A Brief History of Astronomy
Osher Lifelong Learning Institute
October 1, 2013
Dick Dahlberg
What Is So Special About Astronomy?
• For 3000 years: Astronomy = Science
– From ancient Babylon to Copernicus (15th C.)
• But with a little geometry thrown in.
• The heavens were visible.
– There was a pattern to the behavior of the Sun,
Moon, stars, planets.
– Was there also a message???
• Creation myths frequently had a cosmic basis.
Astronomy Also The Basis For Many
Early Religions
• Tribes and villages with a common set of beliefs were more
stable .
• Belief systems (religions?) frequently had a cosmic
component.
• There must be some explanation for the locust invasion.
– OF COURSE: the planetary alignment was wrong!!!!
Agenda
• Ancient Babylon (2nd to 3rd millenia BCE):
– Star maps
• Ancient Greeks (3rd to 6th century BCE):
– Remarkable calculations concerning our solar system.
• Aristotle (384 to 322 BCE):
– Earth at the center of a perfect and divine Universe.
• Ptolemy (60 to 168 CE):
– Added bells and whistles to Aristotle’s mistake.
• Copernicus (1473 to 1543):
– Sun centered solar system: Part 1: Simplicity a virtue.
• Tycho Brahe (1546 to 1601):
– Refined astronomical data.
Agenda - Continued
• Kepler (1571 to 1630):
– Sun centered solar system: Part 2: Orbits are ellipses.
• Galileo (1564 to 1642):
– Sun centered solar system : Part 3: More evidence.
– The heavens are not perfect and divine.
• Sun spots; Moon craters
– Jupiter’s moons; phases of Venus
• Newton (1642 to 1727):
– Sun centered solar system: Part 4: The physics.
• Michelson/Morley (1852 to 1931):
– Proved there was no ether.
Agenda - Continued
• Einstein (1879 to 1955):
– Laid the groundwork for the Big Bang.
• Evidence of the Big Bang:
– Lemaitre (1894 to 1966):
• Deduced the possibility of a Big Bang from Einstein’s
Theory of Relativity.
General
– Hubble (1889 to 1953:
• Discovered the red-shift: everything is moving away from
everything else.
– Gamow, Alpher and Hoyle (mid 20th Century):
• Deduced the abundance of elements from first principles.
– Penzias and Wilson (1964):
• Discovered radiation left over from the Big Bang.
Astronomy in Ancient Babylon
2nd and 3rd Millennia BCE
The Babylonian Book
Enuma Anu Enlil
• Enuma Anu Enlil
contained a record of
Babylonian
astronomical
observations.
– Star catalogs.
– Data on Mercury, Venus, Mars,
Jupiter and Saturn.
Tablet 63: The Venus Tablet: 7th c. BCE .
• Babylonian data were
extensively used by the
Greeks and Egyptians.
ANCIENT GREEK SCIENTISTS
The Emergence of Real Scientists
Ancient Greeks
Greek Scientists in Raphael’s
Painting:
Pythagoras
Anaxagoras
Aristotle
Euclid
Ptolemy
Plato
Many other philosophers and
scientists
School of Athens
Raphael Fresco (1509), Vatican City
Aristarchus: 310 to 230 BCE
• Proposed a suncentered solar system.
• The Earth rotates on its
axis once a day.
– Estimated distance to
the Sun.
Aristarchus
Relative Distances: Sun and Moon
• At half-moon, the Moon,
Sun and Earth for a right
triangle.
• The Moon-Earth-Sun angle
can be measured.
– 87 degrees by Aristarchus.
• The Sun is 20 times farther
than Moon.
• Good science: wrong
answer.
– The actual multiplier is 400.
– The actual angle was close to
90 degrees: hard to measure.
Eratosthenes: 275 to 195 BCE
• Greek mathematician and
astronomer.
• Determined the
circumference of the
Earth
• Determined the diameter
of the Moon and its
distance from the Earth.
Eratosthenes
Circumference of the Earth
• Find a spot where Sun is directly
overhead: Syene (Aswan, Egypt)
• Place a pole a known distance
from that spot.
– Alexandria, 550 miles from Syene..
• Measure the angle between pole
and sun’s ray:
– 7.2degrees.
• Then: 7.2 / 360 =
550/Circumference.
• Circ. = 27,500 miles.
• Radius of the Earth:
• L = length of shadow cast at
Alexandria by pole of height H:
• L/H = 550/radius
Julian Rubin: julianTrubin.com (2011)
Hipparchus: 190 to 120 BCE
• The greatest astronomer in
antiquity.
