1. The Universe

3. The study of the structure and the evolution of the whole universe is called cosmology.

4. How did the universe begin?
The universe formed from an expansion of concentrated matter and energy.
This concentrated matter occupied a space about as big as our current solar system.
We call this expansion the Big Bang.
Energy left from the Big Bang is known as background radiation.

5. How old is our universe?
We think the universe is about 13.7 billion years old.

6. Is the universe staying the same size?
We believe that the universe is expanding.
We think that the rate of expansion is speeding up.

7. What evidence supports this idea?
There is background cosmic radiation in every direction.
All galaxies appear to be moving away from each other.
Edwin Hubble found that distant galaxies are moving at much faster velocities away from each other than closer galaxies.

11. Are we at the center of the universe?No
From every point of view in the universe, galaxies appear to be moving away from the observer.

12. What came before the Big Bang?
We think that in the first fraction of a second, the Universe greatly expanded from a dense hot concentration the size of a proton to something the size of our solar system.
We call this the Inflationary Period.

13. Some cosmologists want to figure out what came before the Inflationary Period.
We think the Universe at that time was all energy(or radiation), with no matter, but at the present time it remains hard for us to describe.
Some people believe that our present universe could be one in a series of universes. This is called the bubble universe theory.

14. What do we believe is going to be the future of our universe?
Open Universe or Big Bore Theory Expansion could continue until the stars eventually die off leading to total emptiness.

15. Closed Universe or Big Crunch Theory Gravity between galaxies will cause the expansion to slow down. The universe will halt. Gravity will pull galaxies back together. The universe will periodically expand and contract back on itself every billion years.

16. Static Universe or Flat Universe Theory - The expansion caused by the Big Bang and gravity could neutralize each other. The universe would stay more or less the same size that it is now.

17. Which theory is most likely?
At this time, we believe that there is not enough mass in the Universe for gravity to stop the cosmic expansion. The Universe is Open.
If large quantities of dark matter (mass that does not give off radiation) exist, then there may be enough mass for the Universe to be Closed.

18. At the present time, we believe that the matter we can see accounts for only about four percent of all matter. The rest is dark matter.

20. How did galaxies form?
As matter collided during and after the Big Bang, gravity caused atoms of hydrogen gas to condense into galaxies.
We will talk more about the the life story of galaxies another day.

22. How did stars form?
Within galaxies, gravity caused matter to be condensed into stars.
The temperature and pressure in the core of a star powers nuclear fusion reactions which give off tremendous amounts of energy.
Many stars orbit in pairs, called binary stars.

23. How many stars and galaxies are there?
Scientists estimate that there are about 200 billion billion stars in our galaxy, the Milky Way.
The Milky Way is one of about 125 billion galaxies in the universe.

24. What is beyond our universe?
Scientists do not know.
We call the edge of our observable universe the cosmic horizon. There may be something beyond, but we cannot “see” what is there.
We can see no farther than the distance light travels in a time span equal to the age of the universe.

26. What are the most distant objects in the universe?
Quasars are the most distant objects in the universe.
They are brighter than entire galaxies.
Scientists believe that they are related to black holes and may be early galaxies just forming.

27. What are some of the barriers to our exploration of the universe?
Distance - Everything is so far away.
Time- It takes longer than a human lifetime to reach distant stars.
Technology - We have lots of things to invent (like faster vehicles) to make extended space travel more practical.