While doing my EPQ research which was on General Relativity, I did a little background reading on Special Relativity and thought I'd share it on here. Just the fundamental ideas, not the maths (because its hard to enter the maths equations into blogger and because its kind of hard to explain). In special relativity, Einstein considers only inertial frames of reference, which are frames in which particles have constant velocity (i.e. moving in a straight line, no forces, no acceleration). Because it is at constant velocity, inertia applies here. First of all, the part most of you have probably heard is that the speed of light is constant to everyone observing it, no matter how fast they are moving relative to it. By establishing this, Einstein could move onto something even better: time dilation and length contraction. The idea that time moves at different rates to different observers or that lengths can be different when observed by two different observers. Here's a thought experiment explaining how this works.
Imagine you are in a rocket with a laser in your hand. The laser shoots light up to the ceiling, which has a mirror there and reflects it to the ground, where there is a light detector. The time for the detector to pick up the signal is fixed from where you're looking. Now imagine that the rocket is flying at a constant velocity and for the sake of experiment, this velocity is 0.5c. To you, the path of the light beam still looks the same and it takes the same amount of time for the detector to pick up the signal. However, to someone from the outside and is stationary, peeking through a window on the rocket, they would see a slanted path for the light beam, which suggests that there is a longer path for the light to go through. It is already established that the speed of light is fixed. Therefore, as there was a different path length for the two different observers, depending on their relative velocity. And thus, it takes different amounts of time for each of the observers for the light to leave the laser and reach the detector. And this is how time and length can be different for different observers. However, these effects are not seen much in everyday events and are only noticeable at relativistic speeds (ones which are comparable to the speed of light like 0.6c).
Another major component of special relativity that Einstein established in his theory of Special Relativity is that space and time are interwoven and thus we actually exist in a spacetime continuum. He chose to use the coordinate system (or if you want to be more poetic, he chose to set the stage of this grand proposition) to be Minkowski spacetime. Here, an element of spacetime is called an event , which is given by both a location and time. Also, vectors(either position or velocity vectors) are fixed at an event. These vectors are known as four-vectors because they now have four components: x-, y-, z-axis and ct which is time multiplied by the speed of light, which, for the sake of simplification, can be set to 1 in the calculations.
Imagine you are in a rocket with a laser in your hand. The laser shoots light up to the ceiling, which has a mirror there and reflects it to the ground, where there is a light detector. The time for the detector to pick up the signal is fixed from where you're looking. Now imagine that the rocket is flying at a constant velocity and for the sake of experiment, this velocity is 0.5c. To you, the path of the light beam still looks the same and it takes the same amount of time for the detector to pick up the signal. However, to someone from the outside and is stationary, peeking through a window on the rocket, they would see a slanted path for the light beam, which suggests that there is a longer path for the light to go through. It is already established that the speed of light is fixed. Therefore, as there was a different path length for the two different observers, depending on their relative velocity. And thus, it takes different amounts of time for each of the observers for the light to leave the laser and reach the detector. And this is how time and length can be different for different observers. However, these effects are not seen much in everyday events and are only noticeable at relativistic speeds (ones which are comparable to the speed of light like 0.6c).
Another major component of special relativity that Einstein established in his theory of Special Relativity is that space and time are interwoven and thus we actually exist in a spacetime continuum. He chose to use the coordinate system (or if you want to be more poetic, he chose to set the stage of this grand proposition) to be Minkowski spacetime. Here, an element of spacetime is called an event , which is given by both a location and time. Also, vectors(either position or velocity vectors) are fixed at an event. These vectors are known as four-vectors because they now have four components: x-, y-, z-axis and ct which is time multiplied by the speed of light, which, for the sake of simplification, can be set to 1 in the calculations.
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