Transcript The Miracle of Stars or Why We are Here

The Miracle of Stars or
Why We Are
Michael Bass, Professor Emeritus
CREOL, The College of Optics and Photonics
University of Central Florida
Orlando, FL 32816
© M. Bass
Cosmologies
Biblical and Mythical.
Aristotle’s universe of spheres with the
earth at the center.
Copernicus’ sun centered universe.
Newton’s universe of absolute motion.
Einstein’s universe of relative motion.
Einstein plus quantum mechanics and
the Big Bang Universe.
© M. Bass
A scientific cosmology
must explain
The night sky is dark.
The universe can not be static.
Hubble’s law of galaxies rushing apart.
The 2.7 K (loosely called the 3 degree)
black body radiation that fills the
universe.
The fact that there is 1 helium atom
for every 10 hydrogen atoms in the
universe.
© M. Bass
More Facts to Explain
There are stars, galaxies, clusters of
galaxies, clusters of clusters, and other
structures in the universe.
The rotation of galaxies indicates that
there is about 10 times more matter than
we can see – dark matter and energy.
There are novas and super novas and
places in galaxies where stars are
continually formed.
There are planets.
There is US!
© M. Bass
The Big Bang
The outward rush of the galaxies
from one another can be run
backwards to an initial beginning.
About 13.5 billion years ago the
universe was no bigger that a sub
atomic particle, it was very, very
hot and it started to expand.
Everything that we see around us
was determined in this moment of
creation.
© M. Bass
Big Bang Nucleosynthesis
This is a big name for the cooking of
atoms during creation.
The Big Bang model explains many
observed features of the universe - the
He:H ratio, the 2.7 K black body
radiation, the Hubble law and so on - but
it only explains atoms of H, He, D and Li
and these were formed in the first 3
minutes.
For all the other atoms we need stars!!
© M. Bass
Hubble Telescope Ultra Deep Field Image – all spots are galaxies
and all galaxies have many, many stars!
© M. Bass
The formation of stars
 As the universe expanded
turbulences formed as they must.
 These gave rise to stars and
galaxies of stars.
The first stars were probably
supermassive, lived fast, died young
and seeded the next generation.
 The question we want to address
is what does it take to get the
kind of stars we need to cook the
other atoms that we need to get
us.
 To do so requires a universe with
some very special properties.
Stars forming in small
protrusions from the Eagle
Nebula
© M. Bass
How do stars cook up
elements?
The first stars were formed by the hydrogen
(plus a little helium) gas produced in the Big
Bang.
Gravity pulled the gas in on itself and
collisions heated up the gas.
When a certain temperature was reached
nuclear fusion began and so called stellar
burning gets going.
The end products of nuclear fusion
reactions were higher atomic number
elements.
© M. Bass
Star burning
The rate with which a star burns its
hydrogen fuel increases with its mass.
Massive stars burn up fuel much faster
than smaller stars - makes you glad the
sun is a very average star, not a giant.
In such burning stars can produce all
the elements through iron
that includes carbon, oxygen, nitrogen ...
© M. Bass
The next step
 To get past iron you must
have temperatures much
higher than just nuclear
fusion allows.
 Thus, to get more massive
atoms you must have super
novas.
 So, stars burn, crash, spew
out their remains into the
galaxy and seed the
formation of newer stars.
© M. Bass
The next generations
 This process of one
generation of stars seeding
the next produces new stars
containing more than just
Big Bang elements
 So too does the residue of
star formation.
 Therefore, so do the planets
that form around the stars,
and
Spinning cloud
 therefore so do we.
flattening into a disk and
 We are star stuff.
condensing into a star
and planets
© M. Bass
What is required?
 We have pronounced the sequence of events
but haven’t explained why it occurs exactly
as it must for us to exist.
 To do this we will employ our knowledge of
modern physics - particularly the Standard
Model of Modern Physics
The current versions of the theories of Quantum
Mechanics and Gravitation
 (You do not have to know quantum
mechanics or general relativity to follow this
discussion.)
© M. Bass
Fundamental Constants
The Standard Model demands that certain
constants be just what they are.
About 20 numbers giving such things as the
gravitational constant, the charge on the
electron, the speed of light, and etc.
If they aren’t, things don’t happen the way
we observe that they do.
