Einstein’s Thought Experiment: How a Simple Question Revolutionized Physics

 

Title: -

Topics Covered:-  

1. **The Curious Question**  

   - Einstein’s childhood curiosity about the speed of light  

   - How his question challenged Newton’s theories  

2. **Newton’s Three Theories**  

   - Gravity, particle theory of light, and relativity  

   - How they seemed unrelated but later connected  

3. **The Wave vs. Particle Debate**  

   - Huygens vs. Newton on the nature of light  

   - Young’s double-slit experiment proving wave theory  

4. **The Luminiferous Ether Hypothesis**  

   - Scientists’ assumption of an invisible medium for light  

   - Michelson-Morley experiment disproving ether  

5. **Einstein’s Thought Experiment**  

   - Contradiction between Newtonian relativity and constant speed of light  

   - Einstein’s realization that time itself is relative  

6. **Special Theory of Relativity (1905)**  

   - Explanation of time dilation  

   - How motion affects time perception  

7. **The Birth of General Relativity (1915)**  

   - Einstein’s search for a deeper explanation  

   - Space-time curvature as the cause of gravity  

8. **Experimental Proofs of General Relativity**  

   - Mercury’s orbit anomaly explained  

   - Eddington’s solar eclipse experiment confirming light bending  

9. **Einstein vs. Newton: Was Newton Wrong?**  

   - How Einstein refined rather than disproved Newton’s gravity  

   - The importance of questioning existing theories  

10. **Unanswered Questions in Physics**  

   - The limits of Einstein’s theory  

   - Mysteries like black holes and the Big Bang  

11. **The Future of Science**  

   - How today’s scientists are tackling relativity and quantum mechanics  

   - The need for new thinkers to challenge and expand physics .

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In the year 1894, a 16-year-old German boy sitting on the last bench asked his teacher a question. Instead of answering his question, the teacher threw him out of the class. The boy's name was Albert Hermann Einstein.

Now, Einstein left the class at that time, but the question still lingered in his mind. The question was, how will the world look if you run at the speed of light? Now, this sounds like a childish question, right? Like, who will win between a lion and a tiger? But this childish question was going to shake the foundation of the entire gravitational theory of a genius scientist like Newton. And the most groundbreaking theory of physics will give birth to relativity.

So, how did Einstein turn this simple question into a whole new concept theory? And what did Einstein see in Newton's theory? Because of which, the theory that everyone believed for 200 years was proven wrong. Now, I know, this question comes to everyone's mind. Like, how can someone think of such a groundbreaking theory, such groundbreaking ideas? How do these scientists think? Can I also think of something like this? If yes, then how? Well, today you will understand from the story of Einstein that how his entire theory was born and evolved.

How did he get those deep ideas? Who showed him the truth that millions of people could never see. And that's why I would highly suggest that you read this content in full.. Because being a science enthusiast, when I read Einstein's story, I personally found it quite eye-opening.

Which inspired me to see this world from a different perspective. So, let's get right into it. Now, friends, in the beginning, I would like to highlight this point.

Many people think that Einstein's relativity, which explains gravity, was invented by Newton's theory of gravity. So, let me tell you, you guys are absolutely wrong. Because Einstein's relativity was actually invented by Newton's two theories, which have nothing to do with gravity.

So, it so happened that Newton had presented three fundamental theories to the world at his time. The first theory was gravity, according to which two bodies, which also have mass, attract each other. The second was particle theory, according to which light travels from one place to another in the form of small particles or corpuscles.

And the third was relativity. Yes, Newton also gave a theory of relativity. According to this theory, if two cars are moving in the same direction at the same speed, then they will appear to be stopped.

But if they travel in the opposite direction, then their speed will be doubled. In short, speed or motion is relative. The speed of everything depends on your own speed.

Now, here you can see that these three theories are very different things, which explain gravity, light and motion. In their first view, there was no connection with each other. But you know what's the weird part? These three unrelated theories were going to be combined by Einstein's time and give rise to Einstein's relativity.

In fact, the combination of these three theories began in the year 1678 when Dutch physicist Christian Huygens challenged Newton's light corpuscular theory. According to Newton, light travels in the form of corpuscles, i.e. small packets of energy. But according to Huygens, light bends from one medium to another.

And that's why it should travel in the form of a wave, not a particle. But because Huygens did not have any experimental evidence to prove his theory at that time, no one accepted his theory for the next 100 years. Until 1801, when a British physicist Thomas Young proved Huygens' wave theory with his famous double-slit experiment.

