Transcript D2. Origins of the Universex

THE UNIVERSE
HOW DID THE UNIVERSE COME TO BE???
The Big Bang Theory
The Big Bang Theory was proposed by George Gamow & Ralph Alpher
Cosmologists believe that 14 billion years ago, the universe was
extremely compact, small, and unimaginably dense.
According to the Big Bang Theory, this hot, dense state suddenly &
violently exploded causing a rapid expansion of matter & energy
This moment marks the beginning of the universe and time
The universe continues to expand (Hubble’s theory)
WHAT IS THE EVIDENCE FOR THE THEORY?
There are 2 key pieces of evidence for Big Bang theory.
• Red Shift
• Cosmic Microwave Background Radiation.
RED SHIFT
You may have noticed that when an ambulance or police car goes
past, its siren is high-pitched as it comes towards you, then
becomes low-pitched as it goes away. This effect, where there is a
change in frequency and wavelength, is called the Doppler effect.
This happens with light too.
Our sun contains helium. There are black lines in the spectrum of
the light from the sun, where helium has absorbed light. These
lines form the absorption spectrum for helium.
RED SHIFT (continued … )
When we look at the spectrum of a distant star, the pattern of lines
has moved towards the red end of the spectrum.
Spectrum of the Sun
Spectrum of a Distant Star
This is called RED SHIFT.
It is a change in frequency of the position of the lines.
COSMIC BACKGROUND RADIATION
The universe was initially filled with gamma rays – rays that have
a very short wavelength
As the universe expanded, the wavelengths stretched into other
parts of the electromagnetic spectrum.
The radiation left over from the Big Bang has been travelling
through space ever since
BLUE SHIFT
Red Shift = wavelengths are stretching out and galaxies/stars are
moving away
Blue Shift = wavelengths are shortening and galaxies/stars are
moving closer together
SPECTRAL SHIFTING
As Hubble was observing the galaxies, he made measurements of the
spectral shift in the lines
All of the galaxies were shifted toward the red end of the spectrum,
indicating that the planets were moving away from each other
If planets were moving towards each other, they would shift to the blue
end of the spectrum
THE RED SHIFT IS EVIDENCE THAT THE UNIVERSE IS EXPANDING!