One of the biggest conundrums in the Universe surrounds the question of how quickly the Universe is expanding. Questions like what is the Universe made of, how old is it, what is it's ultimate fate, etc., absolutely depend on this. For generations, we argued over the details of this, seeming to have finally reached a consensus in 2001 with the Hubble Key Project's results: 72 km/s/Mpc, with an uncertainty of about 10%. But the modern results, as of 2019, seem to depend on how you measure it. Some teams are consistently getting 67 km/s/Mpc, while others get 73-74 km/s/Mpc, with uncertainties that don't overlap.

This may not be a controversy, but rather a clue, and Nobel Prizewinner and co-discoverer of dark energy Adam Riess joins me on this special edition of the Starts With A Bang podcast. Don't miss it!

(Image credit: NASA / GSFC)