Images are now being taken on the world's most powerful digital camera. For over 500 nights over the next five years the Dark Energy Camera will photograph the light from more than 100,000 galaxies up to 8 billion light-years away in each image.

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

This year's Nobel Prize in Physics was awarded for a discovery that proved Einstein wrong and right at the same time.

What's the mysterious stuff that makes up 70% of our Universe?

The mathematical maps in theoretical physics have been highly successful in guiding our understanding of the universe at the largest and smallest scales. Linking these two scales together is one of the golden goals of theoretical physics. But, at the very edges of our understanding of these fields, one of the most controversial areas of physics lies where these maps merge: the cosmological constant problem.