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

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

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”

In other words, to make the theory consistent with the Physics and our presence, assume that evolution happened more rapidly in the past!

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?

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

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

This is fine tuning

Fred and the Sun… 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 Hoyle

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?

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…

The Moderate Anthropic Principle

“The contingent fruitfulness of the universe is a fact of interest calling for an explanation”

John Polkinghorne