• His quantitative models of the
motions of the Sun and Moon
have survived.
• Achievements:
– Predicted eclipses.
– Distance to Moon: 250,000
miles.
– First star catalogue.
– Calculated length of year to
within 6.5 minutes..
• Hipparchus’ work was
extensively reported in
Ptolemy’s “Almagest”.
The “First Authority”
Aristotle
384 to 322 BCE
Aristotle’s Early Life
• Born in northern
Greece.
• Aristocratic family.
• At age 18, student at
Plato’s Academy.
• At age 42, became head
of Royal Society of
Macedon.
– Alexander the Grea
Aristotle
The Pre-Eminent Teacher
Aristotle studied under Plato for 24 years.
• Founded the Lyceum in 335
BCE (at age 49).
• Studied and taught anatomy,
astronomy, geology, physics,
rhetoric, theology, philosophy,
logic …..(almost everything)
• Sought the general principles
of nature.
– By observation.
• Wanted to unify all branches
of knowledge
– Wrote 150 treatises.
Plato and Aristotle
From Raphael’s Painting
“School of Athens”
• For 2000 years, he defined an
educated man.
Aristotle’s Universe
• The Universe is divine and perfect.
• Heavenly bodies move naturally in perfect circles.
• The circular motions are in harmony with theology:
perfect.
• The heavens are a nest of spherical shells with the
Earth at the center
• The largest is a Devine Sphere, self-moving, carrying the
fixed stars.
• An “aether” fills the Universe and makes up the stars
and planets.
The Earth Centered Universe
Claudius Ptolemy
2nd Century CE Egyptian Astronomer
Claudius Ptolemy
Last Great Astronomer of Ancient Times
• 90 CE to 168 CE.
• Roman citizen
• Greek ancestry
– Wrote in Greek.
• Lived in Alexandria
• Ptolemy built on
Aristotle’s Universe.
Early Baroque Artist’s Rendition
The “Almagest”:
The “Greatest Compilation”
• Ptolemy’s major work on
astronomy.
– Much due to Hipparchus.
– Divided into 13 books.
• Goal: write down
everything that was
known.
– Star catalogues.
Picture of George Trebizoud’s Latin
Translation of the “Almagest” (15th c..)
• Locations for 1022 stars
and 48 constellations.
– Tables for computing
planetary locations.
Ptolemy’s Universe
• The Earth was at the center
(of the Universe).
• Earth did not move
• All motion was in circular
paths.
• Universe imagined to be
composed of nested
spheres.
Ptolemy’s Model
Complicated But Accurate
• Epicycles necessary for
accuracy.
– Accurately gave locations
of planets, stars.
– Predicted eclipses.
• Better than initial
versions of the suncentered model.
Ptolemic Model of the Universe
1747 Icelandic Manuscript
1524 Engraving
Library of Congress
Comparison
Earth-Centered vs. Sun-Centered
Criterion
EarthCentered:
Ptolemy
Success
Sun-Centered:
Early Greek
Success
Common
sense
Obvious
Good
Leap of
imagination
Not so good
Awareness of
motion
None detected
Good
None detected
Not so good
Stellar parallax
None
observed
Good
None observed
Not so good
Planetary
predictions
With epicycles
Good
Simplicity
Very complex
Not so good
Not so good
Naturally
simple
Good
What Is the Parallax Effect?
Astronomy 161 Lectures
Dept. of Physics and Astronomy
University of Tennessee
Ptolemy’s “Ecumene” Map
Map Of the Known World
• Devised a
latitude/longitude grid.
– Located the grid
coordinates for 8000
locations on the world
map.
1482 Johannes Schnitzer Engraving
(British Library Board)
• Even though Ptolemy’s
estimates of latitude and
longitude were wrong by
about 15%, his maps
were used into the 16th
Century.
The Sun Centered Universe: Part 1
Nicholas Copernicus: 1473 to 1543
Nicholas Copernicus
Renaissance Astronomer (1473 to 1543)
• Polish mathematician,
astronomer, physician, jurist,
diplomat, cleric, artist, poet,
economist, and linguist
(translated ancient Greek texts
into Latin).
• Was a strong Catholic.
– Received a doctorate in canon
law .
– Did not want to antagonize
the Church.
• Church strongly favored the
Ptolemaic model of the Universe.
– Biblical references to the
relative positions of Sun and
Earth.
Biblical References?
