Download Constraints on a Chance Universe & The Anthropic Principle

Constraints on a Chance
Universe & The Anthropic
Principle
Physical Science 410
James Mackey
James Mackey
ASSUMPTIONS
In all of the following discussion, it is
assumed that life is carbon based.
While silicon based life has been
discussed by a few individuals, the
length of amino acid chains based on
silicon are no more than a few hundred
at the most - insufficient for the
complexity required for life as we know
it.
James Mackey
Additionally, boron has been advocated
as an alternate basis for life; however,
boron is relatively rare in the universe
compared to carbon or silicon, which
would make life even less probable
than it is.
James Mackey
Boron
7.0 X 10-7
2 x 10-9
James Mackey
It is also assumed that physical laws,
as best as we understand them,
operate the same at all places and
times in the evolution of the
universe. No unknown physical laws
can be postulated to explain
currently unexplainable phenomena.
James Mackey
It is possible for something to be so
improbable that even in the
possible time span of the universe,
13.6 Billion years or about 4.3x1017
seconds, it will never happen.
Any argument from design is usually
faith strengthening not faith
producing!
James Mackey
The Anthropic Principle
The Universe possesses narrowly
defined characteristics that permit
the possibility of a suitable
habitat for humanity
James Mackey
This principle has been recognized by
numerous scientists in recent years, and
has been increasingly publicly stated.
Physicist Paul Davies
“[There] is for me powerful evidence that
there is something going on behind it all…It
seems as though somebody has fine-tuned
nature’s numbers to make the Universe…The
impression of design is overwhelming.”
The Cosmic Blueprint (New York, Simon &
Schuster, 1988) p203
James Mackey
Theoretical Physicist Tony Rothman
in a popular article wrote:
“The medieval theologian who gazed at
the night sky through the eyes of Aristotle
and saw angels moving the spheres in
harmony has become the modern
cosmologist who gazes at the same sky
through the eyes of Einstein and sees the
hand of God not in angels but in the
constants of nature.......
James Mackey
....When confronted with the order and
beauty of the universe and the strange
coincidences of nature, it’s very tempting to
take the leap of faith from science into
religion. I am sure many physicists want
to. I only wish they would admit it.”
"A ‘What You See is What You Beget ‘
Theory," Discover (May 1987) p99
James Mackey
Cosmologist Bernard Carr
Studied relativity and cosmology
under Stephen Hawking at the
Institute of Astronomy in
Cambridge and at Caltech. Prof.
of Math & Astronomy at Queen
Mary College
“One would have to conclude either that the
features of the universe invoked in support
of the Anthropic Principle are only
coincidences or that the universe was
indeed tailor made for life. I will leave it to
the theologians to ascertain the identity of
the tailor!”
"The Anthropic Principle and the Structure of
the Physical World," Nature 278 (1979) p53
James Mackey
Physicist Vera Kistiakowlsky, past president of
Association of Women in Science
“The exquisite order displayed by
our scientific understanding of the
physical world calls for the divine”
Cosmos, Bios, and Theos, Margenau
& Varghese, ed. (LaSalle Il,Open
Court,1992) p52
James Mackey
George Ellis, a colleague of Stephen
Hawking and Roger Penrose
“Amazing fine-tuning occurs in the
laws that make this [complexity]
possible. Realization of the
complexity of what is
accomplished makes it very
difficult not to use the word
‘miraculous’ without taking a
stand as to the ontological status
of that word”
”The Anthropic Principle : Laws and Environments,” in
The Anthropic Principle, Bertola & Curi, ed. (New York,
Cambridge University Press,1986) p30
James Mackey
Cosmologist Edward Harrison
• “Here is the cosmological proof of the existence
of God – the design argument of Paley – updated
and refurbished.
• The fine tuning of the universe provides
prima facie evidence of deistic design.
• Take your choice: blind chance that
requires a multitude of universes or design
that requires only one…
• Many scientists, when they admit their
views, incline toward the theological or
design argument.”
Masks of the Universe (New York, Collier
Books,1985) pp252,263 (emphasis mine)
James Mackey
Mathematical Physicist Robert Griffiths
“If we need an atheist for a
debate, I go to the
philosophy department. The
physics department isn’t
much use.”
”Cease Fire in the
Laboratory,” Christianity
Today, 3 April 1987, p18
James Mackey
Planet hunters Geoff Marcy and Paul Butler
In discussing the 33 (at that time) known planets
discovered orbiting other star systems, the authors
observe that most such systems are dominated by
highly elliptically orbit giant planets.
• "The predominance of elliptical orbits implies that
planetary systems with circular orbits may be the
exception rather than the norm.
• Apparently our nine planets were just far enough apart
and low enough in mass to avoid this chaos [referring to
the tendency of giant planets to slingshot neighbors out
of their systems].
•The nine planets do perturb one another, but not
enough to cause close passages.
James Mackey
•The planetary house of cards that we call our
solar system may be one of the rare systems that
remains just barely stable.
• If our solar system is unusual in its circular orbits,
we humans would seem to be extraordinarily lucky to
be here.
• After all, the circular orbit of earth keeps solar
heating nearly constant, minimizing temperature
fluctuations.
•Perhaps biological evolution would not have
proceeded to intelligence if Earth's temperature were
fluctuating widely.
