My science family came from all over the world, and members were of varied backgrounds, cultures, and abilities. The diversity in this "small world" I worked in daily provided the most stimulating environment, with many challenges and much optimism. Over the years, my research group has had close to 150 graduate students, postdoctoral fellows, and visiting associates. Many of them are now in leading academic, industrial and governmental positions. Working with such minds in a village of science has been the most rewarding experience – Caltech was the right place for me.

The friends with whom I sat on graduation day have been my friends for life. They are my children’s godparents, the people to whom I’ve been able to turn in times of trouble, people who have been kind enough not to sue me when I took their names for Death Eaters.

Remember, if you sit at your desk for 15 or 20 years, every day, not ­counting weekends, it changes you. It just does. It may not improve your temper, but it fixes something else. It makes you more free.

The reason I've been able to keep going for so long is because of how much I love my sport. I still haven't lost that drive. I'm still as passionate about my sport today as I was when I first laced up a pair of boxing gloves. I love preparing for battle and getting into that mindset you must reach when you're putting your body through torture in training camp.

To be forgotten too is to die a little. It is to lose some of the links that anchor us to the rest of humanity.

Even if we do not achieve perfect peace on earth, because perfect peace is not of this earth, common endeavours to gain peace will unite individuals and nations in trust and friendship and help to make our human community safer and kinder.

If I advocate cautious optimism it is not because I do not have faith in the future but because I do not want to encourage blind faith.

It is in human nature to contain both the positive and the negative. However, it is also within human capability to work to reinforce the positive and to minimize or neutralize the negative.

As you look at me and listen to me, please remember the often repeated truth that one prisoner of conscience is one too many.

Every kindness I received, small or big, convinced me that there could never be enough of it in our world. To be kind is to respond with sensitivity and human warmth to the hopes and needs of others. Even the briefest touch of kindness can lighten a heavy heart.