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Science
Science
• Is this course science?
A. Yes
B. No
Science
• Is this course science?
A. Yes
B. No, this course is about the results of science
Science
• Is this course science?
A. Yes
B. No, this course is about the results of science
• But it is not science
Science
• Is this course science?
A. Yes
B. No, this course is about the results of science
• But it is not science
• Then what is science?
Science
• Science is a way of explaining the physical world
• Religion and philosophy offer explanations of the physical world, too
• I think you can also consider the arts as ways of explaining what’s going
on in someone’s mental world
• The bottom line is that we humans are explanation machines
• We can’t help it
• We are born that way
• And when we communicate our explanations to others…
• …we contribute to human culture
Science
• The various aspects of culture help us understand and appreciate the world
• Science is no different from the others in this regard
• But science is unique among them in one very important way:
It demands that the world actually be the way it says
• Understanding this, and the scientific process, is one of the most important
things you can take away from this course
Science
• Believe it or not, science is not contrary to normal human nature…
• In fact, science is everyday human behavior, formalized…
• That formalization has a special name...???...
• The Scientific Method
Science
• The Scientific Method
• Observation
Science
• The Scientific Method
• Observation
• Hypothesis (model)
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
• If predictions fail, revise hypothesis and continue
experimentation and/or observation
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
• If predictions fail, revise hypothesis and continue
experimentation and/or observation
Hypothesis
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
• If predictions fail, revise hypothesis and continue
experimentation and/or observation
•This may not seem much like
everyday human behavior, but...
Hypothesis
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
• If predictions fail, revise hypothesis and continue
experimentation and/or observation
•This may not seem much like
everyday human behavior, but...
Hypothesis
Science
• The Scientific Method
• Observation
• Hypothesis (model) ==> predictions
• More observations or experiments (or both) to test predictions
• If predictions fail, revise hypothesis and continue
experimentation and/or observation
Hypothesis
•This may not seem much like
everyday human behavior, but…
•It’s just the way we humans
normally solve problems
•Granted, scientists do it more
methodically and carefully and
document what they do
•But it’s really the same thing
•It’s how humans work
•And it’s how “scientific theories”
are created
Science
• Scientific Theories
• “Theory” in science means something different from the everyday use of the word,
as in “I’ve got a theory about that”
• That’s more like an educated guess, which is more like a hypothesis…
• Scientific theories are very different from educated guesses…
Science
• Scientific Theories
• Scientists very carefully document how they test their hypotheses and publish their
results
• Other scientists can then check their methods and repeat the tests to see if they
get the same results
• If a hypothesis is tested by many scientists and found to pass all the tests, then
(usually together with other hypotheses) it can become a scientific theory
• The most successful scientific theories explain things that weren’t even on the
minds of the scientists who originated them
Science
• Scientific Theories
• But even the most strongly supported scientific theory can be disproved!
• In fact, if a theory cannot be proved, then it’s not a scientific theory at all!
The Process of Science
•The process of science is a cycle of
observation/experimentation, hypothesismaking, and prediction
Hypothesis
•One of the earliest observations to which
this process was applied involved the way
celestial objects move in the sky
•People saw the stars and planets
apparently moving around the motionless
Earth fixed to a nested set of celestial
spheres
•But sometimes planets didn’t move in a way
that fit this idea…
Retrograde Motion
• The path of Mars through the constellations of the celestial
sphere is generally from the west to the east
• But periodically, it reverses its path and travels “backwards”
toward the west in “retrograde motion”
• All the planets show some amount of retrograde motion
Retrograde Motion
• The ancients came up with elaborate explanations for retrograde motion
• The most influential was due to Claudius Ptolemy (of horoscope fame)
Retrograde Motion
• The ancients came up with elaborate explanations for retrograde motion
• The most influential was due to Claudius Ptolemy (of horoscope fame)
• Ptolemy’s model consisted of a set of nested spheres with the Earth in
the center
Retrograde Motion
• In Ptolemy’s model, each planet moved on its own sphere along two
circular paths
• It moved around the Earth on its circular “deferent”
• And it moved around a point on the deferent on a circular path called an
“epicycle”
Retrograde Motion
• The epicycles are necessary to explain retrograde motion
• The paths of Venus and Jupiter are traced in dashed lines above
Retrograde Motion
• Ptolemy’s model explained two observations:
• Observation 1: Retrograde motion
•Planets move backward when on the near side of their epicycles
• Observation 2: Planets are brighter when they are moving retrograde
•They are nearer then and therefore brighter
Retrograde Motion
• Ptolemy’s model also did a decent job of predicting the
positions of planets in the sky
• But it was complicated, with all these epicycles
• And how to explain epicycles?
