Physics theories provide the basis upon which all of physics is built. As more theories are presented, experiments test them, attempting to falsify them and ultimately prove them ... but before this process can begin, the theory has to exist.

Fundamentals of Theoretical Physics

When attempting to develop of physical theory, scientists follow the concepts defined in the scientific method. These are not hard and fast rules, but rather a set of guidelines that remind the scientist that great care must be used in carrying out the study of science.

Classical Physics Laws

Some theories have weathered the test of time and moved from the realm of theoretical conjecture to become a cornerstone of the very foundation of scientific knowledge.

Modern Astronomical Theories

Astronomy is a field which has a great deal of questions ... probably because it's so darn big! From the beginning of the universe until now, the universe is full of questions and scientists continue to search for answers.

Quantum Physics

The first half of the 20th century was spent refining quantum theory, which, along with Einstein's theory of relativity, represents the sum total of all of our knowledge about how matter and energy interact in the universe. The result? There are four basic interactions that can take place between particles.

A Theory of Everything - Quantum Gravity Theory

One goal of modern physics, at least for some physicists, is to develop a comprehensive theory of everything, which reconciles gravity with the other three fundamental forces. Such a theory would have to define the nebulous boundary between Einstein's theory of relativity and quantum theory, and is thus referred to as a theory of quantum gravity.

What is String Theory?

Question: What is String Theory?

I've heard the term string theory, but don't really know what it means. How does it relate to quantum physics?

Answer: String theory is a mathematical theory that tries to explain certain phenomena which is not currently explainable under the standard model of quantum physics.

The Basics of String Theory

At its core, string theory uses a model of one-dimensional "strings" in place of the zero-dimensional particles of quantum physics. These strings, the size of the Planck length (i.e. 10^-35 m) vibrate at specific resonant frequencies. The formulas that result from string theory predict more than four dimensions (10 or 11 in the most common variants, though on version requires 26 dimensions), but the extra dimensions are "curled up" within the Planck length.

String theory was initially developed in the 1970s in an attempt to explain some inconsistencies with the energy behavior of hadrons and other fundamental particles of physics.

As with much of quantum physics, the mathematics that applies to string theory cannot be uniquely solved. Physicists must apply perturbation theory to obtain a series of approximated solutions. Such solutions, of course, include assumptions which may or may not be true.

The driving hope behind this work is that it will result in a "theory of everything," including a solution to the problem of quantum gravity, to reconcile quantum physics with general relativity, thus reconciling the fundamental forces of physics.

Variants of String Theory

Bosonic String Theory: The first string theory, which focused only on bosons.

Superstring Theory: This variant of string theory (short for "supersymmetric string theory") incorporates fermions and supersymmetry. There are five independent superstring theories:

Type 1
Type IIA
Type IIB
Type HO
Type HE

M-Theory: A superstring theory, proposed in 1995, which attempts to consolidate the Type I, Type IIA, Type IIB, Type HO, and Type HE models as variants of the same fundamental physical model.

Research in String Theory

At present, string theory has not successfully made any prediction which is not also explained through an alternative theory. It is neither specifically proven nor falsified, though it has mathematical features which give it great appeal to many physicists.

A number of proposed experiments might have the possibility of displaying "string effects." The energy required for many such experiments is not currently obtainable, although some are in the realm of possibility in the near future, such as possible observations from black holes.

Only time will tell if string theory will be able to take a dominant place in science, beyond inspiring the hearts and minds of many physicists.

What is Unified Field Theory?

Question: What is Unified Field Theory?

Answer: Albert Einstein coined the term "Unified Field Theory," which describes any attempt to unify the fundamental forces of physics between elementary particles into a single theoretical framework. Einstein spent the latter part of his life searching for such a unified field theory, but was unsuccessful.

In the past, seemingly different interaction fields (or "forces," in less precise terms) have been unified together. James Clerk Maxwell successfully unified electricity and magnetism into electromagnetism in the 1800s. The field of quantum electrodynamics, in the 1940s, successfully translated Maxwell's electromagnetism into the terms and mathematics of quantum mechanics.

In the 1960s & 1970s, physicists successfully unified the strong nuclear interaction and weak nuclear interactions together with quantum electrodynamics to form the Standard Model of quantum physics.

The current problem with a fully unified field theory is in finding a way to incorporate gravity (which is explained under Einstein's theory of general relativity) with the Standard Model that describes the quantum mechanical nature of the other three fundamental interactions. The curvature of spacetime that is 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:

Quantum Gravity
String Theory / Superstring Theory / M-Theory
Loop Quantum Gravity
Theory of Everything
Supersymmetry

Unified field theory is highly theoretical, and to date there is no absolute evidence that it is possible to unify gravity with the other forces. History has shown that other forces could be combined, and many physicists are willing to devote their lives, careers, and reputations to the attempt to show that gravity, too, can be expressed quantum mechanically. The consequences of such a discovery, of course, cannot be fully known until a viable theory is proven by experimental evidence

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Saturday, November 1, 2008

Theoretical Physics