Planets & Life

Planets & Life

PHYS 214

PHYS 214

Dr Rob Thacker

Dr Rob Thacker

Dept of Physics (308A)

Dept of Physics (308A)

thacker@

astro.queensu.ca

thacker@

astro.queensu.ca

Please start all class related emails with

Please start all class related emails with ““214:

214:””

Today

Today’’ s Lecture

s Lecture

��Life in Cosm

os: The

Life in Cosm

os: The Anthropic

AnthropicCosm

ological

Cosm

ological

Principle

Principle

��We

We ’’ll discuss a number of philosophical issues today

ll discuss a number of philosophical issues today

��(N

ext week we

(Next week we ’’ll start working from the book)

ll start working from the book)

If you want to make an apple pie from scratch,

you must first create the universe.

Carl Sagan

Preface

Preface

��Science has been phenomenally successful at explaining

Science has been phenomenally successful at explaining

the features of the observed Universe in the last 40 or

the features of the observed Universe in the last 40 or

so years

so years

��DNA

DNA

��Big Bang

Big Bang……

and so on

and so on……

��We now (tend to) believe that there is a fully scientific

We now (tend to) believe that there is a fully scientific

explanation for anything we observe

explanation for anything we observe ……

��Yet, as we

Yet, as we ’’ll see in this course, certain aspects of the

ll see in this course, certain aspects of the

Universe appear strongly at odds with the idea that

Universe appear strongly at odds with the idea that

humanity is

humanity is ““average

average ””

��Some of the ideas in this lecture m

ay seem totally crazy

Some of the ideas in this lecture m

ay seem totally crazy

––that

that’’ s O

K, some of them

s OK, some of them

areare

Ptolemaic Cosmology

Ptolemaic Cosmology

��This is a geocentric view of

This is a geocentric view of

the Universe

the Universe

��Planets, Sun, stars

Planets, Sun, stars etc.

etc.are all

are all

view

ed as revolving around

view

ed as revolving around

the Earth

the Earth

��Actually predicting orbits

Actually predicting orbits

was very difficult in this

was very difficult in this

model because it is

model because it is

obviously wrong

obviously wrong

��Nonetheless, its moderate

Nonetheless, its moderate

successes made it attractive

successes made it attractive

for hundreds of years

for hundreds of years

Earth at the center, the Moon

Mercury, Venus, Sun, Mars,

Jupiter, Saturn and lastly

the fixed Stars

The Copernican Principle

The Copernican Principle

��Prior to the 16

Prior to the 16

ththcentury the philosophical

century the philosophical

view

of the Cosm

os was

view

of the Cosm

os was Ptolemaic

Ptolemaic

��Placing the Earth at the centre of the Universe

Placing the Earth at the centre of the Universe

also influenced philosophical thought about how

also influenced philosophical thought about how

special the Earth was

special the Earth was

��Nicolaus

NicolausCopernicus (1473

Copernicus (1473-- 1543) is credited advancing the idea

1543) is credited advancing the idea

that the Earth is

that the Earth is not special

not special

��This idea lead to him showing the motions of the planets could b

This idea lead to him showing the motions of the planets could be e

explained by a Solar System with the Sun at its center

explained by a Solar System with the Sun at its center

��The step lead to the

The step lead to the ““Copernican Revolution

Copernican Revolution””

��The same idea can be extended to Cosm

ology, and is partially

The same idea can be extended to Cosm

ology, and is partially

motivation for the Cosm

ological Principle

motivation for the Cosm

ological Principle

(Copernicus was a Catholic Cleric)

Mediocrity Principles

Mediocrity Principles

��The philosophy underlying the Copernican revolution

The philosophy underlying the Copernican revolution

can be extended

can be extended

��There is nothing special about the Human Race

There is nothing special about the Human Race

��There is nothing special about the Earth

There is nothing special about the Earth

��There is nothing special about the Sun

There is nothing special about the Sun

��There is nothing special about the Milky Way

There is nothing special about the Milky Way

��and so on

and so on……

��Most scientists like to adopt this stance

Most scientists like to adopt this stance

��Im

plying we aren

Implying we aren’’ t special means that we expect physical law

s t special means that we expect physical law

s

we derive to be typical of elsewhere

we derive to be typical of elsewhere

The fundamental constants of nature

The fundamental constants of nature

��There are many (unexplained) constants used in

There are many (unexplained) constants used in

the equations for the physical forces

the equations for the physical forces

��e.g.

e.g.GG, N

ewton

, New

ton’’ s gravitational constant, or the unit of

s gravitational constant, or the unit of

charge on the electron,

charge on the electron, ee

��If any of these values were changed

If any of these values were changed --by even a

by even a

small am

ount

small am

ount --stars would not form

stars would not form

��Since the form

ation of stars is a precursor to the

Since the form

ation of stars is a precursor to the

form

ation of life,

form

ation of life, is the Universe in fact tuned

is the Universe in fact tuned

to form life

to form life??

