Download Histroy of Cosmology - Physics & Astronomy

History of Cosmology
Newton to The Big Bang
What is science?
a) Finding the truth.
b) A set of facts.
c) Performing experiments and observations.
d) All of the above.
What is the difference between
scientific laws and theories?
a)
b)
c)
d)
Laws have been proven.
Theories have not been proven.
Theories become laws.
Theories and laws are two different kinds
of scientific information.
e) a, b & c above.
Some Aspects of NOS
• Scientific knowledge is tentative.
• Scientific knowledge has basis in empirical
evidence.
• There is a difference between data and evidence.
• Scientific laws and theories are separate kinds of
scientific knowledge.
• Scientific knowledge is based upon observations
and inferences.
Some Aspects of NOS
Continued
• Scientific knowledge is created from human
imagination and logical reasoning.
• Scientific knowledge can be obtained by a
variety of scientific methods.
• Scientific observations are inherently
subjective based on interpretations.
• Science is a human endeavor influenced by
society and culture.
Revolutionary Science
and
Normal Everyday Science
• Copernican revolution turned science upside
down. Old theories are abandoned for new
theories. These are rare scientific times.
• Everyday science is the normal development of
science based on the revolutionary ideas.
Charles Messier (1730-1817)
• French comet hunter
• Looking for Halley’s
Comet to return as
predicted.
• Complied catalog of
annoying fuzzy things in
the sky that were not
comets.
• Most of these could not be
resolved by telescope
available at the time.
http://www.messiermarathon.com/about.htm
Messier Catalog
M1 – M110
M13
Globular Cluster
M42
Orion Nebula
M31
Andromeda Galaxy
M1
Crab Nebula
http://www.ipac.caltech.edu/2mass/gallery/messiercat.html
Joseph von Fraunhofer
(1787-1826)
• Studied dark lines in
the Sun’s spectrum
during the years 18121814.
http://www.hao.ucar.edu/public/education/sp/images/fraunhofer.html
http://www.harmsy.freeuk.com/fraunhofer.html
Gustav Kirchhoff (1824-1887)
• Was from Prussia.
• Developed three laws
of spectroscopy.
• These laws describe
the condition that
produce the three
types of spectra
observed.
http://www.hao.ucar.edu/public/education/sp/images/kirchhoff.html
Kirchhoff
st
1
Law
• Continuous spectrum
• A luminous solid or
liquid, or a sufficiently
dense gas, emits light of
all wavelengths (colors)
and produces a
continuous spectrum.
Kirchhoff
nd
2
Law
• Emission line spectrum
• A low-density, hot gas
emits light whose
spectrum consists of a
series of bright emission
lines. These lines are
characteristic of the
chemical composition of
the gas.
Examples of Emission Spectra
Kirchhoff
rd
3
Law
• Absorption line
spectrum
• A cool, thin gas absorbs
certain wavelengths from
a continuous spectrum,
leaving dark absorption
lines in their place. These
lines are also
characteristic of the
chemical composition of
the gas.
Sodium Spectrum
Emission and Absorption
Christian Doppler (1803-1853)
• Studied wavelength shift
produced by moving objects.
• He stated this relationship in
1842 in Über das farbige
Licht der Doppelsterne und
einiger anderer Gestirne des
Himmels (On the Coloured
Light of Double Stars and
Certain Other Stars of the
Heavens) while working in
Prague.
Doppler
Effect
V = (Dl/l) S
Where:
V = velocity of moving object
l = wavelength emitted
Dl = chance of wavelength
S = speed of the wave.
Math of the
Doppler Effect
For light waves this becomes,
V = (Dl/l) c
Where:
c = speed of light = 300,000 km/sec.
Lord Ross Giant Telescope (1850)
• It was (recently restored) a 6 foot (72 inch) diameter
telescope, which made it largest in the world.
• Some of Messier’s nebulae were seen to have distinct
spiral structure.
