BBC_Knowledge_2014-06_Asia_100p

be created or destroyed. If the black

hole eventually vanishes, where does

the information that described the star that

spawned the black hole go? In recent years,

physicists have concluded that Hawking

radiation is ‘modulated’ – just as a carrier

wave of a radio station is modulated by

human voice – and gradually returns the

information about the star to the Universe.

Untangling black holes

But black holes have not stopped surprising

physicists. Not by a long chalk. In 2012, Joe

Polchinski of the University of California

at Santa Barbara and his colleagues were

thinking about Hawking radiation and

‘entanglement’. This is the bizarre ability

of quantum particles that are born together

to forever ‘know about each other’, almost

as if they are the same particle. A Hawking

particle is entangled with its partner that falls

into the hole. But Polchinski proved that,

if a Hawking particle streaming away from

the hole is to carry information back to the

Universe, it must also be entangled with

other Hawking particles emitted at earlier

times by the hole.

The problem is that quantum theory

permits a particle to be entangled with

TYPES OF BLACK HOLE

“It sounds like

Stephen Hawking

is replacing a [black

hole’s] firewall

with a chaos-wall”

Theoretical physicist Joe Polchinski of the

University of California, Santa Barbara

of galaxies. No one knows how they for

grows by sucking in matter.

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blblack holesack holes

TThese can weigh up to 30 billion timhese can weigh up to 30 billion timesessss

tthe mass of the Sun and exist in the heahe mass of the Sun and exist in the heartrtrtrtttttttssssssssssssssss

of of galaxies. No one knows how they forgalaxies. No one knows how they formmmmmm......

OOne possibility is that a dense cluster ne possibility is that a dense cluster

ofof stars collapses under its gravi stars collapses under its gravityty

tto form a black hole, which theno form a black hole, which then

grows bgrows by sucking in matter.y sucking in matter.

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mmass black holesass black holes

TThis is a hypothetical class of black hohis is a hypothetical class of black holeleeeeeeeessssssssssssssss

wiwith masses in the range of hundredsth masses in the range of hundreds

tto thousands of times the mass of theo thousands of times the mass of the

SuSun. Possible evidence for them comen. Possible evidence for them comes s ss

ffrom ultra-luminous x-ray sources.rom ultra-luminous x-ray sources.

They mThey might form by the merger of ight form by the merger of

sstellar-mass black holes.tellar-mass black holes.

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blackblack holes holes

TThe violent conditions in the Big Bahe violent conditions in the Big Bangnggggg

may have created ‘prmay have created ‘primordial’ black hoimordial’ black holeleeess.sssssssssss.......

Conditions at the so-called Conditions at the so-called quark-hadrquark-hadrononnnnnnn

ttransition, when the Universe was aransition, when the Universe was a

mimillionth of a second old, could havellionth of a second old, could have

sspawned Jupiter-mass black holespawned Jupiter-mass black holes

the sthe size of a fridge.ize of a fridge.

only one other particle. Something

must therefore intervene to destroy the

entanglement between the particle that

escapes the hole and its partner that falls

into the hole. Since entanglement is an

extremely strong bond, this requires the

input of an enormous amount of energy to

smash it apart. Polchinski and his colleagues

concluded that the in-falling particle, as

it crosses the horizon, must be met by a

searing hot wall of high-energy particles.

This ‘firewall’ creates a paradox since a

cornerstone of Einstein’s theory of gravity,

which describes black holes, is that the world

to an observer free-falling into a black hole

Two particles can be entangled, with a

change to one affecting the other no matter

the distance between them; it’s arelationship

that could be torn apart by a black hole

PHOTO: SCIENCE PHOTO LIBRARY X2

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massmass black hole black holessssssss

TThese form from the runawayhese form from the runaway

ggravitational collapse of a massiveravitational collapse of a massive

sstar that has reached the end of itstar that has reached the end of its

liflife and no loe and no longnger has aer has anyny fuel to burnfuel to burn

tto stave off catastrophe. They weigho stave off catastrophe. They weigh

iin at anything between three andn at anything between three and

several tens oseveral tens of times the maf times the massss

oof the Sun.f the Sun.

ASTROPHYSICS