How many people died? It's one of the first questions asked in a war or violent conflict, but it's one of the hardest to answer. In the chaos of war many deaths go unrecorded and all sides have an interest in distorting the figures. The best we can do is come up with estimates, but the trouble is that different statistical methods for doing this can produce vastly different results . So how do we know how different methods compare?

Plants are amazingly good at something that is still flummoxing us humans in our quest for sustainable energy sources: turning sunlight into energy in an efficient way. Around 100 bilions tons of biomass are produced annually through photosynthesis. The question is, how exacty do plants do it?

From flattening the Earth to dining with the jellyfish, Plus chats about our first day at the AAAS meeting in Vancouver, Canada.

The number 1 can be written as a sum of unit fractions, that is fractions with 1 in the numerator. But how long can we make such a sum?

Yesterday's refusal by the UK government to posthumously pardon Alan Turing makes sad news for maths, computer science and the fight against discrimination. But even if symbolic gestures are, symbolically, being rebuffed, at least Turing's most important legacy — the scientific one — is going stronger than ever. An example is this week's announcement that scientists have devised a biological computer, based on an idea first described by Turing in the 1930s.

Some of the things I overheard at Stephen Hawking's 70th birthday conference did make me wonder whether I hadn't got the wrong building and stumbled in on a sci-fi convention. "The state of the multiverse". "The Universe is simple but strange". "The future for intelligent life is potentially infinite". And — excuse me — "the Big Bang was just the decay of our parent vacuum"?!

This is the first part of the lecture given by Astronomer Royal Martin Rees at Stephen Hawking's birthday symposium.

This is the second part of the lecture given by Astronomer Royal Martin Rees at Stephen Hawking's birthday symposium.

What's a multiverse? What's the future for intelligent life? And what happened 380,000 after the Big Bang. Find out in these interviews with the physicists David Spergel and Raphael Bousso, who we spoke to during Stephen Hawking's 70th birthday conference.

Stephen Hawking turned 70 in January 2012 and to celebrate, the University of Cambridge put on a scientific conference as well as a public symposium. Plus went along, of course, and here are the articles and podcast we have produced from the conferences. Happy reading and listening!

This is one of our podcasts from Stephen Hawking's 70th birthday conference, which took place in January 2012 in Cambridge. Rachel Thomas talks to Renata Kallosh from Stanford University about a theory that promises to unite the physics of the very small — quantum physics — and the physics of the very large — Einstein's theory of gravity.