Even though it is possible to categorize all electromagnetic fields as carriers of reciprocal action between charged particles, it is better to concentrate on the phenomena related to free fields. Free electromagnetic fields or radiation fields are connected to properties of matter such as energy, momentum, and angular momentum (Keller 3). Notwithstanding that low-resolution conditions might suggest that those properties of electromagnetic radiation are continuous, under closer examination, it becomes clear that they are divided into discrete jumps or quanta. Moreover, classical physics almost equates the position of radiation fields to that of matter.

Quantum physics, on the other hand, explains the autonomy of the electromagnetic field with the help of the photon concept (Keller 3). Therefore, it could be argued that photon is “the elementary excitation of the electromagnetic quantum field” that stands on an equal footing with massive elementary particles associated with other quantum fields (Keller 3). Even though forces exerted by electromagnetic fields are not limited to radiation, it is the only force that is quantized.

To define what photon is, it is more fruitful to consider the question “What do photons do?” (Roychoudhuri, Kracklauer and Creath 23). Photons unite electric charges and electric multipoles through the process of discrete photon emission and absorption that is associated with the irreducible process of propagation. Therefore, it could be said that electromagnetic radiation is a congregate of photons that have their energy-momentum and angular momentum (Roychoudhuri, Kracklauer, and Creath 23).

## Discovery

In the 17^{th} century, Francis Bacon and Isaac Newton surmised that light consists of elementary particles; however, radical expansion of that concept started to take place only in the 20^{th} century (Roychoudhuri, Kracklauer and Creath 24). Processes commute if their resultant is not contingent on their order. The common trait in the development of an understanding of photon is a lack of a particular sequence of discoveries related to the concept.

Therefore, it could be said that the radical expansion of the concept of light was non-commute. Every expansion was made without connection to other discoveries making scientists come up with such terms as non-integrability, inexactness, curvature, anholonomy, or even paradox for the description of the same phenomenon (Roychoudhuri, Kracklauer and Creath 24). It should be said that non-commutative theories are superior to all commutative predecessors in terms of their stability. Moreover, every non-commutativity is proportional to its expansion constant.

The following are fundamental constants and noncommutativities associated with the photon that is known so far: *G* – gravitational constant, for general relativity; *k*—Boltzmann’s constant, for the kinetic theory of heat; *c*—light speed, for special relativity; *h*—Planck’s constant, for quantum theory; *e*—the electron charge, for the gauge theory of electromagnetism; *W—*the mass of the *W* particle, for the electroweak unification; *g*—the strong coupling constant (Roychoudhuri, Kracklauer and Creath 24).

These expansions are also known to have inverse processes were fundamental constants are being reduced to 0 allowing to observe preceding commute theories that are less accurate. Each expansion is associated with the refusal to take constants to 0; therefore, they serve as a more suitable starting point for further development (Roychoudhuri, Kracklauer, and Creath 24).

Moreover, the expansion of constants allows pointing to the field of special relativity in the case of the discovery of a particular constant in an equation. Einstein discovered the following non-commutativities: *k, c, G, *and* h *(Roychoudhuri, Kracklauer, and Creath 24). So far, no one has been able to beat the record of conceptual expansion in the physics introduced by him. Einstein’s concept was further developed by Gilbert N. Lewis and Frithiof Wolfers who coined the term photon to name the particle in 1926 (Kragh 265). However, the wide recognition of the photon model came after 1927 when Arthur H. Compton received the Nobel Prize for studying the phenomenon (Kragh 265).

## The Standard Model

The Standard Model is an expanded theory that unites special relativity, gauge theory, and quantum theory allowing to provide the best explanation of photon. The constant *c* or speed of light completely disregards Euclid’s geometry as well as Galileo’s relativity (Roychoudhuri, Kracklauer, and Creath 25). The theory of space and time states that reality can be treated as a group of objects that have particular time coordinates that could be perceived as similar by observers that are in a state of uniform relative motion and space coordinates that are different for each observer (Roychoudhuri, Kracklauer and Creath 25).

