Martin Rees

If you represent the Earth's lifetime by a single year, say from January when it was made to December, the 21st-century would be a quarter of a second in June - a tiny fraction of the year. But even in this concertinaed cosmic perspective, our century is very, very special: the first when humans can change themselves and their home planet.

Science shouldn't be just for scientists, and there are encouraging signs that it is becoming more pervasive in culture and the media.

The most important advances, the qualitative leaps, are the least predictable. Not even the best scientists predicted the impact of nuclear physics, and everyday consumer items such as the iPhone would have seemed magic back in the 1950s.

If we do find ET, we will at least have something in common with them. They may live on planet Zog and have seven tentacles, but they will be made of the same kinds of atoms as us. If they have eyes, they will gaze out on the same cosmos as we do. They will, like us, trace their origins back to a 'Big Bang' 13.8 billion years ago.

We are 'nuclear waste' from the fuel that makes stars shine; indeed, each of us contains atoms whose provenance can be traced back to thousands of different stars spread through our Milky Way.

We can trace things back to the earlier stages of the Big Bang, but we still don't know what banged and why it banged. That's a challenge for 21st-century science.

The 'clean energy' challenge deserves a commitment akin to the Manhattan project or the Apollo moon landing.

Just as there are many Jews who keep the Friday ritual in their home despite describing themselves as atheists, I am a 'tribal Christian,' happy to attend church services.

It is mistaken to claim that global problems will be solved more quickly if only researchers would abandon their quest to understand the universe and knuckle down to work on an agenda of public or political concerns. These are not 'either/or' options - indeed, there is a positive symbiosis between them.

Scientists habitually moan that the public doesn't understand them. But they complain too much: public ignorance isn't peculiar to science. It's sad if some citizens can't tell a proton from a protein. But it's equally sad if they're ignorant of their nation's history, can't speak a second language, or can't find Venezuela or Syria on a map.

The lives of those such as Charles Darwin and Albert Einstein are plainly of interest in their own right, as well as for the light they shed on the way these great scientists worked. But are 'routine' scientists as fascinating as their science? Here I have my doubts.

There are strong reasons for believing that space goes on beyond the limits of our observational horizon. There are strong reasons because if you look in opposite directions, conditions are the same to within one part in 100,000. So if we are part of some finite structure then, if the gradient is so shallow, it is likely to go on much further.