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The beginning of the Universe
It is now generally accepted by most astronomers that the Universe as we know it began with
an unimaginably huge explosion some 14 000 000 000 years (1.4x1010 years). We call this
the Big Bang. The age of the universe is therefore 1.4x1010 years.
Time and space both originated at the same time with the Big Bang. Before that there was no
space and no time – the Big Bang ‘created’ space and time. We cannot ask what happened
before the Big Bang because before that moment nothing existed – no space and no time!
It is interesting to compare time with distance and think of a scale where a distance of one
metre represents a thousand million years. The age of the Universe is then represented by a
distance of around 14m, a million years by 1 mm and one human lifespan by 0.1m!
The fascination of Cosmology is the ability to ‘look back’ to the beginning of the Universe and
predict what may have happened then.
Moments after the big bang
Time after the Big Bang
10-43 s
10-34 - 1010 s
10-10 s
1s
3m
300 000 years
500 000 years
1 million years
1 billion (109) years
15 billion years
Nature of the Universe
Grand unification epoch
Electroweak epoch
Quark epoch
Particle soup dominates
Neutrons and protons formed
Helium nuclei formed
Microwave background fills the universe
Temperature falls further. Infra red.
Atoms form. Stars and galaxies exist
The universe becomes transparent
The first stars. Heavy elements form.
The present day
Temperature
1015 K
1010 K
109 K
6000 K
750 K
18 K (-255 C)
2.7 K (-270.3 C)
The Big Bang - the beginning of the Universe
As thousands of years passed the Universe cooled from the initial enormous temperatures of
the Big Bang (some 1015 K).
At some time in the past, roughly 500 000 years after the Big Bang the Universe became
dark. The radiation emitted had passed over the barrier between visible and the infra red.
From then there was no light until the primeval matter had condensed into atoms and these
had slowly grouped together under gravitational attraction to make the embryo of a star.
Eventually the temperature in the centre of these stars had become high enough for nuclear
fusion to take place - the first star was born and blazed out into the darkness of space - there
was light!
The currant filled loaf of bread 3D model of the expanding universe
Imagine the Universe to be like a loaf of bread filled with currants. As the bread is cooked it
expands - every currant moving away from every other currant. As far as each currant is
concerned it is at the centre of expansion because it "sees" currants moving away from it in
all directions. This is just like the expansion of the Universe - the universe being represented
by the loaf of bread and the currants representing the galaxies
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Another good analogy is to thread three or four large polystyrene balls (to represent galaxies)
onto a length of elastic, one end of which is fixed to a hook on the wall or a secure retort
stand. If the free end of the elastic is pulled all the balls separate from each other.
The Expanding Universe 3
Figure 3
The point about all these analogies is that they make their own space as they expand.
Similarly before the universe began to expand there was no space! Actually there was no
time either - both space and time were "created" at the start of the universe.
The Echo of the Big Bang
As time passed since the Big Bang the Universe cooled. The temperature in deep space
dropped and dropped. The background radiation moved into the infrared and the cooling
continued.
The radiation from interstellar space at present represents a temperature of 2.7K (-270.3 oC)
and this radiation is known as the Echo of the Big Bang. If you look at a "detuned" TV signal
some of it (admittedly less than 1%) is the Cosmic Microwave Background Radiation (CMB)
– the Echo of the Big Bang. The CMB was thought to be uniform but discontinuities have
been discovered within it.
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