The Origin of the Universe,
The term "evolution" usually refers to the biological evolution of living things. But the processes by which planets, stars, galaxies, and the universe form and change over time are also types of "evolution." In all of these cases there is change over time, although the processes involved are quite different.
Earth, and Life
In the late 1920s the American astronomer Edwin Hubble made a very interesting and important discovery. Hubble made observations that he interpreted as showing that distant stars and galaxies are receding from Earth in every direction.
Moreover, the velocities of recession increase in proportion with distance, a discovery that has been confirmed by numerous and repeated measurements since Hubble's time. The implication of these findings is that the universe is expanding.
Hubble's hypothesis of an expanding universe leads to certain deductions. One is that the universe was more condensed at a previous time. From this deduction came the suggestion that all the currently observed matter and energy in the universe were initially condensed in a very small and infinitely hot mass. A huge explosion, known as the Big Bang, then sent matter and energy expanding in all directions.
This Big Bang hypothesis led to more testable deductions. One such deduction was that the temperature in deep space today should be several degrees above absolute zero. Observations showed this deduction to be correct. In fact, the Cosmic Microwave Background Explorer (COBE) satellite launched in 1991 confirmed that the background radiation field has exactly the spectrum predicted by a Big Bang origin for the universe.
As the universe expanded, according to current scientific understanding, matter collected into clouds that began to condense and rotate, forming the forerunners of galaxies. Within galaxies, including our own Milky Way galaxy, changes in pressure caused gas and dust to form distinct clouds. In some of these clouds, where there was sufficient mass and the right forces, gravitational attraction caused the cloud to collapse. If the mass of material in the cloud was sufficiently compressed, nuclear reactions began and a star was born.
Some proportion of stars, including our sun, formed in the middle of a flattened spinning disk of material. In the case of our sun, the gas and dust within this disk collided and aggregated into small grains, and the grains formed into larger bodies called planetesimals ("very small planets"), some of which reached diameters of several hundred kilometers. In successive stages these planetesimals coalesced into the nine planets and their numerous satellites. The rocky planets, including Earth, were near the sun, and the gaseous planets were in more distant orbits.
The ages of the universe, our galaxy, the solar system, and Earth can be estimated using modern scientific methods. The age of the universe can be derived from the observed relationship between the velocities of and the distances separating the galaxies. The velocities of distant galaxies can be measured very accurately, but the measurement of distances is more uncertain. Over the past few decades, measurements of the Hubble expansion have led to estimated ages for the universe of between 7 billion and 20 billion years, with the most recent and best measurements within the range of 10 billion to 15 billion years.
The aim of Thursday's Classroom is to provide a lasting connection between NASA's latest research and the classroom environment.
Back to Homepage
Our Space Picks
- Discovery News - Space
- Dark Matter
- The Sun Does a Flip
- Cosmology is the study of the origin and evolution of the Universe. This web site introduces basic concepts in modern cosmology and describes the MAP mission at a general level.
- - NASA
- Origin of the Universe:
Big Bang Theory
- SUPERMASSIVE BLACK HOLES
There's growing evidence that the ultimate force of cosmological destruction - a supermassive black hole - may in fact breathe life into every galaxy in the Universe.
- Huge concentration of Galaxies
Looking far away and therefore well back in time, researchers have spotted evidence of a huge concentration of galaxies that may be the largest structure in the universe ever observed.
- Stephen Hawkins Universe
- A short story of the Universe
- Science@NASA Headlines Archive
- Space.com science/astronomy
- New Evidence for Black Holes
- Origin of the Earth and Life
- Black light at the end of the quantum tunnel -- Jan 2, 2001
- Boost for Big Bang theory
-- Dec 21, 2000
- High Rate Of Star Births Linked To Supermassive Black Holes
- NASA - Origins - Galaxies, Stars, Planets ... and Life
- Structure and evolution of the Universe - universe.gsfc.nasa.gov
- The Evolution of the Universe
- Scientific America
- Exploration of the Solar System
- The Sun Earth Connection
- NASA Pages that answer general cosmology questions:
- Pictures of Space
- Latest Hubble Space Telescope Observations
- Astronomy Picture of the Day Archive - NASA
- Black Holes FAQ - By Ted Bunn
- Space News from Around the Internet - universetoday.com
- NASA SPACE LINK: Black Holes
- Black Holes and Neutron Stars
- Black Holes and Beyond
- Black Holes, White Holes, Worm Holes - singnet.com
- NOAA Space Environment Center
-- updates and forecasts of solar and geomagnetic activity
- SpaceWeather.com -- news about solar activity, auroras, meteor showers, comets, and near-Earth asteroids
- Supernovas, Black Holes Could Offer Clues To Subatomic Particles
- Solar and Heliospheric Observatory
-- find out what the Sun looks like!
Back to The Origin of Life