"Es gibt nur ein Berlin" (there's only one Berlin) is a cabaret song made famous by Claire Waldoff in the 1920s. But, of course, for many years, that was not true. From 1949-1990 there were two Berlins–East and West. There were two Berlins the first time I came to the city in 1982 as a college student on a foreign-study program. I was mesmerized by the city. It had a special energy that I think was the result of being surrounded by East Germany. I had not realized that all of Berlin, not just the Eastern half of it, was actually inside East Germany. Since there was a West Berlin, I'd assumed the city was on the border between East and West Germany, with half being on the Western side and the other half on the Eastern side. It wasn't until I'd entered the city, after a very arduous trek through East Germany, that I came to understand the geography of the place and even then I found it hard to believe. I was a philosophy major. I had an overweening faith in reason. But the existence of West Berlin seemed to defy all logic. The military presence in East Berlin, and in East Germany more generally, was so strong that it seemed it would be relatively easy for East Germany to take over West Berlin. That it did not, or that the West cared enough about that little piece of land to make its seizure an international offense, was profoundly mysterious to me.

I learned a great deal on that program about the lack of logic of human affairs, about the capriciousness of fate, about how arbitrary is the course of human events. Of course, there is a kind of logic to human events, but one that bears only the faintest of what Wittgenstein would call a "family resemblance" to the logic that is taught in math departments, or even to the logic used in the construction and analysis of everyday arguments.

West Berlin was more vital and dynamic than East Berlin, but it was the latter that fascinated me. There was a little elevated trolley that ran in a loop through both halves of the city. It was one of the ways one could enter East Berlin from the West. I loved that little trolley. Getting on it was like stepping back in time. It was made entirely of wood and had to have predated the Second World War, if not the First! It was truly clattering and ancient, and it carried its passengers from the thriving modern city of West Berlin back in time, back to a time before the war. If you are not so fortunate as to have visited East Berlin while it still was East Berlin, you will not know what I mean. The reason East Berlin seemed not to have changed since the war was that it hadn't changed, not much, anyway. The East Germans didn't do much rebuilding after the war, they simply repaired, when they could, what had been broken. They didn't have the money to rebuild, that is, to put up new construction. The Eastern half of Germany has always been the poorer part of the country. So the East Germans simply nailed boards back that had fallen off buildings, or repaired holes that had been made in walls. And some ruins they simply left as ruins. Everything seemed hardly to have been touched since the war. Even the wretched food, one could imagine, must have been very like the food during the war.

We traveled a bit around East Germany, my little foreign study group. I think we spent more than a week traveling through East Germany before we reached our destination of West Berlin. Everyone complained about it. East Germany was a gray and desolate place, the food was terrible, even the beer was terrible, and there was really nothing to buy with all the money we had been forced to change. Still, I could not get enough of the place. It was strangely fascinating to me.

I returned to Berlin in 2007. I was translating a book by the philosopher Søren Kierkegaard and needed help with some of the more difficult passages. A Danish friend, who had recently moved to Berlin, offered to help. It was a strange visit. The book I was translating was a novel called Repetition, which was actually about the narrator's attempt to recapture the magic of his first trip to Berlin by making a second trip. And, of course, it was my second trip to Berlin as well. Despite the fact that I had lived for many years in Copenhagen, I had not visited Berlin during those years.

The coincidence of my own circumstances with those of the fictional narrator of the book I was translating wasn't the only reason, however, that the trip was strange. Berlin was not the same city anymore. Where there had been two cities, there was now one, one I hardly recognized. I found myself nostalgic for the old city, for East Berlin as I remembered it, so I went one day to the DDR museum. The nostalgia for East Berlin, or for East Germany more generally, is palpable there, just as it is in the film "Good Bye, Lenin!" If I were younger, I would have been surprised by this. I'm not young though, so I'm not surprised. One almost always feels a certain nostalgia, I think, for the things from one's past that are gone forever, because their disappearance is a reminder of one's own mortality. Yes, that world, the world of my youth, is vanished forever, just as is my youth itself. There is something particularly poignant, though, about worlds that vanish suddenly rather than slowly as the result of the gradual accretion of the kinds of changes that are inevitable with the passage of time. Such disappearances give a sense of unreality to personal history. It is much easier to adjust to, and thus accept, gradual changes; sudden changes leave one wondering whether it was not all just a dream, and if one's past was just a dream, what sort of implications does that have for one's present?