James Mackey
•It may be that Darwinian
evolution towards complex
organisms is enhanced by
circular orbits. If so, we owe
our existence to Earth's
stable orbit."
Despite the fact there are currently 1079 extrasolar
planets, these conclusions are still perfectly
applicable
Astronomy, March 2000, "Planets Beyond" by
Geoff Marcy and Paul Butler, page 45
James Mackey
• wed
James Mackey
In an article, “Exploring Our
Universe and Others”, in Scientific
American’s The Once and Future
Cosmos, Martin Rees observed..
“Our universe could not have become structured if it
were not expanding at a special rate. If the big bang
had produced fewer density fluctuations, the universe
would have remained dark, with no galaxies or stars…
..If our universe had more than three spatial
dimensions, planets could not stay in orbits around
stars.”
James Mackey
continuing
“If gravity were much stronger, it would crush
living organisms of human size and stars would be
small and short-lived. If nuclear forces were a few
percent weaker, only hydrogen would be stable:
there would be no periodic table, no chemistry and
no life.
Some would argue that this fine-tuning of the
universe, which seems so providential, is nothing to
be surprised about, because we could not exist
otherwise.”
James Mackey
Always keep in mind, the opposite side of this
viewpoint..
“The more the universe is comprehensible, the more
it also seems pointless.”
Steven Weinberg, The First Three Minutes
“The usual approach of science of constructing a
mathematical model cannot answer the questions of why
there should be a universe for the model to describe.
Why does the universe go to all the bother of existing?”
Stephen W Hawking
James Mackey
To serve as an introduction to the
problem of the probability of intelligent
life having arisen by purely chance
means, we will look at a famous
equation, The Drake Equation, and its
implications for the existence of
intelligent “communicating” life in our
galaxy.
A highly recommended resource is
Rare Earth, by Peter Ward and Donald
Brownlee (Copernicus Books, Springer,
Feb. 2000)
James Mackey
The Drake Equation
Originally postulated by astronomer
Frank Drake in the 1950s to predict how
many civilizations might exist in our
galaxy in order to estimate the
likelihood of our detecting radio signals
from other technologically advanced
civilizations.
N = N*  fs  fp  ne  fi  fc  fl  L
James Mackey
where
N* = stars in the Milky Way galaxy (or often
R* = avg. rate of star formation in galaxy)
fs = fraction of sun-like stars
fp = fraction of stars with planets
ne = number of planets in a star’s habitable zone
fi = fraction of habitable planets where life does
arise
fc = fraction of planets inhabited by intelligent
beings
fl = % of lifetime of a planets with a civilization
capable of communication
L = length of time civilization survives
James Mackey
The initial assumptions made for the
terms in this equation (whose values,
except for N*, were very poorly
known) were exceedingly optimistic.
For example, Carl Sagan assumed that
ALL stars had 10 planets. The results
of these assumptions were an estimate
of perhaps one million civilizations of
creatures in our galaxy capable of
interstellar communication at this time!
Without doubt this is a totally
unrealistic estimate!
James Mackey
Fairly common assumptions made by
SETI supporters are listed as follows:
N* - the number of stars in the Milky
Way galaxy is probably fairly well
known at 200 to 300 billion. This is
normally based on measures of the
mass of the galaxy, and the mass of an
average star (assumed ~ 1 M0).
The actual average size star in the Milky Way
is an M class star about 50% of Sun’s mass
James Mackey
fp - the fraction of stars that have planets
around them
- Current estimates range from 20% to
100%.
ne - number of planets per star that are
capable of sustaining life
For each star that has a planetary system,
how many planets are capable of sustaining
life? Estimates range from 1 to 2.
James Mackey
fl - the fraction of planets in ne where life
evolves:
On what percentage of the planets that are
capable of sustaining life does life actually
evolve? Current estimates are 100%
(where life can evolve it will) .
fi - the fraction of fl where intelligent
life evolves
On the planets where life does evolve,
what percentage evolves intelligent life?
Estimates are 50 – 100 %
James Mackey
fc - the fraction of fi that communicate
What percentage of intelligent life
forms have the means and the desire
to communicate?
Estimates are 10 % to 20%
L - fraction of a planet's life during which
- communicating civilizations may survive
For each civilization that does
communicate, for what fraction of the
planet's life does the civilization survive?
This is the most vague question.
James Mackey
Using the Earth as our model, the expected
lifetime of our Solar System is approximately
10 billion years. Already communication by
radio has been for less than 100 years.
How long can our civilization survive
without destroying ourselves as some
predict or will we beat our problems and
survive indefinitely? If doomsday came
today this figure would be 10-9. If we
survive for 10,000 more years this figure
would be 10-6.
James Mackey
N = N*  fs  fp  ne  fi  fc  L
N = 200 billion (1/4) 2 (1/2) (1/10)
(1/10) (1/100 million)
N ~ 50 technological civilizations in
just the Milky Way Galaxy!
Since there are billions of galaxies, the
assumption is then that there are billions of
technological civilizations capable of radio
communication in the universe!
James Mackey
The Delimma!
Where are they?
(Known as the Fermi paradox)
If there are/have been highly
technological and long-lived civilizations in
our Galaxy, why haven’t we seen them or
their effects?
