Every so often, a Syzygy listener writes in with a cracking question that sends Emily and Chris off spelunking down the deep, deep sinkholes of astronomy and cosmology. This time, listener Eve asked an absolute cracker, to wit: Just how much energy is there in the universe right now? A simple question at first glance. At second glance (and every glance thereafter) it's not simple at all. We need to first consider, what is energy? What is the universe? And even, what is "now"? It's very confusing.

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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.

On the web: syzygy.fm | Twitter: @syzygypod

Things we talk about in this episode:

• Feynman’s discussion of energy

• Dark matter

• Dark energy

• The observable universe

• Critical energy density

• Is the energy in the universe zero?

• The Big Bang Singularity

• The fates of the universe