I will start with these topics:

What is Light?

Light is a type of electromagnetic energy that comprises a small portion of the electromagnetic spectrum along with radio waves, microwaves, infrared rays, ultraviolet rays, x-rays, and gamma rays. The Quantum Theory of Gravity states that all waves can be thought of as having mass. What this means is that light also has a mass. Light is therefore made up of a particle known as photons. The speed of light is exactly 299,792.5 kilometers per second or 187,370.3 miles per second. It is believed that nothing can travel faster than light. People about one century ago used to dispute over whether light was restricted to a certain speed or whether it was instantaneous. Today, we know that light does take time to travel distances. This was proven by a man name Olaus Roemer when he was star gazing one night. He was observing to see Jupiter's moon come out from behind Jupiter. At that time, scientists had been able to predict the exact moment when the moon would come out from behind Jupiter. The moon did come out as predicted.

However, half a year later, when the earth was on the farther side of Jupiter, Olaus found that it took approximately 1,000 seconds longer for the moon to emerge. He knew that the estimations were correct so he deduced that light from the moon had taken a certain amount of time to travel the extra distance between point A, which occurred half a year earlier and point B which occurred half a year later. He was then able to compute the speed of light using the information he had. He however did not have the correct distance between the Earth and the Sun therefore his calculations were incorrect but his method on the other hand was. This is a birds eye view of what had happened.

After it was established that light indeed took time to travel, the next question was raised. What did it travel through? Both sound and light travel in waves. The length of the wave is measured in its wavelength and the number of oscillations per second is measured in frequency. Sound has to travel through things such as water or air and can't travel unless there is some type of matter in which it can vibrate, but light could travel through space, which is a vacuum. Therefore people started to believe that in space, there was something called "ether" and that this ether was used to "carry" the light waves and that its existence was for this sole purpose. The only problem with this idea was that no one could detect this ether. It took the mind of Albert Einstein to solve this mystery.

This is what he proposed. Imagine a calm day at sea with no wind and suppose there was a boat traveling at a constant velocity through the water. Two people are playing a game of catch above deck. Since the boat is traveling at a constant velocity through the water, the air is creating an artificial wind, known as friction, or drag, due to the motion of the boat through the water, and the difference in speed between the boat and the outside air. When person A throws the ball to person B, the wind is pushing the ball towards person B and therefore, person A does not need to throw the ball very hard. However, when person B throws the ball, the wind is resisting the balls passage through the air and as a result, person B must throw the ball harder to get the ball to person A.

Now, using this analogy, if there were ether in space, then light would "slow down" just as the ball slowed down as a result of the artificial wind or would speed up depending on which direction the light was pointed. Scientists attempted an experiment on this and found that the light did not change in speed. That was when it was determined that light did not travel through ether because there was no friction to prove that it existed.

What Does Relative Mean?

The word relative simply means, "compared to". If there is a statement, which has the word relative in it, replace "relative" with "compared to" and the statement will be clearer. Einstein however had a different view of things that were relative. If you were standing on the sidewalk and a car drives by at a speed of 55 miles per hour, you would clock the car at 55 miles per hour and you would say that it was traveling at 55 miles per hour. But, the fact is that you are half-right and half-wrong. The car is traveling 55 miles per hour only relative to the ground or to you if you are stationary relative to the ground.

For example, picture a fly that is traveling from the rear of a car that is traveling at 55 miles per hour to the front at a velocity of 10 miles per hour. Relative to a person seated inside the car, the fly is traveling at 10 miles per hour. However, to someone on the sidewalk, they would say that the fly is traveling at 65 miles per hour relative to the ground because they would add its speed to the speed of the car. What Einstein was trying to say was that nothing is actually stationary. Everything is moving. Stationary is a word meaning that something is not moving relative to something else. For example, if two cars were driving in the same direction at the same speed parallel to one another, a person in one car would say that the other car is stationary relative to them, however, relative to the ground, they are moving.