I bought a book at the DDR museum called The Divided City. It's a very good book, actually (I say actually because those of us who remember the DDR are inclined to think anything associated with it will be of inferior quality), though the translator was clearly not a native English speaker.

I had the strangest experience as I was reading the description of the fall of the wall in 1990. So there is no more East Berlin, I thought. That city, in all its strangeness, that I had experienced in my youth, was gone, completely vanished. It's all one Berlin now, one city that despite its diversity is homogeneous in a way that only those who experienced East Berlin will understand.

But what of the rest of East Germany, I thought, what had happened to it? How could it go on without East Berlin, its former capital? I suddenly felt the way one feels just before catching oneself from falling, that brief dizzying, weightless confusion–and then I remembered that, of course, there was no East Germany anymore. And the Soviet Union?–Also gone. It was a strange chain of thoughts that made me feel old. It hardly seemed possible to forget such things, and yet people do, as they sometimes fear, upon waking, that they're late for school, when they're actually grown, or late for work, when they are retired, or as they reach across an empty bed for a long dead spouse.

Perhaps it is only me, but it seemed sometimes, when I looked at the faces of the people I passed on the streets of the new Berlin, that there was a kind of confusion in them. And yet no city has ever been so conscious of the transitory nature of human existence. This is part of what gives Berlin its unique character, what makes a life of letters and a life of artistic or aesthetic abandon cohere here in a way that it seems to me they do not cohere anywhere else in the world.

At least it used to be like that. It is hard for me to tell whether that's still true, hard to tell whether the present existential confusion is being channeled in the creative ways in which the earlier confusion was channeled. So many people in Berlin now are not from there. Berlin was then, when I returned back in 2007, the cheapest city in Europe, so colonies of expatriate artists and intellectuals, such as my Danish friend, were springing up everywhere. But of course Berlin has always attracted foreigners. So perhaps there is truth in the saying–the more things change, the more they stay the same. Perhaps it is just that it is hard to see the uniformity in the change, or at least hard to see it if one looks too closely. You cannot help but look closely, though, if you are looking for your own past rather than the course of history writ large. Yet there is something tragic in the fact that the closer you look, the less you will see.

There is only one Berlin, but it is not, as the song continues, "my Berlin," not the one I remember. This one is certainly better. I have not let nostalgia blind me to the fact that I am still alive and really not so terribly old that I could not come to love this new city just as much, and perhaps even more, than I loved the old. I determined to throw myself wholeheartedly into the exploration of what the city had to offer. It may yet become "my Berlin," I thought, and perhaps accepting a certain confusion will be part of that process.

There is a part of humanity, though, that lives with a deeper and more enduring sense of disorientation than the one I experienced upon finding "my Berlin" changed. Visit the new Jewish Museum in Berlin and you will begin to understand something with which Western culture still has not come to grips. I'm not talking about the Holocaust, at least not directly, but about something else, that is seldom if ever discussed.

I don't normally find museums moving. "Interesting" is how I would be inclined to characterize them. Berlin is unique, though; because of its history, many of its museums are moving. It is easy to demonize Germans and German culture. The picture one gets of both in the Jewish Museum is not, however, one of a demonically anti-Semitic people. Despite the numerous examples of the anti-Semitism that had always been a part of European culture, the picture that emerges from the various exhibits is of a culture that toward the end of the 19th and the beginning of the 20th century was far more advanced in terms of accepting and integrating Jews into the mainstream than any other culture in Europe.

Social reforms that made life easier for Jews in Germany than anywhere else in Europe go back as far as Frederick the Great in the18th century. By the nineteenth century, unlike Jews in Eastern Europe, Jews in Germany did everything, or at least that is the impression one gets from the museum. They were an integral part of both economic and cultural life. Jewish families had lived in Germany, been German, for generations, had built businesses, careers, had been instrumental in helping to direct the culture in positive and creative ways. German culture, in all its richness, is inconceivable without the strong and vital influence of the Jews. It is the Jewish influence on German culture, I believe, that is the reason the Germans are the most conspicuously intellectual of all the Europeans, as well as the reason they have the most finely developed aesthetic sense.