Retrograde Motion
• Enter “Occam’s Razor”…
• A philosophical principle attributed to the 14th century
English philosopher William of Ockham
• In the modern formulation, Occam’s Razor says that when
comparing two models, the simpler one is usually better
Retrograde Motion
• There is, in fact, a simpler model that explains planetary motion
• But it requires a major change in the perspective people had
held for thousands of years…
EARTH IS NOT THE CENTER
Retrograde Motion
• Once that conceptual leap is made, and the Sun is put in
the center, retrograde motion is revealed as just an illusion
• As planets orbit the Sun, those farther out move slower
• So the ones closer in catch up and pass them by
• The consequence is illustrated above
Retrograde Motion
• So retrograde motion is explained in a simple way by assuming a Suncentered solar system
• Hundreds of years earlier, in 260 BCE, a Greek named Aristarchus of
Samos had suggested the Earth goes around the Sun
• So why didn't the Greeks get it?
• The Greeks did not accept Aristarchus’s
Sun-centered model
• One of the major reasons was that they
could not detect “stellar parallax”
• The parallax for the nearest star is only
0.75“ (1" = 1 arcsecond = 1/3600 degree)
• This is less than the width of a dime at 1
mile
• On the scale of our model solar system,
it’s the width of a dinner plate in St
Augustine viewed from UNF
• It’s only detectable with telescopes, which
the Greeks did not have
•The Greek failure to accept Aristarchus’ ideas illustrates that advances in
science depend not only on ideas but also on technology
•Greek technology was not advanced enough to see stellar parallax or
any other evidence for errors in the their cosmology
•So the Ptolemaic model was the accepted one for 1500 years
•But then technology advanced
•And advances in astronomy gave birth to the scientific revolution
•Now we’ll look at some of the scientists involved in the development of
astronomy and the scientific revolution
Scientists in Astronomy
• Nicolaus Copernicus (1473-1543)
• Formulated heliocentric model
• Described in On the Revolutions of the
Celestial Spheres published 1543
• Still had epicycles
• Practically, not much (if any) better than
Ptolemy’s
• But it turned out to be more correct
• Forensic reconstruction of Copernicus head
Scientists in Astronomy
• Tycho Brahe (1546-1601)
• The best naked-eye observer ever?
• Had his own model of the solar system
• Check out the nose…
• A man of varied interests
• In his household…a dwarf and a moose
• A party animal, but minded his manners
• Death by politeness?
• Or poisoning?
• Who did it?
• Kepler?
• Christian IV of Denmark?
• Tycho?
Heavenly Intrigue: Johannes Kepler, Tycho Brahe, and the Murder Behind One of
History's Greatest Scientific Discoveries
Scientists in Astronomy
• Johannes Kepler (1571-1630)
• Profoundly religious
• Excellent mathematician
• Published a book on planetary motion,
The Mystery of the Cosmos, in 1596
• Sent Tycho a copy of the book, and
became Tycho’s assistant in 1600, hoping
for full access to Tycho’s data
• Tycho didn’t want to give him full access,
so he set him to work on the orbit of Mars
• But using circular orbits, there was an 8’
discrepancy between Kepler’s model of
Mars and Tycho’s observations
Scientists in Astronomy
• Johannes Kepler (1571-1630)
• So Kepler made a bold move…
• He tried elliptical orbits instead of circular
ones
• He didn’t want to—after all, the orbits
ought to be circular
• But they weren’t: With ellipses, the 8’
discrepancy—to which most might have
said “that’s good enough”—was gone
• When Tycho died, Kepler got his data
• And by 1605, Kepler had arrived at the
two of the three of what are now called
“Kepler’s Laws of Planetary Motion”
Kepler’s First Law
• Planets move in elliptical orbits with the Sun at one focus
Kepler’s Second Law
• Planets in orbit sweep out equal areas in equal times
• It took Kepler nearly ten more years to
arrive at his third law of planetary motion
Kepler’s Third Law
More distant planets orbit the Sun at slower average
speeds, obeying the relationship
p2 = a3
p = orbital period in years
a = average distance from Sun in AU
Summary of Kepler’s Laws
1. Planets move in elliptical orbits with the Sun at one focus
2. Planets in orbit sweep out equal areas in equal times
3. More distant planets orbit the Sun at slower average
speeds, obeying the relationship
p2 = a3
p = orbital period in years
a = average distance from Sun in AU
Kepler’s Laws
• Kepler developed his laws of planetary motion by
• Making a model of the solar system
• Using his model to make predictions
• Comparing those predictions to Tycho’s observations
• Adjusting his model as necessary
• Making more predictions
• Etc
• Does this process look familiar?
