The Universe
galaxy cluster
A spectacular cluster of galaxies around 2 billion light years from Earth.
Universe Facts
  • The universe is around 13.7 billion years old.
  • It is thought the universe was born when a super dense object smaller than a sub atomic particle began to rapidly expand.
  • The first galaxies in the universe began to form around 13.2 billion years ago.
  • There are now over 100 billion galaxies in the observable universe.
  • Each galaxy contains billions of stars, our own Milky Way galaxy contains approximately 200 billion stars.
  • Only around 4% of the universe is composed of visible matter, the remaining 96% is composed of invisible dark matter and dark energy.
  • The shape of the universe is unknown, it may possibly be flat or spherical in shape.
  • A flat shape could produce an infinite universe whereas a closed spherical universe would be finite.
  • The universe will not last forever, like everything that exists it has a lifespan.
  • The universe may not be unique, it could be one of many in a finite or even infinite multiverse system.

The Universe

andromeda galaxy
Andromeda is the nearest spriral galaxy to our own galaxy, the Milky Way.
The vastness of the Universe is unimaginable, a massive expanse containing billions of galaxies, each of which contains billions of stars. The distances involved are difficult for us to comprehend, even one of our nearest galactic neighbors, Andromeda (pictured left), is 2.5 million light years away, a modern day spacecraft would have to travel for around 30 billion years to reach it. Some of the furthest known galaxies exist over 10 billion light years from Earth.
When you look at stars in the night sky you are looking into the past, the light from some of these stars can take thousands of years to reach us on Earth. With the right equipment you can see millions and even billions of years of history, we can even build a picture of what the Universe looked like just four hundred thousand years after the Big Bang. The mysteries of the Universe are beginning to unravel as new technology gives us a greater understanding of how it began, how it will evolve and how it will eventually end.

Birth of the Universe - Big Bang Theory

Before the Universe existed there was no space, time or matter, then 13.7 billion years ago an incredibly hot single point smaller than a subatomic particle containing all the matter in the Universe began expanding at an unimaginable rate creating space and time in a trillionth of a second. After this point the Universe continued to expand but at a much slower rate.

For thousands of years after the Big Bang the Universe, much smaller than it is today, was a super heated ball of plasma reaching temperatures of 300 million C (572 million F). After around 400,000 years the Universe had cooled down to 3000C (5400F) allowing hydrogen and helium nuclei to form atoms, at this point the Universe was around one thousandth the size it is now and resembled a huge glowing star scattering visible light in every direction. We know that the ancient light from this period has been stretched by the universe expanding space as it is no longer visible, even though it fills every part of the universe it has been stretched beyond visible light into the microwave and radio parts of the spectrum. Some of the static you hear today when tuning your radio are echoes of this ancient light, known as the Cosmic Microwave Background, or CMB.

Between half a billion and a billion years after the Big Bang the Universe had grown to around one fifth the size it is now, it began to darken and cool down to just a few degrees above absolute zero allowing atoms in the denser areas to bind together and eventually collapse under the force of their own gravity, leading to the formation of the first stars and cores of galaxies. Over the next 12.5 billion years the Universe filled with billions of galaxies each containing billions of stars and continues to expand.

Dark Matter

Many consider the Universe to be made up of galaxies, stars, planets and moons, the visible and directly detectable objects and particles that we can observe. This in fact is incorrect, visible matter only accounts for around 4% of the Universe. Scientists have discovered that there is a different type of matter called Dark Matter that is far more prevalent in the Universe, binding stars and galaxies together, making up around 23% of the Universe.

As its name suggests Dark Matter is dark and doesn’t interact with normal matter, billions of these particles could be streaming through your body right now and you wouldn’t know, in fact no Dark Matter has ever been directly detected. However scientists know that Dark Matter exists by observing how galaxies behave.

In the solar system a planet that is closer to the center, for example Mars, orbits quicker around the sun than a planet further from the center, for example Neptune. This is as a result of the gravitational forces being exerted on each orbiting body by the mass of other bodies. Since the sun is the most massive object in the solar system the closer the planet the higher its velocity will be, the further away the slower its velocity will be. If we add up the total mass of the solar system, which equals its total energy, the speeds that the planets travel around the sun makes sense.

This is not the case with galaxies, when we add up the total visible mass of a galaxy the speeds that the stars are travelling doesn’t make sense. Most stars in a galaxy travel at an almost constant speed, meaning that something that is closer to the center orbits at a similar speed to something further from the center. So galaxies are rotating at greater speeds than the gravitational effects of their visible mass would allow for, this cannot be explained without a far greater mass being involved. Scientists believe this extra mass is a halo of invisible Dark Matter which forms around galaxies keeping them bonded together and rotating at a constant speed.

Dark Energy

Up until the late 20th century it was thought that the rate the Universe was expanding must be slowing down due to the attractive forces of gravity. Then in 1998, due to observations by the Hubble Telescope it was discovered that the Universe is actually expanding quicker now than it was in the distant past. This unexpected discovery shook the world of science as they tried to figure out what was causing this accelerated expansion.

The solution was Dark Energy, an unknown property in the Universe that was affecting its expansion, creating space and sending galaxies away from each other. It is thought that around 73% of the Universe is made up of Dark Energy and is the dominant force, but we don’t actually know what it is. Even though we know it is there and how it affects the Universe it is still in essence a complete mystery.

The End of the Universe

Due to the passage of time everything has a lifespan, planets, stars and galaxies will all eventually cease to exist and the Universe and time itself will come to an end. As the Universe expands matter becomes more dispersed, the gases and material that make up stars will be scattered over larger distances, areas in the Universe that will have enough density to produce star forming regions will become less and less until eventually no new stars will be born.

By this time all the large stars and smaller sun like stars will be gone, all that will be left will be their burnt out remnants in the form of black holes and black dwarfs. The only stars that will remain will be the Red Dwarfs, small dim stars that burn their fuel at a very slow rate allowing them to exist for trillions of years. Any intelligent life that is lucky enough to be on a planet that orbits a Red Dwarf will look up at a black night sky, void of any bright points of light.

These Red Dwarfs too will eventually burn themselves out until only their core remains in the form of a faintly glowing ember known as a White Dwarf, these will be the only tiny points of light left in the Universe. The Universe will exist in this state for trillions of years, but even the small amount of light given off by these White Dwarfs will eventually fade to nothing as any remaining heat disappears. It is now a Black Dwarf, an incredibly dense object made from the cold ashes of a long dead star. These too will be broken down and dispersed until eventually absolutely no matter will remain in the Universe, not even a single atom. The Universe will be a cold, empty unchanging void as time itself will come to an end.

This can seem like a very depressing future but the good news for us is that it won’t happen for a very, very long time. The Universe will continue to form new stars and galaxies for trillions of years, if you consider that at the moment it is only 13.7 billion years old you begin to realize that the Universe is just in its infancy, a baby if you like. Its future in a sense has just begun.

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