Here is a term paper on unified field theory.
Albert Einstein first coined the term ‘Unified Field Theory’ to describe any attempts to unify the fundamental forces of physics, particularly between elementary particles into a single theoretical framework. Einstein himself searched for such a Unified Field Theory, but was not successful. So what brought this about?
In the past, seemingly different interaction fields or forces appeared to have been unified together. For example, James Clerk Maxwell successfully unified electricity and magnetism into electromagnetism in the 1800s. In the 1940s, Quantum electrodynamics translated his electromagnetism into the terms and mathematical equations of Quantum mechanics. During the following decades, physicists successfully unified strong nuclear interaction and weak nuclear interactions, along with Quantum electrodynamics to create the Standard Model of Quantum Physics.
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The current problem with a fully unified field theory is in finding a way to incorporate gravity, which is best explained by Einstein’s theory of general relativity, with the Standard Model that describes the quantum mechanical nature of other three fundamental interactions. The curvature of space time, fundamental to general relativity, leads to difficulties in the quantum physics representations of the Standard Model.
Some specific theories that attempt to unify quantum physics with general relativity include:
1. Quantum Gravity:
Generally is posed that a theoretical entity or a graviton, which is a virtual particle that mediates the gravitational force. This is what distinguishes quantum gravity from certain other unified field theories. In fairness, some theories typically classified as quantum gravity don’t necessary require a graviton.
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2. String Theory:
This uses a model of one-dimensional strings in place of the particles typically used in Quantum Physics. These strings vibrate at specific resonant frequencies. The formulas resulting from string theory predict more than four dimensions, but the dimensions are curled up within the Planck length.
3. Loop Quantum Gravity:
This theory seeks to express the modern theory of gravity in a quantized format. The approach involves viewing space time as broken into discrete chunks. It is viewed by many as the well- developed alternative to quantum gravity outside of string theory.
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4. Theory of Everything:
This theory is a hypothetical single, all-encompassing, coherent theoretical framework of physics explaining and linking together all physical aspects of the universe.
5. Super-Symmetry:
A theory of particle physics, is a proposed type of space time symmetry relating two basic classes of elementary particles. The first are bosons, which have an integer valued spin. The other is fermions, which have a half-integer spin.
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A particle from each group associates with each other, creating a super-partner, with a spin differing by a half integer. Perfectly unbroken super-symmetry, in theory, means that each pair of super-partners shares the same mass and internal quantum numbers, in addition to their spin.
As these theories show, the idea of one unifying theory has been difficult to prove and hard to identify. Unified field theory is highly theoretical, and to date there is no absolute evidence that it is possible to unify gravity with all the other forces.
Historically, other forces have been combined, and many physicists are willing to devote their lives, careers, and reputations attempting to show that gravity can also be expressed quantum mechanically. The magnitudes of such a discovery, of course, cannot be fully identified until a viable theory is proven by experimental evidence.