• Psalm 93.1 and Chronicles 16:30: “The world
is firmly established , it cannot be moved.”
• Ecclesiastes 1:5: “And the Sun rises and sets
and returns to its place”.
Simplicity
The Driving Force For Copernicus
• Was familiar with the Sun-centered model of the Ancient Greeks.
– Had great respect for Aristotle.
– Was a student of Ptolemy’s “Almagest”.
• But simplicity is a virtue.
– William of Occam: 14th Century Franciscan.
– Occam’s Rasor: The simplest of two competing theories is probably
the best.
• “When you hear hoof beats, think horses not zebras.”
The Starting Point: Seven Axioms
1)
2)
The heavenly bodies do not share a common center.
The center of the Earth is not the center of the universe.
3)
4)
The center of the universe is near the Sun.
The distance from Sun to Earth is insignificant compared to the distance
to the stars.
5)
The daily apparent motion of the stars is a result of the Earth’s rotation
on its own axis.
The apparent annual sequence of movements of the Sun is a result of
the Earth’s rotation about it.
6)
7)
The apparent retrograde motion of some of the planets is the result of
our relative position as observer on a moving Earth.
Copernicus’s Seminal Work
“On The Revolution Of the Heavenly Spheres”: 1543
Copernicus’s Universe:
•
•
•
•
•
•
•
Sphere of fixed stars.
Saturn: 30 year orbit.
Jupiter: 12 years.
Mars: 2 years.
Earth.
Venus: 9 months.
Mercury: 80 days.
All orbits circular and uniform
around the Sun.
The Phases of Venus
Model Comparison
Ptolemaic Earth-Centered Model
Venus is between the Earth and Sun
Venus always appears as a crescent.
Copernican Sun-Centered Model
Venus is not always between the Earth and Sun.
The full range of phases is seen from the Earth.
Astronomy 161 Lectures
Dept. of Physics and Astronomy
University of Tennessee
Copernicus’s Work: Small (Initial) Impact
Why???
•
•
•
•
Copernicus died shortly after publication: Could not promote his ideas.
The Church was against him
Dreadful writing style.
An unauthorized preface was added (during printing) implying that the
major hypothesis was not true.
– Apparently Copernicus’s apprentice, Georg Rheticus, and a Lutheran cleric, Andreas
Osiander, added the preface.
– Purpose? A mystery.
• AND: The Ptolemaic Model was more accurate
• CONCLUSION: Need more accurate data
Needed: More Astronomical
Data
Tycho Brahe: 1546 to 1601
The Scientific Bridge Between
Copernicus and Kepler
Tycho Brahe
Danish Scientist (and Character)
•
•
Swashbuckling Danish nobleman
Lost part of his nose in a duel.
•
Employed a
dwarf court jester
who sat under the
table while they
were eating.
Also had a tame elk
•
•
Died from too
much beer.
• Fell in love with Kirsten
Hansen
– Daughter of a Lutheran
minister, a commoner.
• Danish law:
– When nobleman and
commoner live together,
and she has the keys to the
house, their allegiance is
binding in a “morganatic
marriage” after 3 years.
• They lived together for 30
years.
– Had 8 (legitimate) children.
Initial Interest In Astronomy
•
In 1572 (age 26) Brahe witnessed a supernova: Tycho’s Star.
•
In 1577 Brahe observed a comet.
– Accompanying tail suggested an “elongated” orbit.
•
Conventional wisdom at the time:
– Both were atmospheric events.
– The universe beyond the Moon’s orbit? Perfect and unchangeable.
•
Brahe showed both events were not atmospheric events.
* Aristotle: beware.
Brahe: Professional Astronomer
•
Brahe became obsessed with the need for more and better astronomical data.
•
King Frederick II persuaded Brahe to set up shop in Denmark
•
Moved to Prague in 1597.
– At the invitation of HRE Rudolph II.
– Established a new observatory.
• Worked there with Kepler until his death in 1601.
• His legacy: a vast amount of accurate astronomical data.
Late Breaking News
• Body exhumed in 2010 to try to determine cause of death:
– Burst bladder? Judgment at the time.
• 11 days before death, at a banquet, he should have gone to the toilet
but didn’t.
– Kidney failure?
– Killed by Kepler?
– Poisoned (mercury) by his cousin, Eric Brahe, on orders from
Danish king, Christian IV ?
• Tycho was rumored to be having an affair with the King’s mother.
– An accidental overdose of mercury taken by Tycho in medicating
a kidney ailment?
– Autopsy will examine hair samples and conduct CT scan of
bones.
