Today I am excited to tell you what I have learnt about Albert Einstein and his Theory of Relativity
Who was Albert Einstein?
Albert Einstein was a famous scientist who came up with lots of different theories and equations. He was a peace-loving man, with crazy hair, but his discoveries accidently led to the most destructive bomb in history. His most influential theory is the Theory of Relativity and he became famous overnight when it was proven right.
He came up with most of his great theories when he worked at a patent office because they gave him lots of time to think. He was born in 1879 on 14th March in Germany. He didn’t speak until he was 3 or 4 until one day when he was having dinner he said, ‘The soup is too hot’ and when his Mum and Dad asked him why he hadn’t spoken before he said, ‘because everything was fine before now.’
Einstein liked to play the violin to calm his mind. He moved to Italy in 1894 and hiked up mountains and thought. He called these journeys ‘thinking hikes.’ Einstein loved to think, it was his favourite thing to do. His relatives encouraged him to think, so he was quite a quiet boy.
Einstein came up with his Theory of Special Relativity in 1905, his Theory of General Relativity in 1915 and he was proven right in 1919 when his predictions of bending light were shown to be correct during a total solar eclipse.
What is the Theory of Relativity?
The theory of relativity is a way of explaining the relationship between time, distance, speed, acceleration, energy, mass and gravity.
The Equivalence Principle
Imagine you are in a rocket with no windows, you can’t hear anything, and you have no idea how you got there. You think you might be moving but you’re not sure. How do you tell if you are going really fast or if you are not moving at all because everything around you is moving (or supposedly not) relatively to you?
This is actually what is happening on Earth, but you can’t tell because everything you see is moving relatively to you. In fact, if you go into detail, everything on Earth is moving at 67,000+ mph because that is how fast the Earth is moving relative to other objects in space.
Theory of Special Relativity
Einstein realised that, because light travels at the same speed for everyone, this means time is not a constant unit. Take two mirrors opposite each other, one on top and one on the bottom, and then think of a beam of light bouncing between them. Imagine the beam of light takes one second to bounce from the top to the bottom. This could be considered to be a clock that uses light to measure time.
Now duplicate your pair of mirrors and make one pair of mirrors move. You will notice that the light beam in the moving set of mirrors has to travel a longer distance (I have drawn a diagram explaining how this works).
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Now add one person in between each set of mirrors, Bill and Jack. If Jack is in the moving set of mirrors, because light has to move at the same speed for Jack and Bill, Jack’s time must slow down to allow the light to move a further distance. This is called ‘Time Dilation’.
The relationship between time and speed is: the closer you get to the speed of light, the more time slows down and if you get to the speed of light time will stop completely. This must mean if you go faster than the speed of light you will start travelling back in time but this is impossible because the closer an object gets to the speed of light the more its mass increases, which means it will take an infinite amount of energy to reach the speed of light.
Imagine your two sets of mirrors again and remember time dilation. Time dilation works with something called ‘Length Contraction’. This is a theory that an object gets smaller as it nears the speed of light. This means that Jack will still see his beam of light take one second to bounce from the top mirror to the bottom mirror even though the light has to travel a further distance because the mirrors are moving. If you were Jack, your one second would feel normal and Bill’s one second would look really fast. But, if you were Bill, your one second would feel normal and Jack’s one second would look really slow. This explanation shows that time and speed are related to each other and, just as speed is relative to other moving objects, so is time.
Theory of General Relativity
We need the general theory of relativity because the special theory of relativity only works on objects moving at a constant speed. Einstein wasn’t happy with this because most things are often changing speed, so he wanted to improve it. This theory works with objects that accelerate.
First, spacetime – what is it?
Space doesn’t really work without time if you think about it. If you arrange to meet someone at a place with no time you could be waiting there for ages. If you organise a time to go somewhere with no place, you could be waiting in completely different parts of the world. Einstein realised all of this and preferred to think of space and time as one thing, spacetime, which has four dimensions – length, width, depth and time.
Einstein had the idea that gravity is not a force because one day he was looking at the rooftops and imagined a man working on them and thought, ‘what would happen if he fell off?’ He wondered how gravity could be a force if you can’t feel your own weight when you fall.
Now you are back in your rocket with no windows. You feel yourself getting pushed into your chair. You sigh with relief - you must be on the Earth in its gravitational pull, or are you accelerating through space? Terrifyingly, you can’t tell the difference! Einstein thought, maybe gravity is an acceleration not a force.
Imagine a stretched sheet of elastic and then someone puts a heavy ball in the middle. You will notice the sheet of elastic bends around the ball. This is a simple image of what happens to spacetime around objects with large mass. Einstein made a prediction that light from other stars bends when it passes through spacetime that’s been warped. His prediction was proven right five years later when there was an eclipse and you could see a star that should have been hidden (I have drawn a diagram of this). You could see the star because the light from the star had passed through the warped spacetime near the sun and bent.
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Now, imagine a table with a big hole in the middle and around the hole the table is curved in towards the hole. This shape is like the appearance of your elastic sheet around your ball. You roll a ball onto this table and it goes around the hole following the curve of the table. But remember, if the curve of the table wasn’t there the ball would be going in a straight line. This curve in the table causes the ball to move around the hole by changing its direction. This is a type of acceleration.
Pretend the curve in the table is warped spacetime, the hole in the middle is the Sun and the ball is the Earth. Remember the Earth would be travelling in a straight line, just like the ball, but the warped spacetime around the Sun is causing the ball to accelerate around it.
Einstein realised that gravity is the result of an acceleration caused by warped spacetime.
Why is it useful and what technologies is it linked to?
The Theory of Relativity helps us understand the universe better. It helps explain about black holes, orbits and movement through space. GPS Satellites are an example of a technology that uses the Theory of Relativity to work properly. Continue reading about GPS in my next post
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