Our Universe

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We have all sung this song when we were kids in school.
Twinkle, twinkle, little star,
How I wonder what you are.
Up above the world so high,
Like a diamond in the sky.

On a clear night, Most of us have at least caught a glance of the beautiful twinkling stars in the sky above and felt mesmerized by the beauty of its magnificient radiating lights.  If you open up the dictionary and look for the word Universe, you will find the closest interpretation of Universe as one verse.  Uni = one, verse = song.  Universe = One Song.  We are one small entity of this one song.   How did this song ever get created?  SOME people say: ‘Our universe is all a matter of chance.’ Others, especially those who are religious, disagree. Still others are just not sure. What do you believe?

Whatever your view, you will no doubt agree that our universe is a marvel.   This universe is a container of clusters which are a collection of galaxies.  Galaxies are a collection of billions to trillion stars.  Some of these stars like our sun for example have planets revolving around it.  These in turn have satellites like our moon for example revolving around the planets.  What a beautiful dance indeed.  Our planet Earth along with the rest of the planets in the solar system revolve around the Sun which is a medium sized star in the Milky Way Galaxy. The Earth moves around the Sun at 30 kilometers per second (roughly sixty thousand miles per hour). Our Sun moves around the Milky Way Galaxy at 225 kilometers per second.  Milky Way Galaxy is roughly about 100,000 light-years across.  The Milky Way galaxy is a large spiral galaxy comprising of 200-400 billion stars.  One such star is our Sun. The distance from the Sun to the center of Milky Way Galaxy is about 27,700 light-years.

Distance between stars or galaxies is measured in light-years.  A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 186,000 miles (300,000 kilometers) per second.  So in one year, it can travel approximately 186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year.  (* signifies multiplication sign)

Consider the galaxies. It has been estimated that there are about 100 billion of them in the observable universe. Each is a grouping of from fewer than a billion to more than a trillion stars.  Most galaxies are grouped in clusters of from a few dozen galaxies to thousands of them. For example, our neighboring galaxy Andromeda has been described as the twin of our Milky Way galaxy. These two immense star systems are bound to each other by gravity. Together with a small number of other neighboring galaxies, they form part of a cluster.

The universe is made up of an untold number of clusters of galaxies. Some clusters are bound by gravity to other clusters, forming superclusters.  Scientists find that the superclusters are moving away from one another. In other words, the universe is expanding. This amazing discovery suggests that there was a beginning when the universe was in a much smaller and denser state. The birth of the universe is often referred to as the big bang.

How Old is the Universe?

Until recently, astronomers estimated that the Big Bang occurred between 12 and 14 billion years ago. To put this in perspective, the Solar System is thought to be 4.5 billion years old and humans have existed as a species for a few million years. Astronomers estimate the age of the universe in two ways: 1) by looking for the oldest stars; and 2) by measuring the rate of expansion of the universe and extrapolating back to the Big Bang.

“Some Say the World Will End in Fire, Others Say in Ice”

Just as Robert Frost imagined two possible fates for the Earth in his poem, cosmologists envision two possible fates for the universe:

  • Endless expansion
  • The ?Big Crunch?

Since the Big Bang, the universe has been expanding. In the past, galaxies were closer together than they are now.  Therefore, we can measure the expansion in terms of the average (mean) distance between galaxies.

If the gravitational mass of the matter in the universe is not enough to halt the expansion, then the universe will expand forever, and we say the universe is open.

If the gravitational mass of the matter in the universe is great enough to halt the expansion, then the galaxies will reach some maximum separation and then will begin to collapse back on top of each other. In this case, and we say the universe is closed, and we predict that sometime in the distant future, there should also be a Big Crunch which essentially is the Big Bang in reverse.

Now, we’re really starting to get a little bit speculative, so what I want to do is bring us back to earth and remind you of two things. One, that as the universe continues to age, it goes through a whole host of interesting processes which last from now until the universe is at least 100 cosmological decades (10^100 years, in other words put 100 zeros after 1) old. Second, with this grander perspective, we can now look back to where we are now. Although we don’t occupy a particularly important place in space or a particularly important place in time, in cosmic terms, we actually do occupy a pretty good planet for the qualities that we have. We are pretty lucky to be here on Earth.

Author: Allen Martis- USA

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