If history is a big bang, what about the future? Scientists believe that there are three possible models for the future of the Universe. An open model in which the Universe continues expanding forever, a flat model where the expansion continues but slows, and never expands beyond a certain point, or a closed model where the expansion stops and the Universe begins falling back toward it’s center in a big crunch. The answer to which model is correct depends on the overall density of the Universe and it’s rate of expansion. The rate of expansion is known as Hubble’s Constant, but the exact value of Hubble’s Constant was a mystery for a long time. If scientists knew the value of Hubble’s Constant and the overall density of the Universe, they would be able to more accurately determine the age and the size of the Universe.

     If you throw a stone up into the air, it starts slowing down the instant it leaves your hand. It finally peaks and it’s upward momentum ceases and then the stone accelerates downward. It was reasoned that the receding galaxies were slowing down as they moved outward. In the 1990’s, astronomers obtained digital technology for photographing distant objects. Two separate teams of astronomers set out to determine the rate that the galaxies are slowing down.

     By taking digital photographs of the same area on successive nights, any new objects that appear can be found by subtracting a previous night’s image from the current image. Anything new, such as a supernova in a distant galaxy would be left in the resulting image. It could then be focused on and studied. Supernovae are dead stars that suddenly explode in a brilliant thermonuclear fireball. They peak in brightness in about three weeks, and then fade over several months. There are different types of supernovae. The astronomers looked for type Ia supernovae because of the similarity in intrinsic brightness that could be compared along with red-shift to find the rate of slowing. An article about this appears in the January 1999 issue of Scientific American.

     Of course, the research and work done was much more complicated then what I could put in a single paragraph. Lots of people working day and night for several years compiled truckloads of data. The data is still being studied by lots of people working day and night for several more years. The preliminary results are not what the astronomers expected. The distant type Ia supernovae seem to be 25% dimmer than what the astronomers anticipated.

     After discounting every other possibility including intergalactic dust and gravitational red-shift, the scholars are left with the possibility that the distant galaxies are not slowing down as they recede because they are accelerating as they recede. This result appears to be contrary to all the wisdom of 20th century cosmologists. Material objects don’t accelerate by themselves unless they have an engine burning fuel, such as an automobile or a rocket or an animal. Other than that, the only things that accelerate are falling objects.

     Before this supernovae study began, a lot of resources were expended in the search for the "missing matter." Under the cosmological models of the 1980’s and early 1990’s, there appeared to be a lot more gravitational force in the Universe than what the detectable amount of physical matter could account for. The most agreed upon estimates were 90% "missing matter" and 10% detectable matter.

     Most galaxies are disc shaped objects composed of one hundred billion stars or more. The stars rotate around a central axis. There are hundreds of billions of galaxies visible to modern telescopes. Within galaxies, there are clumps of stars called "globular clusters." Galaxies themselves congregate in "galaxy clusters."

     If you hold a coin out at arms length, face towards you, you get one type of view. If you hold the coin edge-wise, you get another. By studying galaxies that are oriented in an edge-wise viewpoint, astronomers could measure the difference in red-shift from one side of the galaxy to the other. If the galaxy is viewed edge-wise, one side of the axis is rotating towards us, and the other side of the axis is rotating away. The difference in red shift indicates how fast the galaxy is rotating.

     It turns out that the galaxies are rotating so fast that they should fly apart from centripetal force, unless there is 10 times as much matter than what is visibly accounted for, exerting a proportional gravitational force on each galaxy. Isaac Newton showed that objects act as if all their mass were located at their centers. Why do galaxies exhibit gravitational forces far beyond what can be visibly accounted for? Is it massive black holes at their centers, or infinitesimally small, and so far, undetectable quantums flitting about and filling the Universe with their massive gravitational force? The question will be answered when they find the "missing" or "dark" matter.

     Now, with the new evidence that the Universe is accelerating as it expands and the work done with the Hubble Space Telescope, scientists have narrowed down a value for Hubble’s constant. In the spring of 2001, scientists stated that for each 3.26 million light-years of distance, galaxies and clusters of galaxies recede by and additional 72 km/second. Scientists now believe that 3% of the mass of the Universe is in the form of visible matter. 30% is in the form of "dark matter," and the other 67% is in the form of "dark energy."