• It’s the Scientific Method in action
Kepler’s Laws
• Kepler’s Laws explained Tycho’s observations better than
any previous model
• But he had no idea why the planets moved this way
• And that’s what scientists really want:
• a model that explains why
• But that would have to await the arrival on the scene of Sir
Isaac Newton
• We’ll get to him later…
• But first, we need to travel south to Italy…
Scientists in Astronomy
• Galileo Galilei (1564-1642)
Scientists in Astronomy
• Galileo Galilei (1564-1642)
• Mathematician
Scientists in Astronomy
• Galileo Galilei (1564-1642)
• Mathematician
• Astronomer
Scientists in Astronomy
• Galileo Galilei (1564-1642)
• Mathematician
• Astronomer
• Physicist
Scientists in Astronomy
• Galileo Galilei (1564-1642)
• Mathematician
• Astronomer
• Physicist
• Lute player
Scientists in Astronomy
• Galileo Galilei (1564-1642)
• Mathematician
• Astronomer
• Physicist
• Lute player
• Not the inventor of the telescope, but
greatly improved on the invention
• And then he put it to use to put to rest
certain misconceptions that could be
traced back nearly 2000 years…
Ancient Errors
• Ptolemy’s model was based on the Greek view of the universe
• This was largely due to Aristotle (384-322 BCE)
Ancient Errors
• Ptolemy’s model was based on the Greek view of the universe
• This was largely due to Aristotle (384-322 BCE):
• The Earth is in the center of the Universe
• The heavens and the Earth are distinct realms, with the heavens being
perfect and the Earth imperfect
• That’s what most people believed for 1500 years
• Then, in the sixteenth century, this view began to change
Ancient Errors
• The paradigm shift began with Copernicus’s heliocentric model
• But his model didn’t work any better than Ptolemy’s geocentric model, and
he had no direct evidence that his model was right and Ptolemy’s wrong
• Kepler’s heliocentric model, based on Copernicus’s ideas, explained the
observed motions of the planets much better than Ptolemy’s
• But Kepler didn’t know why, and he had no more direct evidence than
Copernicus that Earth was not the center of everything
• Then Galileo and his telescope came along, and provided the direct
evidence that had been missing…
Ancient Errors - Earth is the Center
• Galileo turned his telescope on Jupiter
• He saw that there were several objects that
looked like stars always associated with it
Ancient Errors - Earth is the Center
• Galileo turned his telescope on Jupiter
• He saw that there were several objects that
looked like stars always associated with it
• He figured out that the “stars” were actually
moons orbiting around Jupiter
• In the strictest geocentric model, everything
was supposed to orbit around the Earth, and
not around anything else
• So Galileo’s observation of moons orbiting
Jupiter was inconsistent with the geocentric
model
• Celestial objects could orbit around things
other than the Earth
Ancient Errors - Earth is the Center
• Then Galileo turned his telescope to Venus,
and found his most convincing proof that
Ptolemy’s model could not be correct
Ancient Errors - Earth is the Center
• Then Galileo turned his telescope to Venus,
and found his most convincing proof that
Ptolemy’s model could not be correct
• Ptolemy’s model had Venus on an epicycle
that was always between Earth and the Sun
to explain its location in the sky
• So a “full Venus” should never occur,
because the Sun would always be behind
Venus
Ancient Errors - Earth is the Center
• Then Galileo turned his telescope to Venus,
and found his most convincing proof that
Ptolemy’s model could not be correct
• Ptolemy’s model had Venus on an epicycle
that was always between Earth and the Sun
to explain its location in the sky
• So a “full Venus” should never occur,
because the Sun would always be behind
Venus
• But with his telescope, Galileo observed
Venus go through a complete set of phases,
just like the Moon
• This meant that Venus must sometimes be
on the other side of the Sun
Ancient Errors - Earth is the Center
• Then Galileo turned his telescope to Venus,
and found his most convincing proof that
Ptolemy’s model could not be correct
• Ptolemy’s model had Venus on an epicycle
that was always between Earth and the Sun
to explain its location in the sky
• So a “full Venus” should never occur,
because the Sun would always be behind
Venus
• But with his telescope, Galileo observed
Venus go through a complete set of phases,
just like the Moon
• This meant that Venus must sometimes be
on the other side of the Sun
• Ptolemy’s model could not be correct
Ancient Errors – Earth and the heavens are distinct realms
• Aristotle and the Greeks had claimed that the
Earth was the center of the universe
Ancient Errors – Earth and the heavens are distinct realms
• Aristotle and the Greeks had claimed that the
Earth was the center of the universe
• But with his studies of the moons of Jupiter
and the phases of Venus, Galileo showed that
this could not be the case
• Or did it?
