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Glossary of Terms

Some of the terms and expressions used in the field of Theoretical Physics are as follows:

Big Bang: The term is used to refer to the singularity at the beginning of our universe. The Big Bang theory explains how the universe is expanding from its initial state.

Big Crunch: This is one possible fate for the universe among many, where the whole universe collapses to a singularity.

Black Hole: A region of space-time that is bended inward due to the extreme force of gravity. It traps anything even light that passes its event horizon.

Cosmic Strings: These are different objects from strings in string theories. Cosmic strings are theoretical objects that have been developed at the beginning phase of the universe. Extremely long and narrow but massive, they could be stretched across the universe.

Cosmology: Study of the cosmos that deals with the origin and the fate of the universe.

Dark Energy: A hypothetical type of energy that fills the empty space. Together with dark matter they form about 75% of the matter/energy of the universe.

Dark Matter: A kind of matter that cannot be seen directly and its composition is unknown. However, its gravitational effect can be measured. It is estimated that up to 90% of the mass in our universe is made of dark matter.

Entropy: A measure of the disorder or chaos of a closed system.

Exotic Material: Hypothetical material inside of a wormhole which has negative average energy density.

Flatness Problem: One of the three problems associated with the standard models of cosmology. The problem has to do with the basic question, why the universe is close to being spatially flat.

General Theory of Relativity: It formulates how gravity bends space-time and it is used to explain and understand the large-scale structure of the universe.

Holographic Principle: The information about the quantum states of a system is contained on the surface area of the system.

Horizon Problem: One of the three problems associated with the standard models of cosmology. The problem has to do with the large-scale uniformity of the universe.

Inflationary Cosmology: A theory of cosmology which is not part of the standard models of cosmology. It states that the universe went through exponential expansion very early after the big bang.

The Knot Theory: A branch of mathematics that is used in quantum gravity theories.

M-Theory: A theory that unifies five different versions of the string theories and super gravity together, all under one single framework.

Magnetic Monopole: A single hypothetical magnetic pole. Monopoles have not been detected yet.

Maxwell's Equations: Four equations developed by J. C. Maxwell that unified electricity and magnetism.

Multiverse: This term is used to refer to Multi-Universes.

Planck Length: A quantity associated with quantum gravity. It is about 10^-35 cm.

Planck Mass: A quantity associated with quantum gravity. It is about 10^-8 kg.

Planck Time: A quantity associated with quantum gravity. It is the time it takes for light to travel a Planck length interval which is about 10^-34 seconds.

Quantum Cosmology: A branch of cosmology that uses the laws of quantum mechanics to study the cosmos.

Quantum Gravity: A theory that unifies relativity with quantum mechanics under one single framework. It has not been tested.

Second Law of Thermodynamics: Entropy is always greater than or equal to zero. Entropy cannot decrease.

Singularity: A point in space-time where its curvature becomes infinite. Big Bang is an example of a singularity.

Smoothness Problem: One of the three problems associated with the standard models of cosmology. The problem has to do with the basic question why the matter is uniformly distributed in the universe.

Special Theory of Relativity: It states that laws of nature are the same for all observers regardless of how they move. Also, it describes that space and time are connected and no longer individually absolute.

Speed of Light: One of the constants of the nature. It is 299,792,458 m/s. According to the laws of relativity, nothing can travel faster than speed of light.

Standard Models of Cosmology: These are three models of cosmology that use the big bang theory and some concepts of standard particle physics. Inflationary theory is not part of the standard models of cosmology.

String Theories: These theories use one dimensional objects (strings) as the basic building block of the universe including matter. M-Theory is the latest version of string theories.

Time Dilation: A consequence of the Special Theory of Relativity. It states that time slows down for an observer in motion or influenced by gravity.

Twistor Theory: A background-independent theory that was initially developed by Roger Penrose. It formulates space-time using complex numbers.

Uncertainty Principle: One of the basic principles of quantum mechanics developed by W. Heisenberg. It formulates that one cannot precisely specify the values of two conjugate terms such as position-momentum or time-energy.

White Hole: The time reversal of a black hole. Big bang is an example of a white hole. A theoretical region of space-time where matter erupts but cannot enter the region.

Worm Hole: A theoretical object that connects two regions of space-time together. It works as a tunnel and can also connect two regions of different universes together.