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Light And Dark

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In this mind-bending series, Professor Jim Al-Khalili shows how by uncovering its secrets, scientists have used light to reveal the universe.

  • Updated Thursday 2nd November 2017
  • Introductory level
  • Posted under TV, Physics
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Jim Al Khalili at a fairground Copyrighted image Icon Copyright: BBC In this two-part series Professor Jim Al-Khalili will present a thought-provoking account of our quest to discover, understand and manipulate light and dark.

A landscape filled with mountains. The stars in the night sky. The face of a loved one. Everything you see around you is the result of light.

But for our familiar world to exist, almost all the universe has to be dark.

The series will reveal how light has historically been used to make breakthrough discoveries about our place in the cosmos, and that what the human eye can see is only a fraction of the vast amount of matter and energy that exists: our best estimate is that more than 96% of the universe is hidden in the dark.

Light and Dark on TV

The series was first shown on BBC Four in November 2013. For clips and more information about each episode, see below.


The story of how we used light to reveal the cosmos begins in the 3rd century BC when, by trying to understand the tricks of perspective, the Greek mathematician Euclid discovered that light travels in straight lines, a discovery that meant that if we could change its path we could change how we see the world. In Renaissance Italy 2,000 years later, Galileo Galilei did just that by using the lenses of his simple telescope to reveal our true place in the cosmos.

With each new insight into the nature of light came a fresh understanding of the cosmos. It has allowed us to peer deep into space and even revealed the composition and lifecycles of the stars.

In the 1670s, the Danish astronomer Ole Roemer discovered that light travelled at a finite speed, a discovery that had a profound implication. It meant the further one looks out into the universe, the further one looks back in time. And in 1964, by detecting the cosmic microwave background, the afterglow of the big bang, we captured the oldest light in the universe and saw as far back as it is possible to see with light.

Episodes in this series

Episode Description
Light Professor Jim Al-Khalili tells the story of how we used light to reveal the cosmos. Read more
Dark Prof Jim Al-Khalili investigates the 99 per cent of the cosmos that is hidden in the dark. Read more




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