麻豆约拍

How can the large stone currency called Rai stones, from the island of Yap in Micronesia help us understand "bitcoin" and the world of virtual currencies? As US senators this week discussed the merits, and dangers, of these so-called crypto currencies, Justin Rowlatt and his guests delve into the opaque world of digital dealings and ask what on earth is a virtual currency, and what's the point of bitcoin when there are so many conventional currencies on offer?

And the programme's resident chief ruminator, Colm O'Regan, on why he's failed, so far, to grasp the freedom from the rules that bitcoin represents.