The Sun Centered Universe: Part 2
Johannes Kepler: 1571 to 1630
Johannes Kepler
•
German mathematician and
astronomer.
–
–
•
Prof. of Mathematics and Astronomy at
age 23.
Assistant to Tycho Brahe (Prague, 1600 to
1601).
Devout Lutheran
• Believed God created cosmic
harmony through a geometric
arrangement of planetary
orbits.
•
1610 Portrait
[Artist Unknown]
Caught up in Counter Reformation
Kepler’s Goal
Harmonize the Copernican Model With The Bible
• God created a certain
harmony with respect to
planetary orbits.
– What was His plan?
• The Sun is the symbol of “God
the Father”.
•
•
The Son: the stellar sphere.
The Holy Spirit: the intervening
space.
Kepler’s First Attempt:
• Regular polygons: one
inscribed inside and one
circumscribed outside a
circle (orbit) at definite
ratios.
• The basis for a model of
the Universe?
• Did not fit data too well.
• Instead of regular
polygons , try Platonic
Solids.
The Five Platonic Solids
• Their elegance and simplicity
suggested an astronomical
connection.
• Kepler tried to find a connection
between the Platonic Solids and
planetary orbits.
“The Cosmographic Mystery” (1595)
Second Attempt: 3-D Platonic Solids
•
The five Platonic Solids could be
uniquely inscribed and circumscribed
by spheres.
– In a nested arrangement.
•
Six known planets: Mercury, Venus,
Earth, Mars, Jupiter and Saturn.
•
Order of solids: octahedron (8 faces),
icosahedron (20), dodecahedron (12),
tetrahedron, (4), hexahedron (6,
cube).
The model did not fit all the data.
– Inaccurate data?
In 1600, Kepler (age 27) went to
Prague to work with Tycho Brahe to
get more accurate data.
•
•
Success At Last
The Third Attempt
• Using Brahe’s Data, Kepler
Analyzed the Orbit of Mars
• By trial and error, Kepler
discovered the ellipse.
• The First Law: All planets
move in ellipses with the
Sun at one focus.
Kepler’s Depiction of the Geocentric Motion of Mars
Through Several Retrograde Cycles
[Astronomia Nova (1609) ]
Kepler’s Three Laws
Kepler’s Second Law:
University of Tennessee Astronomy 161: The Solar System
•
First Law: All planets move in ellipses
about the Sun with the Sun at one
focus.
•
Second Law: Planets sweep out
equal areas in equal times.
•
Third Law: Square of the orbital
period of a planet is proportional to
the cube of the semi-major axis (half
of the major axis).
– P = period
– R = radius
– P12/P22 = R13/R23
Kepler’s Major Publications
“A New Astronomy” (1609)
• Manuscript was completed in 1605.
• Published in 1609 due to legal disputes with Brahe’s heirs.
“The Epitome of Copernican Astronomy”
• Kepler’s most Influential Work
• Three volumes attempted to explain planetary motions through physical
causes.
Epilogue
• As with Copernicus, Kepler’s work not widely
accepted at first.
– Circular orbits were sacred.
• The Church rejected his findings.
• Kepler could not explain why orbits were
elliptical.
The Sun Centered Universe: Part 3
Galileo Galilei: 1564 to 1642
Galileo: The Father Of Modern
Science
Galileo Galilei
The first mathematical physicist
• Galileo was deeply religious:
• A brilliant and caustic wit.
• Chair of Mathematics Dept., Univ.
of Padua, at age 27.
• The “Father of Modern Science”:
– Scientific method
– Experimentalist and theorist
• Believed the Copernican model
of the Universe.
Galileo And the Church
At the Beginning
• Galileo was a devout Catholic.
• Galileo’s friend, Cardinal Barberini, became Pope Urban VIII in 1623.
• The Church was adamantly opposed to the Copernican model:
– Psalm 93.1 and Chronicles 16:30: “The world is firmly established , it
cannot be moved.”
– Ecclesiastes 1:5: “And the Sun rises and sets and returns to its place”.
• Catholicism was in a 30 years war with the Protestants.
– In no mood to be lenient.
• Aristotle was still deeply revered.
– Galileo was reluctant to criticize Aristotle.
Galileo’s Telescope
Refracting Telescope: 1608
• Flemish spectacle maker won
patent for telescope.
– Light enters at the top and is
focused on the eye at the
bottom.
• Galileo recognized its
potential.
• Built his own, a “refracting”
telescope.
