Objectives:1. relate the cosmological principle to isotropy and homgeneity of the universe.

2. understand how Hubble’s law is used to map the universe, and look back in time.

3. Know each of the major predictions of the Big Bang theory, and corresponding confirmations by observation.

4. relate how and what observations tell us about the properties of the young universe.

Cosmology

vocabularyCosmology

UniverseGalaxy

Hubble law and constantGeorge Gamow

Penzias and WilsonCosmic background radiation

COBE sateliteWMAP

Big bang nucleosynthesisHelium-4

• Cosmology: the study of the universe itself, including the history, origins, and fate.

• Galaxy: A gravitationally bound system that consists of stars and star clusters, gas, dust, and dark matter.

• Immanuel Kant (1724-1804): proposed that little smudges of light were “island universes” separate from our own milky way.

• There are more galaxies than there are stars in our own galaxy.

• There are billions of stars in the milky way galaxy.• The universe contains billions and billions of

galaxies.

Edwin Hubble

• Edwin Hubble: the first astronomer to measure the distance to another galaxy.

• These immense distances are measure in Mega-light years (Mly) = million light years.

The Cosmological Principle

• The cosmological principle: the center of our conception understanding of the universe, and a testable theory that makes predictions that have confirmed by observation.

• Isotropic: the same in all directions.• Homogenous: the stars and galaxies in our

part of the universe are the same as they are in remote corners of the universe.

We Live in an Expanding UniverseHubble Law

• Edwin Hubble: noticed a red shift in the light of all galaxies relative to the milky way galaxy.

• Hubble Law: The amount of red shift (or Velocity of a galaxy) is proportional to the distance of the galaxy from the milky way.

• The further away a galaxy is the greater the red shift, and the faster is it moving away from us.

Interpretation of Hubble Law

• Conclusion: all galaxies are moving away from the milky way.

• Interpretation: the universe is expanding.• Hubble Constant: 22 km/s/Mly

All Observers see the same Hubble expansion

• Since the universe is homogenous and isotropic (cosmological principle), an observer at any point in the universe would also see galaxies moving away from them.

• Big Bang Theory (explains why):

In the image on the left, the universe is isotropic. the right, the universe is homogeneous.

Galaxies are not flying through space

The space around them is expanding, “pushing” them away from each other.

On the small scale gravity holds the closed system of a galaxy together, so we don’t expand.

Prediction #1:the age of the universe

• By using hubble’s constant we can run the cosmological clock backwards.

• Hubbles law implies that everything in the universe was at the same place 13.7 bya (billion years ago).

George Gamow (1904-1968)

• Gamow related the temperature to the early conditions of the universe.

• Predicted that left over energy from the big bang should be detectable as microwave radiation. (1948).

Bell Labs: Penzias and Wilson

• Telstar (1962): The first telecommunication satellite was launched, but phone reception had a strange hissing interference.

• Microwave radiation left over from the big bang was causing the interference.

• The first direct evidence that the universe was created by the big bang.

Cosmic Background Explorer(COBE Satellite)

• Launched by NASA in the mid 1980’s, the COBE satelite took the first picture of the early universe.

• Showed the matter and energy was not uniform during the creation of the early universe, but the early universe had clumps of matter beside vast empty spaces.

• COBE answered none of the essential questions about the age, composition, expansion of the universe.

WMAP

The story of the early Universe is a story about Temperature

• The early Universe is so inconceivably hot that all matter and the forces of nature are combined into one super force.

• As the universe cools and expands matter and the forces of nature are manifested in the universe.

Forces and the Particles of Matter

The Strong Nuclear Force Appears

• Causes Inflation: rapid expansion and cooling of the Universe.

• The first pieces of matter materialize in the universe, the photon and the electron.

• The strong nuclear force is responsible for holding quarks together to form protons and neutrons.

The Electromagnetic Force Appears

• As the Universe further expands and cools, the electromagnetic force separates out.

• For the first time there is light in the universe.• When the electromagnetic force separates, we

have the formation of the first sub-atomic particles called Hadrons.

• Two common examples of Hadrons are the Proton and the Neutron.

• We have the first Atoms in the Universe!

Hydrogen and Helium• The only two atoms that are created

as a direct result of the big bang are the two simplest. H and He

• Gravity begins to work on this matter forming large gaseous clouds of Hydrogen and Helium.

• The gaseous clouds will form the first stars in the universe.

• Big bang predicts a ration of 75% Hydrogen, and 25% helium. Hey that’s what we see in the universe still today.

Stellar Nuclear Fusion

• Nuclear fusion: fuses atomic nuclei together forming larger elements. Example, fusing two Helium atoms forms one Beryllium atom.

• Nuclear fusion produces larges amounts of energy in the form of heat, light, and radiation.

• Nuclear Fusion can form elements as large as Iron (Fe) element number 26

Super Nova

• After a star has fused all of its Hydrogen and Helium, forming mostly Iron, It dies in an enormous of explosion.

• The energy of a Super Nova can further fuse atomic nuclei into the heavier elements, forming elements up to Uranium.