James Mackey
Considering some of the terms in this
equation, let’s try to arrive at a reasonable
estimate based on current discoveries and
understanding. If we rewrite the equation in
more modern terms, and rename the
modified Drake Equation as the:
RARE EARTH EQUATION
N = N* fpm fp ne  ng  fi fc fl fm fj fme
James Mackey
where
N* = stars in the Milky Way
fp = fraction of stars which have planets
similar to earth
fpm = fraction of metal-rich planets
ne = planets in a star’s AHZ
ng = stars in a Galactic HZ
fi = fraction of planets where life (of any
kind) arises
fc = fraction of planets where complex
metazoans arise
James Mackey
fl = % of planet’s lifetime that is marked by
Complex metazoans
fm = fraction of planets with a single large
moon
fj = fraction of solar systems with Jupitersized planets
fme = fraction of planets with a critically low
number of mass extinction events.
James Mackey
Some Definitions
Habitable Zones (HZ) - regions about a
parent star where conditions are conducive
to the development & survival life of any
form:
i.e. temps that allow liquid water
Animal Habitable Zones (AHZ) - regions
about the parent star where complex life
can arise. This is more restrictive than the
simple HZ.
James Mackey
What makes a planet habitable?
• Located at an optimal distance from the
Sun for liquid water to exist.
James Mackey
• Large enough for geological activity to
release & retain water and atmosphere.
James Mackey
Galactic Habitable Zones (GHZ)
regions in the galaxy where solar
systems and planets can safely
form without appreciable danger
from catastrophic events in the
galaxy.
James Mackey
N* - the number of planets in the
Milky Way galaxy is probable fairly
well known at about 400 billion.
This is normally based on measures
of the mass of the galaxy, and the
mass of an average star.
James Mackey
fp - the fraction of stars that have planets
similar to Earth
Based on the most recent successes in finding
extrasolar planets orbiting distant stars, it would
seem that the value of the first ½ of this factor
would be rather high. Optimists placing its value
at 1.0 and pessimists at 0.1 (about 10% of
surveyed stars reveal the presence of planets).
A reasonable value for this alone would be 0.5.
However the “similar to Earth” is vastly more
restrictive, of 1771 planets (3/14/2014) ~ 15 are
similar IN SIZE to Earth… prob ~ 0.008
James Mackey
Exoplanet mass as function of semi-major axis
Red lines locate the Earth at 1 AU and mass 0.00314 MJ
James Mackey
Not one of the Earth size planets has an orbit
even close to 1 AU
The most common stars in our galaxy are M
stars, which are fainter than the sun and
probably about 100 times more numerous.
These can be ruled out because their HZ
(habitable zones - where surface
temperatures would be conducive to life)
are uninhabitable for other reasons…
increased radiation exposures
increased tidal effects
likelihood of no moon
James Mackey
To be in its HZ, a planet must be so close
to these small stars that tidal effects would
lock these stars into synchronous rotation
with one side always facing the star and
the other side always permanently dark. A
real life example would be the planet
Mercury.
If the stars are much more massive than the
sun, their stable lifetimes are only a few
billion years - inadequate time for the
development of advanced life and the
evolution of an ideal atmosphere.
James Mackey
fpm - the fraction of metal-rich planets
The evidence for the importance of
metal-rich stars comes indirectly from the
planet search program.
Spectroscopic studies of the stars about
which we have been able to identify
planets shows that they, like our own
sun, are rich in metals.
Yet general surveys of stars in our
neighborhood show that the metal
content of our sun is abnormally large.
James Mackey
Based on Extrasolar planets as of 3/14/2014
Sun’s metallicity is 0
James Mackey
It would seem to be impossible for
complex life to develop on a planet
formed in the nebula of a metal-poor
star.
The elements so important to life as we
know it are exceedingly rare in the
universe – in a sense human beings are
trace elements in the universe.
A very conservative estimate of the
fraction of stars that are sufficiently
metal-rich like the sun would be ~ 0.5
James Mackey
ne - the fraction of planets in a star’s AHZ
The fraction of planets in a star’s
habitable zone can be reasonably
estimated from our own solar system.
If we take the sun’s HZ to be 1.0 AU 
0.3 AU in a solar system ranging out to
more than 40 AU, we can estimate the
fraction as 1.3/40 or ~ 0.027.
However, as we will see our solar system
is not common, so a smaller value is
likely
James Mackey
Of the 1771 planets discovered about other stars,
only 3 are close to Earth’s mass (smallest is PSR-1257
12b ~ME /50) with KOI-52c at 2/3 ME and Kepler 42
c ~ ME though none of these few orbit within 20% of
1 AU
James Mackey
Solar system
masses in
terms of
Jupiter mass
I would
weigh
more than
900
pounds
6 x ME
Mercury a = .00017
Venus
b = .00256
Earth
c = .00315
Mars
d = .00034
Jupiter e = 1.0
Our solar system
a
b c
d
e
James Mackey
AN EXTRASOLAR
SYSTEM
Unlike our solar system,
the Upsilon Andromedea
System has large planets
orbiting close to the star.
