The Hubble Constant The Hubble constant is the current expansion rate of the universe but it seems to have changed over time. Hiranya Peiris, Professor of Astrophysics from University College London and Adam Riess, Professor of Physics and Astronomy from Johns Hopkins University, are both using different methods to obtain a value for the Hubble constant. But there is a discrepancy in their values. It used to be that the error bars on the two values overlapped, and so cosmologists thought they would converge as the experiments got more precise. But instead, as the error bars have shrunk, the discrepancy is getting more serious, and something must be wrong. They chat to Adam about potential reasons for this difference in calculations and what it could mean for our cosmological model of the universe. Is new physics required to evolve the description of the age of the universe as we know it to be more accurate? A synthetic E. Coli genome Jason Chin and Colleagues at the Laboratory of Molecular Biology in Cambridge have published this week in the Journal Nature their latest work to completely synthesise a new genome of an E. coli bacteria. Not only was the genome designed and manufactured by human means, it was also recoded in a way not used by nature, involving some 18000 edits. In natural DNA, several different codes can do the same job. As Roland Pease reports, the new genome instead uses fewer of these duplicates, demonstrating all sorts of possibilities for future designs of synthetic cells. Von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt was a celebrated Prussian geographer, naturalist and explorer. He influenced Darwin and was the first person to describe human-induced climate change, based on his observations from his travels. Yet he has slipped into relative obscurity, at least in the English-speaking world. Andrea Wulf is an acclaimed author who has previously written about Alexander von Humboldt and is now back with another book about the explorer: The Adventures of Alexander von Humboldt. It’s a graphic novel (illustrated by Lillian Melcher) that celebrates the 250th anniversary of Humboldt’s birth and depicts his adventures on his 5 year expedition through South America. Adam Rutherford chats to Andrea about her book, why she chose to make it a graphic novel and how Humboldt’s views on the environment can be interpreted today. Producer: Alex Mansfield