Space Time, Relativity & Cosmology Lecture

A set of flashcards summarizing key terms and concepts from the lecture notes on Space Time, Relativity & Cosmology.

What is physics?

A science whose fundamental goal is to discover and formulate the fundamental laws of physics in nature.

Gravitational time dilation

Gravity affects time, causing it to run more slowly the stronger the gravitational force.

Light year

A measure of distance, representing how far light travels in vacuum in one year.

The speed of light in vacuum

Denoted by the symbol 'c', it is $c = 3.0 imes 10^8$ m/s.

Observable universe

The totality of galaxies and other objects whose light has reached us in the 14 billion year history of the universe.

Newton's Theory of Gravity

Introduced the first mathematical theory of gravity, predicting gravitational attraction between objects based on mass.

Einstein's Theory of General Relativity

Describes gravity as the curvature of space caused by mass.

The parallax effect

The apparent shift in position of a nearby object due to a change in the observer's position.

Parallax movement

The closer the object, the larger the parallax movement which helps measure distances.

Centripetal acceleration

The acceleration of an object moving in a circular path directed towards the center of the circle.

Potential energy

Stored energy dependent on position, such as gravitational potential energy, $U = mgh$.

Escape velocity

The minimum speed needed for an object to break free from the gravitational attraction of a planet.

Maxwell's Equations

The set of equations that define the laws of electromagnetism.

Quantum Physics

The study of subatomic particles and their interactions, where light is composed of massless particles called photons.

The principle of inertia

An object in motion will remain in motion unless acted upon by an external force.

Relativity theory

A mathematical framework that relates values of position and velocity in different reference frames.

Length contraction

A phenomenon predicted by relativity where a moving object is measured to be shorter in the direction of motion.

Twin paradox

A thought experiment in special relativity where one twin ages slower than the other due to relativistic travel.

Local Group

A collection of galaxies, including the Milky Way and the Andromeda Galaxy that are graviationally bound

Virgo Supercluster

A massive cluster of galaxies that includes the local group and is part of the larger Lanikea Galaxies

Thales of Miletus

An ancient Greek Philosopher considered one of the first to propose theories about the nature of the universe in a rational light

Anaximander of Miletus (610-546 BCE)

“The father of cosmology“; student of Thales who created the first rational model of the universe and defined the earth as a flat cylinder at the center of the universe

Philolaus of Croton (470-385 BCE)

The creator of the first non-geocentric model, proposed the concept of all planetary objects orbiting around a force called the central fire

Aristarchus of Croton (310-230 BCE)

The creator of the first heliocentric theory and estimated the sun as 19 times farther from the earth than the moon

Aristotle (384-322 BCE)

Best known Greek scientist although all his theories were incorrect, created the theory of natural motion which stated that all objects were composed of four elements fire, wind, earth and water

Aristotle’s theory of Gravity

Theorized that heavier objects fell faster than other objects because they contained more earth and proposed a fifth element called the aether

Claudius Ptolemy (100-160 CE)

Developed a mathematical equation based on Aristotles geocentric model, describing the orbits as perfect circles and introducing the concept of equants

Equants

The rotational speed of a planet (degrees/sec) is not uniform with respect to the earth or center of the circle but rather with respect to an offset point

Nicolaus Copernicus (1473-1543)

Polish scientist who revived Aristarchus’s concept of a heliocentric model, creating a new heliocentric model with perfect circular motion and epicycles

Tycho Brahe (1546-1601)

Proposed a hybrid model of the universe in which all planets except earth rotate around the sun while the sun rotates around the earth (geocentricism and heliocentricism), collected data for decades

Johannes Kepler (1571-1630)

Assistant to Brache who stole his data when he passed, used it to create three famous mathematical relations known as Kepler's law

Kepler’s 1st Law

• planetary orbits follow an elliptical path, not a perfect circle

Kepler’s 2nd Law

• the law of equal areas in equal time (planets speed change in correlation with distance from the sun)

Kepler’s 3rd Law

• a mathematical relation between the orbital period ‘t’ and the size of the ellipse ‘a’ (celestial object size and how it affects the size of orbit)

Galileo Galilei (1564-1642)

Founder of modern physics, created the principle of inerta and the principle of relativity

Issac Newton (1642-1727)

Presented the first mathematical theory of gravity and theory of motion

Cosmic rays

Cosmic rays are stable charged particles that originate outside the galaxy and strike the earth

Neutrinos

Electrically neutral, near massless particles that travel at speeds near c

Subatomic Particles

Examples of time dilation and length contraction for spaceships moving at speeds near “c” are experiments or science fiction