225 Me
600 Me
1200 Me
The orbits of the inner planets in our solar
system compared to those of the Upsilon
Andromedea System
James Mackey
ng - stars in a galactic HZ
It is more difficult to estimate the
Galactic Habitable Zone’s percentage
for our solar system.
Based purely on our physical location in
the Milky Way galaxy, one could assign
a fraction of ~0.2.
If the solar system were much closer
toward the galactic center, the
probability of dangerous radiation from
supernova or magnetar, etc. events
would escalate dramatically.
James Mackey
James Mackey
If we were much further away from the
center, we would be near the edge of the
solar nebula as the solar system developed
and the concentration of heavy elements
(heavier than helium) would be too low.
Heavy metals are necessary for dense metallic
cores which are necessary for a planetary
magnetic field and all of its protective effects
and for the radiation heat stemming from the
planet’s interior that helps drive plate tectonics
James Mackey
Again, it should be observed that
there is convincing evidence that
GHZs may be drastically reduced as
our knowledge of more catastrophic
events, such as merging neutron
stars, and better estimates for the
frequencies of such events
improves.
James Mackey
fI - fraction of planets where life arises
Based on current ideas, the probability
of simple forms of life existing on a
planet is very high. Very simple life is
considered ubiquitous by many.
This is based on recent findings that
have demonstrated that life can exist
under conditions previously thought to
make life impossible.
James Mackey
Microorganisms that can survive
under extreme conditions have
been dubbed “extremophiles”.
Such organisms have been found
in sea ice, in highly acidic pools, in
deep sea hydrothermal vents, in
environments exceeding 80 C, and
at depths exceeding 2.7 km below
ground in basaltic rock.
James Mackey
Since life CAN exist under such
conditions, many astrobiologists
believe that life WILL exist under
similar conditions which are found
many places in our solar system.
If we accept these ideas, we would
assign a fraction of at least 0.5 for
the probability that simple life
would exist on a life-capable planet.
James Mackey
fc - fraction of planets with complex
metazoans
The fraction of planets where
complex metazoans (multicellular
organisms) arise is a very different
quantity than fi.
In contrast to the high probability
assigned to fi, the probability for fc
based on current understanding
would be extremely small.
James Mackey
While simple organisms are able to
survive rapidly changing environments
and fairly large extinction events,
multicellular organisms are much more
susceptible to extinction from
significant climatic changes (unless
they have progressed to the point of
extensive diversity).
The history of the Earth shows
evidence of several extinction events
in the past
James Mackey
“kill” curve
Based on the data presented by David
Raup, the probability of extinction for
species (the so called ‘kill curve’), is
essentially negligible over a 100,000
year times scale,
perhaps 5% to 10% over a million year
scale,
approximately 30% over a 10 million
year time frame, and rises to over 70%
on the 100 million year level.
James Mackey
In the book
Extinction: Bad
Genes or Bad Luck,
published in 1990,
he estimated that
extinctions of a level
sufficient to
exterminate all life
should have an
average spacing of
2 billion years.
James Mackey
If life has existed for 4 billion years on
Earth, then we may be pushing our luck.
The well publicized 65 million year old
impact event at Chicxulub that killed the
dinosaurs is an example of an extinction
event that killed many species, but not all.
Had the impacting object been only twice
the estimated size, it could possibly have
sterilized the Earth.
Estimated value ~ 0.001
The significance of such extinctions will be
discussed again under fme
James Mackey
fl - fraction of planet lifetime with complex
metazoans
This is a very controversial value again
depending upon how optimistic one is
about the nature of complex life.
Based on the Earth alone, which may
NOT be a good example, one could
estimate 6x108 animal life/4.5x109 life of
Earth for ~ 0.13.
This value leans strongly towards the
highly optimistic side.
James Mackey
fj - fraction of systems with Jupiter-like planet
Based on the available information from
the 1771 or so planetary systems
discovered as of the present, one would
assign a rather large fraction to this
number, realizing that as techniques
improve and develop that enable
astronomers to identify smaller rocky
planets orbiting other stars, this number
may have to be re-evaluated.
Chosen value 0.5
James Mackey
If, however, Jupiter-like means a Jupiter sized
planet orbiting close to 5 AU, this drops the
probability significantly – only 2 of the 1096
extrasolar planetary systems has a single
Jupiter size planet in an approx. 5 AU orbit
(ups And e @5.24 Au, Mass =1.06 MJ; and
HD 154345 b @4.2 AU, Mass = 1.0 MJ)
2/1771 = 0.0011
James Mackey
Why is such a Jupiter like planet Important?
Computer simulations by Fred Rasio
and Eric Ford (MIT), among others,
show that Earthlike planets are
probably unable to survive the
gravitational tug-of-war in a system
with two (or more) massive, Jupiterlike
giants.
They would be slung out of the solar
system or sent careening into the central
star.
James Mackey
On the other hand, systems with
no giant planets at all might also
have dire consequences for lifebearing planets.
Computer simulations by George Wetherill
(Carnegie Institution of Washington)
indicate that Jupiter acts as the solar
system's gravitational vacuum cleaner,
efficiently thinning out the population of
hazardous comets that venture into
Earth-crossing orbits. (Wetherill died in 2006)
James Mackey
Without a Jupiter the current impact
rate of comets would be 1,000 times
higher, says Wetherill* , with truly
catastrophic collisions (like the one
65 million years ago) happening
about once every 100,000 years.
