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'''Quantum field theory''' is a mathematical theory in physics which attempts, unsuccessfully in experimental physics, to reconcile [[quantum mechanics]]. Quantum field assumes that relativity is true, and then bases the mathematical work on an assumption that elementary particles can be treated as "point-like objects of zero intrinsic size."<ref>http://theory.caltech.edu/people/jhs/strings/str114.html</ref> 

'''Quantum field theory''' (QFT) is a mathematical theory in physics which modernizes [[quantum mechanics]] from its early-20th-century formulation. In the areas of its domain (electromagnetic, weak nuclear, and strong nuclear forces), it is arguably the most precisely verified theory in all of physics.

"Field theory" attempts to describe the interactions between subatomic particles, such as electrons, protons, quarks and photons. However, field theory has a well-known (in theoretical physics circles) "cosmological constant problem."<ref>

"Field theory" describes the interactions between subatomic particles, such as electrons, protons, quarks and photons.

The differences between basic QM and Field Theory are these: in QM, the interactions between more than two particles are increasingly difficult to model, and the creation and destruction of particles cannot be modeled at all. In contrast, Field Theory can describe states containing arbitrary numbers of particles of different energies, masses, charges and types. Field Theory also provides an elegant framework for describing the interactions between particles, and the creation of new particles and destruction of old ones-- for example, the emission and absorption of photons by electrons, and vice versa.<ref>Bjorken and Drell. <i>Quantum Field Theory</i> Chapter 3; McGraw Hill Inc. (1980)</ref>

The differences between basic QM and Field Theory are these: in QM, the interactions between more than two particles are increasingly difficult to model, and the creation and destruction of particles cannot be modeled at all. In contrast, Field Theory can describe states containing arbitrary numbers of particles of different energies, masses, charges and types. Field Theory also provides an elegant framework for describing the interactions between particles, and the creation of new particles and destruction of old ones-- for example, the emission and absorption of photons by electrons, and vice versa.<ref>Bjorken and Drell. <i>Quantum Field Theory</i> Chapter 3; McGraw Hill Inc. (1980)</ref>

For a given interaction of particles, field theoretical calculations generally cannot be solved in a closed, analytical form-- that is, the predicted probabilities cannot be described by one simple equation; however, physicists have developed numerous approximation methods which produce estimates of ever-increasing precision (compared to experiment), with the precision depending upon how much mathematical work is put into the analysis.<ref>Pierre Ramond. <i>Field Theory: A Modern Primer</i>, Chapter VIII; Benjamin-Cummings Inc. (1981)</ref>

For a given interaction of particles, field theoretical calculations generally cannot be solved in a closed, analytical form-- that is, the predicted probabilities cannot be described by one simple equation; however, physicists have developed numerous approximation methods which produce estimates of ever-increasing precision (compared to experiment), with the precision depending upon how much mathematical work is put into the analysis.<ref>Pierre Ramond. <i>Field Theory: A Modern Primer</i>, Chapter VIII; Benjamin-Cummings Inc. (1981)</ref>

The most naive application of Quantum Field Theory to any theory of gravity is known to be unworkable. This is in contrast to the other three forces of nature (electromagnetic, weak nuclear, strong nuclear), which have extensive and impressive experimental confirmation<ref>Chris Quigg. <i>Gauge Theories of the Strong, Weak, and Electromagnetic Interactions</i>; Benjamin/Cummings Co. (1983).</ref>. No alternative formulations of quantum gravity have experimental confirmation. While [[Special Relativity]] is an intrinsic part of quantum field theory, the prevailing theory of gravity (the curvature of spacetime under [[General Relativity]]) has not been reconciled.  Integrating this fourth force of nature into quantum field theory is an extremely active area of theoretical research. Current research in the field involves such things as [[supersymmetry]] and [[string theory]]

The most naive application of Quantum Field Theory to any theory of gravity is known to be unworkable. This is in contrast to the other three forces of nature (electromagnetic, weak nuclear, strong nuclear), which have extensive and impressive experimental confirmation<ref>Chris Quigg. <i>Gauge Theories of the Strong, Weak, and Electromagnetic Interactions</i>; Benjamin/Cummings Co. (1983).</ref>. No alternative formulations of quantum gravity have experimental confirmation. While [[Special Relativity]] is an intrinsic part of quantum field theory, the prevailing theory of gravity (the curvature of spacetime under [[General Relativity]]) has not been reconciled.  Integrating this fourth force of nature into quantum field theory is an extremely active area of theoretical research. Current research in the field involves such things as [[supersymmetry]] and [[string theory]]

== The Forces of Nature ==

== The Forces of Nature ==