Dark Energy

In Our Time: Science

BBC

History

4.5 • 1.4K Ratings

🗓️ 17 March 2005

⏱️ 42 minutes

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Summary

Melvyn Bragg and guests discuss 'dark energy'. Only 5% of our universe is composed of visible matter, stars, planets and people; something called 'dark matter' makes up about 25% and an enormous 70% of the universe is pervaded with the mysteriously named 'dark energy'. It is a recent discovery and may be only a conjecture, but it has been invoked to explain an abiding riddle of the cosmos: if the expansion of the universe is powered by the energy of the Big Bang, then why isn't the expansion slowing down over time as the initial energy runs down and the attractive force of gravity asserts itself? Scientists had predicted a Big Crunch as the logical opposite of the Big Bang, but far from retracting, the expansion of the universe is actually accelerating...it's running away with itself.How do we know that the universe is behaving like this and what's causing it? If dark energy is the culprit, then what is this elusive, though omnipresent entity?With Sir Martin Rees, Astronomer Royal and Professor of Cosmology and Astrophysics, Cambridge University; Carolin Crawford, Royal Society University Research Fellow at the Institute of Astronomy, University of Cambridge; Sir Roger Penrose, Emeritus Rouse Ball Professor of Maths at Oxford University.

Transcript

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0:00.0	Thanks for down learning the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.uk.
0:10.0	I hope you enjoy the program.
0:12.0	Hello, only 5% of our universe is composed of visible matter, stars, planets and people.
0:18.0	Something called dark matter makes up about 25% and an enormous 70% of the universe is pervaded with the mysteriously
0:25.2	named Dark Energy.
0:27.5	It's a recent discovery and maybe only a conjecture, but it has been invoked to explain an abiding
0:32.1	riddle of the Cosmos.
0:33.2	If the expansion of the universe is powered by the energy of the Big Bang,
0:36.7	then why isn't the expansion slowing down over time
0:39.6	as the initial energy runs down and the attractive force of gravity asserts itself.
0:44.1	Scientists had predicted a big crunch as the logical opposite of the Big Bang, but far
0:48.7	from retracting the expansion of the universe is actually accelerating. It's running away with itself.
0:54.1	How do we know that the universe is behaving like this and what's causing it?
0:58.0	If dark energy is the
1:05.0	astronomer Royal, Professor Sir Martin Rees,
1:08.0	Professor Sir Martin Rees, Professor of Astrophysics at Cambridge University.
1:10.0	Caroline Crawford, Royal Society Research Fellow at the Institute of Astronomy, University of Cambridge,
1:15.3	and Sir Roger Penrose, Ameritus Raus Paul Professor of Maths at Oxford.
1:20.4	Martin Rees-Einstein, when he wrote his equations for relativity didn't think the universe
1:25.1	was expanding. So what was the single most important observation made after him that showed us that it was still expanding and accelerating.
1:37.0	In the 1920s people realized that the universe was far bigger than had been thought before.
1:42.0	They realized that our galaxy, the Milky
	...

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