The Universe
notes
Universe

The universe is the biggest thing there is.

It is all existing matter and space.
Necessary Background information

Light-year (LY) = the distance light travels in one year


The further we look into space, the further back in time we look.


1 LY = 9,460,536,000,000 km = 5,878,504,533,524.2188 mi
The light we see from a distant galaxy that is 2 million light years away is 2 million
years old.
Most abundant element is Hydrogen (H)

Second most abundant element is (He)
The big Bang

Current Theory for the Origin of the Universe

Created all visible and invisible matter, energy, space and time.

Universe has and is expanding since that moment

Started as a Hot, dense point that expanded faster than the speed of
light

In a minuscule amount of time, fractions of fractions of seconds, the
universe went from a size smaller than a subatomic particle to the
size of a golf ball

Fractions of time so small that scientists created a new unit of time

Planck time
The big bang (continued)

Current age of the universe: Approximately 13.7 Billion years

Composition of the universe:

21% - Dark Matter

75% - Dark Energy

4% - Visible Matter

Main Force in universe is Gravity

Possible Out comes:

Open Universe: Expansion will continue forever

Closed Universe: Expansion will stop and Universe
will collapse on itself

Flat Universe: Expansion will slow to a halt in infinite time.

Expansion would be so slow it would seem to stop
Evidence for The Big Bang

Mixture of elements we see in old stars is exactly as predicted (new stars
contain different amounts)

How do we know what stars are made of?

Emission spectrum – different elements emit different wavelengths when
photons (electromagnetic radiation - light) of specific energy “hit” electrons
in an atom and then the energy is released
Evidence continued

Hydrogen Atom – Balmer Series

“n” are energy levels of electrons

It takes specific (quantized) energy to
go up or go down energy levels

Going from 3rd level to 2nd level emits
red light at that specific wavelength.
Evidence continued
 Smaller Wavelength means higher frequency which is higher energy
 Larger wavelength means lower frequency which is lower energy
 From: E = h*f = h*(c/u)
 Energy = Planck constant * frequency = Planck constant * (speed of light/wavelength)
Evidence – Red shift

A similar concept with sound is called
the Doppler effect

As a sound source approaches you, it sounds higher pitched. The sound has short
wavelengths.

As the source moves away from you the sound is low pitched, which is long
wavelengths.
Evidence – Red Shift

With light it is the same.

In the visible spectrum, red has longer wavelength than blue.

So any increase in wavelength we call “reddening” (becoming more red),
even if it isn’t in the visible spectrum. (i.e. Radio Wave are more red than
infrared)

And, any decrease in wavelength we say it is becoming more blue, even if it
isn’t in the visible spectrum. (i.e. X-rays are more blue than ultraviolet)
Evidence – Red shift

At the very beginning, the rate the universe was expanding was greater than
the speed of light.

Then it slowed down for an amount of time

Now it is speeding up again, due to a mysterious force called “Dark Energy”
Evidence – Red shift

In 1929, Edwin Hubble discovered that the Universe is expanding. He
discovered this because stars and galaxies were red shifting

This is hydrogen shifting, both red and blue shifting
Hubble constant – Hubble’s Law

Hubble’s Law states that the further a galaxy is, the faster it is moving away.

The current value for the Hubble constant is: 73.8 km/sec/Mpc (give or take
2.4 km/sec/Mpc including, both random and systematic errors)

km = kilometer

sec = second

Mpc = one Million parsec

One parsec is about 30 trillion kilometers, or just over three light-years.
Hubble – Red shift

Hubble and scientists later noticed that all galaxies were red shifted, none
were blue shifted.

How is this possible?

The space in between galaxies was expanding, the galaxies itself was not
expanding. (Confusing, right?)