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Force-some foursome
We read a whole whopper of a science chapter on forces. We study the frictional force, magnetic force, electrical force, mechanical force, tidal force, muscular force and the list goes on till it makes an average 12-year-old brain shake like a jingle in rattle. I wish I had known that the list could be narrowed down to just four basic forces. Then I could have blamed my science teacher for the “F” — just imagine the look on her face. Hey, come to think of it, why not take a short tour of the fundamentals of modern physics: the four fundamental forces. Let’s go!
Charge!
Welcome to the electromagnetic station. Your proportions have been reduced to subatomic dimensions. Your body had to be discarded I’m afraid. As you may have realized by now, we are standing on the nucleus of a hydrogen atom. You can see from your ultra binoculars that there’s an electron whizzing round this proton. The electron must be held in orbit by force, or it would zip out of the atom. That force is provided by electromagnetic attraction.
Electric force and magnetic force were first considered to be completely different entities, until James Clerk Maxwell demonstrated in 1864 that they are, in fact, different aspects of the same thing (such as bun kebabs and burgers).
Watch closely and you’ll see a shaft of light hooking up the electron on to the proton. Puzzled? Let me explain (I’m always waiting for a chance to show off!). You see, all forces have a force-carrying boson (simply speaking, bosons are particles whose dittos do not exist).
The boson for electromagnetism is the photon, the particle of light. It might seem strange but we do perceive electromagnetic interaction as light, hence the name electromagnetic radiation.
All the mechanical forces are caused by electromagnetism. Let’s canter through a few examples. As a train screeches to halt, its wheels spit sparks — observe that the next time when you ride a roller coaster. The sparks are caused by friction between the wheels and the tracks. This means that frictional force is actually residual electromagnetism.
Recall the last time you smacked someone. The amazing thing is that your hand never came in contact with that person! The effect was actually produced by the repulsion of electrons in that person’s cheek by the electrons in your hand. This could also mean your feet never touch the ground beneath you — spooky.
I see the photon beam from the electron coming our way. It won’t be a pretty picture if it zaps us. Stand by, initiating teleportation mechanisms. Hold on, it’s going to be a rough ride!
Brawny chap
I’m analyzing schematics. Hmm, everything went to plan alright. We’re inside a neutron in the Thorium atom. I hope it doesn’t decay for a while. Ever wondered what keeps the nucleus together? Why don’t protons in the nucleus just repel each other? The answer lies in the details of the strong nuclear force. Let’s skim over the basics (yawn).
The strong nuclear force occurs between quarks. Strong nuclear interactions involve exchange of a force-carrying particle called a gluon. Electromagnetic interactions need charge.
Similarly, strong nuclear interactions need colour charge — no relation to colour, it’s just some scientist’s silly idea of a joke: keeping our skulls whirling. Quarks have colour charge, they interact in a way such that their total colour charge is white, that is, neutral. The situation gets tangled up when you know that gluons, too, carry colour charge. Therefore, when a quark emits a gluon, it changes colour, so the other quarks are forced to change colour. In effect the whole particle exists in a steady state of equilibrium with quarks changing colours to maintain a net neutral (white) charge.
May be it’s time for me to abandon my sermon. Get your ultra binoculars ready. Now, do you see there? The quarks are hurling gluons at each other. Look closely and you’ll see that many gluons are headed outside the neutron. This means that strong nuclear interaction also takes place between quarks in different particles. This forms what we call residual strong force. It binds the nucleons together. Let’s move out of this atom.
Three stooges
Sorry, the station name might seem misleading but this is not a cinema. You are currently in a top-secret (not anymore) research facility where you will witness the radioactive beta decay of a Thorium atom in, if my calculations are correct, approximately 1.732 minutes. That’s a pretty long time on the atomic scale. We’ll fill in time by learning about the weak nuclear force.
The weak nuclear force is the fundamental force responsible for radioactive decay. It often takes the back seat in most cases and lets electromagnetism and strong nuclear force do the driving. But in some instances, such as pion decay, and neutrino governing, the weak nuclear force zooms ahead as the Michael Schumacher of the fundamental forces.
The factor that determines weak interactions is the weak hypercharge. All fermions possess some quantity of hypercharge. Great, there’s a decaying atom now. That was nothing short of an atomic firework. There’s a beta particle. It’s whooshing towards us. I’d rather keep my head down (you can’t do that, you don’t have a body).
That was close. But still not close enough to see the weak force in action. You’ll have to endure my lecture for some more time. There are three force carrying particles for the weak nuclear force called the weak vector bosons: W+, Z0, and W- (three stooges). These are the only force-carrying particles that have mass. Because of this, they cannot travel very far. I can see a nearby atom jiggling. Better go for a closer look.
While the strong force keeps the nucleus intact, the weak force is bent upon breaking it and changing some of the particles into other particles. Look, that nucleus is decaying. Things will take a very fast turn from here. Better observe it in slow motion. A neutron consists of two down quarks and one up quark. During beta decay, one of the down quarks emits a W- boson (which we observe as beta radiation), transforming the down quark into an up quark. This changes the neutron into a proton, which contains two up quarks and one down quark. Different vector bosons are emitted in different radioactive decay processes. Brace yourselves. Next stop is the gravity station.
Attractive
Whoa! I guess I pulled the throttle a notch too high. Anyway we’ve been teleported to the inner edge of the oort cloud. Look at the yellow dot of light there. That’s Jupiter. You can also see Saturn. Look carefully beyond Jupiter and you’ll see a smeared luminous ring, that’s the asteroid belt between Jupiter and Mars. And if you’re feeling lucky, you may even catch a glimpse of Neptune. All these celestial bodies are hurtling through space in an elliptical path round the sun. It is gravity that binds them to the sun.
Einstein’s general theory of relativity predicts that gravity should travel in waves. Physicists doubt that it would ever be detected with the current technology. The corresponding particle of a gravity wave is a graviton. Gravitons have still not been detected in a particle detector, though calculations establish their existence.
Gravity is the weakest of the four fundamental forces. This can be demonstrated by using a bar magnet which can easily attract a few paper pins off a table against the gravity acting on them. But it should also be noted that gravity enjoys the longest range. The electromagnetic and the strong nuclear forces for instance weaken dramatically when the distance between the objects in consideration is increased. As a consequence, gravity is the strongest force on the universal scale.
The more massive a body is, the more gravity acts on it. On the contrary, massless photons are also influenced by gravity. However, it can be seen that photons possess a colossus of energy. Can we conclude that gravity is depends upon the energy of an object? After all, mass is also a form of energy.
GUT and beyond
Astrophysicists are looking for a theory that would combine the four fundamental forces to yield a set of equations that can be used to predict any thing that happens under the great dome of this universe, a theory that would hold true even in extremes such as singularities, where all other theories breakdown. They are hunting for a Unified Field theory.
The first part of the puzzle was solved by Professor Abdus Salam in collaboration with Steven Weinburg. The scramble for the Grand Unified Theory (GUT) theory has been triggered off. Physicists are looking forward to unifying the electroweak force with the strong force using symmetry theories.
Massive particle accelerators are being built to provide the experimental evidence. All this will ultimately pave way to every physicist’s dream: the quantum theory of gravity.
Anyway, mooching around the solar system in sub-atomic proportions with your body left behind at the breakfast table, holding a newspaper, isn’t good for health. The tour ends here. Hope you enjoyed it. Science teachers beware - A task force of students is coming forcefully!
The writer is a freelance contributor
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