What is the Anthropic Principle?
Question: What is the
Answer: Anthropic means “human” or “human existence.”
Principle means “law.” The Anthropic Principle is the “Law of Human
Existence.” It is well known that our existence in this universe
depends on numerous cosmological constants and parameters whose
numerical values must fall within a very narrow range of values. If
even a single variable were off, even slightly, we would not exist.
The extreme improbability that so many variables would align so
auspiciously in our favor merely by chance has led some scientists
and philosophers to propose instead that it was God who
providentially engineered the universe to suit our specific needs.
This is the Anthropic Principle: that the universe appears to have
been fine-tuned for our existence.
Consider protons for example. Protons are the positively charged
subatomic particles which (along with neutrons) form the nucleus of
an atom (around which negatively charged electrons orbit). Whether
by providence or fortuitous luck (depending on your perspective)
protons just happen to be 1836 times larger than electrons. If they
were a little bigger or a little smaller we would not exist (because
atoms could not form the molecules we require). So how did protons
end up being 1836 times larger than electrons? Why not 100 times
larger or 100,000 times? Why not smaller? Of all the possible
variables, how did protons end up being just the right size? Was it
luck or contrivance?
Or how is it that protons carry a positive electrical charge equal
to that of the negatively charged electron? If protons did not
balance electrons and vice versa we would not exist. They are not
comparable in size and yet they are perfectly balanced. Did nature
just stumble upon such a propitious relationship or did ingenuity
ordain it for our sakes?
Some examples of how the Anthropic Principle directly affects the
livability of our planet include:
The unique properties of water. Every known life form depends on
water. Thankfully, unlike every other substance known to man,
water’s solid form (ice) is less dense than its liquid form. This
causes ice to float. If ice did not float, our planet would
experience runaway freezing. Other important properties of water
include its solvency, cohesiveness, adhesiveness and other thermal
Earth’s atmosphere. If there was too much of just one of the many
gases which make up our atmosphere, our planet would suffer a
runaway greenhouse effect. On the other hand, if there were not
enough of these gases, life on this planet would be devastated by
Earth’s reflectivity or “albedo” (the total amount of light
reflected off the planet versus the total amount of light absorbed).
If Earth’s albedo were much greater than it is now we would
experience runaway freezing. If it were much less than it is we
would experience a runaway greenhouse effect.
Earth’s magnetic field. If it were much weaker, our planet would be
devastated by cosmic radiation. If it were much stronger, we would
be devastated by severe electromagnetic storms.
Earth’s place in the solar system. If we were much further from the
Sun, our planet’s water would freeze. If we were much closer it
would boil. This is just one of numerous examples of how our
privileged place in the solar system allows for life on Earth.
Our solar system’s place in the galaxy. Once again, there are
numerous examples of this. For instance, if our solar system was too
close to the center of our galaxy, or to any of spiral arms at its
edge, or any cluster of stars for that matter, our planet would be
devastated by cosmic radiation.
The color of our Sun. If the Sun were much redder on the one hand or
bluer on the other, photosynthesis would be impeded. Photosynthesis
is a natural biochemical process crucial to life on Earth.
The above list is by no means exhaustive. It is just a small sample
of the many factors which must be just right in order for life to
exist on Earth. We are very fortunate to live on a privileged planet
in a privileged solar system in a privileged galaxy in a privileged
The question for us now is, with so many universal constants and
cosmological parameters defining our universe, and with so many
possible variables for each one, how did they all just happen to
fall within the extremely narrow range of values required for our
existence? The general consensus is that we are either here by
fortuitous luck against tremendous odds or by the purposeful design
of an intelligent Agent.
Some proponents of the here-by-chance perspective have sought to
level the odds against fortuitous luck by hypothesizing a scenario
whereby our universe is just one among many in what has come to be
termed a “multiverse.” This gives nature many more chances to “get
it right,” bringing the odds against its success down significantly.
Imagine innumerable lifeless universes in which one or more of the
necessary variables fail to fall within the specific range of values
required for life. The idea is that nature would eventually get it
right, and apparently has done so as is evidenced by the fact that
we exist (or so the argument goes). We are the lucky ones whose
universe stumbled upon the right combination of cosmological values.
The Anthropic Principle is often cited as empirical grounds for the
otherwise mathematically hypothetical multiverse.
Intelligent Design Theorists hail the Anthropic Principle as further
evidence in support of their thesis that life was engineered by a
transcendent Mastermind. Not only do biological systems bear the
hallmarks of design (the information content of DNA, specified
complexity, irreducible complexity, etc), the universe which
supports and provides a context for life appears to have been
designed as a means to that end.
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