Looking at the theme of this article, one may wonder - why are we humans so bold? how can and why do we think that we can understand everything about the universe? And if this bold feeling isn't enough, we think that we can summarize everything with one simple equation! No matter how hard one may try, it is next to impossible - at least relative to us - to teach animals physics, their brains just aren't wired to grasp it! But what about us? Well, scientists are certain that we are wired to comprehend the deepest laws of the universe, this article is about picking up from where Einstein stopped on his journey to unification.
Unification
Unification is the idea that we can describe the workings of every phenomenon in the observable universe, from one single equation. We think that there must be a theory like this because, looking at the past two hundred years, everything in science we now know, from biology, chemistry to physics; points us to this fact, that it is an undeniable implication of every Nobel winning theory in physics today.
Isaac Newton may have started the first unification when he proposed that the force acting on an apple is the same force that controls the heavens - Gravity. Gravity was the first law that was actually discovered and about three hundred years later we discovered three more. It would interest you to know that every phenomenon understood in the universe is a manifestation of these four forces.
However, while scientists needed nothing more than Newton’s equations to send men to the moon and were able to describe the strength of gravity with such great accuracy, it still leaves us to beg the question; What is gravity?
Thinking about Gravity
We now know with certainty that the speed of light is constant in every frame of reference. But it refuted, some of Newton's ideas of looking at the nature of gravity, here's why.Imagine being able to look at our solar system - like God. Here we have the sun in the middle been circled by these weird looking balls, they are the planets.
Now according to Newton, if the sun suddenly vanishes, if you are still looking, you will notice that the planets will immediately fly out of orbit! Just like when one ties a rope to a ball, holds it and begins to spin around, if you let the ball go while spinning, it will fly out into the environment with kinetic energy gotten from the motion. But the force of gravity is not a force that acts instantaneously in every direction or distance, if we lose the sun we may not suffer the effects as soon as we think.
This is because light does not travel instantaneously, as a matter of fact; it takes 8 minutes for the rays of the sun to reach us here on earth, travelling about 93 million miles. Einstein had shown that nothing in the universe, not even gravity can travel faster than the speed of light. This results quickly went bad for Newton because if Einstein was right (which he is) then how could the earth get shot out of orbit before the darkness - caused by the disappearance of the sun - reaches the earth?
SpaceTime
Our current picture of the universe notes that the three dimensions of space and the one dimension of time are bonded together as a single fabric, Spacetime. And we could simply think of objects moving on the top of this spacetime fabric, and it is wrapped and stretched by heavy objects like planets and stars.
You can describe how we see gravity by putting a dense round ball on a trampoline let it rest at the centre, if you put any other ball anywhere on the tramp, it will accelerate towards the first ball and - depending on the fabric of the trampoline - you will be able to calculate the force on the ball with Newton's equation for gravity - K (M1 x M2)/r2 and still get the right answer.
It is due to this wrapping and curving of spacetime that produces what we feel as gravity. Now let's go back to our God-like view of the solar system, if the sun suddenly disappears, the earth will not fly out immediately into the rest of the galaxy, instead the disappearance of the sun will cause a ripple through the fabric of spacetime.
(Picture the ripples you see when you drop a dense ball in a pool) the spacetime ripple or gravitational wave will travel at the speed of light towards every direction, and earth will feel the force immediately it experiences darkness.
ElectroMagnetism
Samuel Morse used this phenomenon to send electric pulses to magnets very far away. During this time, the physics of the two phenomena, electricity and magnetism were not yet fully understood, let alone unified as one. If you go to a mountain during a storm and holding out your compass, you will notice that each time a bolt of lightning strikes, the needle in your compass starts to jump all over the place. Maxwell's equations have perfectly unified these two forces.
You see, this unification was so perfect because we have seen that everything we can think of that has to do with Electricity and Magnetism can be described with this four simple equations. Einstein was dedicated to this creed, to unify electricity and magnetism with gravity but ran out of time by dying. Apparently, he thought that if the speed of light and electromagnetic waves move at the same speed then there must be an underlying symmetry, but his greatest challenge was that both forces have greatly different magnitudes - I am talking billions with electromagnetism on the high side.
Quantum
Now quantum mechanics have come into the picture, describing the behaviour of things at very small scales relative to us proofs to be very difficult. Strange things happen in the quantum world, it is a world of uncertainty, because when there are many possibilities and quantum mechanics cannot predict which one it will be, then all of them will happen - popular theories say that this is because each and every possibility happens in all the universes parallel to ours.
Investigating the structure of the atom we found the Strong Nuclear force which holds the nucleus of every atom together, it completely overcomes the power of the electric force between the protons in the nucleus. And we also have the Weak Nuclear force which makes the nucleus unstable by making a neutron decay into a proton and releasing radiation in the process. Gravity is infinitesimal compared to these three forces.
All of the three forces, the Strong Nuclear force, the Weak Nuclear force and Electromagnetism work both in the quantum world and in our universe, but where does gravity fit in? That’s just the challenge, no one has been able to figure out how to put General Relativity and Quantum Mechanics together.
If you try to combine the mathematics of these two together, you get answers like "the probabilities of the events you are looking at are infinite" It just produces… Nonsense? If the laws of physics are supposed to apply everywhere i.e. The laws of Quantum mechanics are supposed to apply everywhere, and the Laws of relativity are supposed to apply everywhere… well, you can't have two separate everywhere. There is just no theory that has successfully described the universe in all scales.
We have come very far in our understanding of the universe even just by reading these articles, but there are depths we may never be able to explore. There are places we may never understand, for instance, what happens in the singularity of a Black-Hole?
Now here is the question…
If physicists want to find out what happens in a black hole which should they use? Quantum Mechanics because the singularity is unbelievably tiny? Or General Relativity because the star is unbelievably heavy? The bigger challenge is that the singularity is both very heavy and very tiny, so to understand whatever happens in there, one must find a way to unite both theories.
String theory, although very controversial, claims to have found a way to accomplish this unification. The theory has a very different way of looking at the world; it claims that everything in the universe both forces and matter - rather than the multitude of tiny particles - are made up of tiny vibrating strands of energy being called Strings. The strings can have many different figures and vibrations, hence many different particles. So unity of the forces can be done because they are just different vibrations of the same string. But string theorists have a problem, there is no way of seeing these strings or investigating them. Many people decide to remain undecided about the credibility of the theory, some do this because of how things like this play out in history. But what do you think?
References
Wikipedia - Grand Unified Theory
The Particle Adventure - Forces and the Grand Unified Theory
