A brief history of Time (4A27)

Date: 23/01/2025

Good morning everyone, today I am gonna introduce a book called “A brief history of Time”, witten by none other than the famous physicist Stephen Hawking. The book covers various topics related to the universe, general relativity, origin of time as well as quantum mechanics.

 

If I were to tell you that two straight lines can intersect each other, you’d probably not believe me. Now let’s assume there’s two people, 1000 km apart from each other on the equator . They both travel in a straight path in constant velocity due North. As time progresses the distance between the two of them gradually shortens, and as if there’s force pushing them together, and they would eventually meet at the North pole. The reason is because both of them are travelling on straight path geodesics on a curved surface. Space time works in a similar way. Spacetime is curved by the uneven distribution of masses, where from an outside frame of reference, the seemingly straight path is indeed curved.

 

This might sound a little confusing and I will explain it with a simple analogy. Imagine being in a train moving at constant speed and direction, without looking outside you would never know if the train is moving or not. It is because everything inside the train could either be at rest or moving in constant motion, just like you. There isn’t an object that could be a reference point. However, an outside observer would be able to easily tell if the train is moving or not as he is at rest with respect to the train. Objects travelling through spacetime at a heavy mass exhibits the same property – the motion of the object is dependent on the frame of reference. If a spaceship travelling in constant speed in a straight line comes across a planet, an external observer might notice that the spaceship slowly bends towards the planet and accelerates towards it, however due to the nature of spacetime, where a straight line around heavy mass would be curved, you being inside the spaceship would not be able to tell the path has changed as well as the increasing acceleration. And would be oblivious until the second of impact.

 

This has already been proven through experiments. Light travels at a constant speed and at a straight path. If you were to hold a flashlight and point it at the other side of the room. The height of the light beam on the other side of the room would be slightly lower than the source of the light, by around the diameter of a photon. As light always takes the shortest path and it bends in a gravitational field, this proves that spacetime is indeed, curved. But why and how is time related? Think of it this way: speed of light =distance divided by time. Speed of light is constant no matter the frame of reference, and an object travelling a curved path would travel a longer distance than one with the same amount of time, thus taking a longer period of time. The greater the curvature of a path, the longer the time required. This means absolute time doesn't exist and time moves slower on Earth than in space.

 

And there you go, you already have the basic understanding of general relativity, which can be concluded by the quote ‘spacetime tells matter how to move; matter tells spacetime how to curve.’. In general relativity gravity doesn't exist and is merely an illusion caused by the warping of space and time. But doesn’t that contradicts with Newton’s universal gravitational laws where there is a force acting on two masses creating an attraction? First of all, light has no mass and could still be bent, and Newtonian physics could not be used to explain all orbits such as that of Mercury’s due to the deviation of the ellipse as curvature of spacetime has not been accounted for. In fact, even Newton himself believed that no force is strong enough to attract objects millions of kilometers away into orbits and was unsatisfied with his discovery. Still that doesn’t mean his theories are flawed as they work well in a wide variety of circumstances, and inaccuracies would only occur at the very largest or smallest scale such as properties of light or quantum mechanics. Einstein’s theory is like a more complete explanation of the so-called” gravitational force”.

 

 

At this point most of you are probably just minding your own business, thinking “how’s that even related to me?” “And even if I study physics, it is not like I have to understand such difficult concepts, this is just absurd.” Imagine living in a foreign country without knowing the language or customs, not knowing physics is like not understanding the fundamentals of the world and not knowing the very origins or the universe, planet earth, the place we live in. Yes you could still live a happy and full life, but you are definitely missing out. That’s when this book comes in handy, through which you could better grasp concepts of time, even entropy, quantum uncertainty. The book might not be school-oriented, however it offers us valuable insights and will definitely enhance our critical-thinking and imagination. Who knows, you might be the next Einstein. After all, if you only follow what you were taught , you won't be able to make a difference to our current society, let alone changing the world.