*1997, he received the National Medal of Science, the
nation's highest scientific award.
This would surely frustrate any slow
evolutionary progress from simple
life forms to higher intelligences.
James Mackey
fm - fraction of planets with Earth-like moon
With our sample size of one (only our
own solar system), only 1 planet of 9 has
the requisite large and close (but not too
close!) moon. Chose a value of 0.08
However, it is well argued that this is a
highly optimistic number based on
considerations of the Earth-moon
system.
James Mackey
The current accepted explanation for the
existence of our Moon is the Impact Model,
in which it is assumed that early in Earth’s
history, it was struck by a large object in a
glancing impact that blew off larges amounts
of the Earth’s outer layers. This debris
ultimately reformed into our Moon.
This is based primarily on the similarity
between the elements found on the moon
and those in the Earth’s surface layers along
with the dearth of heavy metals on the Moon
James Mackey
Dynamical studies by Jacques Laskar
and Philip Robutel (Bureau des
Longitudes, Paris) have shown that
rocky, Earthlike planets show chaotic
variations in orbital tilt that could lead
to drastic climate changes.
Fortunately, Earth's chaotic tendencies
are damped by tidal interaction with the
Moon.
James Mackey
Jacques Laskar: 2006 AAS Brouwer
Award Winner
“Laskar's work has thus been fundamental in helping to reveal the chaotic
nature of the solar system. In the course of such studies, Laskar developed
a new tool based on frequency analysis to discriminate regular orbits from
chaotic ones that is today widely used for a variety of problems in
conservative dynamics. He and his collaborators have also made important
contributions to the study of planetary spin axis dynamics. They expanded
on previous works to show that the evolution of the Martian spin axis is
chaotic and that the motion of Earth's spin axis would be chaotic without
the Moon. Laskar and his student, Correia, have also demonstrated that the
current retrograde spin of Venus could be obtained from almost any initial
condition when the perturbations of Venus's orbit by the other planets, and
plausible models for its atmospheric tides and core-mantle interactions, are
accounted for. “
(emphasis mine)
James Mackey
Without a relatively large satellite, Earth
might have experienced variations in
axial tilt similar to those of Mars,
possibly as large as 20 ° to 60 °.
This would cause extreme variations in
the patterns of the seasons. According
to one analysis of planet formation, a
world like Earth has only about a 1 in
12 chance of ending up with a nice,
mild axial tilt that is safely stabilized by
a large moon.
James Mackey
The existence of large single moon
(a very low probability system based
on the impact formation model of the
origin of the Moon).
• Contributes to stability of the spin axis of
the Earth
•Existence of plate tectonics to recycle CO2----- and O2 in the atmosphere. This has stopped - atmospheric loss or a runaway greenhouse
effect
•Significant volcanic activity to release
atmospheric gases
•Production of continental land masses
James Mackey
fme - fraction of planets with low
extinction rates
Examination of the fossil record reveals
that extinction events have occurred
several times in the discernable history of
the Earth.
There are several extinction mechanisms
that can create planetary disasters (some
have occurred and some, to the best of
our knowledge, have not).
A partial list would be:
James Mackey
Some sources of Extinction Events
Changing a planet's spin rate
Moving out of the AHZ (animal habitable zone)
Changing energy output of the star
Nearby Supernova
Impact of a comet or asteroid
Large gamma ray sources
Cosmic ray jets and gamma ray explosions
Catastrophic climactic change:Icehouse and
Runaway Greenhouse Effect
James Mackey
Six archaeologically identified extinction
events in Earth’s history since the Cambrian.
James Mackey
Changing a planet's spin rate
• The 24 hr spin rate of the Earth is
anomalous when compared to the other
planets in our solar system except Mars.
• The Jovians tend to spin much faster,
while Mercury and Venus spin more slowly
• slowly enough that they are 'tidally
locked' to the sun as they orbit, with one
side always facing the sun or with the
length of a solar day being longer than an
orbital year.
James Mackey
Many astronomers believe that many
of the planets have undergone
serious rotation shifts in their history,
due to chance encounters with large
masses or general chaotic tendencies,
e.g. Venus, Neptune
Such shifts would definitely be
detrimental to any form of evolving
organisms.
James Mackey
Moving out of the AHZ (animal
habitable zone)
Liquid water is a requirement for complex
animal life, and consequently any shift in
orbital radius would move the Earth out
of the liquid water zone with deleterious
effects on any animal life.
Such perturbations are believed to be
fairly common in solar systems with either
close orbiting massive planets or Jupiterlike planets with highly elliptical orbits.
James Mackey
Changing energy output of the star
Any significant change in the energy of
the parent star of a habitable planet
would likely be disastrous to animal life or
its prospects for evolution.
In addition to dramatic changes that
would occur around an unstable star, even
stable main sequence stars such as the
sun experience a gradual increase in
energy output as Hydrogen is consumed
in the core and converted to Helium.
James Mackey
On the Earth, the temperature has
been maintained at a relatively
constant value by a gradual
reduction in greenhouse gases as
the energy output of the sun has
increased.