Photograph of Original Telescope
Discovery of Moons of Jupiter: 1610
• The Galilean moons from
the top: Io, Europa,
Ganymede, Callisto.
• Discovery proved that not
all heavenly bodies circled
the Earth.
Composite Sketch of Galilean Moons
(NASA Archive)
The Phases of Venus
•
•
•
Venus has only one face toward the
Sun.
“Full” exposure appears small from
Earth.
– “New” exposure large.
– “New” exposure visible because
of “halo”.
This should have been the end of the
Ptolemaic model.
Galileo And The Church:
At the End
• Galileo defended the Sun-centered model from the beginning.
– Claimed it was not contrary to Scripture.
• The Inquisition ordered Galileo not to “hold or defend” the
Sun-centered hypothesis.
– But Galileo was free to “discuss” the Sun-centered model.
• Galileo began writing a “Dialogue Concerning the Two Chief
World Systems”.
“Dialogue Concerning the Two Chief
World Systems”: 1632
• Arguments presented as a
dialogue on the issues as
opposed to advocacy.
– Simplicio: Aristotle (Pope
Urban VIII).
– Sagredo: neutral layman.
– Salviato: Galileo
• Ptolemaic system subtly
ridiculed.
• Copernican system
advanced.
Galileo Facing the Inquisition
• Found “vehemently suspect
of heresy”.
• Required to “abjure, curse
and detest” Sun centered
theory.
• Formally sentenced to
prison.
– Commuted to house
arrest.
• “Dialogue” was banned.
1857 painting by Cristiano Banti
Comparison
Earth-Centered vs. Sun-Centered
Criterion
EarthCentered:
Ptolemy
Success
Sun-Centered:
Galileo/Kepler
Success
Common
sense
Obvious
Good
Leap of
imagination
Not so good
Awareness of
motion
None detected
Good
None detected
Not so good
Stellar parallax
None
observed
Good
None observed
Not so good
Planetary
predictions
With epicycles
Good
Kepler’s system
Good
Phases of
Venus
Fails
Not so good
Natural
consequence
Good
Simplicity
Very complex
Not so good
Naturally
simple
Good
And In Addition…………….
• The Heavens are not perfect:
– Sun spots
– Moon craters
– Comets
– Supernovas
• The moons of Jupiter do not orbit the Earth
• Aristotle’s grip on science finally broken.
The Sun Centered Universe: Part 4
Isaac Newton: 1642 to 1727
The Greatest Scientist?
Newton’s Early Life
• Mathematician and physicist.
– Possibly the greatest scientist
in history.
• Unhappy childhood.
– Born 3 months after death of
father.
– Stepfather shunned him.
– Raised by grandparents.
– Came to hate mother and
stepfather.
• Angered by criticism.
Isaac Newton At Age 46
1689 Portrait by Kneller
– Harsh toward enemies.
– Harbored resentment.
• Never married.
Newton’s College Years
•
•
Entered Cambridge Univ. at age 19.
Spent ages 23 to 25 at family home in
Woolsthorpe.
•
•
•
Apple tree: Cambridge Univ. Botanical Garden
[Descended From Newton’s Tree (?)]
•
Due to plague.
Conducted private research.
Major discoveries were made during
this period.
• Gravity.
• Laws of motion.
• Optics.
• Calculus
Prof. of Math. at 27.
Newton’s Theology
• An Arian.
• Did not believe Jesus was the
Son of God.
• God was the master Creator
• Newton believed he was chosen to
understand biblical scripture – to find hidden
messages.
.
• Believed in alchemy; the Philosopher’s
Stone, ESP, magic, spiritualism, numerology.
• Newton: “Gravity explains the motion of
the planets but it cannot explain who set the
planets in motion. God governs all things and
knows all that is or can be done.”
• The “Principia” concludes with an account
of monotheism and an attack on the doctrine
of the Trinity.
Canterbury Cathedral
“Principia Mathematica” (1687)
Considered the Most Important Scientific Work Ever Published
• Major portions of work done
1665 to 1667 when at
Woolsthorpe.
• Aristotle: Earthly things and
heavenly things obey different
laws.
• Newton: The same force governs
bodies on Earth and in the
heavens.
Three Laws of Motion
And the Law of Gravity
1)
Law of Inertia: An object at rest
tends to stay at rest and an
object in uniform motion tends
to stay in motion unless acted
upon by an external force.
2)
Force = mass x acceleration
3)
To every action there is an
equal and opposite reaction.