Does anyone really know how strong was the Jewish influence on German culture? Many German Jews converted to Christianity for social and political reasons in the 18th and 19th centuries and tried to lose their Jewish pasts after that. There's an eerie scene in "Heimat," a German television series that focuses on the fictional town of Schabbach from the period just after the First World War up until the early 1980s. One of the characters, Paul Simon, who had left Germany after the First World War, is trying to return for a visit just before war breaks out again. He can't disembark from the ship, though, because he has no proof that he is Aryan. He telephones his wife and son who are waiting for him on shore. They, in turn, telephone the family back in Schabbach, who search frantically through the local archives for the required proof. But each name their search produces–e.g., Abraham Simon, Daniel Simon–is ambiguous. The town graveyard, they observe, is full of Simons. It does not seem to occur to the Simon family that they may once have been Jewish and that a large part of the town's inhabitants may be descended from Jewish stock, yet the implication is unmistakable to the viewer.

Names we tend to think of as Jewish are really simply German. According to Judaism 101, an online encyclopedia of Judaism, Jews did not originally have traditional surnames, so Jews who immigrated to Germany simply took German names. How many German families that had originally been Jewish retained habits and values from a Jewish past they did not even know they had?

The Jewish museum is full of photos and even home movies and other bits of memorabilia of prosperous Jewish families who were thoroughly German, of businesses and even whole industries that were Jewish in origin. The loss of so many Jewish lives at the hands of the Nazis is a tragedy the magnitude of which defies comprehension. The loss to the culture is different, more palpable. Strength comes from diversity. This is true not simply in the breeding of animals but in the progress and development of cultures. One of the great strengths of German culture, I believe, is the Jewish contribution to it. They were not at the periphery of the culture as was so often the case with respect to the cultures of Eastern Europe, but at the very heart and in myriad ways. Go to the bookstore that is part of the Jewish Museum and you will be surprised to find books by German authors you did not know were Jewish.

And now they are gone. Those businesses, those individuals, who were so much a part of the blossoming of German culture from the 18th century through the beginning of the 20th century, are gone, simply gone. The Jewish Museum put on an exhibition last year called "The Whole Truth...Everything You Always Wanted to Know About Jews." "Most Germans don't know any Jews," explained Bill Glucroft, who sat in a glass box above a caption that read "Are there still Jews in Germany?" and answered questions about what it was like to be Jewish as part of the exhibition that became popularly known as "Jew in a box."

I don't mean to suggest that there are no Jews left in Germany, or more particularly, Berlin; there are, though their numbers are nothing like they were before the war. Even Glucroft is not German by birth. He's from Fairfield, Connecticut. He moved to Germany after he fell in love with a German woman. Most Jews who live in Germany now have had to start from scratch. Everything that was Jewish before the war was seized, destroyed, or handed over to non-Jews so that even if it was not destroyed, it was no longer the same. It wasn't just individuals that were lost, it was a hugely positive cultural force. The culture has been made poorer by that loss. Even today it has not yet recovered.

And the people, the Jews who were not killed, the German Jews who were forced to emigrate, or who somehow survived the devastation that took so many other lives, they are poorer too because their history, their cultural roots, have been cut away. There are so many Jews dispersed throughout the world, whose home, whose real, cultural home is not Israel, but Germany, but whose lives are an effort to forget that rather than to remember and celebrate it. But remembering and celebrating one's past is, to some extent, essential to one's humanity.

The devastation that was the cultural loss to Germany of the destruction of its Jewish population is made so palpable in the Jewish Museum that it is numbing. One emerges from the place staggering under the weight of an entirely new loss, which, though admittedly less than the loss of lives, is still tragic. German Judaism was a way of life that in its heyday was glorious-and is now gone forever.

Yes, the past is always gone forever. But rarely is it lost in so abrupt and horrific a manner. I have a little hope, though, one that I have only recently conceived, and it is that Jews will gradually return to Germany, that the Schwartzes and Kleins and Grossmans, whose names we think of as Jewish, but which are really simply German, will reclaim their own history as Germans and reinvigorate the culture of the new united Germany.

There may be only one Berlin again now, but it is not yet the city it once was. I am hoping, however, like the fictional narrator of Kierkegaard's novel, for a repetition–for a return of the glory that was Berlin before the war, a return of the beautiful city of which Jews were an essential part.