1. Life on Earth Without the Theories of Relativity How would our lives be different on Earth if we did not have any knowledge of the theory of relativity? Meagan Thiedemann Physics 11A Mr. Jennings December 9, 2005

2. Overview In 1905, Einstein published a paper that became known as the special theory of relativity. Other than this theory, there is the general theory of relativity. The special theory of relativity is special because it applies the principle of relativity to a special case of inertial reference frames in flat spacetime. The effects of gravity are ignored in flat spacetime. This theory of special relativity says that there is no set frame of reference, but that physics has to look the same to all observers who are travelling at a constant velocity. The equation E=mc^2 is also explained in the special theory of relativity, and is the only equation in which mass can change. Mass is a magnitude that is dependant on the amount of energy. The general theory explains how the special theory and Newton’s law of universal gravitation tie in with the fact that gravitation is not due to a force, but a manifestation of curved space and time, which is produced by the mass-energy content of spacetime. Spacetime is treated as a 4-d Lorentzian manifold that is curved because there is mass, energy, and momentum within it. What is seen on Earth as the force of gravity, is described in the general theory as continuous physical acceleration caused by the mechanical resistance of the surface of Earth.

3. Without These Theories… Understanding of Gravity Space shuttles, and Satellites in orbit Perception of Straight and Curved Lines in Space Travel

4. Understanding of Gravity Our understanding of Gravity may have been very different today if the theories of relativity had never been produced. It is quite possible that scientists may not know why it is that a block of wood half the size of another falls at the same rate. Because the theory of general relativity states that it is continuous physical acceleration caused by Earth’s mechanical resistance that makes things fall at the same rate as one another, we may not understand why it is that an object that is clearly heavier than another falls at the same rate as it. In this sense, our understanding of why gravity works the way it does would be very different.

5. Space Shuttles, and Satellites in Orbit There would be effects on the people in space shuttles that we would not be able to explain if it weren’t for these theories. The special theory states that the closer an object travels to the speed of light for prolonged periods of time, the time will actually be slower for them than it is for people on Earth. This means that the astronauts traveling on space shuttles would actually age a bit slower than the rest of the population on Earth. We would not understand why this happens without the theories of relativity. Satellites in orbit would be difficult to explain as well without the theories of relativity. We may not understand why it is that these satellites can be suspended in space, and travel around the Earth at very high speeds. The equation E=mc^2 can be derived to E/m=c^2. This means that if the energy of these satellites goes up, the mass will go up as well. This makes the satellites seem heavier when they are in space, allowing them to stay in orbit, although they will never reach the speed of light (c).

6. Perception of Straight and Curved lines in Space Travel What our mind translates as a curved line in space, for example if we see something flying through space, is actually a straight line. It is difficult for our minds to see that there are actually 4 dimensions in space, the fourth dimension being time. Our minds have a much easier time picturing space as flat, much like a map of the Earth that is drawn out. Because of this, we see straight lines as being curved. Whatever it is that we see flying is actually going straight, from one destination to another, and is in fact not making an arc. Einstein’s theory explains that the curvature of spacetime is caused by the presence of stress-energy. This is when there is an object with a very large mass, in this case the Earth, that is causing the local spacetime geometry to produce a curve. The larger this object is, the more curvature there will be. This causes everything to accelerate towards the object causing the curvature. So objects that are accelerating towards Earth against this curvature, which almost seems like a ‘dent’ look like the are creating a curved line in their travel, when they are in fact moving straight.

7. It Goes Unnoticed The theories of Relativity are something that we don’t pay much attention to in our daily lives. It is something that is simply there, and it is difficult to imagine what would be different about life without it. These theories have become a part of our lives in many ways, and have maybe influenced many people in many ways. The theories of relativity are not something that we can simply ignore, but they are also not something that everyone must know everything about. We, as people, do not notice the effects of the Theories of Relativity until we stop to actually think about it.