We don’t know why these constants are
what they are, just that they have to be
what they are if things are to make sense.
© M. Bass
A needle standing upright
on its point
 Why these constants must be exactly what
they are is asking why our universe is like a
needle standing upright on its point.
 The random probability that the several of the
20 constants that must have the precise
values needed to explain us is unbelievably
small.
About one chance in 10234
 The anthropic view, the one that says ours is a
universe designed for our existence, assumes
that a God set the values of the constants just
exactly right and then let things go.
© M. Bass
Constants needed for stars
 The part of the universe that concerns us is
mostly protons, neutrons, electrons and
neutrinos.
There is much more dark matter but it isn’t us.
 These interact through four forces - gravity,
electromagnetism, weak nuclear and strong
nuclear (in order of increasing strength)
 Forces are characterized by strength, range
and type of particles they affect.
 Particles participate in forces through
coupling constants
mass for gravity
charge for electromagnetism
© M. Bass
Gravity
It is the only universal interaction.
every particle having mass feels
gravity.
Its range is infinite.
Its strength is proportional to the
product of the masses that interact.
The proportionality constant, G, is
incredibly small, in units of proton
masses, it is 10-38.
© M. Bass
G
If this constant were any larger
stars would
live much shorter times than they do
they would not last long enough for
us to evolve
If this constant were any smaller
stars would
not collapse, ignite, and fuse H into
He and other necessary elements
© M. Bass
You need nuclear reactions
As gravity causes the gases of a star to
collapse nuclear reactions must take place
without nuclear reactions the internal pressure
of the gases can not compete with gravity and
the whole mess would collapse immediately into
a black hole.
For nuclear reactions to proceed as they
must to cook up the elements
the proton and neutron can differ in mass by
only 2 parts in a thousand and the electron must
be ~1800 times less massive than the proton
© M. Bass
n, p, e and n
Any larger differences and protons and
neutrons would not stick together in atoms
under the effects of the nuclear forces.
There would be no atoms, no chemistry, no
biology and the universe would be very boring.
Neutrinos are particles essential to
conserve momentum in nuclear
reactions.
It turns out that the neutrino mass can
not exceed ~10-9 of a proton mass.
© M. Bass
The scale of the universe
The universe must be big enough to
accommodate us.
To do so the mass density of the universe,
must be no larger than 10-40 in units of
proton mass.
If it were any larger the universe’s
expansion would not have happened.
If it were any smaller the universe would
have already expanded out of sight.
© M. Bass
There must be light
Electromagnetism is the force that governs
the radiation of light.
It must be present exactly as it is in order
to carry energy away from stars so that
stars stay in equilibrium long enough to
cook the elements and warm our planet.
This balance of gravitational collapse,
nuclear burning, and electromagnetic
radiation enables stars to last billions of
years.
© M. Bass
e, h and c
The demands for electromagnetic
radiation to maintain the energy balance
of stars requires that
the charge on the electron be no more and no
less than 1.6 x 10-19 Coulombs,
 Planck’s constant be exactly 6.3 x 10-34 Jsec., and
 the speed of light be 3 x 108 m/sec.
Any more or less and stars don’t make it.
© M. Bass
The probabilities if these
numbers occurred randomly
 For the existence of particles with the necessary
masses (in units of the Planck mass, the mass of
an elementary particle that would collapse on itself
and form a black hole or 1019 proton masses):
the proton
=1 part in 1019
the neutron
=1 part in 1022
the electron =1 part in 1022
the neutrino =1 part in 1027
 For the cosmological constant
(density of empty space)
=1 part in 1060
 For the ranges of the forces
=1 part in 1080
 For the strength of the forces =1 part in 104
© M. Bass
Add ‘em up
 The total probability of all of these numbers being
just what they must be to have us is the product of
all the probabilities or
1 part in 10234
 This is so astonishingly small that we are forced to
seek some deeper understanding of how so special
a universe could come about.
 What we have so far is a theory that fixes these
numbers so that it agrees with observed facts.
 What we don’t have is a theory that explains these
numbers.
© M. Bass
Possibilities
Some say it is God’s doing.
Some suggest something like
cosmological natural selection where
universes that generate many universes
generate universes like themselves.
Some suggest simply that in the infinity
of possible universes, we exist in the
only one in which we could exist.
© M. Bass