Cosmology Experiment C-1

Synthesis of Elements in the Big Bang


The first book of Moses, commonly called Genesis, states In the beginning God created the heavens and the earth.  But it offers no details of how that was done.  Much later Thomas of Aquinas (d 1274 A.D.) in his Summa Theology suggested that God created observable evidence that could be used with reason to determine what had occurred.  While Saint Aquinas discussed the possibility of error in human reason, he also claimed that if done right, there would be no contradiction between revelation and what has become known as science.

Today, after much observation and much reasoning by some of the best human minds, much has been learned about how our universe and particularly the constituent building blocks called elements came to be.  While some people still reject this understanding, there is a strong consensus that the general explanations describe what nearly certainly happened.  What follows describes the best current understanding.  But as always, you as an individual can accept or reject all or any part as you so choose.  The intent is not to challenge any of your religious faith, but rather to provide explanation of what conscientious scientists have observed and concluded.

It is well understood that light travels at a very fast, but finite speed of 3.0 x 108 m/s.  So light coming to earth from some of the most distant objects visible in the sky carries with it information about the universe long ago.  In 1929 Edwin Hubble (1889-1953) realized from atomic spectra embedded in that light that the universe seems to be expanding.  About mid-century George Gamow (1904-1968) realized that the universe may have been expanding from having been nearly in a single point at some time in the past, a concept that Fred Hoyle (1915-2001) derisively called the Big Bang.  While originally very controversial, such overwhelming evidence has been gathered that most scientists now regard these as established fact.

The laws of physics require that the universe would have been much hotter earlier.  Light coming from the most distant parts of the universe carries evidence of what an extremely hot universe was like.  That evidence has been confirmed by experiments at the world's most powerful particle accelerators where collisions have comparable energy to those which would have also occurred shortly after such a Big Bang.  The consistent evidence gathered from many different sources has allowed physicists and chemists to piece together an understanding of how our current chemical elements were constructed.

Perhaps to understand what is known about the synthesis of elements it may be helpful to present a quick review of what the human race has discovered about the constituents of our material world.  Evidence was observed over many centuries leading John Dalton (1766-1844) to propose in 1801 that the ancient Greek concept of atoms is needed to account for mathematical ratios comparing the masses of elements in chemical compounds.  It took another century for the community of scientists to develop a consensus that matter is composed of miniscule particles must be right.  By 1896 J.J.Thomson (1856-1940) had found evidence of electrically charged particles inside atoms (now called electrons.)  By 1932 Ernest Rutherford (1871-1937) and James Chadwick (1891-1974) seemed to complete understanding of the interior of atoms with discovery of protons and neutrons respectively.  But the discovery of a whole zoo of similar particles over three decades led Murray Gell-Mann (1929- ) to propose in 1964 that protons and neutrons are each composed of three quarks.  Quarks have now been confirmed by much evidence.  Meanwhile physicists trying to unify and make logically consistent all that is known about the universe have proposed that everything must be composed of much smaller, perhaps 10-dimension strings.  Scientists are currently seeking ways to confirm or deny the existence of such things.

Evidence reaching us from the most distant, most far-back-in-time reaches of the universe suggest that after the first 10-12 of a second, with the temperature about 1016K, the universe was a high energy plasma of electrons, quarks, and similar particles.  Such quark plasma is currently being studied at Brookhaven National Laboratory by extremely high speed head-on collisions between heavy Au atoms.

In the remainder of the first second, cooled enough by the expanding universe, particles such as protons and neutrons formed.  Over the next hundred seconds, as the universe continued to expand and cool, nuclei of the simplest atoms formed.  But after that the average collisions speeds were insufficient to overcome the electrical repulsion between protons allowing additional or larger atomic nuclei to form.  There was still a considerable concentration of neutrons which were not prevented from fusion by electrical repulsion.  However, with a half life of less than 15 minutes, the neutrons were soon either fused or decayed to protons.  Scientists have been colliding protons and similar particles at particle accelerators around the world for decades meticulously measuring the conditions needed for each type of fusion reaction.  From these measurements it has been estimated that the early, hour old universe was composed mostly of 1H with 4He about 24% of the total mass, both 2H and 3He about 10-5 of the total, and 7Li about 10-10 of the total.  A variety of astronomical observations confirm these numbers.  Their agreement over nine orders of magnitude is both impressive and powerfully constrains the possibility of alternate explanations.  Note that none of the heavier elements such as Carbon, Nitrogen, Oxygen, or metals other than Lithium were formed in the early universe.  The synthesis of the rest of the elements will be explained in the following pages.Dalton's symbols


John Dalton used a series of partially filled in circles as symbols for the elements.  (Page from Dalton's notebook shown at right; Azote is still used in France for what in English is now called Nitrogen.Jöns Jakob Berzelius in Sweden proposed in 1813 proposed using letters for chemical symbols because they could be written more easily and did not disfigure the printed book.  Berzelius suggested using the initial letter of the Latin name of each element because Latin was used more widely than any other language for scientific terms..  Some elements are represented with a single capital letter:  e.g., C = Carbon, N = Nitrogen, O = Oxygen.  Because there are more elements than letters, it is necessary to use a combination of two letters to symbolize most elements.  When two elements start with the same letter, Berzelius suggested adding the next letter which they don't have in common.  To indicate the start of a new symbol, the first letter is always capitalized and any second letter is always lower case;  e.g., Cl = Chlorine, Cr = Chromium, Ca = Calcium, Cu = Cuprium (Latin) = Copper (English).  This system is still used by chemists today.

When isotopes were proposed independently in 1913 by Frederick Soddy (1877-1956, in England (see Soddy papers 1, 2, 3) and Kasimir Fajans (1887-1975) in Germany (see Fajans' paper), a system of subscripts and superscripts were added for atomic number and atomic mass respectively;  for example, 42He represents Helium, atomic number 2, with mass of 4.  The atomic number also describes the number of protons, 11p, in the nucleus while the balance of the mass number is accounted for by neutrons, 10n.  Thus this isotope of Helium has two protons and two neutrons as well.  Determine the number of protons and neutrons in the isotopes produced by the Big Bang.  You may need to look up the atomic number for each element.  Note that isotopes are two or more kinds of atoms that share the same number of protons.  Two or more kinds of atoms that share the same number of neutrons are called isotones. Two or more kinds of atoms that share the same atomic mass are called isobars.


To become familiar with the conventions for using isotope symbols, answer the following:

  1. Fill in the missing information in the Table
    symbol A (atomic mass) Z (atomic number) # of protons # of neutrons

  2. Select from the following list which pairs are isotopes, which are isobars, and which are isotones:

  3. In reactions involving elementary particles the sums of A (atomic mass) and Z (atomic number) after reaction remain the same as the sums before reaction.  This conservation of Z is described as conservation of electric charge.  Conservation of A is described as conservation of baryon number.  Scientists find such conserved properties immensely useful rules for predicting what could happen and what can't happen in our universe.  Use these conservation laws to predict the missing particle in the following reactions:
    1. 10n +             ⇒   21H
    2. 21H +             ⇒   32He
    3. 32He +             ⇒   42He

Communicating technical information such as observations and findings is a skill used by scientists but useful for most others.  If you need course credit, use your observations in your journal to construct a formal report.



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created 1/13/2005
revised 2/21/2005
by D Trapp
Mac made