The Expansion of the Universe
At school we did a project where we worked in groups at a topic that interested us. Together with two friends I chose the topic "The Expansion of the Universe". We wrote our project in German and this little summary in English.
In the last months, we worked on the topic "The Expansion of the Universe and the Hubble Constant" for our project. We informed ourselves about the following topics: Big Bang, the expansion of the universe, possible endings of the universe, the life of Edwin Hubble, the Hubble constant and the determination of the Hubble constant. We occupied ourselves with those theories, which are the most represented ones at the moment.
The universe' existence began with an event called the "Big Bang", when space and time came into being. At first, the space was very, very small, less than 10-35m, and filled with energy. But the universe began expanding, what it still does. Expansion means, that the space between galaxies gets bigger. So the galaxies "run away" from each other.
A parameter for this expansion is the Hubble constant. It is named after Edwin Powell Hubble, who lived from 1889 to 1953. He worked at the Mt Wilson Observatory and explored the movement of the galaxies. What he found out is, that the bigger the distance between a galaxy and the observer is, the faster they move away from each other. The Hubble constant describes the relation between the distance and the velocity. The red shift, that means how much the light is redder than usual, is used to determine a galaxy's velocitiy. For the measuring of a galaxy's distance, the real brightness of a star in that galaxy is needed, which can be determined with the help of cepheids or supernovae. Cepheids are bright, pulsating stars and supernovae are dying stars.
How the universe may end, depends on the density of the universe. If the density is smaller than a critical worth, the universe will expand eternally. If the density is greater, the universe is going to stop expanding and will start to collapse.
But all cosmolical theories are to some point speculative. The problem is, that nobody can travel through space and time to find out how it really is.
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