3-T HE U NIVERSAL C ONTEXT OF L IFE
3.1 - T HE UNIVERSE AND LIFE
WHAT MAJOR LESSONS DOES MODERN ASTRONOMY TEACH US ABOUT OUR PLACE IN THE UNIVE?SE
The universe is vast and old.
o Vastness implies many planets on which life may arise
o Age means there was lots of time for life to start and evolve
The elements of life are widespread
o Organic building blocks have been found throughout the galaxy.
o Basic chemicals that make up Earth are present through the universe.
The same physical laws that operate on Earth operate throughout the universe
o The process that evolved life on Earth can happen anywhere
3.2 – T HE STRUCTURE , SCALE ,AND H ISTORY OF THE U NIVERSE
WHAT DOES MODERN SCIENCE TELL US ABOUT THE STRUCTURE OF THE UNIV?RSE
Our Cosmic Address
Earth is a planet on our solar system.
o Our solar system consists of the sun and its orbiting objects, including
the planets, their moons, and rocky asteroids and icy comets.
Our sun is only one of about 200 billion stars in the Milky Way Galaxy.
o A galaxy is an island of stars in space.
Our milky way galaxy is part of the local group
o Billions of galaxies are found in groups
Our local group is located in the local super cluster.
o Regions in which groups are tightly packed are called super-clusters
Together, all these structures make up the universe.
The Scale of the Solar System
o 1 light year = 300,000,000 m/s X 1 year x 365 days x 24 hours x 3600 seconds = 9.46 trillion km
At Voyager 2’s speed of 50,000 km/hour, it would take 100,000 years to get to Alpha Centauri
You could circle the Earth 8 times at the speed of light in a second.
The Orion Nebula is 1500 light years away, thus, we are seeing what it looked like 1500 years ago! And any
communication would take 3,000 years for a response!!!
Our galaxy is 100,000 light years across and 100-200 billion stars The contents of the universe
The universe is the sum of all matter and energy
Matter that we can see is called baryonic matter and
In the galaxies flat disk, most of the mass lies unseen in a
spherical halo that surrounds the disk. It is called dark
matter to indicate that it emits no light but has a gravitational
pull. It represents 23%.
There is another unknown energy called dark energy that is pushing galaxies apart. It represents 73%.
WHAT DOES MODERN SCIENCE TELL US ABOUT THE HISTORY OF THE UNIVERSE ?
The Big bang and the expanding universe
The universe is expanding. If we go back enough, we reach where
expansion began. This is the big bang. It occurred 14 billion years
o Two lines of evidence for the big bang
1) Radiation from the Big Bang
The universe was hot and small in the past so it made a
bright light. When it expanded and cooled, it must have
left a glow of radiation.
2) Overall Chemical composition of the universe
If Big Bang occurred, chemical composition of universe
must be ¾ hydrogen and ¼ helium which is close to
The universe has continued to expand since the Big Bang but on the smaller scale, individual galaxies and
galaxy clusters to not expand. Their dark matter gravitational force beat dark energy.
How do we know that the universe is expanding?
We thought we were special in the center of the universe.
When you make a cake, no matter what raisin you are in, all the raisins are
running away from you and you are running from other galaxies!!!
Stellar Lives and Galactic Recycling
Stars are created by gravity which collapses clouds of gas and dust until the
center is dense and hot enough for nuclear fusion.
Stars release energy from nuclear fusion which is 4H He + Energy
Massive stars live for shorter periods but can make heavier elements.
When its fuel is exhausted stars die. Massive stars have supernovae. We are star stuff
Towards the end of their lives, stars can fuse helium into carbon, then
oxygen and silicon, etc.
Other elements are produced by nuclear reactions that occur when stars die
which disperse into atmosphere to produce new stars.
This is proven as the theory of nuclear fusion in massive stars makes
predictions about relative abundances which is true in the universe.
The Scale of Time
There ought to be many worlds that have had plenty of time for life to arise and evolve. If these worlds have had
histories like Earth’s, they might have had civilizations in the past!
H OW BIG IS THE U NIVERSE ?
The observable universe
The greater distance we look, the further back into the past we see
In a universe that is 14 billion years old we cannot see anything more than 14 billion light years away.
Beyond that, there is nothing to see.
The observable universe consists only of objects within the 14 billion light years.
Two important implications of this
o Just because we cannot see beyond 14 billion light years, it does not mean that nothing exists.
o We are the center of our observable universe. Other observers would see 14 billion light years in all
directions from them and there would be some overlap. 3.3. The Nature of Worlds
H OW DO OTHER WORLDS IN OUR SOLAR SYSTEM COMPARE TO THE EARTH ?
Two Major types of Planets
Terrestrial Planets Jovian Planets
Small size and ma