User:Mrandrewnohome/Science's most needlessly complicated theories, simplified

Principle of Least Action
This says, essentially, that things happen in the way that requires the least amount of effort. For instance, a beam of light will travel in a straight line because that is the shortest path between the two points. If you drop a ball, it will travel towards the centre of the earth.

Note:This theory does not apply on the quantum scale.

Laws of Motion
Discovered by Isaac Newton, these laws assess how things move. First, he said that objects have 'inertia', which is a measure of resistance to changes in their motion. Inertia means that things remain static unless they are given a push. Similarly, objects that are moving already will continue to move unless something stops them. Second, the mass of the object determines what effect a particular push will have on the motion, if there is any. The third law states that every action has an equal and opposite reaction; for instance, if I push somebody, I feel a push of equal force in return. This is the principle by which space rockets work: when they push out exhaust gas from the nozzle at the rear, the engines get a push forward.

Note: These laws are universal except when objects travel at the speed of light, in which case the theory of relativity would apply.

Universal Gravitation Theory
Universal gravitation theory states that there is a mutual attraction between anything, made up of ordinary matter, that has mass. This attraction is dependent on the distance between them, and a 'gravitational constant'. One of the key insights of this theory was that the gravitational force follows an 'inverse-square law'. This means that the square of the distance between the two objects affects the attraction between them; if the square distance is larger, the attraction is weaker, and vice-versa. This law was crucial in explaining the motion of the planets in the solar system.

Thermodynamics
Thermodynamics deals with heat and how it travels; the principles of thermodynamics are encompassed by three laws. The first states that whatever is going on, the total energy in the Universe stays the same; meaning that energy cannot be destroyed, only changed into another type of energy. The second law states that an isolated system's entropy always increases. Entropy is a measure of the part of the system's energy that cannot be put to any use. For instance, as a watchspring unwinds, it has less and less power to keep the watch running. Its entropy rises because the spring's potential energy is being transferred to the watches hands as kinetic energy. The third law says that, as a system's temperature drops towards absolute zero, all natural processes cease to occur.

Electromagnetism
Electromagnetism describes the events that occur when electric charges, movement and magnetic fields interact with one another. For example, moving a metal wire within a magnetic field will cause an electric current to flow in the wire; this is the process by which electricity is created. On the other hand, passing an electric current through a wire will generate a magnetic field. Thirdly, if an electric current is passed through a wire which is already in a magnetic field, this will cause the wire to move.

Theory of Relativity
The theory of relativity describes how matter, energy, space and time interact. There are two theories: general relativity and special relativity. General relativity describes time as a dimension that interacts with the other dimensions - length, width and height - and combines them into something called spacetime. Anything that has mass or energy warps spacetime, creating a gravitational field. This field has an effect on any matter that travels through it; it even bends light rays which pass through it. Special relativity says that nothing can travel faster than the speed of light. It also indicated that the passage of time is different for people travelling at different speeds. The theory states that if two twins are separated by one taking a journey through space at near the speed of light of light, they will have significantly different ages when reunited. The theory also encompasses the equation E = mc2 which describes how matter can be converted into energy, and vice versa.

Atom Theory
This states that all elements are made up of microscopic, indivisible particles; electrons, protons and neutrons. The distribution of these units in an atom determines whether the atom will be either hydrogen, gold or another element.

Quantum Mechanics
This theory asserts the belief that theories concerning forces and gravity do not apply in subatomic physics; thus, a new set of theories are needed, collectively known as quantum mechanics. Quantum mechanics does not give simple answers; it theorizes that the same subatomic particles can exist in a variet of different states at the same time. The theory makes predictions about the microscopic world that seem to contradict common sense; for example, it theorizes that a single atom can exist in more than one place at the same time until we check to see what it is doing. It also states that electrons can spin in both clockwise and counter-clockwise directions at the same time until we measure it.

The Uncertainty Principle
Also known as the Heisenberg uncertainty principle, this is a statement about the way quantum objects, such as atoms and the particles that make up atoms, behave. The principle says that we can never know, for example, where an electron, say, is located, while at the same time knowing exactly how fast it is moving. Either property, its speed or its position, can be measured to an infinite degree of accuracy, provided we abandon knowledge of the other property. The uncertainty principle can be explained in another in terms of energy and time; we are able to measure the exact energy of a particle, provided that we are not interested when it has this energy, and vice-versa.

Schrödinger's Cat


This is a thought experiment devised by Erwin Schrödinger in the mid-1930s to highlight just how bizarre quantum mechanics was. The theory suggests taking a box in which we place a cat, some lethal poison and a source of radiation. According to quantum mechanics we are unable to say, unless we are checking, whether a radioactive atom has broken apart, or decayed, within a given time. Thus, the only way we can describe it is by saying that it is has both decayed and not decayed at the same time. In Schrödinger's box, the experiment is designed so that any decayed atom will have spat out a particle that triggers the release of the poison, killing the cat. Since the cat is composed of atoms it is subject to the laws of quantum mechanics; this means that, without checking, the cat is simultaneously alive and not alive, at the same time. Only by opening the box do we force everything into a single state.