GETTY^ X2 ,^ SCIENCE^ PHOTOLIBRARY,^ NASA^ X25 Universe remains in the form of
this primordial hydrogen and helium.
Only two per cent of the original
atoms have been processed into
heavier chemical elements while
inside stars.CHAPTER 4: THE DECOUPLING
OF MATTER AND ENERGY
380,000 years after the Big Bang
This is the moment when the radiation
detected by the Planck probe was
released into space. Until then, the
Universe had been a searing mass of
atomic nuclei, lighter particles and
energy. It had been impossible for
whole atoms to form; whenever a
nucleus and an electron particle
bonded together, the torrent of
radiation smashed them apart again.
Now, the continual expansion of
space had weakened the radiation so
much t hat it could no longer brea k
apart the atoms. This was a watershed
moment because, wit h most of t he
previously free particles now
conf ined into atoms, it was as t hough
the fog cleared.
In the same way that we are able to
see to the horizon on Earth on a clear
day, the Planck probe enabled us to see
this radiation, which has spent in the
region of 14 billion years travelling
across space while preserving a record
of the density of the various clumps of
matter t hat beca me gala xies. It’s t his
record that now provides troubling
insights into the previous inflation.CHAPTER 5: THE COSMIC DARK AGES
1 million years after the Big Bang
Initially, the decoupled radiation
would have been visible to the human
eye – not that there were any humans
around to see it. But the continued
expansion of space stretched the
radiation into the infrared and then
the microwave sections of the
electromagnetic spectrum.
The Universe became dark.
Even after a million years, there
were no celestial objects, so no
sources of light. These were the
Cosmic Dark Ages. Slowly, the sea
of atoms spread across the Universe
began to form into clumps, pulling
themselves together to become thefirst celestial objects. This was driven
by the gravity of ‘dark matter’ clouds
composed of particles that formed
shortly after inflation.
The Cosmic Dark Ages ended with
the first celestial objects. The first
stars were purely hydrogen and
helium, and some could have been
thousands of times the mass of the
Sun. They lived for just hundreds of
thousands of years before destroying
themselves and seeding the Universe
with the heavier elements needed to
form planets and life.
In March 2013, the Hubble Space
Telescope pinpointed one of the
Universe’s oldest stars right on our
celestial doorstep, ‘just’ 190 light-years
away. Known as the Methuselah star,
it has an estimated age of 14.5 billion
years – give or take 0.8 billion years.
It’s only t his ma rgin of er ror t hat
means it’s potentially consistent
with the supposed age of the Universe.
This might ma ke it seem as if t he sta r
is older than the predicted age of the
Universe, but it’s more of a quirk of
how accu rately we’re able to measu re
the age of a star.
The first black holes were those
found at the centres of galaxies.
Although a black hole emits no light,
matter falling into its gravitational
clutches does heat up and emit
radiation. They would have ended
t he Cosmic Da rk Ages as su rely as
the first stars.
The first galaxies – known as
quasars – were voracious monsters.
Their feeding black holes gave out
as much light as their collections of
stars. Gradually, the black holes
consumed all the matter in their
vicinity, leaving only the stars to
shine within the galaxy.CHAPTER 6: THE FORMATION OF
THE SOLAR SYSTEM
8.8 billion years after the Big Bang
The Solar System started out as a huge
cloud of gas (hydrogen and helium),
which collapsed and rushed towards
the centre of the mass, fusing together
until it burst into life as the star that
we now know as the Sun.
As the Sun was forming, so were
the planets. Before our star was born,TIMELINE
1929
Edwin Hubble
discovers the distance
of a galaxy from us is
directly proportional
to the velocity implied
by its redshift. Georges
Lemaître had published
this in 1927, but nobody
had noticed.1931
Lemaître writes:
“We could conceive
the beginning of the
Universe in the form
of a unique atom,
the atomic weight of
which is the total mass
of the Universe.”Ralph Alpher (left)
and Robert Herman
calculate that the
leftover radiation from
the primeval fireball
should still fill the
Universe today, with a
temperature of about
5 Kelvin (-268°C).1964
Arno Penzias and Robert Wilson discover
a weak hiss of radio noise coming from all
directions in space. The following year, this
is explained as the leftover radiation from
the Big Bang.1948
1989
Launch of the Cosmic Background Explorer
satellite (COBE), which detected tiny
irregularities (ripples) in the background
radiation, confirming the accuracy of the
Big Bang model.2001
The Wilkinson
Microwave
Anisotropy Probe
(WMAP) launches,
making precision
measurements that
pin the age of the
Universe down as
13.8 billion years.THE FUNDAMENTALS OF PHYSICS