1. Gravity & The Big Bang Theory
The Universe
Gravity & The Big Bang Theory

2. All things with mass are affected by gravity.
Two objects, whether large or small, always have a gravitational force between them.
Gravitational force increases as mass increases.
Gravitational force decreases as distance increases.

3. THINK! What are two examples of gravity at work?
Why is a cat easier to pick up than an elephant?

4. DEFINITION OF THE UNIVERSE
UNIVERSE: sum of all space, matter, and energy that exist, that have existed in the past, and that will exist in the future.
We see the universe NOW as it was in the past.
It takes time for light to travel in space.
The farther away an object is, the older the light that we receive from that object.
Earth is 8 light minutes away from the Sun

5. PROFILE OF THE UNIVERSE
Age: billion years old
Size: Diameter of observable universe is 93 billion light years away
Shape: Latest data supports a flat universe
Contains: 125 billion galaxies
Space is a vacuum with no air and no air pressure
Most of the universe is empty space
Average Temperature: Kelvin (0 Kelvin is the coldest temperature possible)

6. TECHNOLOGY USED TO STUDY THE UNIVERSE
New technology helps scientists test theories.
Space telescopes (not affected by Earth’s atmosphere)
Hubble
Observatories (Earth telescopes)
Mauna Kea, Hawaii
Probes
Voyagers I and II
Spacecrafts
Mars Rover
Scientists make observations to test theories and develop new explanations.

7. Edwin Hubble discovered the universe is expanding.
STUDYING THE UNIVERSE
Edwin Hubble discovered the universe is expanding.
Made observations of light from distant galaxies which indicated they were moving away from earth and each other
Used the doppler effect to show moving objects show a red shift
DOPPLER EFFECT: observed change in the frequency of a wave when the source or observer is moving.
Shorter wavelength in front of the moving source
Longer wavelengths behind the moving source
RED SHIFT: an apparent shift toward longer wavelengths of light (red light) caused when a luminous object moves away from the observer.

9. THINK!
What happens to waves as they get farther away from a source? (Think of a pebble dropped in a pond)
Why does a siren sound higher pitched as it approaches and lower pitched after it passes and moves away?

10. The light source (S) is moving toward the left.
RED SHIFT DIAGRAM
S = light source
The light source (S) is moving toward the left.
The light waves in front of the light source (S) bunch up which causes the light to appear more blue (BLUE SHIFT) to the observer that the light source is approaching.
The light waves behind the light source (S) spread out which causes the light to appear more red (RED SHIFT) to the observer that light source is moving away from.
Observer the light source is approaching
Observer the light source is moving away from

11. Hubble’s Law
Hubble’s law is statement of correlation between the distance to a galaxy and it’s (recessional) velocity which is determined by red shift.

12. Expansion implies that the universe was once smaller.
BIG BANG THEORY
Expansion implies that the universe was once smaller.
Universe began in an extremely small space called the “point of singularity,” then began to rapidly expand or “explode”
BIG BANG THEORY: theory that all matter and energy in the universe was compressed into an extremely small volume that 10 to 20 billion years ago exploded and began expanding in all directions
Georges Lemaitre - the Catholic priest who came up with the idea of the Big Bang

13. EVIDENCE SUPPORTING THE BIG BANG THEORY
COSMIC BACKGROUND RADIATION (CBR): steady but very dim signal from all over the universe in the form of radiation at microwave wavelengths.
Dim remnants of the radiation produced during the big bang (left over from the unimaginably hot explosion).
Red Shift = the expansion of the universe means we can “rewind” time to when it started from a single point

15. THINK!
What is the big bang theory (in your own words)?
What is one piece of evidence that supports the big bang theory?