Picture this situation. If two cars were to travel in opposite directions both at the same speed, which we will say is 55 miles per hour, when they passed each other, a person in one of the cars would clock the other car as traveling at 110 miles per hour. Now read on to the next section where you will find that this gets more complicated than just adding them together.

What is E=mc²?

As we have said before, light is a constant hence, the letter "c" is used to represent it in this equation. 1c equals the speed of light, which is measured in m/s. The letter "m" represents the mass of an object. This is measured in kilograms. The letter "E" represents energy and is measured in joules.

When we put all this together we get E=mc². What this equation means is that if we took some mass, we could transform that mass in to an enormous amount of energy. For example, if the mass were equivalent to 1 gram, then it would be transformed in to E=0.001kg x 299 792 500m/s x 299 792.5m/s, which is equal to 89875543056250 Joules!  This is a huge amount of energy.  In fact, one gram of matter can produce enough energy to power a brand new car for its entire usable life. E=mc² applies to all transformations from matter to energy or energy to matter. For example, if we took a candle and set it burning, it is releasing energy in the form of heat. If we stop the burning, we will find that we have ashes. These ashes were the remains of the wick, which had not been transformed to energy. We now know that the energy released is very small. Only about 0.0001% of all the matter had been transformed to energy. The stuff that you didn't see was carbon dioxide, and evaporated wax as well as many other chemicals that didn't go through the transformation process.

As for nuclear energy, if we fuse two atoms of hydrogen together, we get a lot of energy, but we also get helium. So we in fact didn't get the full potential from the matter. Maybe some time in the future scientists will devise a way to transform any kind of matter in to energy. Fusion for example only converts about 1% of matter in the form of hydrogen atoms, into energy.

There is another use for the equation E=mc². As was said before, nothing travels faster than the speed of light and it is impossible for mass to be accelerated up to this speed. As an object approaches the speed of light, its mass increases as well. Therefore, to increase the speed of the object that is approaching the speed of light, more and more energy is required to speed it up.  Eventually it will reach a certain speed, where the mass of the object is so large that it not even all the energy in the universe could increase its speed. Einstein’s equation in this sense works in this fashion. "E" represents the amount of energy required to accelerate the object. Eventually, as you approach the speed of light, the equation shows that the more energy you add, the more the mass of the object increases and the harder it becomes to accelerate the object.

What is Time Dilation?

Now we are stepping in to some of the more complicated parts of Einstein's theory. In this section of his theory, Einstein stated that time is not constant and that it is different in every location. Every person has a different perception of time. At the speed of light, a person’s perception of time would completely come to a halt, however, the theory states that it is impossible to travel at this speed and so it has never been proven.

Now, suppose we had two spaceships traveling in opposite directions each traveling around 100 000 miles per second (note that it's seconds). Also suppose that in each spaceship there is a scientist. Each scientist is conducting an experiment with a beam of light. The light is leaving from a light source and then it is being reflected back by a mirror to the light source. Right next to the scientists that are doing their experiment, is a small window. When the two ships pass each other, scientist A would probably clock the other spaceship as traveling at twice their speed or 200 000 miles per second. But as we have said before, nothing can travel faster than the speed of light but you are clocking the other spaceship at 200 000 miles per second! The answer is that the scientist wouldn't clock the other spaceship at 200 000 miles per second. He would clock him at only 155 000 miles per second.

This may sound completely out of order because you would be wondering why the two cars that were traveling at 55 miles an hour, weren't affected. The reason is simple. The two cars were in fact affected but the speed at which they were traveling was so insignificantly slow compared to the speed of light that you don't notice the change in speed as a result of this phenomenon.

Now, as the two spaceships in space pass each other, scientist A would look in through the window of the other spaceship. As he looks in through the window of scientist B at his experiment, he doesn't see the light traveling up and down. He sees it traveling diagonally because as the spaceship moves, so does everything inside it. Here is a diagram of the situation.