What causes this reduction?
probably plate tectonics
James Mackey
Nearby Supernova
Astronomer's calculations have estimated
that a supernova occurring within 10
parsecs (32.6 light years) would produce
energy fluxes of Electromagnetic and
charged particle radiation sufficient to
destroy Earth's ozone layer in 300 years
or less.
James Mackey
VELA Supernova
Remnant
About 800 light-yrs
James Mackey
Based on the number of stars within 30
light years of Earth and the rates of
supernova explosion among stars, it is
highly likely that one or more such events
have occurred within 30 lys of Earth during
the last 500 million years.
The probability of such explosions would be
much higher closer to the galactic center.
James Mackey
Impact of a comet or asteroid
All planetary systems are full of debris
left over from planetary formation. In the
early years of solar system life, all
planets were heavily bombarded by this
debris making the development of life
impossible until the bombardment
frequency decreases.
James Mackey
However, even at the present, the
probability of such impacts is not zero.
approximately 65 million years ago a large
impact killed off the dinosaurs and many
other species living near the end of the
Mesozoic Era.
Mass Extinctions and the Rare Earth Model
The following chart illustrates the rate
of meteor impacts at the top of Earth's
atmosphere as a function of size:
James Mackey
Chixulub
James Mackey
According to the Earth Impact Database there are 182 verified impact
craters on Earth
http://www.passc.net/EarthImpactDatabase
James Mackey
Impacts are still occurring!
Tunguska meteorite exploded about 300 m
above the uninhabited Siberian countryside in
1908.
Because it was so isolated, it was several
years before any outsiders observed the site.
The picture seen next is the first picture
taken at the site almost 10 years later.
James Mackey
James Mackey
View of the Impact Site after more than
20 years
James Mackey
Peekskill Meteorite
Peekskill, N.Y. 10/9/92: Car trunk, floor, pierced by meteorite.
James Mackey
November
30th, 1954
Sylacauga,
Alabama.
Elizabeth Anne Hodges
James Mackey
•Chelyabinsk
meteorite
2/15/2013
James Mackey
Large gamma ray sources
Gamma ray satellites have detected
numerous sudden bursts of gamma
radiation from various galaxies.
While the origin and mechanism for
these bursts is not established, they
would be extremely lethal to life on
any nearby planetary systems.
James Mackey
1998 event
20,000 yrs ago while Mammoths, Mastodons, etc.
roamed North America - a distant neutron star in
constellation Aquila (SGR 1900+14, ~45000 light-yrs)
underwent an unknown type of cataclysm..
A violent explosion propelled a sphere of hard
radiation out at the speed of light.
For 20,000 years this sphere expanded until on Aug.
27, 1998 it hit the Earth over the Pacific Ocean and
then passed on through space.
James Mackey
For about 5 minutes Earth was bombarded
by a high level of gamma rays & X-rays.
Even after 20,000 lyrs the energy level sent
radiation sensors on 7 satellites to max. or
off scale. Two of these satellites shut down
to avoid burnout.
The radiation penetrated to within 30 miles
from the Earth’s surface. The first time ever
such an event from outside our solar system
had a measurable effect on the atmosphere
of Earth.
James Mackey
Cosmic ray jets and gamma ray
explosions
In recent years astronomers have postulated
that the merger or collapse of neutron stars
would generate massive cosmic rays jets
and gamma ray bursts potentially lethal to
nearby galaxies. Gamma-ray Bursts: These
events are the most powerful in the
Universe. Over a few seconds a gamma-ray
bust can release most energy than our Sun
will during its entire lifetime
James Mackey
One of the latest proposals (1999) has been
offered by James Annis, an astrophysicist at
Fermilab near Chicago, Illinois.
Annis says that giant gamma-ray bursts
(GRBs) occur in every galaxy, including ours,
from time to time. Such explosions, he says,
emit so much radiation that they probably wipe
out almost all the life in the whole galaxy. If
so, intelligent life forms might not usually have
time to evolve to the space-faring stage before
being exterminated.
He calculates a rate of such events as about
1 burst every few hundred million years.
James Mackey
Should such an event occur in the Milky
Way, and the energy from such an event
strike the Earth, it would kill all life on our
planet, even if the event were at the
galactic center.
It is also argued that such events would
have been much more likely in the earlier
history of the universe.
James Mackey
Catastrophic climactic change:Icehouse
and Runaway Greenhouse Effect
Under certain conditions, radical climactic
changes can cause mass extinction.
Major glaciations and greenhouse heating
are examples, with both depending upon
the amount of CO2 or other greenhouse
gases.
These are the killing mechanisms produced
by reduction or increase in stellar output or
by alteration of the planet's orbit.
James Mackey
Are considerations of such catastrophic
events and possible extinctions
reasonable?
There is some geological &
paleontological evidence for a number
of "mass" extinctions in Earth's past. An
abbreviated list of these events and
their approximate date are given as
follows:
James Mackey
The bombardment extinctions : 4.6
to 3.8 billion years ago
This period of intense bombardment of
all the planets from residual solar
system debris would have sterilized the
Earth's surface at least several times.
James Mackey
The advent of oxygen - : 2.5 to 2.2
billion years
The rise of oxygen in the Earth's
atmosphere would certainly have
doomed most anaerobic bacterial
species existing on Earth at that time.
Beyond this general idea, there is no
other information known.
