Theory of special relativity
Hello readers, I haven’t posted for a long time however, I thought this new year would be a good time to restart the flow. In this article I will introduce the theory of relativity which is an extremely important aspect of modern physics. Almost all of physics and most sciences lay on top of relativity as a base. Relativity has revolutionized physics of the 20th and 21st century. There has been lot of misunderstandings on theory and some people are totally unaware of this theory. The theory of relativity is usually mis understood as extremely hard or complicated and associate it with physicists alone which is alarming because this theory is extremely interesting and allows phenomena found in science fiction alone in reality such as wormholes and time travel.
This mysterious theory of relativity itself is based upon the curious behaviour of light in different conditions. Relativity is derived based on the contradiction of James Clerk Maxwell’s theory and sir Issac Newton’s theory of light and several paradoxes that occur due to it. To newton time was an arrow that when released cannot stop and the universe was a rigid stage where time and space where two different things, the universe was a place where time was same to everyone.
This may seem obvious, which is a very common thing because our intuition is just built for things we experience on daily life, we evolved in that way. Our speed and mass are a tiny speck of a humongous spectrum of types of things int the universe ranging from sub-atomic particles like electrons and quarks to the great extent of the universe itself. To solve these problems, famed physicist Albert Einstein made two theories, that are: General relativity, to explain the behaviour of space and time during extreme mass and gravity and special relativity to describe the behaviour of objects in extreme velocity and motion.
In this article, we will discuss about the theory of special relativity. During Einstein’s university life and post university life, reality treated him as if it hated him. During that period Einstein had a freewheeling bohemian life style so his professors hated him. He already knew most of the syllabus and often cut classes. Which resulted in a difficult job situation due to his professors’ unflattering letters of recommendation. After a lot of hardships, he finds a job as a third-class patent clerk in Bern which was slightly humiliating. However, the patent office offered him a lot of time.
There Einstein sees something other physicist were glaring at for centuries. Newton’s laws permit one could race alongside a beam of light and see it frozen as long as you run fast enough with constant velocity and zero acceleration. However, Maxwell’s equation does not permit this; it is impossible to reach the speed of light.
If a tank fires an artillery shell while moving forward in a velocity of 150 km/h and the shell is launched at a speed of 2448 kilometre per hour, The shell travels at 2248 + 150 = 2398 km/h if there is zero friction and air resistance and the tank has no functionality issues. So here we understand that object’s velocity has the ability to add and subtract.
However, if the tank however is also holding a laser to focus where exactly to shoot. Now when the laser is turned on and at the same time a speedometer that measures the velocity of whatever goes through it. When the beam of light entered the meter, the speed was recorded as 299,792,458 m/s. Now, fine the same experiment is held while the tank is moving towards the meter at the same velocity as before, the speed must be higher than when the tank’s velocity is zero, right? Wrong. According to maxwell’s laws, this method of Galilean velocity addition does not work and the speed of light is same no matter what. So, space and time must warp in some way to explain these events. These will be shown very soon in this article.
Similarly, another property of speed that is known even before Einstein is that speed is relative. Imagine there are two space probes in a place far beyond where there are galaxies. So first the probe A sees the probe B traveling towards it and it goes away. However, the same footage was seen from probe B, it seems that the probe B sees the probe A traveling towards it and it goes away. Both cannot be right, right?
Or can they? It turns out that none of the probes were faulty. It is just that no matter what velocity if it is constant and there is nothing in the environment that could be compared to, the object feels constant and as the only object each probe could see was the other so each probe saw felt that it was constant and the other was moving.
During the 19th century there was a lot of research going on related to the speed of light, however most of them did not have an idea of what light actually was. Then due to the experiments of Michael Faraday and James Clerk maxwell on electromagnetism, they found that the velocity of the electromagnetic disturbances is exactly at the speed of 299,792,458 m/s-which somehow happened to be the speed of light. The conclusion Maxwell gave for this interesting phenomenon is that light is an electromagnetic wave.
Now that we know what light exactly is, we must know what it is moving relative to, which was not specified by maxwell in his papers. So, scientists theoretically made up a substance called luminiferous aether in which light travels. However, there was no evidence on aether whatsoever. Plus, if aether is a substance spread through space around earth and sun, why does it not affect planetary motion?
So, Einstein concludes that Light does not travel relative to anything. Its speed is invariant in all inertial frames, which invoked the theory of special relativity. Now all these problems could be easily answered and special relativity explained by a simple experiment.
This experiment needs a new kind of clock a light clock. This clock has a laser on bottom of a glass which has another parallel glass right under it and acts as a mirror, now when the laser is fired, touches the top mirror and bounces back to the mirror of the laser it is recorded as one unit. All well and good. Now if you put that kind of clock in a rocket and start comparing both clocks, something interesting happens. The light takes a longer distance to hit the top clock and the bottom clock. Therefore, special relativity could be concluded that space and time warps so that faster the object, slower time takes place. This conclusion successfully resolves all the problems mentioned before. Massive objects cannot reach the speed of light as the time interval diverges and slowly becomes infinite.
So many people including myself had some scepticism of this theory so one experiment that prover this theory is the muon life time experiment. So first what is a muon? It can be described as a heavier and more unstable cousin of the electron. Muons are created high in Earth’s upper atmosphere, roughly 10–15 km above the surface, when cosmic rays collide with air molecules. According to classical physics, Even if a muon moved close to the speed of light, Its short lifetime should cause it to decay long before reaching the ground. But according to relativistic physics the muons will experience slower time so will mostly survive the journey from the upper atmosphere. This explanation matched the findings that the muons are found in large amounts in sea level.
So, you might be thinking that these effects could rarely be measured how will this affect us humans in daily life? Well, there are several uses of special relativity.
GPS satellites travel at roughly 14,000 km/h therefore the time on clocks of GPS satellites run considerably slower than clocks of earth. Here the time difference is around 7 microseconds per day which may not seem very big but loses around 2.1 km of accuracy.
Astoundingly relativity even finds its way into the medical field, because modern medicine heavily relies on high energy particles radiation travelling at near the speed of light. For example, in the Positron Emission Tomography (PET), a positron (antimatter for electron) contacts an electron and that reaction produces two gamma photons. Since photons are light, they travel at the speed of light so Position reconstruction assumes relativistic invariance of light speed. Therefore, the pet scanners produce imagery at nanosecond precision.
Another important use of special relativity appears in nuclear physics, especially when explaining how energy is released during nuclear reactions. Einstein’s popular mass–energy equivalence or the E=MC^2 shows that mass is not just matter, but stored energy. In both nuclear fission and nuclear fusion, a very small loss of mass turns into a huge amount of energy. This is the basic reason nuclear power plants can produce electricity on a large scale. It also explains why stars, including the Sun, can keep producing light and heat for billions of years. Classical physics alone cannot fully explain these energy releases. Relativistic reasoning is required. In this way, special relativity is not only a theoretical idea but a practical foundation for real energy production that affects the physical world.
In conclusion, special relativity is not a theory limited to classroom discussion or written equations. It emerged from clear problems within classical physics and was confirmed through repeated experiments and real-world use. It changed how scientists understand space and time, and this change had direct effects on the physical world. Ideas that once seemed difficult to accept are now essential to modern science and technology. Relativity shows that nature does not follow human expectations. However, when its rules are understood accurately, they provide strong explanatory power and a clearer picture of how the universe works.
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