30.3 Big Bang Theory

Doppler Effect

• Doppler effect = apparent shift in the wavelengths of energy emitted by an energy source moving away from or towards an observer

Spectroscope

• Scientists used a spectroscope to study what elements were in stars– Spectroscope = instrument that splits

white light into a band of colors

• Scientists were able to determine chemical make-up of stars

Red Shift

• Scientists soon found that the spectra of many galaxies were shifted toward the red end of the spectra

• Showed that almost all the galaxies were moving away from the Earth

• That means the solar system is still expanding

Theory

• Observing the red shift led scientists to form a hypothesis about the expanding universe– Billons of years ago, all matter and

energy was compressed into a small volume

– Sudden event = BIG BANG = sent all the matter and energy outward

– Some matter gathered in clumps and formed galaxies

Big Bang Model

• The theory that the universe began as a point and has been expanding since is the Big Bang theory.

Big Bang Model

• In the Big Bang model, the momentum of the outward expansion of the universe is opposed by the inward force of gravity acting on the matter of the universe to slow that expansion.

Big Bang Model

Outward Expansion• When the rate of expansion of the universe

is known, it is possible to calculate the time since the expansion started and determine the age of the universe.

• Based on data from the Hubble Space Telescope and the data on the cosmic background radiation, the age of the universe can be pinpointed to 13.7 billion years.

Big Bang Model

Based on the Big Bang theory, there are three possible outcomes for the universe.

1. The universe could be an open universe and continues to expand forever.

Possible Outcomes

2. The universe could be a closed universe where the expansion stops and all of the mass is pulled back to the original point of origin

3. or it could be a flat universe where the expansion becomes so slow that it seems to stop.

Closed universe

Flat universe

Critical Density

• All three outcomes are based on the premise that the rate of expansion has slowed since the beginning of the universe, but the density of the universe is what is unknown.

Cosmic Background Radiation

• In 1965, scientists discovered a persistent background noise in their radio antenna.

• Persistent background noise was caused by weak radiation, called the cosmic background radiation, that appeared to come from all directions of space and corresponded to an emitting object having a temperature of about 2.735 K (–270C).

Cosmic Background Radiation

• The temperature was very close to the temperature predicted by the Big Bang theory, and the radiation was interpreted to be from the beginning of the Big Bang.

• Earth’s atmosphere blocks much of the cosmic background radiation, so it is best observed from high-altitude balloons or satellites. – An orbiting observatory called the Wilkinson

Microwave Anisotropy Probe (WMAP), launched by NASA in 2001, mapped the radiation in greater detail.