The twentieth anniversary of 9/11 is a significant milestone, in the paradoxical way that the ordinary turning of the calendar somehow is both mundane and mysterious. Many of us will be asking “Where were you when…?” this week and next week, in an effort to locate ourselves and each other in relation to the event itself and the “normal” world that we left behind without knowing it on the night of 10 September, 2001. It is an attempt to find the rhythm of life without the assumption that such things could happen.

Telling the stories of ruptures is problematic. As Alan Mintz has written, “a destructive event becomes a catastrophe when it convulses or vitiates shared assumption”, so we can no longer trust either the tale or the teller. The tale is not yet formed, and the teller does not yet know what to say. We lose what Barthes called our mythology – the language in which we speak – just as another is being tragically born. I remember hearing the sentence “A plane has hit the World Trade Centre” that afternoon (I was living in Krakow at the time) and thought: how terrible, what an awful accident. In the days before smartphones, it was not until I returned home to find the footage on television that I understood. Like many others, I had thought it was an accident: the tram home in the coolness of a Polish autumn had been quiet: the world seemed on its rails.

As the reality sank in, however, the trauma started to complicate things further. We often say “I was traumatised” or even “I am traumatised” but neither construction does it justice – it is truer to say “I am being traumatised” but there is never time to form that thought. The moment of impact is, by definition, not described, even when it is replayed endlessly, over and over again, making the viewer beg for the pause button or, better yet, rewind. “It’s like something from a movie” was something I heard a lot in the following days and weeks.

The interrupted quality of the most valuable kinds of witnessing means that even in investigating, there is trauma, as we know the witness may have said more, thought more: but we cannot know. Instead the screen crashes to black, the tape clicks off, the diary ends. First-person witnessing always promises an ending which, if not happy, at least holds some promise of continuity. We know, picking up a published memoir, that the witness survives. This is what makes films like The Pianist watchable – we know, though the artefact’s very existence, that the story did not end on the last page – it is equally why the most shocking part of the diary of Anne Frank is the insertion of the editors: “ANNE’S DIARY ENDS HERE”. The tragedy is that she could not finish her story, a symbol for many others whose stories had barely started.

Alongside this, the witnesses have to begin incorporating the previously impossible into their awareness, redrawing the frontiers of possibility and probability. Primo Levi, in a quote I often refer to, described how the liberators of Auschwitz struggled to recognise what had happened as something that could happen, that belonged in “the world of things that exist”. In trauma, we are confronted with things that just moments earlier were unthinkable, precisely when our minds lose the ability to do more than record because the routines and operating assumptions of our world are upside-down. We see people throwing themselves from a burning building and numbly watch, trying to make sense of what will not make sense. Things of which, to be honest, there is no sense to make. It is happening, live and on-camera, and we have no choice but to sit on the sofa, strapped into history as it carries us who knows where. And yet our understanding may far outstrip those on the scene.

A couple of weeks ago, we watched the fall of Kabul, completing an arc which began its upward drive on that day twenty years ago. And the experience of that day allowed us to see terrible things more clearly: Afghans falling from their desperate handholds on a departing cargo plane, their twisting and flailing bodies a contrast to the almost balletic grace of the jumpers from the towers.

The photo of “The Falling Man” captures the duality of all traumatic testimony: that it describes both what happened, and what it is like to have experienced it. For the only experience that we can access, come even close to, is that of the onlookers whose only decision is what to allow into the lens of history, helpless as the thought hundreds of metres above turns into action that can only be witnessed, never truly understood.

As the event unfolds, the shift in metalanguages accelerates. Comparisons and analogies are sought, however hackneyed, however inadequate, to convey something of the unthinkable in terms that have already been thought, relating it back to their own lives and preoccupations. A few weeks later, my MA adviser commented on a draft of my dissertation, saying “You know, this is the end for a certain conception of Auschwitz.”

