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A feast for the mind

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MEET THE AUTHOR

Lisa Randall

Bodley Head

The Astounding Interconnectedness

Of The Universe

At first sight, Dark Matter And The

Dinosaurs looks like a title thought up by

the marketing department. “Hmm, what

interests the public? Dark matter is trendy.

And who doesn’t love a dinosaur, right?”

To be fair, physicist Lisa Randall does make

a tenuous connection between a new

dark matter theory and the comet that is

thought to have caused the extinction of

the dinosaurs, but that is by no means the

most interesting aspect of this book.

Much of the content takes us on

a solid, if surprise-free, tour of the

history of the Universe, zooming in

to see how the Solar System reached

its present form, and exploring the

nature of comets, meteors and asteroids.

But where Randall really triumphs is

with her coverage of extraterrestrial

impacts on the Earth. The detective

story that led to the identification of

the Chicxulub crater as the site of the

dinosaur-killing meteoroid strike is

extremely engaging.

Better still, the chapters on dark

matter go far beyond most other

popular books on the subject. Randall

paints a truly fascinating picture of the

possibility that dark matter is as rich

and varied as normal matter, perhaps

forming dark matter suns that pour out

dark light, or are even orbited by dark

planets hosting dark life.

Where the book could do better is in

hitting the right level of detail. Randall

dismisses modified Newtonian dynamics

(MOND) – the alternative to dark matter

based on a tweak to Newton’s laws – with

an example of a star cluster unsupported

by the modified theory. Yet she continues

to support dark matter, despite listing four

or five examples where it fails to match

observation, and it’s never made entirely

clear why dark matter is given the benefit

of the doubt but MOND isn’t. Elsewhere,

it seems as if the book hasn’t been

adequately edited – it isn’t unusual for

Randall to take a page to say something

that only required a couple of lines.

The climax of Dark Matter And

The Dinosaurs is the discovery that a

possible regular cycle of comet strikes

• for which the evidence, it should be
  pointed out, is rather thin – combined
  with an unsubstantiated dark matter
  theory just might explain the extinction
  of the dinosaurs. But to consider this the
  highlight misses the point. This book
  is not about the destination, but the
  journey. And that is often delightful.

“Randall paints a

fascinating picture

of the possibility

that dark matter is

as rich and varied

as normal matter”

BRIAN CLEGG IS A SCIENCE WRITER WHOSE MOST

RECENT BOOK IS TEN BILLION TOMORROWS

Hardback Paperback

Could you explain the ‘double-disc dark

matter’ theory that you propose in your

book?

Most dark matter in our Galaxy surrounds us

in an approximately spherical halo. But why is

dark matter in a spherical halo, and ordinary

matter in a disc – the plane of the Milky Way?

This is because ordinary matter can radiate

photons and cool down, which allows it to

collapse into a disc. We suggest that dark

matter can also radiate – not ordinary photons,

but a new kind of ‘dark light’. This would mean

that it too could collapse into a dense disc,

embedded inside the Milky Way’s disc of

ordinary matter.

How could we detect such a disc?

We could look for its gravitational influence.

Stars go up and down through the plane

of the Milky Way, and the speed with

which they do so responds to gravity. So

if there’s a dark disc, you’d expect to see

a spatial variation in the speed. Right now,

the Gaia satellite is measuring the position

and velocity of a billion stars in our Galaxy,

and that information will help us pin down

whether or not this disc exists.

So how might this disc be linked to the

dinosaurs?

If you look at the dataset for large impact

craters on the surface of the Earth, you find

that there’s marginal evidence for a periodicity,

where every 30-35 million years the rate of

impacts increases. We realised that this could

be caused by the Solar System passing

through the dark matter disc. This would

give icy objects in the distant Oort cloud a

gravitational kick, potentially sending them into

the inner Solar System as long-period comets.

We suggest that this is what happened 66

million years ago, when a huge impact wiped

out the dinosaurs.

Lisa

Randall

MEET T

d k li ht bit d b d k

PHOTO: CHRISTOPHER KIM/RANDOM HOUSE

Dark Matter And

The Dinosaurs