Now as we have said before, light is a constant, which means that it never changes in speed. From scientist B's point of view, he sees the light traveling up and down. As for scientist A, he sees scientist B's light traveling diagonally. Now we have a paradox. (A paradox is when two opposites are true.) Both are correct. The light is going up and down as well as diagonal. However, the light in the spaceship is taking the same amount of time to travel up and down as well as diagonal. This is impossible because the light has to travel a greater distance when traveling diagonally then when traveling up and down and it also has to do it in the same amount of time. But as we have said before, light can't change its speed because it is a constant. Therefore, the only explanation is that scientist B’s perception of time has actually decreased as a result of their speed to allow the light to make it to the light source in the given amount of time.

To the scientist in the spaceship, he doesn't notice the change in time. He still perceives time the same. Only scientist B notices the difference when looking at scientist A and vice versa. None of them, however, will notice anything wrong with the time in their spaceship.

Here’s another example. Supposing a man is in a spaceship traveling at 100 miles per second. As he is traveling, he shines a flashlight in front of him. Now, he is already traveling at 100 miles per second, therefore the light that he is shining only has to travel at 187,270.3 relative to the man. However, if the man clocks the flashlight, it will calculate that the light is traveling at 187,370.3 because light is a constant no matter what happens. Therefore, time has slowed down in the ship as a result of their speed in order to keep the constant of light the same.

Now, supposing that the spaceship that the man is in accelerated to the speed of light. Now of course this is impossible, but for the sake of knowledge, supposing it did. If he shined the light in front of him, how fast must the light travel in order to remain a constant? It has to travel at 0 miles per second. Now we have a problem. No matter how slow time passes, the light will never shine and therefore the person will never be able to clock light at the speed of light. The spaceship is already traveling at the speed of light and the light will therefore not project itself. So therefore, time stops for the man within the spaceship because he will not be able to perceive time slow enough to see light travel at its constant speed. Since there is no evidence of time passage to people, the man within the spaceship would travel across the universe in zero time in his perception of time. If he were able to perceive time, he would see the entire passage of the universe and the end of the universe in the smallest measure of time.

What is the Principal of Equivalence?

Einstein's general theory, which was published in 1916 deals with gravity and so in this section we will talk about gravity.

When you drop anything from any height, it will fall to the ground. If there were no air resistance, all objects dropped at the same time would hit the ground at the same time. For example, if you drop a feather and a bowling ball, they would both hit the ground at the same time providing there was no air resistance. Neil Armstrong confirmed this when he dropped these two objects on the moon.

All objects when dropped will increase in speed at a rate of 32 feet per second. What this means is that after something has been falling for 1 second, it would have fallen 16 feet and would be traveling at 32 feet per second. Here is a diagram.

Now, what does this have to do with the theory of relativity? Isaac Newton provided the equation to gravity in 1679, however, his equation started to break down as the gravity well of an object increased. Einstein’s General theory, which was much, more complicated managed to work in all circumstances. In this part of the theory, Einstein states that not only is matter affected by gravity, but that light is also affected. This was proven in 1924 when Einstein and a group of scientists measured where a star was located during a solar eclipse. He measured and found that the star that was right beside the sun 5 months earlier in a solar eclipse was off by a few degrees. Einstein said that this occurred because the sun had actually "bent" light as the light of the star passed next to it during the eclipse.

If you were in an elevator and it was falling freely you would experience no gravity and there would be no way that you could experience it without being stationary, relative to the ground. Like wise, if the elevator was rising, you would feel an increase in gravitational force and you would never know that it was artificial unless you could see the elevator rising. If your elevator started to rise, and someone outside saw you drop an orange to the ground, they would see the elevator rise to hit the orange. To you inside the elevator, you would see the orange fall faster because you have nothing with which to compare the elevator’s movement.

What is the Space-Time Continuum?

The space-time continuum is what you walk in, talk in, sleep in, or in simple words do everything in. If you had a train running along a track, it is moving in a 1 dimensional space continuum. An ocean liner travels either forward and backward, or right and left. Therefore the ocean liner is traveling in a 2 dimensional space continuum. An airplane flying in the air can go up and down, right and left and forward and backwards. Therefore, the plane is traveling in a 3 dimensional space continuum.

