BBC Focus

Brian Clegggisaprolificsciencewriter.Hismost

recent book isHowManyMoons Does The Earth

Have??(£6.99, Icon Books).

BuyWondersOfTheUniverse,

presented byBrianCox,for£4.99

intheBBCStoreatstore.bbc.com

DISCOVER MORE

BELOW:Dark

energy, as

visualised

here, is

causing the

Universe’s

expansion to

accelerate

1

THERE WILL BE

COSMIC DEATH

The Universe as we know it

can’t last forever. It’s not

just that stars will burn out

• the whole cosmos is
  running down at the same
  time a s it expands f a ster
  and faster. Eventually,
  billions of years in the
  future, we expect our
  Universe to come to an end.

2

THERE ARE

ALTERNATIVE

ENDINGS

Exactly how the Universe

will end isn’t clear. However,

most cosmologists think

that the expansion of the

Universe will continue to

accelerate, ending up with

everything ripping apart.

3

THERE ARE

KNOWN

UNKNOWNS

As yet we still don’t

understand two

fundamental components

of the Universe: dark matter,

which makes up over 80 per

cent of the mass of the

Universe, and dark energy,

which drives the

accelerating expansion.

Until we do, which will

require us to combine our

understanding of gravity

and quantum theory, this

will all remain speculation.

IN A NUTSHELL

NEXT MONTH: HOW DO

WE KNOW WHAT MATTER

IS MADE OF?

Albert Einstein

establishedthe

relationship

between matter,

gravity, space and

time, allowing us

to crudelymodel

the Universe

PH

OT

OS

:SC

IEN

CEPH

OT

O LIBRARY X

2

developedhis GeneralTheory of

Relativity, scientists have made simple

mathematical models of the Universe

and how it could developwith time.

Over the years, these have become

more and more sophisticated. But in

theendthemodels remainfar simpler

than thething they’re modelling. Bear

in mind that we can’t even predict the

weather more than afewdays ahead.

Modelling the behaviour of the whole

Universe for billions of years to come

isfarmoreofachallenge,especially

when we don’t understand what dark

energyis,northenatureofthe‘dark

matter’ that seems to makeupfar more

of the Universe than ordinary matter.

Could anything survive the end

ofthe universe?

In the favoured scenarios where

everything either runs down or splits

apart, it’shardto seehow this would

be possible. In a bounce, though, in

principlesomethinggcould survive,

thoughitismorelikelytobe

fundamentalproperties suchas the

laws of nature than anything with

structurelikealivingbeing.

Will another universe be born

after ours dies?

Ifeither theBigCrunchor Big Bounce

happens, definitely. However, even the

morelikelyever-expanding options

don’t mean the end of everything.

Most cosmologists believe that our

Universe is one of many in a larger

‘multiverse’, with Big Bangs

happening regularly. So even ifour

Universecomestoanend,thelarger

multiverse wouldcarry onforever. It’s

the universal circleoflife.

energy into themixandthe

acceleration could go on forever.

How is dark energy created?

‘Darkenergy’isjustalabel,andthere

are severalpossibleexplanations

foritsexistence.Itmightbea

fundamentalproperty of empty space

• a kind of intrinsic energy that’s
  present throughout the Universe. This
  mightcomeaboutthroughstrange
  quantum effects, with the uncertainty
  of energy levels meaning thatparticles
  are constantlypopping in and out of
  existence. Alternatively,darkenergy
  mightbeanewkindofenergyfieldor
  fundamental force, filling all of space
  buthaving the opposite effects to
  normal energy and matter. Finally, it
  mightbethat Einstein’s theory of
  gravityisincorrect,andthatanew
  theory is needed.Theperson who
  solves this mystery will be an instant
  Nobel Prize-winner.
  On the scale with which we’re
  familiar, dark energy is trivially small


• unnoticeable. But when taking the
  Universe as a whole, so muchenergy is
  requiredtoaccelerateitsexpansion
  thatdarkenergy is estimatedto make
  upabout 68per cent of the mass/
  energy content of the Universe.
  Whatever it is,it’s the dominant
  ingredient of our cosmos.

Can wepredict the end of the universe

with computer models?

To a degree. Ever since Einstein