However, special relativity made the possible restoration of reciprocity between simultaneity and locality of objects distributed over space. The constancy of *c *presupposes the reciprocity. The discovery of the reciprocal relationship between time and space has allowed establishing reciprocity between energy and momentum, which in turn has allowed for recognition of photon’s mass and energy (Roychoudhuri, Kracklauer, and Creath 25).

Those parameters are connected to the rest mass *m*_{0 }in special relativity by *E*^{2}* – c*^{2}*p*^{2}* = (m*_{0 }*c*^{2}* )*^{2}, where m_{0 }for the photon is 0 if *E=cp*. Even though it is often being said that photon’s mass is 0, its actual mass equals *E/c*^{2} (Roychoudhuri, Kracklauer, and Creath 25). There is an archaic saying that “the photon is a bundle of energy”; however, the *c* expansion allowed to recognize that mass is energy (Roychoudhuri, Kracklauer and Creath 25). Therefore, it should be said that energy just like spin or momentum is only one of the photon’s properties.

## Life Cycle of Photon

Nonzero photon mass has been used for both experimental and theoretical studies for many decades. However, there are theories under which photons might have a non-zero rest mass. They indicate that the upper limit for photon mass is restricted to 10^{–18} eV or 10^{–54} kg (Physics World par. 3). Under such conditions, photons could decay into smaller particles such as neutrino and antineutrino with even lower mass.

Research conducted by a member of the Max Planck Institute for Nuclear Physics Julian Heeck in 2013 changed the discourse related to a finite photon lifetime (Physics World par. 4). The scientist argues that modification of the mass of a photon, particularly its upper limit, would allow constraining its life cycle (Heeck 021801-1). Photons without mass in quantum electrodynamics are only stable because of kinematical reasons since there are no other quantum numbers that would prevent their decay (Heeck 021801-1).

Cosmic microwave background (CMB) has been explored in more than 100 studies since its discovery (Physics World par. 4). Therefore, Heek decided to use extremely precise measurements of the CMB spectrum that has “the oldest photons in the visible Universe” for his calculations (Physics World par. 3; Heeck 021801-1). He was able to find constraints on the lower bound of the photon lifecycle that amounted to three years if its mass was at the upper limit (Heeck 021801-1). The lifetime of microwave photons was equal to 10^{15 }(Heeck 021801-1).

## Applications

There are numerous technological applications of photons that have been known to people for many decades. Simulated emission was discovered by Einstein and was described within the structure of the old quantum theory (Haroche and Raimond 124). It is a process that allows incoming photon that has a certain frequency influencing an excited electron to reduce its energy level thereby causing controlled emission (Haroche and Raimond 124). Simulated emission was the heart of laser amplifiers and other superluminescent sources for many years (Haroche and Raimond 124).

Semiconductor charge-coupled chips technology is based on the photoelectric effect that allows photons to generate an electronic charge that can be detected by a microscopic capacitor (Haroche and Raimond 126). The devices like hardware random number generators also rely on the detection of individual photons. Geiger counter exploits the capacity of photons to ionize molecules of gas inside the device thereby allowing to register a minor change of its conductivity (Haroche and Raimond 126).

## Conclusion

A photon could be described as basic excitation of the quantum field. It is a particle that unites electric charges and electric multipoles through the process of discrete photon emission and absorption that is associated with the irreducible process of propagation. The study conducted by Julian Heeck in 2013 showed that under certain conditions the lifetime of microwave photons could be equal to 10^{15}. There are numerous technological applications of photons that have been known to people for many decades.

## Works Cited

Haroche, Serge, and Jean-Michel Raimond. *Exploring Quantum*. Oxford, Oxford University Press, 2010. Print.

Heeck, Julian. “How Stable Is the Photon?” *Physical Review Letters* 111.2 (2013): 021801-1- 021801-4. Print.

Keller, Ole. *Light*.*The Physics of the Photon*. New York: CRC Press, 2014. Print.

Kragh, Helge. “The Names of Physics: Plasma, Fission, Photon.” *The European Physical Journal* 39.3 (2014): 263-281. Print.

Physics World. *What is the Lifetime of a Photon?*. 2013. Web.

Roychoudhuri, Chandrasekhar, Alan Kracklauer and Katherine Creath. *The Nature of Light*. Boca Raton, CRC Press, 2010. Print.