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) Laws have been proven.

b) Theories have not been proven.

c) Theories become laws.

d) 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 NOSContinued

• 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 Scienceand

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 CatalogM1 – M110

http://www.ipac.caltech.edu/2mass/gallery/messiercat.html

M13 Globular Cluster

M42 Orion Nebula

M31 Andromeda Galaxy

M1 Crab Nebula

Joseph von Fraunhofer (1787-1826)

• Studied dark lines in the Sun’s spectrum during the years 1812-1814.

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 1st 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 2nd 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 3rd 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

Math of the Doppler Effect

V = ) S

Where:V = velocity of moving object = wavelength emitted = chance of wavelengthS = speed of the wave.

For light waves this becomes,V = ) 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 100-inch 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 ExplorerCOBE

• 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 UniverseThe 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 UniverseThe 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

• 2 years of data.• There are temperature variations.• Fluctuations maybe the seeds of galaxy formation.• A PICTURE OF CREATION!

http://aether.lbl.gov/www/projects/cobe/cmb_fluctuations_big.jpg

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 UniverseAt 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).