BBC Focus

(Marcin) #1
PHOTOS: GET T Y, SCIENCE PHOTO LIBRARY X2

2 existedbeforeitarespeculative–
there areplenty ofpossibilities. But
the basics of the last 13.8 billion years
of growth are clearly understood.

So how might the universe end?
This is where we enter therealmof
cosmological speculation. It ispossible
toproduce all kinds of hypothetical
outcomes,but there arefourbroad
scenarios thathave themostsupport.
Two of these scenarios involve the
Universe continuing to expand,
continuously getting thinner and more
dispersed,althoughthefinal
outcomes are very different. The most
conventional,theBigFreeze,issimply
theultimateoutcomeofstandard
thermodynamics. Everything evens
out untilthere is simplynothing
happeninginatotallydiffuse
Universe. Themoredramatic version
incorporates the observation that the
Universe is not just expanding,but
that the expansion isaccelerating. If
this accelerating expansion is
extrapolatedto theextreme,wegetthe
BigRip,inwhichallofthematterin
the Universe,from planets and
galaxies to fundamentalparticles and
space-time itself,ispulledapart as the
expansion heads off to infinity.
By contrast, theother two scenarios
see the expansion of the Universe
eventuallyreversing.Ifeverything
endsintheBigCrunch(sorry about
the corny names, but we’re stuck with

JARGON BUSTER

Brane
Some theories combining
quantum physics and gravity
require there to be at least
10 dimensions. In such
scenarios, objects with fewer
dimensions called branes
(short for membranes) could
float in the multidimensional
environment.

Cosmology
The branch of astronomy
concerned with the origin,
evolution, and eventual fate
of the Universe.

Quantum particles
Small particles such as
electrons and photons of light
obey completely different
physical rules to ordinary
objects. Such ‘quantum
particles’ respond to the
probabilistic rules of
quantum theory.

Singularity
Various physical models
predict that certain
characteristics of cosmic
objects – their density, for
example – will get bigger and
bigger until they become
infinite. When this happens,
it’s called a singularity and
current theory breaks down.

Space-time
Albert Einstein showed that
space and time were not
separate but linked in a
structure known as
space-time. This is
the underlying framework
of the Universe.

thinktheUniverse
isoneofmanyina
largermultiverse

them),weseeareversalofeverything
we’ve experienced to date, returning
to an infinitely densepoint – a
‘singularity’. This can thenproduce a
new Big Bang and a new Universe,
givingapossibilityforacycleof
universes.Inthesubtlydifferent Big
Bounce, the Universe again reaches a
peaksizeandbeginstocontract,butin
this instance, it never gets asfar as a
singularity before bouncing and
expanding again. The difference from
theBigCrunchisthatsomeaspects of
the earlier Universe can carry over
into the next one. In effect, the Big
Crunchgenerates a new Universe,
whereas the Big Bounce sees the
same Universe repeatedly expand
and contract.

What does it depend on?
Allthese possibilities aredevisedby
takingtheobservedbehaviourofthe
Universe andthen extrapolating some
key aspects of physics into the future,
notablythe GeneralTheory of
Relativity. This theory, Einstein’s
masterpiecedescribing the
relationshipbetween matter, gravity,
space and time, can be used to model
the entire Universe in a crude fashion.
Ofallofthefactorsinvolvedin
predicting thefuture ofour Universe,
the existence of the accelerating
expansion is the most reliable. First
discoveredin 1998,we now even
have a figure for the rate of 2

TheBigBounce
isascenarioin
whichthe
Universewill
contract,
before
bouncingand
expanding
againtoform
thesame
Universe

UNDERSTAND

THE ENDOF THE UNIVERSE

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