Young basically passed the light through two slits and observed it on a screen. And saw that both the light beams coming out of the slit were showing an interference pattern like a wave, i.e. alternate light and dark bands. That is, for the first time, Young's experiment proved Newton's theory wrong and proved that light is indeed a wave.

But wait, let's hold on a bit over here. We all know that to travel any wave, a medium like water or air is needed. In such a medium, there is only vacuum in the outer space.

So how does light travel there? This question was troubling many scientists at that time. But before understanding how scientists found the answer to this, I want to discuss a big problem that is happening with you in India. I don't know about you, but nowadays I see this trend that people are getting bald at a young age.

Their hair is also breaking. Now, the main reason behind this is stress throughout the day. But no one can stop working.

We were discussing that there is only vacuum in outer space. So how does light travel there? Now in response to this, a group of scientists hypothesized that from where light comes to earth, there is a field within that space medium which we cannot see, touch or feel.

But light travels through that medium. That medium was named Luminiferous Ether. Now as I said, this was just a hypothesis.

It has not been experimentally proved yet. And that's why two scientists of the same group, Albert Michelson and Edward Morley performed an experiment in 1887. And you won't believe, the results of that experiment were so embarrassing that it is still considered the greatest failed experiment.

See, the theory of Michelson and Morley was very simple. According to them, if there is ether and it is flowing in one direction, for example, west to east. So in such a case, when light will travel in the direction in which ether is flowing, then its speed should be fast.

And at the same time, when it will travel in the opposite direction of ether, then its speed should be slow because resistance of the field is being created. Simply speaking, Michelson and Morley thought that if we change the speed of light, if we prove it, then automatically the existence of ether will also be proved. But in front of them, of course, the question was how to prove it.

Then they realized that in Young's double slit experiment, both the light waves were coming from the same direction and the same speed, creating an interference pattern. Now in such a case, if two light waves of different speeds collide with each other, then the interference pattern between them should break. And to verify this assumption, they sent the light wave in two opposite directions and reflected it with a mirror so that it came back to the same point and created an interference pattern.

But when they performed this experiment, once again, they were extremely, extremely disappointed. They did not see any change in the interference pattern of both the light waves. That is, two important things were proved from this.

First is that there is no medium like luminiferous ether. And second is that light has always traveled in the same speed in all directions. That is, its speed is constant.

Which means, all in all, the ether that was experimented to prove its existence, because of that, the concept of ether was disproved forever. But as soon as Michelson and Morley proved that the speed of light is constant, Newton's second unpopular theory, Relativity, came back again. And because of this, later on, Einstein had to create his own new theory of relativity.

So in 1905, Einstein had a thought in his mind that according to Newton, speed is relative. Which means, the speed at which I am traveling, if someone comes in front of me at the same speed, then his speed will be double perceived by me. So let's say I travel by sitting on the beam of light.

And another beam of light comes from the front, so its speed should also be double perceived by me. But just now we saw that Michelson and Morley proved that the speed of light is constant. Which means, if the speed of light is double, then it is not constant.

And if it is constant, then the speed is not relative. Which means, clearly, if one thing is right, then the other thing is breaking. And a paradox is being created.

So here, who is right and who is wrong? For this, Einstein performed a thought experiment. He imagined a train traveling at the speed of light. At both the end points of the train, the light is flashing.

Now, when they stand on the platform, they will see both the lights flashing at the same time. But when Einstein will board the same train, then he will see the light of the first box of the train flashing first. This is because the light beam coming from the first box will have to travel less light distance to travel to Einstein's position.

And the light coming from the last box, which has to come upside down to Einstein, will have to travel more distance. Means, long story short, Einstein saw that just by looking at two different perspectives or frame of references, the speed of light is coming out differently. But, as we discussed earlier, the speed of light is constant, right? So what exactly is changing? Well, Einstein thought that if both the lights are reaching at the same time when standing at the station, and when sitting in the train, both the lights are coming at different times, then what if time is that thing which is actually changing? And this is where Einstein's special theory of relativity was born.

According to which, the faster we travel in space, the slower time will be for us. And there will come a point when our speed will be so fast that then time will completely stop for us. In short, Einstein's thought experiment proved that time is a relative concept.

Which works in different ways in different frame of references. But, there was a twist. You can see how ironic this is in itself.

Because usually, the general version of anything comes first. And then after that, its special version comes. But this is probably the only theory where its general version has come because of the special version.

Now the question is, how did Einstein's special theory of relativity become the general theory of relativity? So in 1905, Einstein published his special theory of relativity. But he himself was not completely satisfied with his theory. Because his special relativity theory was telling that time will stop at the speed of light.

