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The Expanding Universe???
Big Bang theory – Origin of the Universe
Big Bang marks the inception of the universe
• Occurred about 15 billion years ago
• All matter and space was created
Not a huge explosion that hurled matter in all directions. Technically, there was no “bang”
Technically, matter is not moving outward in all directions. Reality: space expands
The Expanding Universe???
Big Bang Theory -- the scientific theory
of the universe’s earliest moments,
stating that all the matter in our
observable universe came into being at
a single moment in time as an extremely
hot, dense mixture of subatomic
particles and radiation.
The Expanding Universe???
There are 4 evidences that led scientists
to widely accept the Big Bang theory.
1) Hubble’s Law
2) Cosmic Microwave Background (CMB)
3) Galaxies that are spread apart
4) Chemical Composition of the Universe
Hubble’s Law
Edwin Hubble
(1889 – 1953) – an
American astronomer
who discovered
galaxies outside of
the Milky Way.
Hubble’s Law
Hubble’s Law -- the farther away a
galaxy is, the faster it moves away from
the observer.
The Expanding Universe???
Raisin bread analogy of an expanding universe
Red Shift – Blue ShiftIn 1929, Edwin Hubble observed that spectral lines emitted
by stars in distant galaxies were considerably Red shifted.
The spectral lines (fingerprint or bar code) of stars coming towards Earth were shifted to the blue light end of the spectrum (shorter wavelength)
The spectral lines (fingerprint or bar code) of stars going away from Earth were shifted to red light end of the spectrum (longer wavelength)
RED SHIFT – BLUE SHIFT
The greater the degree of shift of the spectral lines, the faster the object is moving away
The star light DOES NOT appear red or blue (it still appears as white light from the star)
The “bar code” for each element either shifts to the shorter wavelength blue end of the spectrum or to the longer wavelength red end of the spectrum
Cosmic Microwave Background (CMB)
Arno Penzias &
Robert Wilson –
discovered the CMB
in 1964 at Bell Labs in
Holmdel, NJ. They
were award the Nobel
Prize for Physics in
1978 for this
discovery.
Cosmic Microwave Background (CMB)
The CMB is about 2.73 K and varies by
about .00001 K across the sky.
Galaxies that are spread apart
The slight variation of temperature would
lead to galaxies that were separate and
spread apart.
Galaxies that are spread apart
Since we see separate galaxies that are spread
apart, there are 2 things we can conclude.
1) The Universe is changing and not
infinite.
and / or
2) There are a finite number of stars.
Scientists have widely accepted both of these
ideas which both point to the Big Bang.
Chemical Composition of the Universe
75% hydrogen
25% helium
Chemical Composition of the Universe
Space is too cold to make helium. Only
the inside of a star is hot enough to
make helium.
The helium from all the stars could only
produce at most 10% of the helium in
the Universe.
Where did the helium come from?
Chemical Composition of the Universe
The mathematics of the Big Bang Theory
predict an environment hot enough to make
helium and predicts a 75% hydrogen 25%
helium ratio.
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