1. The big bang theory

2. Who remembers Doppler shift?
The Doppler Effect is the perceived change in wavelength of a wave that is emitted from a source that is moving away or toward an object.

3. Red Shift When objects move away from us, they appear red
When objects move toward us they appear blue
Observations made in the early 1900’s revealed that most of the galaxies we can see have Doppler shifts toward the red end of the spectrum
The light waves are being stretched
The Earth and the source of light are moving away from each other

5. Hubble’s Law
Edwin Hubble wanted to explain why the galaxies appeared to be moving away from us.
Hubble realized that dimmer galaxies were most likely farther away from us than were brighter galaxies.
He tried to find a relationship between the distance to a galaxy and their red shift.
He found that galaxies exhibiting the greatest red shift are the farthest away
Greater red shift = greater speed The universe is expanding!!
Edwin Hubble was an astronomer that discovered that the universe was expanding.
He did this by using the red shift of the spectra of stars.
He observed the light from the galaxies at different distances from earth. From this light he could determine that the farther something was from earth, the faster it seemed to be moving away.

6. Hubble’s Law
Galaxies are retreating from us at a speed that is proportional to their distance
i.e. the farther away galaxies are, the faster they are moving away from us

7. v=Hd where v = speed at which a galaxy is moving away (km/s) and d = distance to the galaxy (Mpc) and H = Hubble’s Constant representing the expansion rate of the universe CURRENT VALUE OF H = 73.8 km/sec/Mpc
Hubble’s law

8. This means the universe is expanding!

9. The big Bang theory?

10. The big bang theory
The Big Bang Theory says that once the entire universe was confined in a hot, dense, supermassive ball
Approximately 13.7 billion years ago, a “violent explosion” occurred, hurling the material in all directions
Everything in our universe came from that ball

11. Evidence of the Big Bang
Red Shift – Hubble’s Law
Cosmic Background Radiation
Radio signals from all over the universe, could be leftover from Big Bang (H-pg 848)

12. Evidence for the Big Bang cont.
Cosmic Microwave Background radiation (CMB’s) : the existence of an isotropic radiation bath that permeates the entirety of the Universe
In 1964, two young radioastronomers, Arno Penzias and Robert Wilson, accidentally discovered the CMB using a well-calibrated horn antenna.
They were trying to determine what was causing static in telephone lines. They worked for Bell Telephone company.
It was soon determined that :
the radiation was diffuse,
emanated uniformly from all directions in the sky,
had a temperature of approximately 3 Kelvin (2.73K).
Isotropic radiation has same intensity no matter what direction

13. Cosmic Radiation Background
Cosmic Background Radiation

14. Steady-state theory Alternative to BBT
Proposes that the universe looks the same on large scales to all observers, and that it has always looked that way.
Doesn’t change with time.
However, if the universe is expanding, new matter is created and added which keeps the density of the universe constant.
Most astronomers do not accept this model, because it cannot explain CMB

15. Idea One: Open Universe
What happens at the end?
Idea One: Open Universe
Universe expands forever, ends in “ Big Rip”
Stars burn out, leaving many black holes and other matter
Idea Two: Closed Universe
Universe eventually starts contracting (coming back together)
Galaxies collapse on each other forming the “Big Crunch”
Idea Three: Flat Universe
Expansion will slow to a halt but it will never contract

16. Critical density
Average density of matter in the universe is studied
Critical density ( kg/m3) is the dividing point between a closed or open universe.
If the average density > critical density  closed universe
If the average density < critical density  open universe
If the average density = critical density  flat universe

17. Sources