James Mackey
"Snowball Earth" : 750 to 600 million years
ago
Beyond geological evidence of massive
glaciation, even as far as the equator, we
know little of these events, whether there
were many such glaciations and
corresponding extinctions, or only a few is not
known.
It is probable that in such extensive ice ages,
even the oceans were frozen to significant
depths.
There is some fossil evidence of extinctions of
stromatolites and other planktonic organisms.
James Mackey
PLANETARY ALBEDO: The fraction of incoming
radiation that is reflected back to space.
[sea water ~0.1; bare land ~0.3; sea ice ~0.6; fresh
snow ~0.9]
ICE-ALBEDO FEEDBACK: For any imposed cooling
(or warming), the resulting higher (or) lower albedo
will cause further cooling (or warming). Thus, ice
advance is self-stabilizing.
RUNAWAY ICE ALBEDO: If ice lines close to within
~30° of the equator, the ice albedo feedback
becomes unstoppable and ice quickly covers the
tropics.
James Mackey
Snowball Earth and
the CO2 cycle
Earth’s ice ages end
as oceans freeze
over and volcanoes
release CO2 into the
atmosphere
James Mackey
Much work has been done on this hypothesis in the
last 5 years, and a great deal of supporting
evidence has been presented. Interestingly is a
connection between the effects of a “Snowball
earth” and the Cambrian “explosion” occurring
after the end of the ice coverage.
For much more detail about this idea, see the article
“Snowball earth” listed on my 410 website, and if
you search “Snowball Earth” on YouTube or the web
you will several BBC documentaries on the topic.
James Mackey
The Cambrian mass extinctions
: 560 to 500 million years ago
This is the most enigmatic and important
of the extinction events.
During this brief time in which a large
number of phyla apparently disappeared
from the Earth, we also see the
appearance of all the animal phyla still
existing on Earth.
Since this event, no new phyla have
appeared.
James Mackey
James Mackey
There are a number of extinctions
suggested by scientists around this
period, however the cause of the
major Cambrian extinctions and
others of that time period remains
an enigma.
The explosion of animal life since this
event suggest that this extinction
may have had very positive benefits
for more complex organisms.
James Mackey
The Ordovician & Devonian
extinctions : 440 & 370 million years
During this period (Paleozoic era) these
two major mass extinctions apparently
destroyed the majority of sea species.
The causes of these extinctions are not
known, though a number of suggestions
(anoxia, temperature change, seal level
change, etc.) have been advanced, as
well as a possible impact event.
James Mackey
The Permo-Triassic event : 250 million
years ago
On most measures of extinction (% of existing
species, genera, or families eliminated
worldwide) this is the most catastrophic of all
mass extinctions that have occurred on the
Earth.
Specialists in compiling extinction records point
out that more than 50 % of marine families died
out, and anywhere from 80 to 90 % of all
species went extinct.
During this event, the majority of the plant and
animal life on Earth disappeared.
James Mackey
The end-Permian mass extinction event
ranks as the most devastating to
terrestrial faunas in the history of the
Earth.
Marking the end of the great Paleozoic era,
it saw to the death of about 95% of marine
species and land families. This is the most
extensive extinction event ever, the closest
that metazoans have come to being
exterminated in the 600 million years since
they first evolved in the Cambrian radiation.
James Mackey
The following diagram shows the number of organism species
present on Earth since the Cambrian radiation. The mass
extinctions can be seen when this plot has sharp declines.
There have been 5 major mass extinctions, of which it can be
seen that the drop of families at the Permo-Triassic boundary
has been the greatest.
James Mackey
This event has been extensively
studied, and currently it is believed
that a combination of things
contributed to its severity.
The most important of these was a short
time outgassing of CO2 from the ocean
floors during unusually severe volcanic
eruptions about 250 million years ago.
The sudden release of large quantities of
CO2 directly killed many marine
organisms by carbon dioxide poisoning.
James Mackey
Could such events cause or add to a mass extinction event?
The largest eruption of the 20th century, Mt Pinatubo is tiny
compared to the Siberian Traps but caused a 0.5 degree drop
in global temps the year after it erupted.
The largest eruption in historic memory occurred on Iceland in
1783-84 spewing out 12 km3 of lava onto the island (the
Siberian Traps erupted about 3 million km3). The poisonous
gases given out are recorded as killing most of the islands
crops and foliage and lowering global temps by about 1
degree.
If events this size can affect temperatures and large areas then
the effects of a large scale flood basalt are incomprehensible.
James Mackey
The sudden increase in
greenhouse gases produced a
large increase in the amount of
heat trapped by the atmosphere.
This produced a heat spike of 5 to
10 degrees persisting for 10 to 100
thousand years which killed off large
amounts of terrestrial life.
James Mackey
Currently this event is believed to be a
double or triple cause event spread over
nearly 100,000 years. A CO2 increase caused
by the silurian traps volcanic activity, a
possible impact added to the problem of ~ 5
degree temp. increase, causing an ocean
temp increase that released huge amounts
of Methane (a strong greenhouse gas)
producing a addnt 5 degree for a total of 10
degree increase – sufficient to kill most
organisms on land or sea.
James Mackey
The end-Triassic mass extinction : 202
million years
This was a significant event eliminating about
50 % of genera, especially destructive to
marine life.