Vesto Slipher (1875-1969)
• Discovered red shift in
spectra of several
spiral nebulae using
Lowell 24-inch
refractor.
• This later became the
first evidence that the
universe is expanding
(1912 -1917).
http://www.lowell.edu/AboutLowell/clark.html
Henrietta Leavitt (1868-1921)
• Discovered 2400 variable
stars.
• Observed Cepheid
variable stars in LMC and
SMC.
• In 1912 discovered
Period-Luminosity
Relation for Cepheids
• Cepheids could be used to
estimate distances.
Cepheid Variable Stars
Period-Luminosity Relation
Period-Luminosity Relation for Cepheid’s and
RR Lyrae Variable stars.
Harlow Shapley (1885-1972)
http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1920.html
Shapley’s Observations
• In 1918 Shapley used
the 60-inch telescope
on Mt. Wilson to
observe variable stars
in globular clusters.
Shapley’s Huge Discovery
• Found that Sun was
2/3 of the way out
form the center.
• Center was located in
direction of
Sagittarius.
• This set off the Great
Debate.
The Shapley - Curtis Debate of
1920
• They debated the size of the universe.
• Are the spiral nebulae close or are they far
away and separate universes outside our
universe, island universes.
• Shapely claimed they were close and within
our universe.
• Curtis thought they were far away and
outside for our universe.
• Shapley won debate but was wrong!!
http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1920.html
George Hale (1868-1938)
• Built 100-inch
telescope on Mt.
Wilson in 1917
• Largest telescope in
the world until
200inch was built in
1940’s
• Named after John
Hooker who paid for
the mirror
http://www.mtwilson.edu/History/
Albert Einstein (1879-1955)
• General Theory of
Relativity
• Predicted an expanding
universe.
• He rejected idea and
introduced the
cosmological constant to
force a static universe.
This removed the natural
contraction caused by
gravity.
• Mass is distributed evenly
within the universe.
http://www.humboldt1.com/~gralsto/einstein/einstein.html
Alexandra Friedmann (1888-1925)
• Russian meteorologist
• Proposed an
expanding universe
model in 1925 based
on Einstein’s theory.
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Friedmann.html
George Lemaitre (1894-1966)
• Roman Catholic
clergyman at the Vatican.
• Independently proposed an
expanding universe that
had a moment of creation.
• Sent his idea to Einstein
who rejected it claiming
Lemaitre’s physics was
bad.
http://astro4.ast.vill.edu/mendel/lemaitre.htm
Edwin Hubble (1889-1953)
Mt Wilson Observatory
• In 1923 used 100-inch to observe Cepheid’s in
the Andromeda Spiral Nebula.
• It was one-hundred thousand times farther
away than the nearest stars!!!!!!!
• THAT SETTLED THE ISLAND UNIVERSE
DEBATE! Curtis was right, even though he
lost.
Hubble’s Image of Andromeda
Galaxy
In 1923, Edwin Hubble was examining photographic
plates of the Andromeda Nebula taken with the 100inch telescope in order to find novae -- stars that would
suddenly increase in brightness. On this place from the
night of October 5-6, 1923,
Hubble located three novae, each marked with an ``N.''
One of these novae, however, turned out to be a
Cepheid variable, a star that changes predictably in
brightness, and the ``N'' was crossed out and the star
was relabeled ``VAR!'' This Cepheid, and others
subsequently discovered in the Andromeda Nebula,
enabled Hubble to prove that the Nebula was not a star
cluster within our own Milky Way, but a galaxy more
than a million light years away.
http://www.mtwilson.edu/History/cal90/cal1090.html
Hubble Discovers
Expansion of Universe
• In late 1920’s hubble
used 100-inch to
observe spectra of
many galaxies.
• They ALL had red
shifts.
• This implied they
were all moving away
from Milky Way.
Hubble’s Law
• Hubble’s Law (1929) says
that the farther away a
galaxy is the faster it
moves away from us.
