Some thoughts on the Standard Model of Particle Physics – Kashmir Reader
It doesn’t answer the most fundamental mystery: what constitutes the dark energy and dark matter that make up the majority of our universe?
The Standard Model became the fundamental model of elementary particle physics in the second half of the 20th century. It is considered today as the best description of the constituent elements of the universe. It explains how quarks (which form protons and neutrons) and leptons (electrons, etc.) make up all known matter. It is also an explanation of how quarks and leptons are influenced by the exchange of intermediate force carriers. It describes three of the four fundamental interactions that sum up the structure of matter up to the measurement of 10 high at -18 meter. It is in short a quantum theory of three basic theories of electromagnetic interaction, strong interaction and weak interaction. The development of the Standard Model has been led by a large number of experimental and theoretical physicists alike. The structure or mathematical framework of the Standard Model is provided by quantum field theory
According to the standard model, all matter is made up of three types of elementary particles: leptons, quarks and their mediators. There are six leptons divided into three generations. There are also six anti-leptons, so the total number of leptons is 12. Similarly, the number of quarks is six, each of which comes in three colors (this color bears no resemblance to the concept of color in our daily life), which represents 36 quarks in total, including the antiquarks. Quarks like leptons have three generations. Finally, for each interaction, we have a mediator. The carrier of the electromagnetic interaction is a massless photon while the carriers of the weak interaction are called intermediate vector bosons, which are two charged Ws and a neutral heavy Z. Finally, for the strong interaction exchange, we have 8 gluons.
The missing link of the Standard Model, the Higgs boson theoretically predicted by Peter Higgs in the early 1960s, which explains the mass of elementary particles via the Higgs mechanism, involving chiral symmetry breaking, was discovered in 2012 at Large Hadron Collider in Geneva, Switzerland. The marvelous achievement of the Standard Model can be measured by the simple fact that it has led to more than 50 Nobel Prizes in Physics so far.
Even though the Standard Model is currently the best description we have of the subatomic world, but despite its robust predictions, there is a consensus among physicists that the Standard Model is neither complete nor the final theory. “There is a certain degree of ugliness in the standard model,” says Steve Weinberg, one of its main architects. First, the standard model is completely silent about dark energy and dark matter. This does not answer the question of what constitutes the dark energy and dark matter that make up the majority of matter in our universe. Second, it fails to explain neutrino oscillations and, more importantly, it fails to incorporate one of the most fundamental interactions, gravity, which explains the large-scale structure of the universe. At a more fundamental level, he fails to explain why there are precisely three generations of quarks and leptons. Likewise, the difference in masses of the elementary particles that they acquire due to their interaction with the Higgs field via the Higgs boson remains a mystery.
In order to accommodate many of the shortcomings of the Standard Model listed above, physicists over time have come up with different theories and approaches. All of these theories and approaches fall under the category “Physics Beyond the Standard Model”. Theories that lie beyond the Standard Model include the various extensions of supersymmetry and entirely new explanations and theories such as string theory, looping quantum gravity, and extra dimensions. But the theory that has gained most prominence among them is string theory. String theory has captured the imagination of a generation of particle physicists over the past 40 years. String theory not only promises the reconciliation of quantum mechanics with Einstein’s general relativity and eliminates the infinities that plague quantum field theory, it also provides a unified theory of everything from which all elementary particle physics , including gravity, would emerge as an inevitable consequence. But the bottleneck of particle physics, as string theorist and Nobel laureate David Gross puts it, is experimental, not theoretical, so in the absence of experimental evidence to back up his predictions, the future of string theory seems grim, or at least you have to cross your fingers. If string theory lives up to expectations, which seems unlikely, it will be the ultimate triumph of the human spirit.
—The author is a physics student