Are we, in fact, special in some way?

Are we, in fact, special in some way?

Selection effects

Selection effects

��Before drawing conclusions from any scientific process

Before drawing conclusions from any scientific process

we must always be aw

are of possible

we must always be aw

are of possible observational biases

observational biases

��Suppose a

Suppose a ratcatcher

ratcatcher

tells you that all rats are longer

tells you that all rats are longer

than six inches

than six inches……

��Your first reaction should be to check the size of his traps!

Your first reaction should be to check the size of his traps!

��Similarly, just because your highest probability of seeing

Similarly, just because your highest probability of seeing

an elephant is in a zoo

an elephant is in a zoo……

��Doesn

Doesn’’ t m

ean all elephants are in zoos

t mean all elephants are in zoos

��Or even that m

ost elephants are in zoos

Or even that m

ost elephants are in zoos

Suppose the fundamental constants

Suppose the fundamental constants

were slightly different

were slightly different

��If gravity was weaker, stars wouldn

If gravity was weaker, stars wouldn’’ t collapse as fast or

t collapse as fast or

get as hot

get as hot

��If electromagnetism was different matter might repel

If electromagnetism was different matter might repel

too strongly to form

stars

too strongly to form

stars

��If we can

If we can’’ t form

stars we can

t form

stars we can’’ t form

elements

t form

elements ““heavier

heavier””

than

than HeHe, such as

, such as O,Si,Al,Fe

O,Si,Al,Fethat m

ake up m

uch of the

that m

ake up m

uch of the

Earth

Earth

��Without the Earthlike planets

Without the Earthlike planets we can

we can’’ t form life as we know

t form life as we know

itit

��Thus if we change the constants

Thus if we change the constants we won

we won’’ t be here to see

t be here to see

them

them

What about the age of the Universe?

What about the age of the Universe?

��After we have form

ed

After we have form

ed H,He

H,Hefollowing the Big Bang the only

following the Big Bang the only

place hot enough left to form

heavy elements is the center of

place hot enough left to form

heavy elements is the center of

stars

stars

��HH

and

and HeHeare fused into progressively heavier elements (we

are fused into progressively heavier elements (we ’’ll ll

talk about this later in the course)

talk about this later in the course)

��The most m

assive stars die in supernova explosions that

The most m

assive stars die in supernova explosions that

distribute the heavy elements into the space between stars

distribute the heavy elements into the space between stars

��This m

aterial can later be used to form

planets

This m

aterial can later be used to form

planets

��Scientists estimate this has to take between 4

Scientists estimate this has to take between 4-- 8 billion years

8 billion years

��By this time the Universe has to be extrem

ely large

By this time the Universe has to be extrem

ely large

��Another selection effect!

Another selection effect!

A more biological perspective

A more biological perspective

��Aside from the

Aside from the

form

ation of stars,

form

ation of stars,

the chem

istry that

the chem

istry that

results from the

results from the

values of the

values of the

fundam

ental

fundam

ental

constants is

constants is

responsible for the

responsible for the

form

ation of DNA

form

ation of DNA

Speed of light

Newton’s Gravitational

Constant

Charge of the electron

Planck’s constant

So let

So let ’’s think about ourselves for a

s think about ourselves for a

second

second……

��We are a carbon

We are a carbon-- based

based lifeform

lifeform

that was

that was

produced via evolution

produced via evolution

��Living on an Earthlike planet

Living on an Earthlike planet

��Revolving around a yellow dwarf star

Revolving around a yellow dwarf star

��Revolving around the center of a spiral galaxy

Revolving around the center of a spiral galaxy

��Evolving in a Universe capable of form

ing

Evolving in a Universe capable of form

ing

structures like stars and galaxies

structures like stars and galaxies

��In a universe with roughly 10 H atoms for each

In a universe with roughly 10 H atoms for each

He

He

A pretty strong set of selection effects

The Weak

The Weak Anthropic

AnthropicPrinciple(WAP

Principle(WAP))

““ The observed values of all physical and

The observed values of all physical and

cosmological quantities are not equally

cosmological quantities are not equally

probable but they take on values restricted

probable but they take on values restricted

by the requirement that there exist sites

by the requirement that there exist sites

where

where carbon

carbon-- based life

based lifecan evolve and by

can evolve and by

the requirements that the Universe be old

the requirements that the Universe be old

enough for it to have already done so.

enough for it to have already done so. ””

Barrow & Tipler

An immediate consequence

An immediate consequence

��The possibility of biological evolution is strongly

The possibility of biological evolution is strongly

dependent upon the global structure of the

dependent upon the global structure of the

Universe

Universe

��This is really a restatement of the apple pie

This is really a restatement of the apple pie

statem

ent!

statem

ent!

