1. Chapter 13: Neutron Stars and Black Holes Einstein’s theories of Relativity Albert Einstein (Al) is best known for his two theories of relativity Special theory of relativity General theory of relativity

2. Chapter 13: Neutron Stars and Black Holes Special theory of Relativity Proposed in 1905 to support the observations of A.A. Michelson and E. W. Morley that the measured speed of light is independent of the motion of the observer or source. No matter what our speed, we always measure the speed of light as 299,792.458 km/s.

3. Chapter 13: Neutron Stars and Black Holes The special theory of relativity allows us to extend our laws of Physics from low speeds to speeds approaching the speed of light. Some predications Moving objects appear to contract in direction of motion Moving clocks run slow Mass appears to increase All predictions have been repeatedly verified to very high accuracy.

4. Chapter 13: Neutron Stars and Black Holes General theory of relativity General relativity explains what gravity is and how it fits in the special relativity framework. Proposed in 1915. It equates gravity to accelerating reference frames. You can’t tell the difference. There is no experiment you could perform to tell the difference except looking outside.

5. Chapter 13: Neutron Stars and Black Holes To incorporate accelerating frames into special relativity, Einstein had to treat time just like he treated space and thus our new coordinate frame is called space-time. It is a four dimensional space. Thus matter curves space-time and objects follow that curvature and we call the effect Gravity.

6. Chapter 13: Neutron Stars and Black Holes Consequences of Relativity Theories The study of black holes Let us suppose we get funding to send an unmanned space probe towards a black hole. The probe will radio back information like temperature, time, etc.

7. Chapter 13: Neutron Stars and Black Holes We discover that as the spacecraft approaches the black hole, the frequency we have been communicating with slowly changes to a lower frequency. This is because the light losses energy as it tries to escape from the region around the black hole. As time goes on the frequency shifts so low we can no longer communicate with it. It has slipped past the event horizon.

8. Chapter 13: Neutron Stars and Black Holes We also notice that has the probe approaches the black hole, the time reported back continues to be slow. It is as if we are aging faster than the probe is. This is called time dilation. As the probe enters the event horizon it appears that its clock slows to a stop and we never actually see the probe enter the horizon.

9. Chapter 13: Neutron Stars and Black Holes The extra amount of precession of planet Mercury’s orbit is explained by GTR. The bending of light by gravity is predicted

10. Chapter 13: Neutron Stars and Black Holes Gravity from other galaxies bend the light from other galaxies to form Einstein rings and crosses.