"What goes up must come down"

-Sir Isaac Newton

MY CHILDHOOD QUEST

On a fine night, while crossing the road, cutting through the heart of the traffic, my eyes got stuck on a young kid who seems to be 4-5 years old, observing the stationary cars stuck in the traffic through the window of his car, while his dad was driving the car in the opposite direction of the traffic. Suddenly, I got transported to my childhood. When I used to do the same, I remember that I got confused at that time.

As I can't understand why everything seems to be moving away from me when only my car is moving and nothing else is moving, it can only happen, if my dad was driving everything in the opposite direction to the direction in which he is driving, even the moon, stars, and trees. Implying my father is a demigod, who can control the motion of every object in this universe.

Jokes apart, as I grew up, my curiosity about the nature of fundamental forces we encounter every day in our lives, kept on increasing.

So to understand why everything in the universe seems to move in the opposite direction to the direction in which your car moves, while your dad drives home to why earth attracts every object towards itself, we have to figure out the true nature of the forces and their causes.

BREAKING UP THE FORCES

Let's start with the good old definition which we all have listened to, regarding the force acting on a body, A force can be defined as an action that changes the movement of a body, usually, a body seems to conserve its motion in a particular direction and speed, sometimes however due to some event happening randomly out of nowhere, like the body ( the subjected body) getting hit by a drunk truck driver on a clear road, not that bad at all, the drunk bike riders are even worse they vomit on you, after crushing their rusty bike on you, completely worthy of getting burned up in hell, at least in my eyes, getting back to our topic, so the body changes its direction or speeds up, results in changing its movement and we say that it experiences a force.

We can classify all the forces in the universe, into three types or categories:-

1) The first category is all about those forces, that pull us back when a car accelerates or the centrifugal force that pushes us to one side when we are sitting in a giant wheel, These kinds of forces are usually called inertial forces, and they most often appear in the case of non-inertial frame of reference ( a frame of reference attached to an observation which is moving with some acceleration, usually Newton's laws of motion do not apply in these frame of reference), later on, we will see why they are also called as pseudo forces in nature.

2) The second category is about the forces that act at a distance, the two giants in this category are gravity, which attracts massive bodies and the other one is electromagnetism which attracts or repels charges and magnets.

3) The third category includes all the forces which are associated with 'contact' and also called contact forces, forces such as pressure, traction, torsion, deformation, or even friction too.

All these forces which we observe in nature can be fitted into one of these three categories or can we?

INERTIAL FORCES

An observer sitting inside a car that is moving with some acceleration will experience an unknown force and will be pushed by this unknown force, from the point of view of the observer (who is sitting in the car) this force appears as soon as the car started to move and pushes every object in the car in an opposite direction to the direction in which the car is accelerating. This problem does not end here, as soon as the observer looks out of the window, he realises that not only he is moving backward due to this force but all the objects in the universe (as far as he can see) including the objects present in the car, all are moving in the backward direction, it seems that this force applies everywhere all at once, instantly, like magic.

The main question that arises here that how could the car influence our whole universe that too so instantaneously, so we have to change the point of view of the observer to resolve this issue, instead of saying that objects are moving backward the observer will now say that the car is moving forward from the outside, while the rest of the universe stay still, the passenger was thinking previously that a force is acting upon it as he is observing everything from inside the car which itself is subject to a force, the friction of wheels against the ground.

This is why inertial forces are considered fake or pseudo forces, they are only illusions that observe experience because he is located in a frame that itself is subject to a force.

GRAVITY IS AN ILLUSION

At first glance, gravity may appear as a force that belongs to the second category but by taking a deep look, we will come across the fact that it's not even an actual force, it is just the by-product of our space-time geometry i.e the space-time curvature.

Let's say we have dropped an apple, it will start to accelerate towards the ground and we say that it undergoes a downward force, the pull of the earth, as long as the apple has not touched the ground, the earth will keep on attracting it towards the ground, but by the logic the apple is the only thing on which gravity is acting upon, it will be attracting all the other objects in the universe which are at distance from its center, but how can it come to that earth is affecting all the universe simultaneously, can you relate this situation to anywhere else?

How reasonable it is to think that the earth could influence, the entire universe, after all as with the car it would be simpler to say that the universe is not influenced by its motion so we resolve it by changing the point of the observer, similarly, we have to change the point of view here also, which is the objects are not falling towards the ground but actually, it's the ground that rises upward like the inertial forces of car, the force gravity is only an illusion here when the observer is observing things from the ground.

This explanation alone seems incomplete and non-intuitive. The first thing which came to our mind after listing this explanation is if the ground is indeed moving towards the object, why do we not observe any expansion of earth happening in front of us, why it appears static?

The answer to this question hides the most important discovery of our times the earth does expand, the ground does rise, the surface is constantly accelerating outwards because of the internal pressure of the material of which our earth is made up, and the reason earth doesn't seem to grow because the fabric of space-time around it, kept on shrinking in the opposite direction, this phenomenon is called as space-time curvature.

Just like the inertial force inside the car is an illusion, in the same way, the force is also an illusion, we think that the apple is falling downwards but in reality, it is the surface that is subject to a force 'the internal pressure of the planet' coming towards the apple.

FUNDAMENTAL FORCES OF OUR UNIVERSE

So in our investigation so far, we are left with only two types of forces, the first one is 'contact' and the other is at a distance let's take a look at contact forces,

Contact forces in reality are nothing but just an approximation of the electromagnetic forces acting between the atoms of the surfaces that are in contact, for example when we push something, the contact force here didn't exist in reality, it is only the sum of the electromagnetic forces of atoms that are acting between our hands and the surface of the object, so contact forces are nothing but just an effect of electromagnetic force that appears us.

So it appears as the forces which we encounter on the surface of sanity, are all illusions and the only real forces exist at the scale of atoms, generally, we came across three forces at the atomic scale, which are strong forces, which bounds the protons and neutrons together in the nucleic, then weak force from radioactivity arises and the last one the electromagnetic force which appears due to the charged particles present in an atom i.e protons and electrons. These three forces are also called the fundamental forces of our universe.

WHAT IS THE CAUSE OF FUNDAMENTAL FORCES?

Suppose we have two electrons, kept at a distance they will repel each other for sure, but how it is possible actually that an electron suddenly finds out the presence of the other electron and they both start to repel each other, seems like they could communicate with each other without coming into the contact, again the situation seems illogical.

To understand what is happening here, take the example of two people (person A and B ) playing catch in space, so what will happen when person A throws the ball toward person B, person A will be pushed back as soon as the ball will leave his hand, a similar thing will happen to person B as soon as he catches up the ball and rethrows it towards the person A, again he will be pushed back, so as long as they kept on playing the catch, they both will be pushed back.

Similarly, we can think of the force of repulsion acting between the electron as the result of playing catch, I am not kidding here, what is happening here is that they are electrons passing a virtual photon with each other which pushes them back from each other just as we say in the example of the two persons playing catch.

This is all part of what we call quantum field theory, it tells that the particles are constantly exchanging messengers which we call virtual particles, and it is this effect that we see in all types of interactions happening at the atomic level.

For electromagnetic forces this carrier is the photon, for the strong force it is gluons and for the weak forces, it is Z & W bosons.

The exchange of virtual particles between the real particles gradually changes the motion of objects and it is the Recoil effect when a particle emits or absorbs a virtual particle, is what we interpret as a force at our scale.