Contents:
Relativity
Curved Space-Time
E=mc²
Relativity
| What is General Relativity? |
| General Relativity refers to a revolutionary theory developed by Albert Einstein in the early 20th century. This theory differed from Newtonian theory, because Einstein stated that there is no absolute time or co-ordinates. Newton believed that time always moved at the same rate of speed. |
The basic precept of relativity is that the laws of physics remain the same for everyone everywhere. Neither acceleration nor actual movement will change the laws. In addition, the speed of light (c) is the same for all observers. This means that if someone on a train moving 60 mps (although this is a difficult speed to attain) turned on a flashlight, the speed is not 60 mps + 186,000 mps. The speed of light would remain the same, no matter where it is observed from.
Effects:
1) All time is relative: there is no "Absolute time." This means that two people moving at different rates of speed are aging differently. It is also the most radical departure from Newtonian physics. Newton believed that time was the same for everyone everywhere. Einstein abolished this concept.
2) An increase in gravity leads to a corresponding decrease in the relative rate of time. This is difficult to explain. If you were on this massive planet, time would seem normal. But if you viewed life on the planet, people would appear to move slower.
3) It is impossible to accelerate objects to the speed of light.
4)Objects appear to be shortened at high speeds. This is similar to the effect of lengthened time.
* It is important to note that the effects are only truly noticeable near the speed of light. Using sensitive equipment, scientists have detected differences in time between satellites and buildings, but only at around 99.9% the speed of light can the human eye detect a noticeable difference.
There are many side effects. One is called the "Twin Paradox," which isn't an actual paradox, but remains interesting. Suppose a twin flies off in a rocket at very fast velocities. When he arrives back at Earth some time in the future, his twin will appear to be much older than he, although they are actually the same age. Of course, this has never been tested in real life, but it serves as a bold illustration of the effects of general relativity.
Curved Space-Time
| What is the difference between General and Special Relativity? |
| Special relativity was the precursor to general relativity, and it basically states that the laws of physics are the same for all observers. General Relativity extends that to include acceration of observers with respect to one another. |
This is not a complex concept. Curved space time is based on the assumption that time and space are intermeshed. With this in mind, everything can be explained with a simple analogy. Suppose that space-time is like a trampoline. A star would be represented by a bowling ball, and an object by a marble. The bowling ball stretches the trampoline. This would be like a star bending space-time with gravity. When an object, such as a spacecraft, passes, its path gets bent by the stretched trampoline. This applies to anything, from a comet to light. You've probably heard of black holes. This is an object which scientists hypothesize tears space-time. The effects of a tear in space-time are unknown, but may include travel to alternate universes. In the trampoline analogy, the black hole would be represented by a car. (The analogy breaks down somewhat, because a black hole is very small.) Any object that passes close enought to get caught in the gravity is sucked into the hole. But the effects are more bizarre than this. Remember, we assume (correctly) that space and time are meshed together. This means that when an object such as a spaceship passes near a large object, time appears to slow down. This is not apparent from the ship, but another observer will see that people move in what they think is slow motion. This is a side-effect of general relativity.
The confirmation for curved-space time was made in 1919 by Arthur Eddington. Eddington observed the positions of certain stars in the night sky (the Hyades) and then observed them during a solar eclipse. The positions changed after the light from the stars was bent by the sun's gravity! Since then, there have been further confirmations of curved space-time. Go to the Space Topics website for more information about the confirmation.
E=mc²
Perhaps the most famous equation, ever, E=mc² is part of Einstein's realtivity. The parts of the equations are:
E - Energy
m - Mass
c - The speed of light (186,000 mps or 300,000 kms)
The effects of this basic principle are incredible: a very small amount of mass can yield tremendous energy. The equation was the basis behind the development of the atomic bomb. The atom bomb splits an atom, very little mass, to release the energy stored inside. As you know from Hiroshima and Nagasaki, there is a great deal of energy. The same idea is used for nuclear reactors. The converse, turning energy into mass is accomplished in particle accelerators. Particle accelerators are the tool that elementary particle physicists use to observe sub-atomic particles. Small particles are accelerated to speeds near the speed of light and smashed into one another. This energy prouces many tiny particles.
