Why Is The Universe The Same Everywhere?

[Music]

a great

orbiting telescope floats serenely in

the black

collecting light from the heavens above

it adjusts its field of view slightly

turning away from the nearby stars

and peers deeper into the darker reaches

of the night sky

beneath it the planet turns its white

clouds

swirling serenely in the faint stellar

glow and positioned as it is

above the turbulent atmosphere this

telescope

has an unrivalled view of the cosmos

closest just a few light years away are

individual stars

unique suns just like the one now hiding

out of sight behind the planet

they cluster thickest in a wide bright

band that cuts the blackness in two

this is the galactic plane looking along

it

is to look to the center of the galaxy

some 100

000 light years away and the galaxy is

an immense

flattened spiral home to 400 billion

suns but the little telescope turns its

gaze away

from this blinding light looking up

above the galactic plain

the stars are more sparsely scattered

but the sky is lit instead by

dim multi-coloured smears each is a

galaxy in its own right

containing billions of stars that burn

just as brightly as those nearby

but whose intensity is masked by sheer

distance

mapping the positions of these diverse

galaxies the orbiting telescope sees a

few dozen cluster loosely together in a

local group

deeper into the blackness even dimmer

smudges hint at more distant

galactic clusters with enough time the

telescope can map these too

finding that they cling together in even

vaster

superclusters several hundred million

light years across

and bordered by gaping black voids where

no galaxies are to be found at all

and at the very edge of its magnified

site the instrument glimpses

the very edge of the observable universe

45 billion light years away

thus the structure of the universe is

revealed in the simple curved mirror

of an orbiting telescope but this

instrument

does not orbit the earth

it is a machine of another world

orbiting an

alien planet that itself orbits an alien

sun

the bright streak of the galactic plane

is not that of the milky way

and the nearby galaxies are also foreign

and unfamiliar

our home planet is somewhere else in

that extraterrestrial instrument

sites although it would be almost

impossible to pinpoint

there are no landmarks in the

large-scale structure of the cosmos

no major differences from place to place

that help us find our way

the universe looks surprisingly similar

wherever you happen to be looking from

it has broadly the same temperature

and the same lumpy structure of dense

superclustered galaxies and hollow voids

looked at from an omnipotent external

point of view where entire galactic

clusters are reduced to mere points of

light

the cosmos is remarkably uniform

but how did this come to be

how could such distant parts of the

universe separated by tens of billions

of light years

be so similar places so distant

that they could never ever have had any

contact

it is a mystery that has plagued our

accepted cosmological histories

since they were written a gaping hole in

our understanding

is our story of the origin of the

universe incomplete

or is this evidence of uniformity merely

a freak occurrence a bizarre coincidence

localized to our view

of the infinite cosmos to truly

investigate this mystery

cosmological detectives must take an

explosive journey

right back to the very beginning we must

probe improbable connections between the

minuscule quantum world

and the gigantic realm of superclusters

and open our minds to the even wider

even weirder

possibility of a nested multiverse

hiding within our very own cosmos

we must ask what put the bang

into the big bang or if the bang

should even be there at all

[Music]

about 13.8 billion years ago

the universe began

we don't know for sure how it happened

what it looked like or how it behaved

during its very first moments but all of

the evidence we have suggests that

at the beginning it was very very small

and very very hot calculations by the

physicist and priest george lemaitre

in the 1920s revealed that we live in an

expanding universe

which logically must have begun much

smaller than it is today

subsequent observations have bolstered

his mathematical viewpoint

the light from distant galaxies appears

more red than it should do

as if the wavelengths themselves have

been stretched

the further those galaxies are the more

red they appear

so the faster they are receding such a

pattern could only arise if the entire

cosmos were expanding

and had been since the beginning of time

thanks to the finite speed of light

those distant far reaches of the

observable universe are also

gaping windows into the distant past and

they too

bear the marks of a smaller hotter

beginning

based on this startling agreement of

mathematical theory and highly precise

observations

the so-called big bang has become the

most widely accepted

theory for the origin of our universe

but there is a problem

there are many features of our modern

universe that don't

fit with a simplistic expanding big bang

origin story not least an infinitely

small infinitely dense and infinitely

hot beginning violating

all known laws of physics but there is

more

there are features of the cosmos today

that are very hard to explain

if the universe had simply been

expanding at a steady rate

all this time thorns in the side of the

big bang theory

that threaten to bring it all crashing

back down

the first is known as the horizon

problem

an alien observer looking at the

universe from tens of billions of light

years away would see a cosmos almost

indistinguishable from our own in

particular

the background radiation which raises

the average temperature of space to a

few degrees above absolute zero

wherever in the observable universe one

happens to observe it

the chances of this being the case under

a simplistic big bang regime are

vanishingly small

the only way that the temperature of the

cosmos can be so homogenized

is if all parts of that cosmos were in

contact

long enough for them to reach

equilibrium

a cold room with a single heat source in

one corner