But the mechanism behind it was not able to explain why this would happen. That is, Einstein was also going through the same dilemma that Newton was going through 200 years ago. There were also some observations in his theory that he was not able to explain completely that what is its reason, what is its origin.

For example, Newton was not able to explain how gravity is created. Well, today we know that the answer to both these things is the curvature of the space-time fabric. But at that time, both Einstein and Newton were unaware of this.

And that's why very soon Newton's gravity and Einstein's special relativity were going to merge. It was just going to take 10 years for Einstein to understand this. Actually, Einstein asked himself, suppose you are walking on an empty road, when will your speed decrease? Obviously, when there will be a hole or some kind of resistance in front of you.

So what if time also travels through a medium that affects its speed? And then, to explain this, Einstein imagined a space-time fabric, the hypothetical medium of time, whose structure had the ability to speed up and slow down time. This immediately solved two problems. First, what is the relationship between mass and gravity in Newton's theory? The problem that had arisen was solved.

And secondly, why would time slow down while keeping the light constant? He also got the answer. Basically, he thought that all celestial objects like planets, black holes and the moon, whose mass is also concentrated, they all create holes in the space-time fabric. And when an object falls into this hole, then we will feel that the object is being attracted towards another massive object.

With this visualization, Einstein gave the answer as to why and how gravity attracts objects. Along with this, when a fast object like light travels through this curved space-time fabric, then it will have to travel a longer distance than flat space-time. And because the speed of light is constant, and that's why time will slow down for light while passing through this curved space-time.

So, you can see how with the help of a simple thought, Einstein easily explained the mechanism of his special theory of relativity and Newton's gravity. Now it was necessary to connect all these links and verify this theory experimentally. For this, in 1915, Einstein published his paper on General Theory of Relativity, in which he mathematically proved the connection between gravity, light and space-time.

But maybe you don't know this, along with mathematical proofs, Einstein also successfully experimentally proved GTR theory. With the help of General Relativity, he came up with a solution to such a big problem, which no scientist has been able to solve for the last 200 years. So the thing is, when Newton's gravitational theory was applied on the planets of the solar system, then Newton saw that his theory was accurately predicting the orbit of all other planets, except for Mercury.

Because when astronomers observed Mercury, then they saw that Mercury's orbit was tilting at a specific angle every 100 years. But in Newton's calculations, no such tilt was predicted. That is, clearly, in the case of Mercury, Newton's predicted results were not matching his observed results.

Now, many scientists tried to solve this problem, but they were all failing. Now, when Einstein applied the principles and equations of his General Theory of Relativity on Mercury's orbit, then his results matched the observed results. And that's why Einstein used it as an experimental proof and published his paper.

In fact, four years after the paper was published, in 1919, British physicist Arthur Eddington experimentally proved the other phenomenon of General Theory of Relativity, i.e. the bending of light due to gravity, in which he found that the stars behind the Sun are not visible where they actually are. They are visible only a few degrees away. That is, the light of those stars is reaching us by bending due to the gravity of the Sun.

And this was the point when the whole world considered Einstein's General Theory of Relativity to be true and considered his theory as a landmark theory. And this unique explanation of gravity established Einstein as a genius. Now, if you have listened to this story carefully, then you would have understood that we have not said anywhere that Newton's theory of gravity was completely wrong.

In fact, Einstein himself did not believe this. The point was that Newton's theory had a limited area of operation and was not able to predict the observations outside that area properly. There were many missing links in his theory, which Einstein identified, solved with his new and updated theory, and increased his area of application.

And in my opinion, this is what makes Einstein different from other scientists. He asked a simple question on these fundamental theories, identified the gaps in them, and then tried to fill those gaps with logical explanations. And if you are pursuing science or physics, then you can also use this approach to advance the legacy of scientists like Newton and Einstein.

Because like Newton's theory, Einstein's theory also has many loopholes. Einstein's theory also has an area of application and there are some observations outside it that he is not able to predict properly. For example, what happened before the Big Bang? Why did the Big Bang happen? And what happens inside the black hole? Einstein's theory is not able to predict all these observations.

Now, if any of you can fill this gap, then you will become an important part of this legacy. But it is not so easy to solve this problem. Because we have not yet been able to get a precise explanation of how gravity works at the quantum level.

Now, what problem is gravity creating at the quantum level? Why is it almost impossible to mix relativity and quantum mechanics? I have covered this in detail in this content, which you can read by clicking on the link above. And you have to understand the struggle of today's modern scientists. I

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