Option D. 3

Universe was born around 13.8 billion years ago in process called Big Bang In the beginning, all matter & energy in the entire universe was concentrated in a single point called a singularity The universe was initially SO hot and dense, atoms did not even exist During the first second of its life, the universe expanded very rapidly As the universe expanded, the density and temperature decreased As it cooled, hydrogen and helium atoms formed Stars were first formed about 1 billion years after the Big Bang Big Bang Model

Space AND time started with the Big Bang As the universe expands, space-time itself increases Typical questions of what was before the Big Bang, what started it and what does the universe expand into have not meaning because: Time originated in the Big Bang (nothing before) Space itself is expanding The rate of expansion of the universe has been increasing (accelerating universe) Big Bang Model

A major piece of evidence supporting the Big Bang model is the cosmic microwave background (CMB) radiation Was first observed inadvertently in 1965 by Penzia & Wilson Radiation was acting as a source of excess noise in a radio receiver they were building The CMB radiation is a kind of echo of the original Big Bang still resonating around the universe They discovered that microwave radiation was coming towards us from all directions in space Radiation was good match to theoretical black body radiation produced by very cold object (temp of just 2.7K) CMB is thermal radiation from the early universe, when p + and e - first combined into atoms Cosmic Background Radiation

Doppler Effect Distant galaxies are moving away from us In astronomy, the Doppler effect was originally studied in the visible part of the electromagnetic spectrum Today, the Doppler shift applies to electromagnetic waves in all portions of the spectrum Also, because of the inverse relationship between frequency and, we can describe the Doppler shift in terms of Radiation is red- shifted when its increases, and is blue-shifted when its decreases

Red Shift

Expanding Universe Cosmological redshift is due to space itself being stretched out by expansion, not the Doppler effect Electromagnetic waves are also stretched out and therefore red shifted Expansion of space can cause the energy of emitted light to be reduced Extreme levels of radiation from the Big Bang have been red shifted 1100 times longer than their original wavelength (CMB radiation)

Cosmic Scale Factor

Hubble’s Law states that distant galaxies are moving away from the Earth with a speed that is proportional to their distance Where: d is the distance to the galaxy (in Mpc) v is its recessional speed (in km s -1 ) H 0 is known as Hubble’s constant and its average value is 72 km s -1 Mpc -1 Hubble’s Law

Hubble’s Law has a few limitations: Constant in space but varies with time Means that the rate of expansion of the Universe was NOT the same throughout its expansion There are uncertainties in the distances measured precisely Quite difficult to measure distances to remote galaxies accurately

Hubble’s Law Hubble’s Law is determined by: Measuring the distance to distant galaxies Measuring their recessional speeds using Doppler effect Plotting a graph of v against distance Hubble’s constant is the slope of the graph

Age of Universe

Latest research has revealed that the expansion of the universe is accelerating Cosmic scale factor increases non-linearly Recession velocity of a distance galaxy increases continuously with time Research is based on using Type Ia supernovae as standard candles Type Ia supernovae are very rare, but it was found that they all have the same peak luminosity With peak luminosity and apparent brightness, distance can be found Accelerating Universe

Main Evidence 1.Expansion of Universe 2.Background Radiation 3.He Abundance He produced by stars is little No other explanation for the abundance of He in the Universe than the Big Bang model Big Bang