But for most, the early period is a time of confusion. As Muska Dastageer, a university lecturer in Kabul, tweeted on 19 August: “You feel like a speck of dust in some uncontrollable convulsion of history. It is not true, of course. There was a causal chain, decisions, failures. But that is how you feel. And from this shaking ground, it is hard to speak.” One strategy is to take pieces from the wreckage, hoping the specks of dust resolve themselves into a whole that can be understood. But that wholeness comes from without the storm, as we see what the others saw.

Slowly, however, dust does settle, creating the first symbols out of what comes to hand, as people try to position themselves and sift their memories as rescue workers sift ashes. Art Spiegelman, author of the graphic novel MAUS, found himself both the child of survivors (of the Holocaust) and the parent of a survivor (his daughter’s school, within Ground Zero, became a triage centre). Commissioned to design a cover for the New Yorker magazine, he later described himself as “reeling on that faultline where World History and Personal History collide” – realising that the “indescribable” smell of burning flesh his father had described in Auschwitz was now a sense memory for him too. Otherwise, the image of “the looming north tower’s glowing bones just before it vaporised” was the essential image as he tried to “sort out the fragments of what I’d experienced from the media images that threatened to engulf what I actually saw.” His eventual design was black, the silhouettes of the towers picked out in a deeper ebony, “in the shadow of no towers.” The legacy of trauma is ongoing, and sometimes all the more indelible for being invisible.

Symbols are created with dizzying speed, to try and provide an ending, or at least a way station to recovery, triage for the mind. I remember the way the twisted metal silhouette whose disintegration so transfixed Spiegelman was suddenly everywhere: on television, in newspapers, on the covers of magazines. A shorthand of ruin, a stage-set for a president to proclaim the invincibility of the American spirit as it smouldered, it was woven into the fabric of everyday life, as hard to remove as the stench of smoke from clothes. The way the essence of the image was distilled from photograph to graphic reminded me of the way the terror and complexity of Auschwitz is reduced to the symbol of the Birkenau gate and rail tracks: simplifying and smoothing the roughness of the real into the manageable symbol.

But symbols allow healing, of a kind. The Polish poet Andrzej Bursa of how “Inside Auschwitz’s barren rib-cage/ Through which the setting sun flowed/ Like blood/We journalists wandered around looking/ into the black holes of crematoria”. The ruins can be viewed, studied, understood – even if this can be “Blasphemously objective”, it presupposes that there was life afterward, even if only of a kind. The “ribs” of the towers are now museum pieces.

The challenge of the next catastrophes will be that they will not come roaring out of a cloudless sky, raining death with vicious suddenness. It will not be, as Jonathan Safran Foer wrote, Extremely Loud and Incredibly Close, but something which we will have to make an effort to hear. News will come slowly, confusingly, in scattered reports of disease, in sudden silences from remote settlements, in the repetition of “once-in-a-generation” events. It is announcing itself now, in a microscopic virus that brings nations to their knees, in sea levels that only reach their deadly new point of advance for a few moments of a turning tide, in air that is imperceptibly less easy to breathe, even in the increasing intensity with which fools insist it is not happening, that all is well, that the sky is not falling.

But if we do not do something, the question the children will ask will not be “Where were you when…? but “Why did you not…?” And we will have no answer, because the task of making sense of now was often hard enough, and the future is unknown. But in moments of silence, as we measure the distance from the certain tragedies of the past, we can perhaps stop and ask what has changed, what is changing, what could change before the next anniversary arrives, unbidden, unexpected and yet completely anticipated. Listen carefully for the storm beginning: all we can do is wait for loud noises, hollowly consoled that if we can hear them, we have escaped the first stage, at least for now.

For Julian Bessa, an accidental survivor, and Dr Syed Tabatabai, who works to save the world from both Covid and itself, and narrates its complications in stunning prose poems. Eyewitness accounts of 9/11 are taken from The Only Plane in The Sky: An Oral History of 9/11 by Garrett M. Graff. The lines from ‘Auschwitz – Excursion’ by Andrzej Bursa come from Killing Auntie & other work, translated by Wiesiek Powaga.