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Getting older than your mother, bending light, being squashed or stretched in a car and gaining mass by running; it's the Theory of Relativity!
Scientists proved that it's 100% correct. Einstein wrote the Special Theory of Relativity in 1905 and the General Theory of Relativity in 1926. But how do these phenomena occur?
A Greek philosopher called Aristotle stated that there's no 'empty space' and that space was occupied by a transparent, smooth 'sheet' called ether. Later, scientists used ether to explain how light waves travel. At the beginning of the last century, a famous experiment called the Michelson-Morley experiment had a controversial result.
In this experiment, 2 light waves travelled in 2 different directions: one of them was moving against the Earth's motion and the other was moving in the direction of the Earth's motion. According to the ether theory, one light wave should travel faster than the other. However, both waves had exactly the same speed.
At the age of 26, Einstein explained this phenomenon. He wrote in a scientific article in a German newspaper, that all light waves have the same speed even if they were pushed and that nothing can move faster than light in a vacuum. He revolutionized science by saying that ether doesn't exist.
But why can't anything move faster than light? What will happen if anything tries to exceed this speed? After thinking for a long time, Einstein wrote 3 equations which were stranger than fiction. The first one stated that the faster an object moves, the more squashed it is. A car moving at a speed of 120 km/h will have its length decreased by 1 trillionth of a centimetre, so you won't notice anything. If it reaches the speed of light, it will squash to a singularity (a dimensionless object).
The other equation, which was simplified to e=mc(squared), stated that the faster an object moves, or the more energy it possesses, the heavier it gets. The third one stated that the faster an object moves, the slower time moves in it. That means that if an object moves faster than light, it will have an infinite mass, time will stop completely in it and its length will be zero. So, if you invent a car which moves at half of the speed of light and ask your mother to drive it for one day, you will become older than her. That's because while she's driving, her clock will move slowly, but she won't notice anything because her eyes and brain are also working slowly. So, one day for your mother will be equivalent to 20 years for you!
energy of an object = its mass x 90,000,000,000
Scientists invented the atomic bomb using this equation. An atomic bomb works by converting 0.001% of its mass into gamma-rays, a form of energy. The Sun produces all types of waves and energy by converting 0.01% into energy. For this reason, the Sun loses 4 million tons every second! When you burn something, you convert one trillionth of a gram into heat!
Scientists proved the 3rd equation to be true by sending a plane to fly around the world. It had an accurate clock which was exactly the same as another clock on Earth. When the plane completed its journey, the moving clock was one billionth of a second slower than the clock that was on Earth.
Einstein made another discovery. He said that if someone held a white light bulb and ran towards you at an incredible speed, the light bulb would look blue. Also, if someone ran away from you at an incredible speed, his light bulb would look red! Scientists proved that this was correct. But why does it happen?
White light consists of 7 colours. The wavelength of the first one is big: red. The wavelength of the last one is small: blue/violet. When a white light bulb moves towards you, its waves get squashed, and its wavelength decreases. If it moves fast enough, its wavelength will get so small that they will become blue. We call that blue-shift.
Red-shift occurs when a light source moves away from you. This time, the waves stretch and the wavelength increases until it becomes red. Einstein also said that blue-shift could be caused by gravity.
At the beginning of the 20th century, astronauts discovered that Mercury's orbit gets smaller every year. Newton's laws failed to explain this phenomenon. Einstein managed to explain it by imagining space as a fleet sheet. Einstein called this imagination: gendanken. If an object is placed somewhere on it, it'll 'warp' the sheet or form a 'dip'. If another object gets near it, it will fall into this dip. This is what we call gravity. This 3-D sheet is called space-time. Although it's difficult for mathematicians and philosophers to imagine a 3-D sheet, Einstein succeeded in explaining why Mercury's orbit changes every year.
Space-time can be warped in 2 ways. The first one is movement. If any object moves, it will warp or bend space. The second one is what we call gravity. If an object is placed in space-time, it will warp space. Anything passing through warped space will either bend, stretch or get squashed. This explains Einstein's 1st equation. Also, time in that object will move slowly because space-time "determines" the future of an object as it passes through it. If an object travels through unwarped space-time, time will go on normally. This explains the Einstein's 2nd equation.
If someone says, "Mum, go to Jupiter and live there for a few years and I'll live on the Moon for a few years. After that, we'll meet on Earth," he'll become older than his mother because the Moon's gravity is much weaker than Jupiter's!
Einstein said that anything including light, travelling through warped space-time would get bent. In 1909, the Sun came in between 2 stars. Suddenly, the image of the 2 stars moved downwards and appeared to be bigger. Scientists explained this by saying that the Sun's gravity, just like refraction, bent the light waves produced by the stars.
Although students still study
Newton's laws in schools, most scientists are convinced that his laws of
motion and gravity are wrong. Although Einstein's equations were simple
compared to Newton's, many people think that he was the cleverest scientist
of all time.