalism is in trouble because of the very fact that people are once again widely calling it "capitalism" – with the implication that we can dissent from it.

Socialist parties first got traction in the 1880s in the economic contraction that Victorians called their "Great Depression". In the capitalist crisis of the 1930s, western intellectuals admired Stalin, Welsh miners fought for the Republican cause in Spain, but many more in western Europe turned to the right. What collapsed was the liberal centre ground.

What we see collapse in this photograph is the post-1989 global consensus that unfettered market economies provide the greatest happiness for the greatest number. The slump is making people notice that another way to describe the free market is as Karl Marx's ruthless, tempestuous, darkly creative, but divisive and crisis-creating "capitalism". To say the word is to break a spell.