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.