Last summer, swimming in a waterfall in Cumbria with my daughters.

In my 40s: I had two children young enough to think their parents wonderful, my business was booming, I was happily married and living in the Cotswolds with a veg garden and ponies in the paddock. Who could not be happy?

Preparing for Sound Of Metal. Feeling challenged and overwhelmed and lost in something is very fulfilling.

Being happy is not a constant. But I am very happy when I am spending time with my family and my friends, and going on hikes with my dogs.

For example, I was a little surprised when I was talking to a friend who was going to go on the radio. He does work on cosmology and astronomy, and he wondered how he would explain what the applications of this work were. "Well," I said, "there aren't any." He said, "Yes, but then we won't get support for more research of this kind." I think that's kind of dishonest. If you're representing yourself as a scientist, then you should explain to the layman what you're doing—and if they don't want to support you under those circumstances, then that's their decision.

It is necessary, I believe, to accept this idea, not only for science, but also for other things; it is of great value to acknowledge ignorance.  It is a fact that when we make decisions in our life we don't necessarily know that we are making them correctly; we only think that we are doing the best we can – and that is what we should do.

the colonel said I shouldn't tell them how the neutrons work and all the details because we want to keep things separate, so just tell them what to do to keep it safe.

Then there was Von Neumann, the great mathemati-cian. We used to go for walks on Sunday. We'd walk in the canyons, and we'd often walk with Bethe, and Von Neumann, and Bacher. It was a great pleasure. And Von Neumann gave me an interesting idea; that you don't have to be responsible for the world that you're in.

There was no importance to what I was doing, but ultimately there was.  The diagrams and the whole business that I got the Nobel Prize for came from that piddling around with the wobbling plate.

I don’t believe I can really do without teaching.  The reason is, I have to have something so that when I don’t have any ideas and I’m not getting anywhere I can say to myself, “At least I’m living; at least I’m doing something; I’m making some contribution”—it’s just psychological.