Origin and Destiny of the Universe
Why is our Universe the way we see it to be? And what will ultimately
of it? These are two fundamental questions which have long interested
humankind. Since the 1929 discovery that Universe is expanding, we have made some significant steps in
understanding how the Universe began and how it must have evolved to be
it is today. We know this: galaxies and clusters of galaxies formed from
fluctuations in the early Universe. We can measure these fluctuations by
mapping the cosmic background radiation and relate them to the
which we observe today. However, many challenges remain such as:
What is the Age of the Universe? - or - How Fast is the Universe
In the 1920s, Edwin Hubble used the 100" telescope (2.5 meters) at the
Mount Wilson Observatory in California to detect variable stars in
nebulae. He discovered that the stars he observed had the same characteristic
variations in their brightness as a class of stars called Cepheid Variables.
Earlier, astronomer Henrietta Levitt had shown there was a
precise correlation between the periodic change in brightness of a Cepheid Variable and its
luminosity. Hubble was able use this correlation to show that the nebulae
variable stars he observed were not within our own Galaxy; they were
galaxies far beyond the edge of our Milky Way.
Hubble determined the distances to the galaxies and the velocities that they
were moving at, relative to Earth. From this, he discovered an amazing
the farther galaxies were away from us, the faster they were moving away
from us. In other words, the Universe was expanding!
Tell me more about Cepheid Variables and their
Use as Cosmic Yardsticks!
What is the Shape of the Universe?
The density of the Universe determines its geometry or shape. If the density of
the Universe exceeds the so-called "critical density", then the shape of
space is curved like the surface of a huge sphere. If
the density of the Universe is less than the "critical density", then the
shape of space is curved like the surface of a saddle.
If the density of the Universe exactly equals the "critical density", then the
shape of the Universe is flat like a sheet of paper.
Astronomers are still trying to accurately measure the shape of the
Universe. The most widely accepted theory predicts that the density of the
Universe is very close to the critical density, and that the shape of the
Universe should be flat, like a sheet of paper.
Tell Me More about How We Measure the Size and Age
of the Universe!
What is the Fate of the Universe?
Cosmologists envision two possible fates for the Universe: The Big
Freeze or the Big Crunch. The evolution of the Universe is determined by a
struggle between the outward momentum of expansion and the inward pull of
gravity. The strength of gravity depends on the density of the Universe. If the
density of the Universe is less than the critical density, then the Universe
will expand forever. If the density of the Universe is greater than the
critical density, then gravity will eventually win, and the Universe will
collapse back on itself.
Thank you to the WMAP project for contributing to this article. Find out
about the Wilkinson Microwave Anisotropy Probe at http://map.gsfc.nasa.gov/.