Is the Expansion of the Universe Accelerating?

YES!

...but lets find out why...

In the late 1990s astronomers made a revolutionary discovery: the expansion of our Universe is accelerating. Ever since the days of astronomer Edwin Hubble’s ground-based telescope observations, astronomers have known it's true. However, many astronomers, physicists, and mathematicians have wondered: will the Universe expand forever? NASA missions have discovered that it will expand forever, and are helping to understand how this expansion comes about.

Quintessence is a physical characteristic that causes the expansion of the Universe to accelerate. Most forms of energy slow the expansion down because of gravity. But quintessence gravitational force is repulsive which pushes the Universe outward, causing it to accelerate.
The expansion is accelerating because Dark Energy is pushing outward separating all of the galaxies and stars. it is creating space in between everything that was never there before. This is forcing everything further apart. This process is accelerating because the further it moves away the faster it moves.

Type 1a supernovae explode with a characteristic energy. If scientists know the absolute and apparent brightness of the explosion, they can determine the distance. Once they know the redshift, they can see how fast the supernovae are moving away. They found that the further the supernova was away the faster it was moving.

CRITICAL DENSITY= the precise density marking the dividing line between eternal expansion and eventual collapse.

White dwarf supernovae are used to determine whether gravity has been slowing the Universe’s expansion HOWEVER the expansion appears to be speeding up. Astronomers determine this by measuring the distance of the supernova, essentially when the supernova occurred, and its redshift, which shows how much the Universe has expanded since the time of the explosion.

The accelerating model fits the best when astronomers plot actual supernova data on a graph comparing all of the expansion patterns, if this model is correct then the Universe must be 14 billion years old!

Expansion Patterns the expansion rate of the Universe depends on the balance between gravity, which acts to slow the expansion, and dark energy, which acts to accelerate it
A RECOLLAPSING UNIVERSE : no dark energy and the matter density of the Universe is larger than the critical density, the collective gravity of all its matter will eventually halt the Universe’s expansion and cause it to collapse on itself. Galaxies will come crashing back together and the Universe will end in a “Big Crunch”. This final state would look very similar to the state in which the Universe began in the Big Bang.
A CRITICAL UNIVERSE : no dark energy and then matter density of the Universe equals the critical density, the collective gravity of all its matter is exactly the amount needed to balance the expansion. The Universe will never collapse but will expand more and more slowly as time progresses.
A COASTING UNIVERSE : no dark energy and the matter density of the Universe is smaller than the critical density, the collective gravity of all its matter can’t halt the expansion. The Universe will keep expanding forever with little change in its rate of expansion.
AN ACCELERATING UNIVERSE : dark energy exerts a repulsive force that causes the expansion of the Universe to accelerate with time, this then causes the expansion rate to grow with time as well. Galaxies will retreat from one another with increasing speed, which will in turn cause the Universe to become cold and dark more quickly than a coasting Universe.

Expansion Patterns

To better understand, the Universe can be thought of as the surface of a balloon being blown up. Just as the points on the surface of a balloon move apart from each other as the balloon is inflated, so do the objects in space move apart from each other as the Universe keeps expanding.

Web Page Made By:

Tim Barr, Andrew Combess, Gabby Garcia, Michelle Lazzara, Vitus Pelsey, and Drew Thiele

Students of Dr. Stephen G. Alexander, Miami University, PHY 111