The decision to pursue physics in my tertiary years sprang from a rather naive mindset of my youth: the belief that this constantly evolving field had cracked open the chest of mysteries that we normally call ‘life’. As much as I struggle to recall the specific impetus that drove such an arrogant assumption, I am equally satisfied that my desire, founded on a false basis, has led to my current understanding of the truth – not the truth of life but the truth of reality. The proverbial notion that our knowledge of the universe is like a grain of sand on the beach became increasingly apparent as I peered more deeply into the silicinate structure of the physical realm as portrayed by the brilliant minds of the past and present.
Like all things, my pursuit has reached its end because I have set my heart on another discipline. Thus, I am compelled to illuminate just a corner of the vast crystal that is physics and filter the reflected light through the polaroid that is my perception in the spirit of advancing, publicising and sharing the accomplishments that subserve our quest for knowledge and ultimately, the understanding of life.
This is written from my own memory and understanding. Should an error be found, please let me know.
The term “physics” is associated with all things mechanical, energetic and tangible to the mind. Its alternate name is natural philosophy (for a good reason) which may still have some influence today.
Magnetism was already familiar to the earliest human civilisation but its true nature was not fully appreciated until the nineteenth century as we shall see later.
Perhaps the most notable discovery was gravity by Sir Isaac Newton in the seventeenth century. It is one of the four fundamental forces of Nature as we now believe. Newton’s genius did not rest solely on his ability to conceive ‘gravity’ but also his formulation of the gravitational force itself. Summarily speaking, he made use of the now well-known calculus which was entirely absent in his era. Newton was truly a man ahead of his time.
The discovery of the electric force and its intimate connection to magnetism soon surfaced, following the works of Coulomb, Faraday, Ampere, Lenz and many others. In the nineteenth century, Maxwell successfully summarised the electric and magnetic concepts in his celebrated equations that escalated physics to its acme of glory. Together with Newton’s gravity and Maxwell’s equations of electromagnetism, the scientific community were confident that Nature was entirely within the grasp of our feeble human minds - the fact that we fully comprehended the scope of the now named classical mechanics.
Entered Einstein and his groundbreaking theory of relativity.
But let’s step back (conceptually) a bit. Electromagnetism is the necessary unification of two inseparable forces: electricity and magnetism (more accurately, the propagation of electric and magnetic fields which are orthogonal to each other), which were successfully described by the concept of waves and their interactions. However, a problem arose: the ubiquitous Black Body Radiation that appears in any quantum mechanics introductory class. Using the wave theory, one arrived at Rayleigh’s ultraviolet catastrophe where energy diverged to infinity at small wavelengths while experimental data suggested a completely different outcome. The problem was ingeniously solved by Planck: an ad hoc equation coming from the necessitated discretisation of wavelengths (that is, only an integer number of wavelengths were allowed). This was called quantisation. It does not take a strenuous exercise of the mind to figure what would be the logical consequence of Planck’s revolutionary assumption. Yes, it is the modern day’s quantum mechanics.
Now back to our good old Einstein who shed an immensely luminous beam on our understanding of light (pardon the pun) through his explanation of the photoelectric effect which earned him the Nobel prize. Light, which had always been believed to be of wave nature, was indisputably demonstrated to behave like particles. The wave-particle duality of light eventually became the standard framework in mainstream physics (It is worthwhile to add that light particles are called photons which are the quanta, or “discrete packets”, of the electromagnetic field). Afterwards, it was clear that Einstein was born to turn the world of physics upside down and around: his popular equation E = mc^2 and his ultimate formulation of the theory of relativity which existed in two flavours, Special Relativity and General Relativity. Initial scepticism and ridicules of Einstein’s theory as something that defied commonsense quickly lapsed into silence and as we now see, vocal exaltation of his pure genius. There is a reason why “it doesn’t take Einstein to understand this” these days, right?
However, Einstein was not the whole of modern physics even though his brilliance continued to permeate our current experimental and theoretical device. Even the man himself was not always correct – one of his mistakes was criticising quantum mechanics which granted us remarkable insights into the world of little particles and achieved striking experimental accuracy. It is this co-existence of two equally successful but often irreconcilable disciplines – quantum mechanics and relativity – that put us in many a time great dilemma. The fact that gravity in Einstein’s formulation is an intrinsic property of the spacetime continuum, suggesting that it is a fundamental identity of Nature, has haunted us for decades in our (constantly thwarted) attempts at unifying it with the other three forces: the strong and weak interactions and electromagnetism. Moving on from Einstein’s work, we have continued to innovate and the many great names of modern physics, such as Schrodinger, Heisenberg, Dirac, Yukawa, Cabibbo and an interminable list of others, embellished the now highly regarded branch of science called physics.
Not too long ago, another unification of two of the fundamental forces was achieved: the electroweak theory which fully described both the electromagnetic and weak interactions. It was another step forward since the induction of electromagnetism. But, allow me to take you back (again) a bit and examine the progress of the now particle physics which is growing at a scale previously unseen.