• It still didn’t feel like Earth was moving…
• There was no evidence for Earth’s rotation…
• There was no evidence for stellar parallax…
• And there was a competing geocentric model
that explained Galileo’s observations as well…
Ancient Errors – Earth and the heavens are distinct realms
• It was due to Tycho Brahe
• Moon, Sun, and stars
went around Earth
• The 5 known planets went
around the Sun
•
•
•
Convincing evidence for heliocentrism appeared in the late 18th and 19th century
New technology (Foucault pendulum, better telescopes, etc) solidified it
Another example of how better technology is often needed to support a better idea
Ancient Errors – Earth and the heavens are distinct realms
• While he might not have proven heliocentrism
correct, Galileo showed that Ptolemy’s model
could not be correct
• But what about the Greek idea that the heavens
were perfect and the Earth imperfect?
• Heavenly bodies like the Moon were supposed
to be perfectly smooth spheres
• The dark spots on the Moon were explained as
perfectly smooth patches that absorbed or
emitted light differently than the rest of the
Moon’s surface
Ancient Errors – Earth and the heavens are distinct realms
• While he might not have proven heliocentrism
correct, Galileo showed that Ptolemy’s model
could not be correct
• But what about the Greek idea that the heavens
were perfect and the Earth imperfect?
• Heavenly bodies like the Moon were supposed
to be perfectly smooth spheres
• The dark spots on the Moon were explained as
perfectly smooth patches that absorbed or
emitted light differently than the rest of the
Moon’s surface
• Galileo and his telescope helped put this idea to
rest as well
Ancient Errors – Earth and the heavens are distinct realms
• With his telescope, Galileo observed the
dark splotches and lines on the Moon
• By looking carefully at different times, he
noticed that the dark lines near the
terminator changed size with the angle of
the Sun’s rays
• He concluded that these dark lines were
not merely variations in the properties of
the perfectly smooth surface
• They were mountains sticking up off the
surface, just like we have here on Earth
• Heavenly bodies were not perfect after all
Ancient Errors – Earth and the heavens are distinct realms
• But it was Newton and his apple who
demonstrated most elegantly that Earth
and the heavens are not distinct realms
• We’ll get to that…
• But first, a bit about Sir Isaac…
From University of Tennessee Astronomy 161 web site
http://csep10.phys.utk.edu/astr161/index.html
• Isaac Newton (1642-1727)
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Bible scholar
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Bible scholar
• Warden and Master of the Royal Mint
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Bible scholar
• Warden and Master of the Royal Mint
• President of the Royal Society
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Bible scholar
• Warden and Master of the Royal Mint
• President of the Royal Society
• Behavior was erratic at times
• Isaac Newton (1642-1727)
• Arguably the smartest person who ever
lived…certainly one of them (IQ has
somehow been estimated at ~180-190)
• Scientist
• Alchemist
• Bible scholar
• Warden and Master of the Royal Mint
• President of the Royal Society
• Behavior was erratic at times
• But certainly one of the most influential
people who ever lived
The 100