Just before this BBC podcast gets underway, here's something you may not know.

My name's Linda Davies and I Commission Podcasts for BBC Sounds.

As you'd expect, at the BBC we make podcasts of the very highest quality featuring the most knowledgeable experts and genuinely engaging voices.

What you may not know is that the BBC makes podcasts about all kinds of things like pop stars,

poltergeist, cricket, and conspiracy theories and that's just a few examples.

If you'd like to discover something a little bit unexpected, find your next podcast over at BBC Sounds.

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For more details about In Our Time and for our terms of use, please go to BBC.co. UK forward slash radio for. I hope you enjoy

the program.

Hello in the beginning runs one secular account was the Big Bang. All matter in existence today

originated around 13,000 million years ago in a phenomenally hot, extraordinarily condensed

primordial atom that exploded with incredible force.

Hydrogen and helium were shot across the firmament,

gravity caused the gases to condense into clouds, and in these clouds the first

stars were formed.

Then galaxies came and more galaxies in

clusters onwards and outwards ever expanding. It's still expanding runs the Orthodox

account and may even be speeding up. It's still creating new galaxies and it continues to colonize more and more

infinite space despite the fact that it's supposedly infinite itself. The word

billions dominates all discussions here. So if our universe is expanding, what's it's expanding into?

If it's already infinite, how can it be getting any bigger? And is there really only one universe?

With me to tackle some of the riddles of the universe is the Astronomer Royal, Professor Sir Martin Reese, Royal Society Research Professor in Astronomy and Physics at Cambridge University, and author of a new book Our Cosmic Habitat.

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