Aristotle, one of the most famous Greek philosophers, believed the universe had existed forever. The reason he believed why we are not more developed was that floods, or other natural disasters, repeatedly set civilization back to the beginning.
Today we are developing ever faster. Our knowledge is growing exponentially and with it, our technology. But as humans we still have the instincts, and in particular the aggressive impulses, that we had in caveman days. Aggression has had definite survival advantages but when modern technology meets ancient aggression the entire human race and much of the rest of life on Earth is at risk.
Today in Syria we see modern technology in the forms of bombs, chemicals and other weapons being used to further so-called intelligent political ends.
But it does not feel intelligent to watch on as 100,000 are killed or whilst children are being targeted. And it feels downright stupid to prevent humanitarian supplies from reaching clinics where Save the Children is reporting that children are having limbs amputated for lack of basic facilities and newborn babies are dying in incubators for lack of power.
What's happening in Syria today is an abomination, one that the world is watching coldly from a distance. Where is our emotional intelligence; our sense of collective justice?
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.