BBC Focus

PHOTO: SCIENCE PHOTO LIBRAR

Y

Cosmologists are always telling us

about the beginnings of our Universe,

but where are weheading? Can

anything, the Universe included, last

forever? It’s hard enough being sure

exactly what the Universeis,but

thinking about how it ends is arguably

even tougher. So strap infor abumpy

ride to the end of everything.

Will the universe be ending soon?

No need topanic. We don’t envisage

anything close to an endto the

Universefor manybillions ofyears.

Depending on thescenario,wehave

between20billionand 1 00 billion

billion yearslefttoenjoyourcosmos.

That’slong after theEarthbecomes

uninhabitableinamerebillion years

orso,andbythen,humans are likely

tohave gone anyway.

Theidea that the Universe can’tlast

foreverhas its origins in thesecond

lawofthermodynamics,whichstates

thatsystemshaveatendencyto

degenerate when left to their own

devices. Thislaw wasdevisedto

explainhowheat works, always

moving from warmer to colder places

unlesswepreventit(for exampleina

fridge, where electric power moves

heatfrom thecolder insidetothe

warmer outside).Thismeansthat

everything shouldeventuallyeven

out,leaving a uniform nothingness.

UNDERSTAND

Another way todescribethis is that

disordernaturallyincreases–notjust

inteenagers’bedrooms,but anywhere

thatdoesn’thaveenergypumped into

it to create order. The outcome is total

disorder – there can be no stars, no

planets, nolife.

How oldisouruniverse?

It’s easier tolookbackthanforward,

partlybecause the Universe islikea

visualtime tunnel.Lighttakes time to

reachus, so thefurther out welook

intospace,thefurtherbackintimewe

see. When,for example, welookat the

Andromedagalaxy–thenearestlarge

galactic neighbour to theMilky Way

WilltheUniverseendinabangorawhimper?

We gaze into our cosmologicalcrystalball...

WORDS:BRIANCLEGG

THE END OF

THE UNIVERSE

–weseeitasitwas2.5million years

ago, because its light takes about 2.5

million years to reachus. Modern

telescopes enable us to see back

billions of years.

The other big contributor to our

knowledge ofhow thingsbegan was

thediscoveryinthe1930sthatthe

Universe is expanding, andhowever

far out(and hence back in time)we

look,that expansionhasbeen going

on. This enables us to workout that the

Universe we can see appears to have

originated around 13.8 billion years

ago,beginning to expandwiththe

so-calledBig Bang. Thedetailsofhow

this occurredandwhat, if anything, 2

We see the Andromeda galaxy as it appeared 2.5 million years ago, because its light takes that long to reach us