What about carbon?
From pages 69-72, The Heavenly Time Machine
The currently accepted standard model for
the universe posits that everything began with a so called "big
bang" about 15 billion years ago. The initial big bang universe
was very small, very dense and very hot. It consisted of energetic
matter particles mixed with radiation quanta in a hot mixture
at equilibrium distribution. New particles of matter constantly
sprang up out of E = mc^2 type energy-to-matter conversions,
and likewise matter was annihilated back into energy. This super
small, dense and hot universe expanded very quickly, and it cooled
as it expanded. Neutrons and protons started to stick around
at a temperature of ten million million (10^13) degrees on the
absolute Kelvin scale, where the energy of radiation photons
equals the rest-mass energy of neutrons and protons, and the
environment was cool enough not to turn all of these back into
radiation. This is the beginning of the element hydrogen. The
energetic high temperature neutrons and protons knocked into
each other frequently. And when the collisions were just right,
they stayed together. We now have the formation of helium-4,
consisting of two protons and two neutrons. In the meantime,
the universe was expanding and cooling very quickly. In fact,
this process proceeded so quickly that the temperature and density
soon dropped below the point where higher level elements could
form. The result is that the matter of the early universe consisted
of about 74% hydrogen, 26% helium (by weight) and very little
of anything else. So where does all the other stuff come from?
It was cooked in stars and spread out in supernova explosions.
Let's take a look at what it takes to get
a supernova and the implications of our being around to talk
about it. A heavy star gets more compressed and hotter as it
burns more and more complex elements. Finally, at a temperature
of over a billion degrees, silicon is transformed into iron-56,
and the process ends. Soon the iron core of the star is compressed
with enormous force, as gravity takes over without the counterbalance
of the heat and pressure from the burning fuel. The iron turns
into a ball of pure neutrons. But neutrons have a very much more
compact structure than iron, and the whole core collapses in
size. A ball about the size of the sun suddenly collapses to
the size of a large mountain. We now have a neutron star core.
The surrounding material falls onto the neutron star core at
a speed which is an appreciable portion of the speed of light,
and the shock wave tries to squeeze the neutron core even further.
But the core cannot really be compressed, and it bounces back
in an enormous explosion which is the beginning of the supernova
process.
But now we have a problem. The reaction from
the neutron core is not strong enough to scatter all the surrounding
material, including the life-giving carbon, into the cosmos.
The reverse shock wave needs a boost. The boost comes from a
heavy flood of neutrinos. Neutrinos are very strange particles.
They simply don't interact with matter. So how come there is
an interaction in this case? Everything works out just right,
provided the weak force is of exactly the right value. The weak
and strong forces, electromagnetism and gravity are the four
basic forces of this universe. Change the weak interaction a
tiny bit to one side or the other, and we would not be here.
The same weak interaction is also involved in determining the
ratio of hydrogen to helium in the early universe. We need both
supernovae and a reasonable amount of helium, and the range of
weak interaction that permits this is very narrow. So why is
the universe this way? I do not know.
Now comes the interesting story of that element
of life, carbon. Helium is a very stable element. It is so stable
that for a while physicists thought that it was a fundamental
particle, and it was named the alpha particle. Carbon has a mass
number 12, and consists of three helium atoms stuck together
in a stable configuration. Unfortunately, two helium atoms, which
make beryllium, are very much unstable. The stuff sticks around
for less that 10^–16 of a second before disintegrating.
It takes an additional neutron to make stable beryllium-9. Therein
lies our problem. A collision of stable beryllium-9 with helium-4
will not add up to carbon-12. The unstable beryllium-8 does not
last long enough to permit any reasonable level of carbon formation
by interaction with helium. Finally, the odds of three helium
atoms hitting each other simultaneously in just the right way
to stick together as carbon is out of sight. It looks like there
isn't any way to make carbon. And as noted, without carbon there
is no life. Now, it is important to understand that without carbon
there is still a universe. It does not even look very different
from what we have, on a superficial level. The basic fuel for
stars is here, and the stars burn very nicely. The only important
difference is that we are not around to enjoy it. But we know
that we are, in fact, around. And we know that there is lots
of carbon around. So where did it come from?
In 1954, Fred Hoyle of Cambridge proposed
a solution. He suggested that there is a resonance between helium-4,
beryllium-8 and carbon-12. A resonance describes an effect where
one gets a big result from a relatively small effort. Pluck a
string in a certain way and you get a big sound for a small pull;
do it some other way and it goes flat. Taking into account the
mass-energy of each nucleus, and the calculated kinetic energy
of the moving particles based on the temperature in the star,
Hoyle predicted a hitherto unsuspected energy level, at 7.82
million electron volts, in the carbon-12 nucleus that would cause
a resonance for the combined energies of the three elements.
This resonance causes three helium-4 particles to stay together
just a bit longer than usual, and that is long enough for these
to rearrange themselves into the compact and stable configuration
of carbon-12. The prediction was tested in the laboratory and
found to be correct. The question to ask is, what is it in the
basic laws of the universe that requires this resonance, involving
three elements and the conditions inside a star, to be there?
Why not have a universe without carbon? We do not know the answer.
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