This was thought by many to have been an
impact event, but there is currently no
identified impact site associated with this
event. The Manicouagan Crater in Quebec is
about 100 km in diameter and of the correct
size, however it is currently dated at 214
million years, which is too early. There are
environmental changes associated with this
period, but nothing of a severity to produce
the observed effect. Its probable cause
remains unknown.
James Mackey
The Cretaceous/Tertiary boundary event
: 65 million years
This mass extinction event, resulting in the
death of the dinosaurs, is one of the most
well known extinction events.
A team of scientists directed by Luis Alvarez
proposed that this was an impact event
occurring about 65 million years ago.
This was based on evidence of large iridium
concentrations found at several sites around
the world, and an association with high
iridium concentrations in many meteorites.
James Mackey
Based on this, and other evidence, it is
widely accepted that an approximately
10 km diameter comet or asteroid struck
the ocean off the coast of Yucatan
blasting a crater between 180 to 300 km
wide and precipitating a chain of events
exterminating the dinosaurs and over
50% of other species on Earth at that
time. The impact, in addition to shock
waves and massive fires, produced
major and long lasting climactic
changes.
James Mackey
Based on all of this information
one would assign a very small
fraction to fme since the evidence
indicates that significant mass
extinctions are not uncommon in a
planet’s history. A value of
0.000001 will be assumed, i.e. a
one in a million chance!
James Mackey
If we assume ~ 400 billion stars in the Milky
Way galaxy, and assume 4 planets per star,
then the likelihood of finding a planet with all
of the requisite requirements for complex life to
develop, evolve, and survive would be.....
(4x1011)*.003*.01*.027*.2*.5*.001*.13*.08*.005
*1x10-6 or about 0.0000000017 =1.7x10-9 in our
Milky Way galaxy.
Based on extremely optimistic values for the
various factors in the Rare Earth Equation.
James Mackey
Even assuming ~ 1012 galaxies and and 4
planets per star yields
6.7 x 103 planets out of 1.6x1024 planets
or 1 part of 4,000,000,000,000,000,000,000
for the probability of the correct system arising
by chance!
What reasonable conclusion should one make?
James Mackey
Recall that the estimates made by supporters
of SETI are much more optimistic and
generous......yielding much larger numbers..
One such estimate gave 100,000 radio
communicating civilizations currently active
in the Milky Way galaxy.
James Mackey
That figure of 100,000 would mean there is
one radio-emitting civilization right now per
4 million stars -- reason enough to tune in
on the heavens and start hunting for them.
If they were scattered at random throughout
the Milky Way, the nearest one would
probably be about 500 light-years from us.
A two-way conversation would require a
time equal to a good part of recorded
human history, but a one-way broadcast
might be audible.
James Mackey
However, 50 years of SETI have failed to
find anything, even though radio telescope
apertures, receiver techniques, and
computational abilities have improved
enormously since the early 1960s.
Granted, the "parameter space" of possible
radio signals (the possible frequencies,
locations on the sky, signal strengths, on-off
duty cycles, etc.) is vastly larger than the
tiny bit that has yet been searched.
James Mackey
But we have discovered, at least,
that our galaxy is not teeming with
powerful alien transmitters
continuously broadcasting near the
21-centimeter line.
No one could say this in 1961!
James Mackey
According to many life scientists, it is naive to
suppose that the evolution on another planet
should necessarily result in intelligence as we
know it.
In his bestseller Wonderful Life, paleontologist
Stephen Jay Gould (Harvard University) asserts,
"We probably owe our own existence to . . . good
fortune. Homo sapiens is an entity, not a
tendency."
James Mackey
Evolution is unpredictable and chaotic.
Gould has pointed out again and again that..
“..if we could rewind the tape of biological
evolution on Earth and start over, it is
impossible that humans would again
appear on the scene.
We are the result of too long a chain of
chance flukes and happenstance.”
James Mackey
Gould notes that there is no overall pattern in
evolution, no preferred direction.
Our notion that the increase of biological
diversity is necessarily accompanied by an
increase of mental capabilities may be dead
wrong.
If some recently evolved animals are bigger and
smarter than any earlier ones, that could just
be a fluke.
Human levels of planning and technology may
be even more so. There are no firm indications
that increased intelligence is an inevitable
product of biological evolution.
James Mackey
Contrary to popular belief, the fact that
intelligence has arisen once tells us
absolutely nothing about how often it
happens -- for the simple reason that we
ourselves are the one case! We are a
self-selected sample.
Even if intelligent life is so improbable that
it appears just a single time in one remote
corner of the universe, we will necessarily
find ourselves right there in that corner
observing it, because we are it.
James Mackey
"Physicists still tend to think more
deterministically than biologists," wrote
Mayr in the May 1996 issue of The
Planetary Report.
"They tend to say that if life has originated
somewhere, it will also develop intelligence
in due time. The biologist, on the other
hand, is impressed by the improbability of
such a development."
James Mackey
Based on almost any reasonable criteria that
one could devise, the existence of intelligent
life on Earth
and perhaps in the Universe as well
is an ENIGMA....
without GOD
James Mackey
Based on political events of the last
few years, this is a good closing
comment
James Mackey