• V = HD
where V = velocity
D = distance
H = Hubble’s
constant
(slope of the
line)
Interesting Big Questions
•
•
Does this imply that the
Milky Way is the
center of the universe?
Does this imply a
creation event that
formed the universe?
The Raisin Cake Model
The entire Universe is expanding similar to an expanding raisin cake.
There is NO center to the expansion. Every raisin is getting farther
away from every other raisin.
No matter which raisin you live on, ALL other raisins appear to be
going away from you.
The Expansion of the Universe
• The universe expands
but the individual
galaxies do not expand.
• The cosmological red
shift is cause by the
stretching of light waves
as universe expands.
Fred Hoyle (1915-2001)
A Big Bang or a Steady State?
• Disliked the idea of a
creation event and made
fun of it by calling it “The
Big Bang”
• Developed the Steady
State theory (1948),
which said that as the
universe expanded new
matter was formed to fill
the void left by the
expansion.
http://www.coseti.org/hoyle.htm
George Gamow (1904-1968)
• Suggested a test to see which
theory was most likely.
• If universe was created in an
explosion the current
temperature of that explosion
should be about 3 Kelvin.
• Look for background radiation
of the temperature.
• Where do you look?
http://www.colorado.edu/physics/Web/Gamow/life.html
The Cosmic Black Body Curves
As the universe expands
it should cool. Gamow
predicted the universe
should now have a black
body curve following
3 Kelvin, observable in
microwaves.
Robert Wilson (1936- )
Arno Penzias (1933- )
• In 1965 they used a horn
antenna to accidentally
observe the 3 Kelvin
microwave background
radiation left over from
the Big Bang.
• IS THE BIG BANG
CONFIRMED?
• IS THE STEADY STATE
THEORY DEAD?
Cosmic Background Explorer
COBE
• Launched November 18,
1989.
• Obtained black body
curve for a temperature of
2.7 Kelvin!
• WAY COOL!!! (Pun
intended).
http://space.gsfc.nasa.gov/astro/cobe/cobe_home.html
The Inflationary Universe
The Horizon Problem
Why does the early
Universe look the
same in all directions?
Rapid expansion says
that universe expanded
so fast that it could
remember how its
neighbors looked.
The Inflationary Universe
The Flatness Problem
The Universe appears
to have formed with
exactly the amount of
mass necessary to
make it flat. WHY?
The Inflationary Universe
The Flatness Problem
• Early in the formation
of the Universe it
expanded very rapidly,
which makes it appear
flat.
• It may not really be
flat. It may only look
flat.
COBE Microwave Map
http://aether.lbl.gov/www/projects/cobe/cmb_fluctuations_big.jpg
•
•
•
•
2 years of data.
There are temperature variations.
Fluctuations maybe the seeds of galaxy formation.
A PICTURE OF CREATION!
The Fate of the Universe
• Two possible futures
1) A low density universe will expand forever.
2) A high density universe will collapse in the Big
Crunch.
The Fate of the Universe
At the moment we cannot
tell the difference.
Critical density is the density that is
required to cause the universe stop
expanding in infinite time.
The Fate of the Universe
• Type Ia supernovae all
have about same
actual brightness.
• They help us
determine distances.
• Universe appears to be
accelerating!!
This is inconsistent with The Big Bang Model!!!!!!
The Fate of the Universe
Again it is very difficult to sort out how the universe will end!
The Fate of the Universe
• Are distances to
supernovae correct?
• Is there a dark repulsive
force, Dark Energy?
• Do we need to rethink
Einstein's cosmological
constant?
This is the fun of science and it is why humans DO science!
Resources
Chaisson & McMillan, (2002, 2004). Astronomy Today (4th & 5th Ed.)
Bennett et al. (2004) The Cosmic Perspective (3rd Ed.)
Shipman, Wilson, and Todd, (2003). An Introduction to
Physical Science (10th Edition).