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Matthew Dolan
  Big Bang

The Universe as we see it today, is expanding from a widely accepted theoretical, event called the Big Bang occurring approximately 15,000 million years ago. We can observe that each group of galaxies is receding from each other group of galaxies, including our own. An analogy, commonly made of our expanding Universe is that of a balloon with spots drawn on it being blown up. As the balloon expands so to does the distance between the spots. This is the situation between each group of galaxies in our Universe.

We may, appear to be watching the galaxies recede from us and believe ourselves to be stationary, however this is simply our relative view of the universe. For example, a galaxy receding from us at a rate of "x" km/sec would see our galaxy relative to itself moving away also at the same speed of "x" km/sec. Some galaxies do not recede from each other, as their gravitation holds them together as a whole. These groups of galaxies are called "clusters".

If the galaxies are accelerating in speed, with respect to their distance, every galaxy will inevitably reach the Speed of Light and in affect no longer able to be observed. This distance will be the boundary of the observable universe but not necessarily the universe itself. This limit is assumed to be somewhere in the region of 15,000 million and 20,000 million light years, a distance we have yet to penetrate. This acceleration with distance is termed as the Hubble Constant, and is thought to be around 50 to 70 km per second per megaparsec. At a certain time it was thought that the universe was only 10,000 million years old. Which would mean that some stars are older than the universe itself; so it is obviously flawed but can be corrected with a reasonably accurate value of the Hubble Constant and in turn give us approximate age of the universe.

It was Edwin Hubble an American astronomer in 1929 who discovered that galaxies all around us were moving away from us. This was discovered, because the light analysed from each galaxy was red shifted. (That is the absorption lines were shifted to the red side of the spectrum, an effect known as the Doppler Effect, indicating in the case of red shift that the light source is moving away from the observer). He put forward the theory that the further a galaxy gets, the faster it will recede from earth. This then became known as the Hubble Constant (Ho). The equation for the Hubble Constant is simple in form, but extremely hard to get precisely because of the inaccuracy of the figures. The formula is, Ho = v/d, where v is the galaxy's radial outward velocity (The motion of the galaxy from our line-of-sight), and d is the galaxy's distance from earth. An accurate result relies on the accuracy of the values obtained for "v" and "d". "d" being the more difficult of the two, as reliable distance markers such as variable stars and super novae must be found in the galaxy to determine it's distance. Even today an exact figure for the Hubble Constant cannot be agreed upon. Two teams of researchers assigned to finding the Hubble constant, have conflicting results on what the Hubble Constant is. The first team associated with Allan Sandage of the Carnegie Institutions has obtained a value of 50 km/sec/Mpc. While the second team associated with Gerard DeVaucouleurs of the University of Texas have obtained a value of 100 km/sec/Mpc. It is primary objective of the HST to refine the value of the Hubble Constant (Ho).

The structure of the Expanding Universe is not fully known. Does it have any boundaries? It is Stephen Hawking's belief that the universe is finite in size but has no boundaries. One could keep on moving in one direction and eventually end up in the same place. For example, an analogy would be if I were to walk in a straight line around the world, I would eventually return to the same point at which I started. However this is a more two-dimensional view, as compared with that of curved space-time.

There is a lot unknown about our expanding universe but there is more and more being discovered every day. Soon we might just know for fact the true story of the universe.



Author: Matthew Dolan

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