Philip Hensher: But that was in another country...

Sometimes, when I'm in Berlin, I seem to glimpse the ghost of a different city inhabiting these same streets. In Prenzlauer Berg, behind the gleamingly restored Jugendstil apartment blocks and chic restaurants serving Sunday brunches, there rises up a shabby, grey street with a single cellar bar; behind the lavish grandeur of Unter Den Linden, the sight of a pathetic shop, its wares pushed to the front, two quiet assistants following passers-by with their eyes. Friedrichstrasse, going in the direction of Kreuzberg, has a slight kink; in the mind's eye a cabin rises up, a barrier, a 10-foot wall, the sign "YOU ARE NOW LEAVING THE AMERICAN SECTOR".

I guess everyone of my age sees these ghosts on occasion when walking around Berlin. Twenty years have gone by since the wall came down, enough time for a human being to grow up without any memory of what lay here before. It was often the same buildings, the same streets, but everything was completely different.

The first time I went to Berlin was in the mid-1980s. The time I spent on the other side of the wall – as we used to say – is now immensely precious to me. The atmosphere was completely different: the odour of brown coal, the smell of the Trabant, as there were literally no other cars on the road, made themselves felt within yards of your crossing.

On one occasion, in the late 1980s, I had read a travel article in The Independent. Some very well-informed writer had recommended that visitors go up to Prenzlauer Berg, where, it claimed, there was a burgeoning intellectual scene, like a reviving Weimar Republic. We went there, and found a glum-looking old lady with a dog and a café serving a sour, beety beer for some bizarre sum like one mark and 63 pfennigs. What happened to all those people in the East Berlin cafes? They gave up, had to learn a job, had to accept that the food they had eaten and quite liked all their lives wasn't good enough and they would have to get to like West German food. Which in any case, they were told, was much better.

I went to Berlin two months after the Wall came down – it is one of the great regrets of my life that I didn't just get myself, somehow, to Berlin on 9 November 1989. There were cars on the East Berlin street that weren't Trabants. And – one abiding memory – filing in and out of the sex shops in the West, around Zoo station, entire families could be seen, marvelling.

I spent a lot of time in Berlin in the early 1990s, ending up writing a novel about the fall of the Wall. As late as 15 years ago, you could still see how East Germany had been when travelling to Leipzig, Dresden and Weimar. Things were changing, but very slowly. Once, in 1996 or so, I decided to clear out the kitchen in the flat on the Kopenhagener Strasse I was living in. At the back, were cleaning fluids, dried goods, coffee substitutes, all made in the DDR, and never thrown away. Even then, they seemed like artefacts from Tutankhamun's tomb.

Last year, in Dresden, I thought of my first visit to a then-empty town, magnificent black ruins at its centre, one of the great art galleries of Europe unvisited and gloomy. Now the trippers were eating Swiss ice-cream in the sun, the Zwinger Palace was crowded, the merchants were smiling.

A great wall rises up between us and what we remember, and our past becomes harder and harder to reach, even in thought. You can glimpse the Berlin Wall in photographs. But soon most people will not realise that the wall between now and the astonishing recent past was ever there.

A British actress's lesson in true star quality

The film of Lynn Barber's memoir, An Education, has rightly been winning plaudits for its star, Carey Mulligan. She is wonderful, effortlessly moving from schoolgirl to sophisticate, and maintaining a constant throb of unspoken longing under a practical exterior.

Some people have said Mulligan is a revelation, as if she has come from nowhere. Perhaps it may seem that way: but some of us knew that she was headed for greatness as soon as we saw her in nothing more elevated than Doctor Who. In an episode from 2006, "Blink", the whole weight of the plot fell on her. It was one of the most ingenious pieces of plot construction of the new Doctor Who, and the ostensible hero and his sidekick appeared, for the most part, only on a video screen. Mulligan was tremendous, warm and human in the part of Sally Sparrow. An instantaneous web campaign sprung up to have her installed as the Doctor's new companion. Well, that would have been nice, but you can't blame Mulligan for being much more ambitious. So far, her choices of scripts have been exemplary, including a fine film of David Haig's Kipling play, My Boy Jack. Her quality shone out in a Saturday tea-time sci-fi special. She is going to be one of the stars of the century.

Sacred art can play tricks with your mind

Anyone will be knocked out by the National Gallery's wonderful exhibition of Spanish golden-age religious art, and especially by the six extraordinary Zurbarans. It is one of those moments when even those not susceptible at all to religious feeling will feel some respect for the depth of those feelings in others.

As for me, I had a definite recollection of a previous encounter with Zurbaran at the National Gallery. I remembered that they were full-length figures of all 12 apostles, all in Franciscan robes, all against a black background, very austere, and very affecting. Though the fact I could find no reference anywhere to a full set of apostles painted by Zurbaran was beginning to dent my certainty.

And then light dawned on my early senior moment. There was a set, but it was of Jacob and his sons. Far from being in monks' robes, they were in a variety of exotic outfits in bright colours. A donkey entered into one, very cheerfully. And they all included a landscape. You can go and see them any time you like at Auckland Castle in Durham.

Disturbingly, my memory of 12 dark-robed figures was very precise – I dare say I had multiplied the great St Francis in the National Gallery to produce a mental dozen. What other completely non-existent works of art can one look forward to our minds producing? Thrillers by Jane Austen? Choral symphonies by Blur? Blank verse epics by Pam Ayres?