The Law Gravity:
Gravitational force: F =
Gm1m2/r2
A “Thought” Experiment
• A dropped ball will fall to the
ground due to gravity.
• Throw the ball horizontally: it will
hit the ground farther away.
• Throw it hard enough, with no air,
and it will circle the earth and
return to the starting point.
• Hence: centripetal motion +
gravity = orbit.
– The Moon continually falls
toward the Earth
Newton’s Great Synthesis
• Kepler developed 3 laws of planetary motion.
– Empirically derived: matched the data obtained
by Brahe.
• Kepler did not know why they gave the right answer.
• Newton explained why they worked.
– Showed they applied throughout the Universe.
Newton Developed the Reflecting
Telescope
• REFRACTORY TELESCOPES:
chromatic aberration problems.
– Lens acts like prism.
– Newton recognized this.
• Problem solved with a
REFLECTING TELESCOPE.
– Invented by a Scot (Gregory),
but improved by Newton.
Most Optical Telescopes are Reflecting
200 Inch Reflecting Telescope
on Mt. Palomar
Left: Replica of Newton’s 2nd
Reflecting Telescope
Isaac Newton’s Tomb
Westminster Abbey
• Alexander Pope:
“Nature and Nature’s laws lay hid in
night;
God said “Let Newton be” and all
was light.”
• In a 1676 letter to
Robert Hooke, Newton
wrote:
“If I have seen further it is by
standing on the shoulders of
giants.”
Newton: Summary
• Discovered 3 Laws of Motion
• Discovered the Law of Gravity.
• Asserted that the laws of physics applied
throughout the Universe.
– The Earth was not unique.
• Invented a reflecting telescope.
The Speed Of Light
Albert Michelson: 1852 to 1931
The “Failed Experiment”
Albert Michelson
•
Born in Poland: to U.S. in 1855.
•
U.S. Naval Academy in 1869.
– Professor of Physics at Academy
in 1877.
•
Conducted first experiments on the
speed of light while at the Academy.
•
Professor of Physics, Case Western
Univ. (Cleveland) in 1883.
• Michelson-Morley experiments in
1887.
• Nobel Prize for Physics in 2007.
– First American so honored in
Physics.
The Speed of Light Through the
Centuries
Light faster than thunder.
Empedocles in 450 BCE Ancient Greece: finite.
Aristotle, 4th c. BCE: infinite.
Kepler, 1609: infinite
Galileo, 1632: between two people on distant hills:
– Between 10,000 km/hr. and infinity.
• Ole Roemer, Danish astronomer (17th century):
– Analyzed data on eclipses of Jupiter’s moon, Io:
• Deduced speed: 190,000 km/sec.
•
•
•
•
•
The Speed of Light Through the Centuries
Continued
• Michelson at age 27 at U.S. Naval Academy
(1878):
– Speed of light is 299,910 (+/- 50) km/sec.
• EXACT VALUE: 299.792.458 km/sec.
– The length of a meter is defined in this way.
The Concept of Ether
[Space “matter”]
• Postulated by Aristotle:
– Fills every point in space.
• Newton: endorsed the notion of an “ether”.
– Speed of light relative to ether.
• Maxwell: equations showed EM waves traveled at
“c” in a vacuum.
– Light is a wave. So what is waving??? Something in the ether.
• Michelson-Morley experiments in 1887 showed
“ether” did not affect light velocity.
– Hence, no ether?
– But the idea finally died with Einstein.
Michelson-Morley Strategy
The Earth’s movement
around the Sun and the
Sun’s movement in
space allow light
measurements to be
made against, with and
across the ether.
Experimental Concept
The Michelson-Morley Experiment
• Work with monochromatic
light.
• Split beam into
perpendicular beams.
• One beam against the Ether.
• One beam across the Ether.
• Reflect the beams back and
recombine into one beam.
• If they arrive back at different
times, interference.
• Expectation: the “cross
wind” time will be less than
the “into the wind” time.
Michelson: Summary
• Measured the speed of light.
Michelson, Einstein and Morley
[California Institute of Technology: 1931]
• Proved that an “ether” did not
exist.
• Signaled the beginning of a
second (and third?) scientific
revolution: relativity and
quantum mechanics.
Einstein credited Michelson with a crucial
experiment on the speed of light.
Theory of Relativity
Albert Einstein: 1879 to 1955
Einstein’s Early Childhood and Education
Einstein at age 25
• Born in Ulm, Germany.
• Family were non-observant Jews.
• In an out of several schools,
Einstein entered Zurich
Polytechnic in 1896.
