A Short Guide to the Wide World of High Energy Physics

Modern physics research is a vast ocean of differing fields requiring different specializations and technical skills. 

For example, someone who hates math but loves space will still have to get a solid foundation in classical mechanics, but may then choose to go deeper into observational astronomy, while someone who really enjoys working with their hands may opt for experimental condensed matter as their preferred career path. Physics caters to individual interests in this way. Common fields of study are cosmology, quantum mechanics, biophysics, nuclear physics and planetary science. Although distinct from one another, the baseline knowledge every physicist has ensures enough understanding to affirm confidence in that field, sometimes sparking newfound curiosity.

In contrast, high-energy physics (HEP) is a field that may feel mysterious to the uninitiated. Unlike most other fields, its basic concepts are difficult to grasp. HEP, also sometimes called particle physics, is the study of the fundamental forces in the universe. 

Primary areas of HEP include particle collision physics, string theory and astroparticle physics. In fact, many of the popular physics buzzwords you may be familiar with, such as dark matter, dark energy and quantum gravity, are intrinsic to HEP. 

Although this mainstream familiarity of common HEP jargon may make it sound very appealing, it requires advanced knowledge of not only math, but other specialized subjects within physics — like quantum mechanics — to be properly understood. The core of HEP is arguably the modern physics framework, quantum field theory (QFT)

What Is QFT?

QFT starts with quantum mechanics, which is effectively the study of micron-scale objects such as electrons or photons. 

After quantum mechanics was largely solidified as an accepted area of study within the physics community, it encountered an emerging issue of incompatibility with another area of physics: relativity. 

Relativity, a theory developed by Einstein, dealt with the effects of objects moving near the speed of light; Einstein focused on very large objects like planets and stars in particular. The theory of relativity accounts for orbital effects like time dilation or the curving of space-time.

Quantum mechanics, while revolutionary, was disconnected from Einstein's aforementioned theory. For example, quantum mechanics relies on the concept of non-local yet instantaneous effects.

QFT is one attempt at unifying these two fields of thought. 

As quantum mechanics uses a small particle as its basis, QFT uses quantum fields as its basis — which permeate all of spacetime, negating direct contradiction. Each of these different fields corresponds to a specific force, or particle; for example, an electron is part of the electron field. When an electron exists, a ripple or disturbance must therefore be in the electron field.

Because of its role in uniting multiple theories of the universe, QFT pushes the very fabric of physics forward. Particle accelerators are an experimental setting where QFT can be studied as they force fundamental particles to be near the speed of light. In a novel forum, both quantum relativistic phenomena can be studied at once!

In HEP, QFT is used to predict how particles in a particle collider interact with one another like the results of a collision and any changes between particles that may have occurred. 

When colliders are concerned, scientists typically look for scattering amplitudes, from which many different tools from QFT can be employed for calculation.

The Standard Model and LIGO

Experimentation confirming the theories of QFT led to the development of the Standard Model. This model is a compendium of all the fundamental forces that can be described by modern HEP, along with every particle to accompany them. It successfully describes electromagnetic force, the force between charged particles like electrons, the strong nuclear force, the force within the nucleus of atoms and the weak nuclear force, which governs nuclear reactions. 

In some ways, the Standard Model represents the most significant achievement of HEP, with a recent experimental confirmation being the detection of the  Higgs boson in 2012, well after its theoretical prediction in 1964. With HEP, very advanced theoretical formulaism utilizes complicated experimentation to confirm the very core laws of the universe.

HEP does not solely deal with particle interactions. Physicists within the field also aim to describe other phenomena like dark energy. In simple terms, scientists originally expected the universe to contract as gravity pulls objects closer together, creating larger objects, which continue to pull objects closer to them. Observationally, though, the opposite has been seen, as the universe is actively expanding.

This unexplained force that causes the universe to slowly drift apart is an ongoing area of research, with scientists using a variety of theories, computations, and tests to find out more about the phenomenon. 

Scientists are currently using the Laser Interferometer Gravitational-wave Observatory (LIGO) to detect events far out in space where two compact objects merge. These events enable the detection of gravitational waves by using lasers operating with bleeding-edge precision. 

LIGO is another way HEP uses experimentation to prove theoretical results. The experiment proved Einstein's theories to be correct, as in 2016, just over a decade ago, gravitational waves were accurately observed and detected.

String Theory and other Mathematical Problems

Beyond the experimental tests in the fields of HEP, there also exists the more abstract field of pure theory. This is where subject matter gets particularly difficult, as the line between math and physics is blurred.

In its most basic and fundamental form, physics directly applies math as its language. Before experiments can be made and results confirmed, phenomena must be predicted using the constantly evolving abstract language of theoretical physics. 

The big “problems” of the 20th and 21st centuries must start at this level. This is where famous theories —such as string theory — come into play. String theory, for example, still remains a very common topic of research, but has evolved beyond the initial goals of its pioneering scientist, Italian physicist Gabriele Veneziano. The theory proposes that every particle is an extremely small string. The strings bend, twist, vibrate and curl into small, unobservable extra dimensions. The exact behaviour of a string produces elaborate higher-dimensional shapes. Studying the characteristics of these shapes can give rise to information about various particles. 

Don’t be worried if this sounds quite complicated. String theory remains one of the most advanced theories in all of physics. It sits on the edge of two knowledge bases: physics and math.  However, its potential to truly unify much of high-energy physics demonstrates the beauty and usefulness of the theory. 

High-energy physics is far too large a field to be properly described by any one body of text, as any single subfield of the topic can differ greatly from the one before it. But the consistent features among all HEP subfields are that they seek to explore the foundational laws of the universe with consistency. 

Discoveries in HEP promise to reveal rich insight into what underpins all of physics, and such a discovery can benefit other fields of research with newly illuminated information. While HEP will always require immensely rigorous study,  it is undeniable that, as a field, it is both very fulfilling and fascinating, but also of paramount importance to the larger world of science.