Finaly — finally! — Chris and Emily get to the meat of the matter in this season on life in the universe. Very special guest Dr Kelly Redeker from the Department of Biology at the University of York breaks down the principles of life, both on Earth and on other worlds (or "slimy rocks" as Emily insists on calling them). Do you need a Frankenstein-esque spark? Is life inevitable? What about complex life? Intelligent life? And Emily asks Kelly the big question: will we find life outside our planet?

On the web: syzygy.fm

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Syzygy is produced by Chris Stewart and co-hosted by Dr Emily Brunsden from the Department of Physics at the University of York.

Some of the things we talk about in this episode:

• Special guest Dr Kelly Redeger

• How to define life

• The origins of life

• Non-carbon-based life