Grand Unified Theory (or Unified Field Theory):
Also known as Grand Unification or GUT, this refers to any of several unified field theories that predict that at extremely high energies (such as occurred just after the Big Bang), the electromagnetic, weak nuclear, and strong nuclear forces are all fused into a single unified field. Thus far, physicists have only been able to merge electromagnetism and the weak nuclear force into the “electroweak force”. Beyond Grand Unification, there is also speculation that it may be possible to merge gravity with the other three gauge symmetries into a “theory of everything”.
Gravity (or Gravitational Force):
The force of attraction that exists between any two masses, whether they be stars, microscopic particles or any other bodies with mass. It is by far the weakest of the fourfundamental forces (the others being the electromagnetic force, the strong nuclear force and the weak nuclear force), and yet, because it is a consistent force operating on all bodies withmass, it is instrumental in the formation of galaxies, stars, planets and black holes. It was approximately described by Sir Isaac Newton’s Law of Universal Gravitation in 1687, and more accurately described by Albert Einstein’s General Theory of Relativity in 1916.
Half-Life:
A measure of the speed of radioactive decay of unstable, radioactive atoms. It is the time taken for half of the nuclei in a radioactive sample to disintegrate or decay. Half-lives can vary from a split-second to billions of years depending on the substance.
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