Oppenheimer. The conversation you can't leave for later.

My son asked me whether nuclear weapons still exist. We were watching Oppenheimer in sections — it's three hours long and not entirely suitable for a nine-year-old, but the question of how to handle it seemed less important than the question of what to do when he's already encountered it through other means and the conversation is already happening.

I said: yes, nuclear weapons still exist. He said: how many? I said: approximately thirteen thousand, across nine countries. He was very quiet for a moment. Then: 'Why?'

Why is a harder question than it looks. The factual answer — deterrence theory, mutually assured destruction, the logic that has kept large powers from using them since 1945 — is accurate but unsatisfying. It describes the situation without explaining the morality of it. And my son was not asking about deterrence theory. He was asking about why human beings would make and keep thirteen thousand of something capable of ending human civilisation.

I said: I'm not sure I have a complete answer to that question. He said: but you're a grown-up. I said: grown-ups have been asking this question since 1945 and haven't agreed on the answer.

He sat with this. Then: 'Did Oppenheimer ask it?' Yes. He asked it for the rest of his life. He didn't like the answer he kept getting.

Three weeks ago I would not have had a way into this conversation. Then a film opened that gave us a shared entry point, and my nine-year-old is now engaged with one of the most genuinely complex ethical questions of the twentieth century. This is not nothing.

So they went anyway. I said: so they went anyway. And we were sitting with one of the most genuinely difficult ethical questions of the twentieth century, at dinner on a Tuesday evening, because a film had given us a way in.

I want to be honest about something: I don't know how to have conversations about nuclear weapons with a nine-year-old and get them right. I don't know the correct calibration of honesty versus reassurance, of historical weight versus present-day context, of this is serious and here is why versus the world has survived this for seventy-eight years.

What I do know is that not having the conversation is also a choice, and not always the better one. Children encounter difficult information through other means — games, fragments of news, conversations overheard — and the absence of a parental framework doesn't protect them from the information. It just means they process it without you.

The twenty-first edition of this newsletter. We've been going since March. I've been writing about screens and boredom and Easter and D-Day and Barbie and now nuclear weapons, which is not a list I would have predicted in March. The summer has been strange and rich and full of the conversations I didn't plan to have.

My son, at the end of the Oppenheimer conversation, said: 'I think it was wrong to make it.' I said: many people agree with you, including some of the people who made it. He found this genuinely surprising — that you could think something was wrong and do it anyway. I said: this is one of the hardest things about being a person. He nodded in a way that suggested he was going to keep thinking about it.

Good. He should keep thinking about it. So should all of us.

The Oppenheimer conversation hasn't ended. My son brings it up occasionally, unprompted, in contexts that have nothing to do with history. Last week he said: 'Is Oppenheimer like the people who invented cigarettes? They made something and knew it was dangerous?' I said: that's an interesting comparison. He said: 'But cigarettes didn't end the world.' I said: no. He said: 'So it's worse.' I said: most of the people who worked on it would agree with you.

He keeps coming back to it because it hasn't resolved. That is, I think, the appropriate state for a nine-year-old who has encountered a genuinely unresolved question. He should keep thinking about it. The question deserves the continued attention.

What difficult conversation have you been putting off because you haven't found the right moment or the right way in?

And: what might happen if you started it imperfectly, with the honest admission that you don't have all the answers, and let your child see you working through it alongside them?

One conversation you've been delaying: start it this week, imperfectly. Say: I don't have a complete answer to this, but I think it's worth us thinking about it together. Then let it be incomplete. Incomplete is better than absent.

This is edition twenty-one. Thank you for reading this far. Next week Alex writes from New York about the Maui fires, which is a different kind of difficult conversation — one about the present rather than the past. See you Thursday.

Names of people and brands in these editions are changed. Whoever was there and reads this knows what we are talking about.