The term “atom”, coined by the wise ancient Greeks, literally means “an indestructible identity” (but don’t take it the wrong way, modern Greeks haven’t lost a single bit of their hereditary wisdom). The word itself gradually lost its meaning with the discovery of electrons which directly suggested that there were more fundamental identities. The electrons were later known to be negatively charged but the atoms in which the electrons were housed were usually neutral. Physicists logically inferred that the atom also contained positively charged materials but had no idea how they were all arranged. The first acceptable model was the Plum Pudding model of the atom which proposed that electrons were immersed in positively charged materials, much like a pudding (yes, physicists are very imaginative in naming their theories). Rutherford kicked this model off the table once and for all with his famous scattering experiment. It then became a matter of fact that the atom was mostly empty with a tiny positively charged nucleus at the centre and the electrons on its periphery. This encouraged Bohr to formulate his model of the atom which is the standard picture in any high school science class: a nucleus with electrons revolving around it in well defined orbits. Like Planck in a sense (but not quite), Bohr had to make several post priori assumptions to ensure that his model worked. It did work, for a hydrogen atom but proved to be problematic for larger molecules (as an aside, Bohr’s model is still constantly used in cases where heavy atoms can be approximated to a hydrogen atom). We now know that the electrons don’t orbit the nucleus like planets orbit the sun but rather, they assume different shapes (clouds) which are directly related to the highest probability of finding them at a given time. The theory is called hybridisation theory and has been the standard model of the atomic electron configuration. If you now look at the science class’s picture of the atom, it is actually not wrong: the orbits depicted do not explicitly relate to the apparent paths of the electrons but rather they serve as pictorial representations of the electrons’ positions at any given time.
Then there was the question whether the nucleus was really a fundamental particle like the electron. This is when modern particle physics widened its wings and soared to a new height. Particle collision is achieved in a monstrous set of equipment called a collider whose one major feature is an accelerator. The accelerator underwent transformations from the linear form (linac or linear accelerator) to the powerful synchrotron. Upon colliding protons and neutrons which were thought to be basic constituents of the nucleus, we observed many other unknown particles spitting out. The logic here is that if protons and neutrons (generally called nucleons) were fundamental (that is, indestructible) particles, the collision would return the same protons and neutrons. The fact that a myriad of different particles were produced suggested that the nucleons were not what we believed. Another interesting fact was that the new particles exhibited the known properties of the nucleons! At this stage, there are two questions that you might ask: how did we detect the new particles and how did we work out what lay inside the nucleons?
To answer the first question, we need to invoke Einstein’s E = mc^2 but with a little variation: m = E/c^2. Algebraically, the two equations are of the same kind but physically, they mean totally different things. E = mc^2 implies that an enormous amount of energy can be obtained from a small mass (the idea behind nuclear bomb) whereas m = E/c^2 refers to mass arising from energy. Indeed, energy, not mass, is a more fundamental property of a system. As such, when we analyse the energy pattern produced by the collider, a distinct peak will correspond to a particle according to m = E/c^2.
For the second question, it is rather a very elegant discovery. It is elegant because the constituents of the nucleons and similar particles, now widely known as quarks, were theoretically predicted by the established group theory before being observed and confirmed experimentally! This is reminiscent of the antiparticles whose existence was inferred from Dirac’s equations and experimentally verified.
The introduction of quarks revolutionised the field of particle physics. Not only did we solve the mystery of the ambiguous “nuclear force” which was then renamed to “strong interaction” but we are also able to construct an expansive framework where the four fundamental forces of Nature and their appropriate mechanisms slowly came to light.
It is not the end of the journey. We are still very far from “knowing it all”. While the weak force partly explains the fact that the current universe is made up principally of up and down quarks, it does not fully account for this observation as well as elucidate on where the antimatters disappeared to even though in the beginning, according to the Big Bang theory, an equal amount of matter and antimatter were produced. The Standard Model, which is the greatest model to date, successfully incorporating the strong, weak and electromagnetic interactions and allowing seamless and effortless formulations based on observations (unlike in the past when one sometimes had to use clever guesswork, like Planck and his equation for Black Body Radiation), is still unsuccessful in integrating the gravitational force into its structure. There exists a need for a larger, better theory in the quest of unifying the known forces. The Unified Field Theories are a strong candidate but it is still imperfect. If we then speculate further theories, one of which is the low-energy supersymmetry, Unified Field Theories instantly becomes a perfect model.
Preceding the Large Hadron Collider, there was the Large Electron Positron (LEP) Collider at CERN. The LEP experiment was the most extensive and impressive international collaboration ever achieved: more than a decade of work just to determine the one single quantity, the mass of the W boson. Perhaps hearing my lecturer, who was involved in the experiment itself, retell the achievement in its grand details was one of the most inspirational experiences in my entire life.
So we look forward, with the knowledge that our current theories, immensely successful yet conspicuously limited, are in need of expansion, extrapolation and solidification. The Large Hadron Collider (LHC) will do just that. Owing to our refined understanding of accelerators, we are able to attempt this ambitious experiment right here and now and because of the enormity of the modern theories that were beautifully devised but still need to be verified, such as the Higgs’ mechanism and its associated Higgs’ bosons which are speculated to give rise to mass (and consequently matter as we know it), the LHC will not only carry just two protons heading for collision but also our ambition, expectation and exultation in hope of finding, for the first time, the new physics which we’ve been consciously waiting for.
That’s science. The way it should be.
A personal perspective on the evolution of physics
By Lam Nguyen | November 18th 2009 01:18 AM | Print | E-mail