Childrens Illustrated Encyclopedia

72

The Big Bang,

13.7 billion

years ago BIG BANG

NEarly 14 billioN yEars ago, the universe

exploded out of virtually nothing. The first scientist to

propose this astonishing theory, now known as the big

bang, was george lemaître (1894-1966). His idea was

supported by the work of Edwin Hubble (1889-1953),

which showed that the universe is expanding. if this is so,

the entire cosmos must have originated from a single point

of explosion. but what was that single point? scientists call

it a “singularity”—a tiny, infinitely dense dot that once

contained all the matter of the universe. such

a thing is impossible to imagine, and even

astronomers do not really understand it. yet within a few minutes of

the big bang, the single point would have been converted

into an immense, expanding cloud of gas. over

millions of years this became the galaxies,

stars, and planets of the universe.

DopplEr EffEcT

christian Doppler (1803-53)

showed that sound waves are

compressed if the source is moving

toward your ear and stretched if it

is moving away. This alters the pitch

of the sound you hear. The same

principle applies to light waves

arriving from distant stars.

rED sHifT

The light from some stars looks

redder than it should. This is due

to the Doppler Effect and shows

that these stars are moving away

from us. Distant galaxies also look

redder, but because the whole of

space is expanding their light waves

are stretched when they reach us.

This is called red shift.

cHaiN of EvENTs

scientists believe that the universe

was created in an explosive event

called the big bang. at the instant of

creation, matter was concentrated in

an infinitely small, dense dot called a

singularity. This then began to expand

and cool, allowing the conversion of

energy into particles. after thousands

of years, these particles joined to

make atoms of hydrogen and

helium that would eventually

form galaxies and stars.

Galaxies started to

form 500 million years

after the Big Bang.

Stars formed in

spinning clouds of

dust and gas.

The sound waves of an ambulance

siren are compressed as it comes

nearer, reducing their wavelength

and raising their pitch.

First life forms

appeared on Earth,

3.8 billion years ago.

If a star is moving away, its

light waves are stretched

out and shift toward the

red end of the spectrum.

If a star is staying in the

same position relative to

Earth, then the wavelengths

of light emitted remain

unchanged.

Earth

Star

Star

Star

If a star is moving toward

Earth, light waves are

compressed and shift to the

blue end of the spectrum.

As the ambulance

moves away, the

siren’s sound

waves stretch,

increasing their

wavelength and

lowering their pitch.

The solar system

formed, 4.6 billion

years ago.

astronomy

physics

stars

Universe

Find out more

frED HoylE

it was astronomer fred Hoyle

(1915-2001) who suggested

the term “big bang” as a joke.

He believed the universe had

no beginning and no end.

Stretched wave, light redder

Compressed waves, light bluer

Wavelength and color

unchanged

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