theists have claimed that the constants of physics had to have been
finely tuned by God for life in the universe to be possible. In my June
2009 column I showed that many of these claims are based on an improper
analysis of the data. Even some of the competent scientists who write on
this subject commit the fallacy of varying just one parameter and holding
all the others constant. When you allow all parameters to vary, you
find that changes to one parameter can be easily compensated for by
changes to another, leaving the ingredients for life in place. This
point is also made nicely in a recent Scientific
American cover story by Alejandro Jenkins and Gilad Perez. In this column I will discuss
perhaps the most cited example of claimed fine-tuning, the Hoyle resonance.
1953 the famous astronomer Fred Hoyle calculated that the production
of carbon would not occur with sufficient probability unless that probability
was boosted by the presence of an excited nuclear state of C12 at about
7.7 MeV. In what appeared to be a remarkable victory for anthropic reasoning,
the existence of such a state was quickly confirmed experimentally.
Anthropic reasoning is inferring that some property of nature must exist
for life, as we know it, to be possible. The Hoyle prediction has been
regarded by theists and others as a miraculous example of the fine-tuning
of the constants of physics needed to make life possible. As Hoyle,
a professed atheist, remarked:
sense interpretation of the facts suggests that a superintellect has
monkeyed with physics, as well as with chemistry and biology, and that
there are no blind forces worth speaking about in nature. The numbers
one calculates from the facts seem to me so overwhelming as to put this
conclusion almost beyond question.
You will find the Hoyle
resonance, usually accompanied by the above quotation, prominently
included in every discussion about fine-tuning. Let us examine the scientific
facts in more detail.
Fig. 1(a) shows
two energy levels: (1) the amount by which the total rest energy of
Be8 + He4 exceeds that of C12, which is 7.3367 MeV; (2) the excited
state of C12 predicted by Hoyle and observed
at 7.656 MeV. Note that Hoyle did not predict this value exactly but
estimated that the energy level should be around 7.7 MeV.
it is often claimed that this excited state has to be fine-tuned to
precisely this value in order for carbon-based life to exist. This is
not true. Life might be possible over a range of carbon abundances.
1989 Mario Livio and his collaborators performed calculations to test
the sensitivity of stellar nucleosynthesis to the exact position of
the observed C12 excited state. They determined that a 0.06 MeV
increase in the location of the level to 7.716 MeV would not significantly
alter the carbon production in stellar environments. A decrease by
the same amount to 7.596 MeV was needed before the carbon production
increased significantly above its value in our universe. This range
is shown in Fig. 1(b). Already we can see the excited state is not very
we note that the problem is not to obtain the exact amount of carbon
in our universe but just sufficient carbon production for life. We get
more carbon when the Hoyle energy level is even lower. Furthermore,
Livio et al. showed that the energy level can be increased by as much
as 0.277 MeV to 7.933 MeV before insufficient carbon is produced. As
Fig. 1(c) shows, an excited state anywhere from this energy down to
near the minimum energy would produce adequate carbon. In short, no
fine-tuning was necessary to produce sufficient carbon in stars for
life as we know it to be possible. While nuclear theorists are unable
to calculate the precise energy level of the Hoyle resonance, they know
enough about how the carbon nucleus is formed to show that a resonance
in the allowed region is very likely.
et al., “A State in C12 Predicted From Astronomical Evidence,” Physical Review Letters 92 (1953): 1096.
et al., “The Anthropic Significance of the Existence of an Excited
State of C12,” Nature 340 (1989): 281–86.
Jenkins and Gilad Perez, “Looking for Life in the Multiverse: Universes
with Different Physical Laws Might Still Be Habitable,” Scientific American (January, 2010): 42–49.