Science - University of North Florida

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Science

Science

•Is this course science?

A. Yes

B. No

Science


A. Yes

B. No, this course is about the results of science

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Science


A. Yes

B. No, this course is about the results of science

•Science is different

Science

•Science is a way of explaining the physical world

•There are other ways…

…religion and philosophy, for example

•The “arts” are also explanations…

…sometimes of the physical world…

…but mostly of what’s going on in someone’s mental world…

…artists, whether they be painters, composers, poets, whatever…

…all want to express something in their mind…

…they want to explain it to others

•The bottom line is that we humans are explanation machines

•We can’t help it

•We are born that way

•And this forms the basis of our entire culture

Science

• The various aspects of our culture help us understand our world…

…whether it’s the external, physical world or the internal, mental world

• Science is no different from the others in this regard

• But science is unique among them in one very important way:

Of all the ways of explaining the world

Only science demands that the world actually be that way

• This is the basis of the scientific process

• Understanding it is one of the most important things to get from this course

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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...

…which is???...

The Scientific Method

Science

•The Scientific Method•Observation

Science

•The Scientific Method•Observation•Hypothesis (model)

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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

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Science

•The Scientific Method•Observation•Hypothesis (model) ==> predictions•More observations or experiments (or both) to test predictions• If predictions fail, revise hypothesis•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•Continue experimentation and/or observation• It’s actually more like a cycle than a linear process:

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

• It’s more like a cycle than a linear process:•This may not seem much like everyday human behavior, but...

Hypothesis

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Science


• It’s more like a cycle than a linear process:

Hypothesis

•This may not seem much like everyday human behavior, but...

Science


• It’s more like a cycle than a linear process:•This may not seem much like everyday human behavior, but…

•It’s just the way we humans normally solve problems

•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 can produce “scientific theories”

Hypothesis

Science

•Scientific Theories

• How many times have you said this to somebody or heard somebody say it?

“I’ve got a theory about ____”

• What you mean is you have a (possibly) educated guess

…which is like a hypothesis

• “Theory” in science means something very different from an educated guess…

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Science


• Scientists carefully document how they test their hypotheses

• Then they publish their results

• Other scientists can then evaluate them and try to replicate them

• And 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 the scientists who originated them didn’t even know about

Science


• But even the most strongly supported scientific theory can be disproved!

• In fact, if a theory cannot be disproved, then it’s not a scientific theory at all!

The Process of Science

•The process of science is a cycle of observation/experimentation, hypothesis-making, and prediction

•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…

Hypothesis

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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 centered on Earth

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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…

…because planets move backward when on the near side of their epicycles• Observation 2: Planets are brighter when they are moving retrograde…

…because they are nearer then and therefore brighter

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Retrograde Motion

• Ptolemy’s model also did a decent job of predicting the positions of planets in the sky

• But it is complicated with all these epicycles

• And how to explain the epicycles?

Retrograde Motion

• Enter “Occam’s Razor”…

…the “law of economy” named for William of Ockham (1285–1347/49 CE)…

…”plurality should not be posited without necessity”

• The modern formulation of Occam’s Razor says……when comparing two models, the simpler one is usually better

Retrograde Motion

•And there is – and was – a simpler model to explain planetary motion•But it required a major change in a long-held and comforting perspective…

EARTH IS NOT THE CENTER

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Retrograde Motion

• With that conceptual leap, and the Sun 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 can be explained with no epicycles with “heliocentricity”• In fact, hundreds of years before Ptolemy (in 260 BCE), a Greek named

Aristarchus of Samos suggested that Earth goes around the Sun• But the Greeks did not accept Aristarchus’s Sun-centered model• Why not?

•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)

0.75” < 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

•So without that evidence they were satisfied with the Ptolemaic model

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•The Greek failure to accept Aristarchus’ ideas illustrates that scientific advances 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 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

• On the Revolutions of the Celestial Spheres published in 1543, described it

• Still had epicycles

• Practically, not much (if any) better than Ptolemy’s

• Conceptually, 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…

…it’s prosthetic

• 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?

• Most likely his lifestyle – PLOS ONE 13, no. 4 (April 19, 2018)

arrogance

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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

• It bothered Kepler

Scientists in Astronomy• Johannes Kepler (1571-1630)

• He wanted his model to match Tycho’s observations, but they didn’t…

• So his problem-solving machine (brain) kicked into high gear…

…and he made a bold move…

• He tried elliptical orbits instead of circles

• He didn’t want to—after all, the orbits oughtto be circular

• But they weren’t…

…the ellipses eliminated the 8’ discrepancy

…heavenly orbits were not circular after all

Kepler’s Laws of Planetary Motion

• When Tycho died, Kepler finally 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”

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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

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Kepler’s Third Law

More distant planets orbit the Sun at slower average speeds, obeying the relationship

p2 = a3

p = orbital period in yearsa = 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 yearsa = 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

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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…


• Galileo Galilei (1564-1642)



• Mathematician

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• Mathematician

• Astronomer



• Mathematician

• Astronomer

• Physicist



• Mathematician

• Astronomer

• Physicist

• Lute player

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• 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):

• Ancient Error #1 - The Earth is in the center of the Universe

• Ancient Error #2 - 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

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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 Error #1 - 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


• 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

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• 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

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• 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

• And that meant that Ptolemy’s model could not possibly be correct


• Aristotle and the Greeks had claimed that the Earth was the center of the universe


• 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…

• …no evidence for Earth’s rotation…

• …no evidence for stellar parallax…

• …and there was a competing geocentric model that also explained Galileo’s observations…

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• 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 (mainly better telescopes) solidified it

• Another example of how better technology is often needed to support a better idea

• But Galileo showed that Ptolemy’s geocentric model could not be correct, even if he didn’t prove heliocentrism correct

Ancient Error #2 – Earth and the heavens are distinct realms

• But what about Ancient Error #2 – the Greek idea that the heavens were perfect and the Earth imperfect?

• Perfect circular orbits…

• Heavenly bodies perfectly smooth spheres…

• The Moon’s dark spots?

…due to differences in how its perfectly smooth surface absorbs or emits light


• But what about Ancient Error #2 – the Greek idea that the heavens were perfect and the Earth imperfect?

• Perfect circular orbits…

• Heavenly bodies perfectly smooth spheres…

• The Moon’s dark spots?

…due to differences in how its perfectly smooth surface absorbs or emits light

• Galileo and his telescope helped correct Ancient Error #2 as well

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• With his telescope, Galileo observed the dark splotches and lines on the Moon

• By looking carefully at different times, he noticed that the dark features 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


• 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)

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• Arguably the smartest person who ever lived


• Arguably the smartest person who ever lived…certainly one of them


• Arguably the smartest person who ever lived…certainly one of them (IQ has somehow been estimated at ~180-190)

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• Scientist



• Scientist

• Alchemist



• Scientist

• Alchemist

• Bible scholar

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• Scientist

• Alchemist

• Bible scholar

• Warden and Master of the Royal Mint



• Scientist

• Alchemist

• Bible scholar


• President of the Royal Society



• Scientist

• Alchemist

• Bible scholar



• Behavior was erratic at times

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• Scientist

• Alchemist

• Bible scholar



• Behavior was erratic at times

• But certainly one of the most influential people who ever lived

The 100

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Science - University of North Florida