Where We All Come From
If you would like to know where you really come from - please read on...
| Astronomers have developed
a description of our universe that seems consistent with
their observations up to now. According to this description, only 5% of the universe exists as ordinary or "baryonic" matter. So all of the stars and galaxies, all of the things we see, including all life on Earth make up only 5% of what's out there, according to modern cosmology. The rest of the universe seems to be made of dark matter and dark energy -- whose effects astronomers can detect -- but which otherwise can't be seen. So what we're trying to do, is we're trying to make more and more precise measurements of the universe, both locally and in very early times, to try and place more and more precise constraints on this cosmological model and to try to find kinks in the armour that will actually tell us, to point us the way to hopefully some description of what dark energy and dark matter are. For the first time, astronomers are making precise measurements of the composition of the entire universe. Astronomers believe that the early universe, nearly 14 billion years ago, was hot and dense. They picture it as what's called a "plasma" -- not whole atoms but parts of atoms -- a hot, dense sea of protons and electrons -- forged in the Big Bang. Ultimately, the universe expanded and cooled enough to let the electrons and protons recombine as the element hydrogen. At that point, radiation was released and began to travel freely through space. With sensitive-enough instruments, scientists can still see that radiation pervading the universe. This is the "cosmic microwave background radiation". And so when we look out, with our telescopes looking at this cosmic background radiation, what we're seeing, is we're seeing radiation that was emitted when the universe underwent this transition and became transparent, when it was only about 400,000 years old. So what's happened is that radiation has now travelled to us over 13+ billion years... And what it brings to us is the information that is encoded, what the density fluctuations in the universe looked like at that very early time. These tiny fluctuations are the seeds from which the stars and galaxies we know today arose. |
Eventually the gravitational pressure at the ball's core is powerful enough to squeeze hydrogen atoms close enough together to form helium atoms - a process that releases tremendous amounts of energy - the ball begins to shine, and a star is born! It's that simple. To create stars, like the Sun, all you need is enough hydrogen to come together through gravity. Take for example a star that starts off with a mass 25 times that of the Sun: - after about 7 million years all of the hydrogen
in its core will be converted to helium, The enormously powerful forces inside huge stars such as these cause the fuel to be consumed rapidly, and they lead relatively short lives of a few million years. What though about a star that starts off with a mass only 0.5 times that of the Sun? Well, after such a star's hydrogen has all been fused into helium, fusion stops and the helium star just cools off - not enough matter exists to produce the powerful forces required to take the process further. The life cycle of a star therefore, depends on its initial mass. The Sun happens to be
of a size that makes it extremely stable - it will take 10 billion years to convert its
entire hydrogen core to helium. And that's one of the reasons we
are here. Yet all living things, including ourselves, are made up of a lot more than just hydrogen and helium
- where did all the other stuff we are made of come from? We know that inside stars with masses less than 8 times that of the Sun the fusion process stops with the formation of carbon. Such stars then begin to slowly shed their remaining outer layers of hydrogen and helium (creating gas clouds we call planetary nebulae), revealing their carbon cores, which we call white dwarfs. This will be the eventual fate of the Sun. Yet when a star starts off with a mass more than 8 times that of the Sun, fusion in its core continues all the way to the formation of iron. In the course of this activity various 'shells' of matter exist around the core, like layers of an onion, all falling inwards - each an element in the process of being fused into the next. Then quite suddenly, during the single day that the core of silicon is converted into iron, everything changes. Instead of releasing energy, when iron atoms are squeezed together they actually start to absorb energy! This means the violent outward explosive force that had for so long been counter-balancing the star's inward pull of gravity, suddenly ceases....and hurtling in towards the now solid iron core, at velocities of up to a quarter the speed of light, come billions and billions of tons of remaining silicon, oxygen, carbon, helium and hydrogen.... Within a matter of seconds the incoming matter slams into the solid core of the star with such powerful intensity that it rebounds and creates one of the most violent explosions possible in nature - a supernova, a release of energy so great that the exploding star momentarily outshines a billion other normal stars in its galaxy. This release of energy is actually so intense that it triggers a final chain of powerful fusion reactions in the outgoing matter - creating everything from phosphorous to magnesium to sulphur to silver to gold - in fact all 92 of the naturally occuring elements. And that is the stuff we are actually made of - star stuff. In time, all this scattered material gradually begins accumulating again through gravity. A swirling mass of gas and dust starts to form with a young star in the middle, blowing the lighter elements outwards, creating gaseous planets like Jupiter and Neptune, and keeping the heavier elements inwards, creating rocky worlds like Venus and the Earth - our home and cradle. It's that simple. To create planets like the Earth, all you need is for the leftover remains of supernovae to come together through gravity. Again, no all-powerful Being is required.
"A human being is part of a whole, called by us the "Universe," a
part limited in time and space. |
 |