• Graduated in 1900 with a
teaching certificate.
• Could not find a teaching
position.
• Bern Patent Office: 1902
• While at the patent office, he
continued education.
• Ph.D. in 1905.
Einstein Escaped From Germany
• 1908: Prof. of Physics, Univ. of
Bern.
• 1914 to 1932: Director of the
Kaiser Wilhelm Institute for
Physics.
• 1933 Hitler’s anti-Jewish
programs prompted Einstein to
flee to England, then the U.S.
• Institute For Advanced Studies at
Princeton until his death.
Einstein Sheds “Pacifism” Wings
Takes Up “Preparedness” Sword
Cartoon In Brooklyn Eagle (1933)
1905: A Year To Remember
[Einstein’s Age: 26]
• Special Theory of Relativity..
• Equivalence of Mass and Energy: E = mc2
• The Photoelectric Effect: Light travels in
quanta (packages of energy).
• Brownian Motion
---------------------------------------------------------------• And in 1916: The General Theory of Relativity.
Theory of Relativity
Important to the History of Astronomy
• Special Theory:
– The velocity of light is a constant
• Independent of the velocity of the source or observer.
• There is no “ether”.
– Nothing can move faster than the speed of light.
• General Theory:
– Gravity is equivalent to the warping of space by celestial bodies
– The General Theory led Georges Lamaitre to propose a Big Bang origin for the
Universe.
The Big Bang
The Origin of the Universe?
Overview of the Big Bang
The Concept:
The Universe emerged from an extremely
dense singularity. The initial expansion was
very rapid. Since then, space has been
steadily expanding carrying galaxies with it,
like raisins in a rising loaf of bread.
Gnixon: Wikipedia Project
Evidence of the Big Bang:
1) The Red Shift and
Hubble’s Law: 1929
2) Abundance of Elements:
Gamow, Alpher and Hoyle:
1948 to 1953
3) Cosmic Microwave
Background Radiation:
Penzias and Wilson:
1964
The Original Idea: 1927
Georges Lemaitre, Roman Catholic Priest (1894 to 1966)
•
•
•
Lemaitre was ordained in 1923.
Educated at Cambridge and Harvard .
Observatory at MIT from 1923 to
1925.
•
General Relativity implied a moment
of creation: “The primeval atom
hypothesis is a cosmogenic
hypothesis which pictures the
present Universe as a result of
the radioactive disintegration of
an atom”.
•
Lemaitre was rebuffed by Einstein.
•
In 1949, this hypothesis had legs and
was called the BIG BANG by Fred
Hoyle.
Time Line From the Big Bang
•
•
Within the first second, a great expansion took place.
* The universe cooled enough so subatomic particles could combine.
* Within a few seconds, Hydrogen and Helium nuclei began to form.
Stars began to form after about 300 million years.
– Carbon and other heavy elements were formed in the stars and spread though out the universe by
disintegrating stars.
“Recent” History
The Red Shift: Hubble’s Law (1929)
Edwin Hubble: American Astronomer (1889 to 1953)
Univ. of Chicago: law and astronomy
Ph.D. thesis from Yerkes Observatory:
“Photographic Investigations of Faint
Nebulae”.
100 inch Mt. Wilson Telescope
Hubble discovered that our galaxy was
not the only galaxy.
The Red Shift: Doppler Effect
•
When object moves away ,light
wave-length gets longer and the
“color” shifts down toward the red.
•
HUBBLE’S LAW (1929): “Degree of
Doppler shift (Red Shift) increases
with increasing distance of galaxies
from our own.”
•
First observational support of the
Big Bang theory.
•
The Universe behaves like it is
exploding.
George Gamow and Ralph Alpher
•
•
•
George Gamow: 1904 to 1968.
Russian-born American physicist.
Tried to leave USSR (with wife) in
1932.
– By kayak to Turkey: failed.
•
Succeeded in 1933: physics
conference in Brussels.
•
•
Ralph Alpher: 1921 to 2007.
In 2005, was awarded the National
Medal of Science, the highest
scientific honor in the U.S.
Hydrogen To Helium Atom Ratio: 10 to 1
• The starting point was a hot soup of gamma rays, quarks and other
elementary particles.
• Between 1 msec and 1 sec, quarks combined to form protons and
neutrons.
• After a few seconds, nuclei could be formed:
– Hydrogen (H-1) + neutron = Deuterium (H-2)
– (H-2) + (H-1) = helium-3 (He-3).