��The existence of life may be no m

ore, but no

The existence of life may be no m

ore, but no

less, rem

arkable than the existence of the

less, rem

arkable than the existence of the

Universe

Universe

Common Sense

Common Sense

��At the end of the day, the Weak

At the end of the day, the Weak Anthropic

Anthropic

Principle is merely a statem

ent of common sense

Principle is merely a statem

ent of common sense

��““If things were different, we wouldn

If things were different, we wouldn’’ t be here to see

t be here to see

them

them

””

��This fact has frustrated some researchers, here is

This fact has frustrated some researchers, here is

a statem

ent from a fam

ous book on cosm

ology:

a statem

ent from a fam

ous book on cosm

ology:

““It is unclear to one of the authors how a concept as lame

It is unclear to one of the authors how a concept as lame

as the

as the ““anthropic

anthropicidea

idea””was ever elevated to the status of

was ever elevated to the status of

a principle.

a principle.””

Fun Frank Zappa Joke

Fun Frank Zappa Joke

““Some scientists say that the major building

Some scientists say that the major building

block of the universe is hydrogen because

block of the universe is hydrogen because

it's the most plentiful element, but my

it's the most plentiful element, but my

theory is that the universe is made out of

theory is that the universe is made out of

stupidity, because it is more plentiful than

stupidity, because it is more plentiful than

hydrogen

hydrogen

””

Explaining the values of the

Explaining the values of the

fundamental constants

fundamental constants

��One of the major goals of fundam

ental physics

One of the major goals of fundam

ental physics

is to explain the values held by these constants

is to explain the values held by these constants

��That said, no accepted scientific theory has been

That said, no accepted scientific theory has been

able to explain these values with any success

able to explain these values with any success

��In response to this, and the fact that the

In response to this, and the fact that the

form

ation of stars is so finely tuned, one

form

ation of stars is so finely tuned, one

cosm

ologist (Brandon Carter) has suggested that

cosm

ologist (Brandon Carter) has suggested that

““The Universe must be such as to admit the creation of

The Universe must be such as to admit the creation of

observers within it at some stage

observers within it at some stage ””

The Strong

The Strong Anthropic

AnthropicPrinciple(SAP

Principle(SAP))

““The Universe must have those properties

The Universe must have those properties

which allow life to develop within it at some

which allow life to develop within it at some

stage in its history

stage in its history””

Barrow & Tipler

Implications of the SAP

Implications of the SAP

��There are at least three possible interpretations of what

There are at least three possible interpretations of what

the SAP m

ight mean

the SAP m

ight mean

��The first is a classic design argument

The first is a classic design argument

��““ There exists one possible Universe 'designed' with the goal of

There exists one possible Universe 'designed' with the goal of

generating and sustaining 'observers.

generating and sustaining 'observers. ‘‘""

��This implies that the purpose of the Universe is to give

This implies that the purpose of the Universe is to give

rise to intelligent life, with the laws of nature set to

rise to intelligent life, with the laws of nature set to

ensure that life as we know it will emerge

ensure that life as we know it will emerge

��This is of course strongly counter to m

ost m

odes of

This is of course strongly counter to m

ost m

odes of

scientific thought and as a scientist you should really

scientific thought and as a scientist you should really

feel uncomfortable with this statement

feel uncomfortable with this statement

SAP Implications II

SAP Implications II

��““ O

bservers are necessary to bring the Universe into

Observers are necessary to bring the Universe into

being.

being.““

��This is an apparently crazy idea stemming from

This is an apparently crazy idea stemming from

quantum m

echanics

quantum m

echanics ––I won

I won’’ t discuss it further

t discuss it further

��““ A

n ensemble of other different universes is necessary for

An ensemble of other different universes is necessary for

the existence of our Universe.

the existence of our Universe.““

��Many different

Many different ““parallel

parallel ””Universes have to exist

Universes have to exist

to create our particular Universe

to create our particular Universe

Why so much interest in this idea?

