Dependence

In billions of galaxies the universe made itself from dust stars from stars dust.

Much later, from dust from stars from dust from stars from dust swirled our Sun and from leftovers the Earth, our home.

Thus, after ten billion years, there was evening and there was morning: the first day.

After some ten billion years, two-thirds of the history of the universe so far, the Earth and the Sun formed. As far as the Earth is concerned, it was not until then that there is a first day. If we are interested in a religious or secular view of our own lives, those first ten billion years without days may seem dull and unimportant. The utmost limit we already have discussed in the preceding scenes, while humans and human cultures are not to appear on the scene for a long time. However, by paying attention to this long period without humans we may become aware of the extent of our dependence upon the larger universe in which we live, move and have our being.

In the first few minutes of its existence - speaking in terms of the Big Bang model - the universe was as hot as the inside of stars. New nuclei formed and broke apart. At the end of those 'first three minutes' ordinary matter in our universe consisted mainly of electrons, protons (becoming the nuclei of hydrogen atoms) and the nuclei of a few of the lighter elements, especially helium. A few hundred thousand years later the temperature had dropped sufficiently for the next big step; out of nuclei and electrons hydrogen and helium atoms formed. Then the universe became transparent; light was no longer scattered continuously by matter.

Matter was distributed very homogeneously. However, there must have been some clumpiness, some minor inhomogeneities. The description and explanation of those is one of the most active areas of research in cosmology. The presence of such inhomogeneities is important. Small concentrations of matter attract more matter, and thereby become the beginnings of (groups of) galaxies.

Within a galaxy there are huge clouds of hydrogen. Gravity makes such a cloud collapse. After millions of years, a dense ball of gas forms. The temperature rises and nuclear fusion takes off. Through this process energy is released - a star is born. The star does not collapse any further; nuclear energy provides enough pressure to withstand gravity.

A star can be understood, unromantically, as a nuclear fusion reactor, merely kept together by gravity. In the core of a star like the Sun, nuclei of hydrogen fuse and form helium with a mass equivalent to four hydrogen nuclei. In our Sun, this process will be going on for about ten billion years; the Sun is about halfway through this life cycle. In bigger stars the temperature and density inside is higher and the transmutation faster.

When the available hydrogen in the core has been used, the energy production stops, the pressure thus generated falls away, and the star will continue its gravitational collapse. In consequence, the density and temperature rise even further. Under these circumstances, helium nuclei will merge, resulting in heavier elements such as carbon and oxygen. This process too releases energy. The star will settle in a stable state for a time, until the supply of helium has been exhausted. After a further collapse (and increasing density and temperature), new fusion processes will take off. In this way, heavier elements such as carbon, oxygen, and phosphorus are formed inside stars until the process results in iron. Further fusion would not produce energy; rather, for heavier nuclei (such as uranium) fission releases energy.

When the 'fuel' inside stars has been converted from hydrogen to heavier elements, the star will collapse under its own weight. This generates a huge amount of heat, resulting in an explosion. For a few weeks the star will burn very brightly, as if there is a very bright new star in the heavens - this is called a supernova. During the explosion the heavier (and rarer) elements such as gold, lead and uranium are formed. In the explosion, the outer layers of the stars are blown away. The remnant may be a dwarf star. If there is enough mass left, it may also become a very dense neutron star, or even a black hole, a concentration of mass so compact that not even light can escape its gravitational pull.

We humans have a special interest in the dust blown away during such explosions. The explosion injects the elements formed inside the star into the interstellar gas. While only hydrogen and helium formed during the first few minutes of the universe, the interstellar gas thus came to contain traces of other elements. These are included in stars of the second generation, which also form from interstellar clouds. These second generation stars at the end of their career further enrich the interstellar plasma.

Our Sun is a star of a later generation. In 1814 the German optician Joseph Fraunhofer made a spectrum of the light of the Sun. (A spectrum is an image in which the different colours, from red to violet, are spread out as the colours of the rainbow.) Fraunhofer discovered dark bands in the spectrum of the Sun. Every set of lines relates to a particular element. In this way, scientists in the nineteenth century discovered that the Sun contains iron, calcium, magnesium, sodium, nickel and chrome. In 1868 an unknown element was discovered in the spectrum of the Sun; it was named 'helium'. In 1895 it was isolated on Earth.

Traces of heavier elements, produced in earlier generations of stars, can be found in the spectrum of the Sun. These elements also form the basis of the planets, including Earth, and they are the basis for all life on Earth, since life is dependent upon carbon, oxygen, phosphorus and much more. All these elements have been formed through nuclear fusion in earlier stars. The only exception are the hydrogen atoms, present for instance in water. For the other elements we owe our existence to the perishing of stars we have never seen. We are not just dust of the earth (Genesis 2:7), but dust from stars from dust from stars from dust. Gratitude might well extend beyond our parents and grandparents to include even the stars that burned long before the Sun began to shine.

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