– He-3 + He-3 = He-4 plus 2 (H-1)
• Gamow and Alpher calculated that the hydrogen to helium atom ratio
should be 10:1.
Atom Ratios In the Universe
• Hydrogen and helium account for 99.9% of all
atoms in the universe: universe:
* Hydrogen:
10,000
* Helium:
1,000
* Oxygen:
6
* Carbon
1
* Everything else:
< 1
• The Sun converts 584 million tons of hydrogen
into 580 million tons of helium each second.
The Formation of Carbon: 1953
Fred Hoyle: 1915 to 2001
•
Hoyle worked at the Cambridge Institute for Astronomy.
– Was a rebel; frequently took contrary positions.
– Rejected Darwinian evolution:
•
Coined the term “Big Bang”, but….
– Rejected the Big Bang theory.
•
Seminal work: “Synthesis of the Elements in the Stars”
(with other authors): 1957.
Difficult to Form Carbon-12
• It is very difficult to create
Carbon by adding nucleons to
Helium.
• The resulting nuclei are
very unstable.
•
Hoyle postulated (1953) that three
Helium nuclei combine in a special
sequence to give Carbon:
– He-4 + He-4 = Beryllium-8
– Be-8 + He-4 = Carbon-12
•
For this to happen, the Carbon
nucleus had to have an (as yet)
unknown energy level.
– Hoyle predicted its existence.
– It was found later at Cal Tech.
The Heavier Elements?
• As the hydrogen gradually disappeared, a star would
cool.
• Gravity would cause it to contract, generating heat.
• Light nuclei would fuse into the heavy elements.
• As the star got steadily smaller, it would eventually
explode.
– “Contaminate” the Universe with heavy stuff.
Cosmic Microwave Background Radiation
•
Initially, the nuclear soup was very dense;
– OPAQUE to light.
•
After 379,000 years, the universe cooled to about 3000oC.
– Atoms had formed and the universe became TRANSPARENT.
– Photons could travel unimpeded throughout the universe.
•
For the next 13 billion years, the universe continued to expand, and cool, and the
photons continued to fill all space.
– The residue of that event is the COSMIC MICROWAVE BACKGROUND
RADIATION.
An Early Estimate of CMBR
Alpher and Herman
•
In 1948 , Alpher and Robert Herman* calculated that
when the Universe became TRANSPARENT the residual
radiation moving about the Universe had a
“temperature” of about 240 oC below zero.
•
As the Universe expanded the temperature
of space would decrease further.
•
Today: about 270oC below zero.
Herman, Gamow, Alpher
* Herman: 1914 to 1997, PhD Physics, Princeton.
The Penzias- Wilson “Experiment”: 1964
•
Penzias and Wilson (at Bell Labs)
accidentally measured background
radiation corresponding to a black body of
about 270 C below zero.
– They had been studying radio waves
from space.
– Could not get rid of the “noise” their
radio telescopes were picking up.
•
This confirmed the predictions of Alpher
and Herman in 1948.
• A major confirmation of the Big Bang
theory.
Left: Cosmic Background Explorer (COBE 1989)
Penzias and Wilson
• Arno Penzias: 1933 to ?
– Fled (when a boy) from
Nazi Germany in 1939.
– PhD in Physics from
Columbia University.
• Robert Wilson: 1936 to ?
– Educated at Cal Tech
• Penzias and Wilson won Nobel Prize in 1978
The Hubble Space Telescope
Hubble Space Telescope
Deployed in low earth orbit in 1990.
Hubble: Reflecting Telescope
Light from a galaxy 13.2 billion years old was
recently seen by the telescope (formed about
480 million years after the Big Bang).
– Earliest galaxy so far seen.
Two parabolic mirrors.
Summary:
So…What Do (We Think) We Know?
Initially a soup of sub-atomic particles.
A rapid expansion of the universe took place.
For 379,000 years, gradual cooling: 3000oK.
The Universe became “transparent”.
8 billion years: the Sun was formed.
Carbon and other heavy elements were formed in the
stars.
• Interstellar space continued to cool to -270 C, today.
•
•
•
•
•
•
• AGE OF THE EARTH: 4.54 +/- 1% BILLION YEARS
• AGE OF UNIVERSE: 13.73 +/- 0.17 BILLION YEARS
What Are We Worried About?
• The initial expansion:
– 100 doublings in 10-35 sec.?
•
•
•
•
Universe still expanding?
Dark matter and dark energy?
The boundary between the Universe and …?
What came before t = zero?