Transcript Anthropic Arguments

Anthropic Arguments
Science and Religion in Schools Project - Unit 4b
What is this?
 Statement of the Weak Anthropic principle (WAP)
“Various features of the Universe, such as its size, age etc. must be
consistent with the fact that we are here to observe them.”
 Sounds like an obvious statement!
 It acts as a ‘test case’ for theories and measurements
 Its not that the universe is wrong, it must be our measurements or
theories
 Classic example: the age of the Sun and the theory of evolution…
Kelvin vs. Darwin
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Kelvin estimated the age of the Earth from the age
of the sun (1819)
He got the age of the Sun by comparing the energy
it gives out with the energy he calculated went into
forming it in the first place
Came out with a figure of less than 500 million years
old
Wrote his paper in opposition to Darwin’s
Origin of Species (1816)
Disagreed with Darwin and had set out to show that
the Sun could not have shone for long enough to
allow evolution to get to mankind
Lord Kelvin, 1824 - 1907
Darwin hedges
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Sixth edition of Origin of Species:
“It is however, probable, as Sir William Thompson
[Lord Kelvin] insists, that the world at a very early
period was subjected to more rapid and violent
changes in its physical conditions than those now
occurring; and such changes would have tended to
induce changes at a corresponding rate in the
organisms which then existed”
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In other words, to make the theory consistent with the
Physics and our presence, assume that evolution
happened more rapidly in the past!
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This is an Anthropic argument
Statue of Darwin in
Shrewsbury
Biology wins in the end!
 We now know that the Sun is powered by
nuclear reactions
 This sort of Physics was totally unknown in
Kelvin’s time
“Is present knowledge relative to the behaviour of
matter under such extraordinary conditions as
obtained in the interior of the Sun sufficiently
exhaustive to warrant the assertion that no
unrecognized sources of heat reside there?”
Thomas Chamberlin 1899
 Nuclear reactions allow the Sun to be old
enough for evolution to take its time
Where did the Anthropic principle come from?
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First suggested by Brandon Carter in 1973
Proposed during the 500th birthday
celebrations of Copernicus
Followed up with a paper in 1974 “Large
Number Coincidences and the Anthropic
Principle in Cosmology”
Later suggested that the principle was
meant as a caution to astronomers and
cosmologists – when they construct theories
to explain observations they have to take
some basic biological facts into account
The WAP is a ‘biological selection effect’
Brandon Carter
Carter goes further…
 In later work, Carter goes to on to suggest a stronger version
of the Anthropic Principle
 The Strong Anthropic principle (SAP)
“The laws of nature and the physical constants in the
universe make it inevitable that some form of intelligent life
would have developed at some time in the universe’s history”
 This is a BIG STEP from the WAP
Fine tuning
You can’t prove the SAP
The SAP is not a selection effect
What is it?
A view about the universe based on observations:
 A large number of fortuitous circumstances had to come about
for life to evolve on Earth
 Various constants of nature need to be precisely a given value
for the universe to exist
 Some aspects of the laws of nature seem well disposed to
life’s formation
 The last two are examples of fine tuning
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Playing a game
 When scientists consider the Anthropic principle they are playing a sort
of game:
They imagine what the universe would be like if the laws of nature
were slightly different, or if the physical constants were different
 They can then calculate what the universe might have been like
 Big surprise!
Don`t need to change much for the universe to be radically different!
Why is this a surprise?
 Did not expect so many things to interlock
 Did not expect so many numbers to be critical
 Changing the mass of the electron by ~0.1% might change the
colour of grass, but not make the universe vanish!
 This is what is meant by fine tuning the universe
The Blue, blue grass of
home!
Examples?
 Many examples are quite technical
 Take the masses of protons, neutrons
and electrons
Mp – Mn ~ 2Me
 Much bigger and all protons decay into
neutrons – so no atoms
 Much smaller, and all protons would join
with electrons to make neutrons – so no
atoms
 Need the value 2Me ~0.1% of Mp
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This is fine tuning
Fred and the Sun…
Fred Hoyle
 Worked on how Carbon is made in
stars
 Carbon is important for life
 Fred worked out that Carbon could be
made in stars if it had the right
properties
 These properties are just right for the
temperatures found inside the core of a
star
 Stars are ‘tuned’ for Carbon production
Fred also wrote some
interesting science fiction!
Often quoted
“I do not believe that any scientist who
examined the evidence would fail to
draw the inference that the laws of
nuclear physics have been deliberately
designed with regard to the
consequences they produce inside stars.
If this is so, then my apparently random
quirks have become part of a deep-laid
scheme. If not, then we are back again
at a monstrous sequence of accidents”
Fred Hoyle 1915 - 2001
Anthropic principle goes large
 Book on the Anthropic Principle published
in 1986
 Huge volume considering many examples
of Anthropic arguments
 Really put the Anthropic principle on the
map
 Lots of detailed examples of Anthropic
thinking and fine tuning
What to make of it all?
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The Anthropic principle is an active
area of research with conferences
on Anthropic arguments in Physics
and in Biology taking place
SAP has certainly been part of the
current revival in Natural Theology
Some scientists take ‘fine tuning’
seriously, but only in the context of
multiple universes
A very English view…
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The Moderate Anthropic Principle
“The contingent fruitfulness of the universe
is a fact of interest calling for an
explanation”
John Polkinghorne