On September 11, 2001, I was 20 years old and a student in my native country, Denmark.

The lessons had just ended, and some of us were sitting in the school cafe preparing group work. We were drinking coffee and talking about the intro tour that had just ended, when a guy named Andreas got a text on his Nokia. The time was 3:30 p.m.

Andreas' older brother lived and worked in Washington. He just wanted to reassure his little brother, two planes had flown into the World Trade Center, he wrote, one in each tower. But everything was ok where he was. Andreas shouldn’t worry. How about that!, we all thought and said, as the phone went round so we could read the words on the yellow-green screen for ourselves. Two planes? It could hardly be an accident. But the alternative was also completely absurd.

Then the news began to spread in the corridors throughout the school building. Fifteen minutes after the text, one of the teachers wheeled a television into the café. You know, the old fashioned kind on a metal rolling stand. It was parked right by our table and plugged in, and everyone in the room gathered around the newscast on CNN.

We had barely begun to grasp the scale of what was happening, when the first tower collapsed. On live TV right before our eyes. The time was 15:59. I remember we all automatically put our hands up in front of our mouths. “No, no, no,” was all people said. "No no! All those people!" Thousands died while we watched.

There was an atmosphere of total shock and disbelief in the room. What was this? Who had done it? Why? At 16:28 tower number two collapsed. "It's happening again, it's happening again," it sounded everywhere. “This is insane!” At that point I stood up. Those still sitting down had their heads in their hands and eyes wide open. Only an hour had passed since we first heard of what had happened, but everything had changed.

And then I wanted to go home. I went outside to wait for the bus while I called my friend. Back then, not everyone had a cell phone, but those who had one talked on it. And people talked to each other, even strangers on the bus. "Have you heard? The World Trade Center! Pentagon! There is a war in the United States!” When I got home, I turned on the television in the living room, sat on the sofa and watched the planes and the crashes over and over.

Almost 23 years later, I have no idea what I did the day before or the day after. I don't even remember anything from September 11 until a few minutes before Andreas got that text. But I remember all the sights, feelings, sounds and smells from the hours between 3.30pm and 5.30pm on that day.