When I discuss intelligent life in the universe, I take this to include the human race, even though much of its behaviour throughout history appears not to have been calculated to aid the survival of the species. And while it is not clear that intelligence has any long-term survival value, unlike aggression, our very human brand of intelligence denotes an ability to reason and plan not only for our own but our collective futures.
We must work together to end this war and to protect the children of Syria. We have watched from the sidelines for three years as this conflict rages, engulfing all hope. As a father and grandfather, I watch the suffering of Syria's children and now say: no more.
I often wonder what we must look like to other beings watching from deep space. As we look out at the universe, we are looking back in time, because light leaving distant objects reaches us much, much later. What does the light emitting from our earth today show? When people see our past, will we be proud of what we are showing them? How, as brothers, we treat each other? How we allow our brothers to treat our children?
We now know that Aristotle was wrong - the universe has not existed forever. It began about 14 billion years ago. But he was right that great disasters represent major backward steps for civilization. The war in Syria may not represent the end of humanity but every injustice committed is a chip in the façade of what holds us together. The universal principle of justice may not be rooted in physics but it is no less fundamental to our existence. For without it, before long, human beings will surely cease to exist.
Stephen Hawking is the former Lucasian Professor of Mathematics at the University of Cambridge and author of A Brief History of Time.