Why so much interest in this idea?

��Scientists studying the Big Bang (such as Stephen

Scientists studying the Big Bang (such as Stephen

Haw

king) have a very hard time making sense of the

Haw

king) have a very hard time making sense of the

mathem

atics involved

mathem

atics involved

��The invocation of an

The invocation of an Anthropic

AnthropicPrinciple m

ay help to

Principle m

ay help to

simplify the math

simplify the math

��i.e. w

e only allow this range of numbers and not a larger one

i.e. w

e only allow this range of numbers and not a larger one

��Some theories associated with the Big Bang start with

Some theories associated with the Big Bang start with

as m

any as 11 dimensions and an

as m

any as 11 dimensions and an Anthropic

AnthropicPrinciple

Principle

seem

s to be the only way of throwing aw

ay all those

seem

s to be the only way of throwing aw

ay all those

useless dim

ensions and leaving us with the 4 we have

useless dim

ensions and leaving us with the 4 we have

Problems, problems

Problems, problems ……

��Design arguments seem to always be a last resort

Design arguments seem to always be a last resort

in science

in science

��When we do not understand

When we do not understand something,

something,a a

natural reaction is to suggest something must be

natural reaction is to suggest something must be

that way because of an underlying purpose

that way because of an underlying purpose

��This bears similarities to Intelligent Design

This bears similarities to Intelligent Design

ideas, although the

ideas, although the Anthropic

AnthropicPrinciples try to

Principles try to

strongly resist the idea of any

strongly resist the idea of any ““higher being

higher being””

Even more unusual

Even more unusual ……

��Before we finish I

Before we finish I’’ ll present two final

ll present two final Anthropic

Anthropic

Principles

Principles

��One is m

oderately interesting, the last one is an

One is m

oderately interesting, the last one is an

amusing poke at the whole concept

amusing poke at the whole concept

Final

Final Anthropic

AnthropicPrinciple (FAP)

Principle (FAP)

““ Intelligent information

Intelligent information-- processing must

processing must

come into existence in the Universe, and,

come into existence in the Universe, and,

once it comes into existence, it will never die

once it comes into existence, it will never die

out

out ””

Barrow & Tipler

Humour

Humour : The Completely

: The Completely Rediculous

Rediculous

Anthropic

AnthropicPrinciple (CRAP)

Principle (CRAP)

��The mathem

atician M

artin G

ardner quoted the last two

The mathem

atician M

artin G

ardner quoted the last two

lines of the book by Barrow &

lines of the book by Barrow & Tipler

Tipler

��““At the instant the

At the instant the Omega Point

Omega Pointis reached, life

is reached, life

will have gained control of

will have gained control ofall

all matter and forces not

matter and forces not

only in a single universe, but in all universes whose

only in a single universe, but in all universes whose

existence is logically possible; life will have spread

existence is logically possible; life will have spread

intointoall

all spatial regions in all universes which could

spatial regions in all universes which could

logically exist, and will have stored an infinite

logically exist, and will have stored an infinite

amount of information, including

amount of information, includingall

all bits of

bits of

knowledge which it is logically possible to know.

knowledge which it is logically possible to know.

And this is the end.

And this is the end. ””

Summary of lecture 6

Summary of lecture 6

��When conducting any scientific experiment you m

ust always be

When conducting any scientific experiment you m

ust always be

careful to avoid selection effects

careful to avoid selection effects

��The Weak

The Weak Anthropic

AnthropicPrinciple is merely the statem

ent that we

Principle is merely the statem

ent that we

see things the way they are because if they were any other way

see things the way they are because if they were any other way

we wouldn

we wouldn’’ t be here to see them

t be here to see them

��The Strong

The Strong Anthropic

AnthropicPrinciple can be interpreted as a design

Principle can be interpreted as a design

argument

argument

��It is usually a last resort when there appears to be no argument

It is usually a last resort when there appears to be no argumentfor why a

for why a

particular system

should be the way it is

particular system

should be the way it is

��Its value is strongly contested

Its value is strongly contested

��It is nonetheless am

azing that interpretation of the mathem

atics

It is nonetheless am

azing that interpretation of the mathem

atics

of the Big Bang can be influenced by the possibility of life

of the Big Bang can be influenced by the possibility of life

��The remaining

The remaining anthropic

anthropicprinciples are far more speculative and

principles are far more speculative and

of less significance

of less significance

Next lecture

Next lecture

��Stars

Stars