Bell Ringer

1. According to The Cosmos, how old is the universe?

2. Define the Big Bang.

Agenda

Notes: The Universe and Galaxy Types What is a theory? The Big Bang theory After the Big Bang Evidence of the Big Bang theory The Future of the Universe

What is a Scientific Theory? A scientific theory an explanation of

some aspect of the natural world Theories are supported by a significant

amount of evidence and years of research

When we say that the Big Bang is a theory, we mean that it is widely accepted by the scientific community due to an overwhelming amount of evidence

The Big Bang Theory

You are not required to agree with the Big Bang theory

However, you are required to know:1. What it is 2. The scientific evidence that

supports it

The BBT: What Happened? The Big Bang theory states that the universe

came into being at a single moment

All of the matter and energy of the universe were at one time concentrated in an incredibly hot region smaller than an atom

The universe began in an instant about 13.8 billion years ago in an enormous explosion

After the Big Bang Shortly after the Big Bang, the universe

expanded and cooled

After a few hundred thousand years, the universe was still hot and small, but cool enough for atoms to form

Gravity pulled atoms together into gas clouds that eventually became stars

Our sun and solar system formed about 4.6 billion years ago when the universe was about 2/3 of its present size

Evidence of the Big Bang

What led scientists to the conclusion that the Big Bang happened?

2 Main Pieces of Evidence:1. Cosmic background radiation

(micro and radio waves)2. Red shift (Hubble’s Law)

Cosmic Background Radiation Scientists use radio telescopes to study the

universe. These telescopes can detect many different wavelengths of light – much more than the visibly light that we can see with our eyes

In 1965, American physicists detected faint signals in all directions

Scientists eventually learned that this faint glow is caused by microwave and radio wave radiation that was produced by the big bang and still travels throughout the universe

Red Shift: Hubble’s Law

Edwin Hubble was an American astronomer that studied distant galaxies

Hubble noticed that most galaxies exhibit a red-shift in their light wavelengths Red-shift means that the light waves are

getting longer If light waves are getting longer, they

are moving farther away from the Earth

Red Shift: Hubble’s Law

The farther away a galaxy is, the greater the red shift will be

This means that the farther the galaxy, the faster that galaxy is moving away from Earth

Hubble’s law states the relationship between a galaxy’s increasing distance from Earth and its increasing speed away from Earth

http://astro.wku.edu/astr106/Hubble_law_anim.gif

Age of the Universe

Since astronomers know the current speed that the universe is expanding we can calculate how long it has been expanding

This is how we infer that the universe started from a single point about 13.8 billion years ago

What Will Happen in the Future? Scientists are currently trying to predict whether

or not the universe will continue to expand forever or whether gravity will pull galaxies back together

The answer depends on the amount of matter in the universe If the amount of matter is sufficient enough to

overcome the gravitational force then the universe will expand

If the amount of matter is NOT sufficient enough to overcome the gravitational force then the universe will reverse its expansion

Assignment

Big Bang Theory & Hubble’s Law worksheet