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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
  • 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.


Today, our best estimate is that more than 99 per cent of the cosmos is hidden in the dark, invisible to our telescopes and beyond our comprehension.

The first hints that there might be more out there than meets the eye emerged from the gloom in 1846 with the discovery of the planet Neptune. It was hard to find, because at four billion kilometres from the sun there was precious little light to illuminate it and, like 89 per cent of all the atoms in the universe, it gives off almost no light.

In the middle of the 20th century scientists discovered something even stranger - dark matter - stuff that wasn't just unseen, it was fundamentally un-seeable. In fact, to explain how galaxies are held together and how they formed in the first place, there needed to be four times as much dark matter as there was normal atomic matter.

In the late 1990s scientists trying to measure precisely how much dark matter there was in the universe discovered something even more elusive out there - dark energy, a mysterious new force driving the universe apart that is thought to make up a colossal 73 per cent of it.

Finally, Jim explores the quest to uncover the nature of dark energy and to see dark matter pull the first stars and galaxies together, a quest that involves peering into the darkest period in the cosmos's past.

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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