Selected Theories and Laws

Summary of a Few Important Theories and Laws

Big Bang Theory

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If you’re going to know one scientific theory, make it the one that explains how the universe arrived at its present state. Based on research performed by Edwin Hubble, Georges Lemaitre and Albert Einstein, among others, the big bang theory postulates that the universe began almost 14 billion years ago with a massive expansion event. At the time, the universe was confined to a single point, encompassing all of the universe’s matter. That original movement continues today, as the universe keeps expanding outward.

Hubble’s Law of Cosmic Expansion

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Hubble not only proved that there were other galaxies besides the Milky Way, he also discovered that these galaxies were zipping away from our own, a motion he called recession. Hubble’s law provides a concise method for measuring a galaxy’s velocity in relation to our own. And perhaps most significantly, the law established that the universe is made up of many galaxies, whose movements trace back to the big bang.

Kepler’s Laws of Planetary Motion

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Kepler’s three laws of planetary motion — formed in the early 17th century — describe how planets orbit the sun.

1. The first law, sometimes called the law of orbits, states that planets orbit the sun elliptically.
2. The second law, the law of areas, states that a line connecting a planet to the sun covers an equal area over equal periods of time. In other words, if you’re measuring the area created by drawing a line from the Earth to the sun and tracking the Earth’s movement over 30 days, the area will be the same no matter where the Earth is in its orbit when measurements begin.
3. The third one, the law of periods, allows us to establish a clear relationship between a planet’s orbital period and its distance from the sun. Thanks to this law, we know that a planet relatively close to the sun, like Venus, has a far briefer orbital period than a distant planet, such as Neptune.

Universal Law of Gravitation

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We may take it for granted now, but more than 300 years ago Sir Isaac Newton proposed a revolutionary idea: that any two objects, no matter their mass, exert gravitational force toward one another. This law is represented by an equation that many high schoolers encounter in physics class.

Newton’s Laws of Motion

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1. The first of the three laws states an object in motion stays in motion unless acted upon by an outside force.
2. The second law establishes a connection between an object’s mass (m) and its acceleration (a), in the form of the equation F = m × a.
3. The third law states for every action there is an equal and opposite reaction.

Laws of Thermodynamics

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Thermodynamics is the study of how energy works in a system, whether it’s an engine or the Earth’s core. It can be reduced to several basic laws,

Archimedes’ Buoyancy Principle

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According to Archimedes’ buoyancy principle, the force acting on, or buoying, a submerged or partially submerged object equals the weight of the liquid that the object displaces. This sort of principle has an immense range of applications and is essential to calculations of density, as well as designing submarines and other oceangoing vessels

Evolution and Natural Selection

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In a basic sense, organism differentiation occurred through evolution, through descent with modification. Populations of organisms developed different traits, through mechanisms such as mutation. Those with traits that were more beneficial to survival such as, a frog whose brown coloring allows it to be camouflaged in a swamp, were naturally selected for survival; hence the term natural selection.

Theory of General Relativity

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Albert Einstein’s theory of general relativity remains an important and essential discovery because it permanently altered how we look at the universe. Einstein’s major breakthrough was to say that space and time are not absolutes and that gravity is not simply a force applied to an object or mass. Rather, the gravity associated with any mass curves the very space and time (often called space-time) around it.

Heisenberg’s Uncertainty Principle

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In postulating his Uncertainty Principle, Heisenberg realized that it was impossible to simultaneously know, with a high level of precision, two properties of a particle. In other words, you can know the position of an electron with a high degree of certainty, but not its momentum and vice versa.

Niels Bohr later made a discovery that helps to explain Heisenberg’s principle. Bohr found that an electron has the qualities of both a particle and a wave, a concept known as wave-particle duality, which has become a cornerstone of quantum physics. So when we measure an electron’s position, we are treating it as a particle at a specific point in space, with an uncertain wavelength. When we measure its momentum, we are treating it as a wave, meaning we can know the amplitude of its wavelength but not its location

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Selected Wikipedia Articles

Significant Theories (Wikipedia Article Links)

Biology/Life Science

• Cell Theory
• Biological Evolution

Chemistry

• Atomic Theory
• Valence Bond Theory

Earth Science

• Plate Tectonics
• History of the Earth

Physical Science/Physics

• Relativity
• String Theory

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Articles summarized by Honeycutt on this page (Big Bang Theory; Hubble’s Law of Cosmic Expansion; Kepler’s Laws of Planetary Motion; Universal Law of Gravitation; Newton’s Laws of Motion; Laws of Thermodynamics; Archimedes’ Buoyancy Principle; Evolution and Natural Selection; Theory of General Relativity; Heisenberg’s Uncertainty Principle) were originally written by Jacob Silverman and published on HowStuffWorks.com.