# AST201H1 Lecture Notes - Lecture 7: Observable Universe, Quasar, Hyperbola

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###### AST201H1 Full Course Notes

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Twin paradox you will both see if each time run slower and think the other is younger. Not true because one has changed reference frame. We can think about the twin paradox using time dilation and or length contraction. Someone on earth would measure the star vega to be 25 light years away. If you fly a spaceship to vega at 0. 999c, you will measure the distance to be: much less than 25 light. The person on earth sees you travel 25 light years at 0. 999c. They think your trip takes: a little more than 25 years. You measure the distance btw earth and vega as only 1 light year. Thus, at a speed of 0. 999c, for you the trip to vega takes only: about one yr. Gravity- infinite. (makes masses attract one another) experience everyday. Infinite (makes atoms cling to each other) experience everyday. Eg. a little magnet has more force than gravity of earth.