If you want to tell someone where your train is, you would give them one co-ordinate, say the number 12. So the person will go to number 12 track or place. For an ocean liner, you need two co-ordinates, and for the plane you need three. Now if someone were to tell you that they would be on an airplane at these co-ordinates at say 6:30, now they are referring to a 4 dimensional space-time continuum because they gave the time they would be in a certain place. It is impossible to show a 4 dimensional space-time continuum but you could show a three dimensional space-time or 2 dimensional space-time. Here's how.
Now as you can see, this is a one-dimensional space continuum. If we add 1 more dimension call time, this is what we get.

Now as you can see, the ballpark and your home are traveling through time but they are not moving up and down. Now look at what happens as you walk to the ballpark. Remember that time is continually traveling at a constant speed.

So as you can see, you can only travel up and down but you are continually traveling sideways through time. You can also make it a three-dimensional space-time continuum. However, time would most likely be measured as depth.

What is a Black Hole?

Back to the gravitational aspect of Einstein’s theory. Supposing you laid a big marble on a sheet of rubber, you would find that it bends the rubber. If you took a smaller marble and laid it near the bigger marble, you would find that the smaller marble rolls towards the bigger marble. This is what happens in space. Dense and very compact objects "bend" the space-time continuum and the gravitational force pulls anything nearby in. This is how Einstein described a black hole. He described it as "a curvature in the space-time continuum.

"Everything existing in the space-time continuum causes a small curvature. Every atom existing causes a curvature in the space-time continuum. Einstein described a black hole as something so great in gravitational force that it actually causes light to "fall" into the incredibly powerful singularity. That is how we got the name "Black Hole". Because no energy can escape a black hole, it cannot be detected.

Einstein predicted in his theory of relativity that all objects generate gravitational waves just like electromagnetic waves. These gravitational waves have never been detected, however, if they did exist, their strength would be directly proportional to strength of the gravity well. What this means is that the stronger the gravitational potential of the object, the more powerful the gravitational waves.

The outer edge of a black hole is called the event horizon. This event horizon is a certain boundary that extends from the center of a black hole. At the event horizon, the escape velocity from the black hole is exactly the speed of light. It is therefore impossible to leave a black hole at the event horizon or beyond. No energy or matter can leave from within the event horizon.

Black holes are usually formed from very bright, dense and large stars. These types of stars fuse hydrogen atoms to create helium. The mass that is lost through the process of fusion is converted to energy. When the star has utilized all of its hydrogen, it attempts to fuse helium. All the while, the explosions caused by the fusing of atoms keep the star from collapsing or imploding under its own gravity! Eventually the star will expend its helium fuel and turn to its by product for use as a fuel. This will continue to occur until the star can no longer fuse atoms together. The star will make one last futile attempt to fuse lead and will completely blow off its outer crust. This is what we call a super nova.The outer explosion of the crust creates an inner implosion as a reaction to the explosion. The stars own gravity adds to this implosion and pulls all the matter into an incredibly dense object. This object is so dense and so compact that the gravity created by the object is so potent that light itself cannot escape. As more and more matter squeeze into the dense singularity, the black hole becomes stronger and stronger and bigger and bigger.

Einstein predicted another aspect to a black hole. He predicted a phenomenon known as gravitational shearing force. This force is so potent that if you came near to a black hole, you would be ripped apart by the gravitational shearing force. This is due to the fact that gravitational potential energy decreases rapidly as you move away from the source. If you went near a black hole, the amount of gravity pulling at your feet would be much higher than the amount of gravity pulling at your head. As a result, your feet would be pulled so hard that you would be ripped apart.

The theory of relativity was one of the greatest revelations ever. It started with Isaac Newton and his theories of gravity. You may have heard that Isaac Newton started his theory of gravity when an apple fell on his head. According to his notes, he saw an apple fall to the ground but he perceived differently. He saw the apple no only falling to the earth, but the earth falling to the apple. Essentially that is what gravity is, the mass of one object attracting another. All matter exerts a certain amount of gravitational force. What really matters, is the mass and density of the object.