http://www.FreeScienceLectures.com The universe began with the big bang, and for the first four hundred thousand years all matter was ionised, indicated by the blue region in the diagram. When the universe had cooled enough to allow atoms to form, there followed a period known as the dark ages, during which matter condensed into the first stars and galaxies. After 150 million years the first stars ignited and began to emit visible light. The grey circle marks this time when the first galaxies can be seen. The white circle represents the spacial dimensions of the universe. As time passes, the circumference of the circle increases, corresponding to the expansion of the universe. Time is represented by the radius of the circle, and travel through space is represented by rotation around the circle. For simplicity, only one spacial dimension is shown in the diagram, but the remaining two dimensions behave in the same way. Matter remains almost stationary on the circle, but light rotates around the circle at a constant angular velocity. The location of our solar system is indicated by the green dot. To examine our view of the universe, lets zoom in to our region, and start from time zero. The blue dot is a supernova explosion that occurred around the time of the first galaxies, and is visible to us today. The light from the supernova explosion propagates in all directions, and its wavelength is gradually shifted towards the red end of the spectrum as the universe expands. It is not visible to us until the light arrives at the Earth at the present time. The only section of the universe visible to us today is along this light path. However, this does give us a representative cross-section of the universe all the way back to the big bang. We can see how the view of the universe from our solar system evolves with time, by restarting again from time zero. The light curves show the cross-section of the universe that is visible at any time. Notice the intersection of the light curves with the time of the first galaxies. As the age of the universe increases, the first visible galaxies continually change as new galaxies come within range of our solar system. --- It's Never too Late to Study: http://www.FreeScienceLectures.com --- Notice: This video is copyright by its respectful owners. The website address on the video does not mean anything. ---
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