By Udita Shukla
It seems surreal that a question that has pre-occupied thinkers from time immemorial (and, still does!) has still not completely yielded itself. An interest in the ultimate microscopic reality of our beings and the world around is justified by the power it gives us to manipulate bulk material by simply playing around with the building blocks (atoms, molecules, etc.) that make it up.
What are quarks?
Quarks come under the umbrella of the most fundamental particles in nature. Together with another type of particle known as leptons, they are widely believed to be the most elementary units of matter. Exhibiting six different flavours, they are usually talked in terms of three pairs, namely, up/down, top/bottom and charm/strange. Moreover, each quark has its own antiparticle known as an anti-quark. Quarks and anti-quarks are the only particles which interact with all the four fundamental forces of nature: gravitational, electromagnetism, strong and weak forces.
One of the chief constraints to the direct measurement of quarks and their properties is their nature to exhibit confinement. This essentially means that instead of existing independently, quarks always occur in combinations with other quarks. Parameters like mass, spin, parity, etc., which are necessary to be measured for a more granular investigation, can only be inferred from particles that are a result of these quark combinations. Consequently, free quarks have been observed.
Mystery particles
Quarks possess a non-integer spin of either +1/2 or -1/2, which makes them a part of the fermionic family of particles, and also subject to the Pauli Exclusion Principle which forbids them to occupy the same state of energy, spatial orientation and momentum. Additionally, quarks interact with each other via specific kind of particles known as gluons.
Interestingly, they smash the age-old sanctity of the electronic charge, e. For years, the negative charge of the electron was believed to be the lower cap to any charged entity that could only be augmented in steps of the same amount (that is, e, 2e, 3e, etc.). The electronic charge borne by them ranges from -1/3e to +2/3e. Fractional charges were among the first oddities observed in these mysterious particles.
Theoretically speaking, the right combination of any of the aforementioned quark flavours and electrons can give rise to any atom, as well as any of the different types of matter in the universe. While protons and neutrons are made up of the up and down quarks, they are also the lightest and the most stable. Heavier quarks can be created for fleeting instants of time in high-energy collisions which further succumb to decay into the up and down quarks.
How were quarks discovered?
Back in the 1960s, the place for elementary particles was still open, and a topic for hot debate among scientific circles. Around the same time, celebrated theoretical physicist, Murray Gell-Mann, proposed The Eightfold Way theory which predicted new kinds of particles known as quarks.
In 1964, the linear accelerator (or, linac) at the SLAC (Stanford Linear Accelerator Centre) detected beams of electrons preferring three specific destinations within the nuclei, after a collision. Subsequent detailed analyses of the distribution of the scattered electrons corroborated the existence of quarks as particles that inhabit the internal realms of protons and neutrons, among many others.
Why probe quarks?
The first quarks and anti-quarks are estimated to have been born just around one-trillionth of a second after the Big Bang, the calamitous genesis of our universe. Thus, these minuscule particles hold the elusive secrets to the scene around the birth of the entire cosmos. An insight into the nature, behaviour and physics of quarks is a much sought-after piece of the puzzle in the debate of the validity of Creation.
An extension of this debate is the quest to justify the disproportionately low amount of antimatter in the universe. In principle, matter and antimatter destroy each other as soon as they come in contact. Therefore, the universe should only consist of photons and few elementary particles, yet antiprotons antiparticles exist. In 2014, researchers observed a charm quark disintegrating into its antiparticle (known as the anti-charm quark). The experiment sheds considerable light on the minor portion of antimatter in the universe.
Another very intriguing rendition of the quark reality is a possible death of our universe about ten billion years from now. It all depends on narrowing down on the mass of the top quark. A slightly higher value (for the mass) than expected has the potential to nullify the energy carried through the vacuum of space. Alternatively, a lower mass can trigger a scenario termed as “Boltzmann brain which could witness self-aware entities spring from random collections of atoms.
To be or not to be?
Although there is no doubt about the existence of quarks, there is substantial debate pertaining to them being the most fundamental building blocks, and not without reason. Subsequent to the discovery of quarks and their strange properties, scientists could not get around the fact as to why do the up and down quarks and the electrons have so many cousins.
This has led to popular conjecture that quarks may not be the innermost layer of the subatomic onion. Clearly, the study of quarks holds within them the truth about a possible apocalyptic fate of our cosmos.
This is an exciting time for particle physicists to pursue unexplored territories in the subatomic realm. The LHC (Large Hadron Collider) at CERN, Switzerland, is set to test theoretical predictions about the tiniest particle that may be lurking in unimaginably low volumes of space, right up to the birth and demise of the universe.
It is certainly amazing to see how the existence of immeasurably small particles not only controls the fate and evolution of our world but also the scientific principles that apply to it. After all, there is always a chance to discover a hidden pearl in the vast ocean of unknown that makes us who we are.
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