The Scientific Method:
Research in Science
How do we learn anything about
the Universe?
The key element is curiosity!
One of your main goals as a teacher Is to maintain
that innate characteristic in your students or to try to
restore it if poor teaching has beaten it out of them.
The First Steps in the Scientific Method
1.
Observe: use your senses or augmentations of
them (microscope or telescope).
Example: the sky is blue.
2. Hypothesize (come up with a possible explanation
of the observation).
Someone has painted it blue.
The blue color is a reflection of the oceans.
Blue light is more easily scattered than red in the
atmosphere, so the blue sky is scattered sunlight.
3. Test HYPOTHESIS through a PREDICTION.
If
the latter is true, then if sunlight passes through
more of the atmosphere, the sun should lose green
and yellow light too and appear red.
(When does this happen?)
Blue light scatters more in the atmosphere
• Off molecules (strongly) and off dust (less so, however).
Testing Hypotheses
4a. perform EXPERIMENT
4b. OR make new OBSERVATION
Sun is indeed red/orange near dawn and dusk
5a. If in agreement, perform new test (and keep doing
so).
5b. If in disagreement, discard or modify hypothesis
GO BACK TO STEP 2!
Only if MANY tests are passed can a HYPOTHESIS be
called a THEORY.
If the THEORY applies in a wide range of
situations, it may be raised to the status of a LAW
(e.g., Newton's LAW of Gravity)
In SCIENCE nothing is ever PROVEN
STILL, even a LAW can be wrong (or partly right):
Einstein showed that Newton's Laws of motion and
gravity don't hold exactly if:
• velocities are close to the speed of light
(special relativity) OR if
• lots of mass is concentrated in a small volume
(general relativity).
SO NOTHING IN A REAL SCIENCE IS EVER
ABSOLUTELY PROVEN TRUE,
although most of what is discovered and tested in a
"hard" science is VERY LIKELY to be correct.
Healthy Skepticism
• is imperative for learning science.
• Encourage your students to ask challenging
questions.
• Don’t penalize them for too much curiosity,
but don’t go off on tangents for too long.
• If you don’t know the answer, admit it.
• But promise to find out an answer, and then
follow through!
Types of “Hard” Sciences
• Categorize:
astronomy, biology, chemistry, geology,
medicine, meteorology, oceanography,
physics as
• OBSERVATIONAL or EXPERIMENTAL
sciences.
The REAL Scientific Method
• But the preceding is idealized.
• In reality, even good scientists often don't discard
hypotheses when they fail an experimental or
observational test.
• Why not?
• A. Experiment is wrong.
• B. Experiment is misinterpreted.
• C. Psychological/sociological/political difficulty in
giving up long-held beliefs.
• Eventually the weight of evidence becomes
overwhelming and there is a PARADIGM SHIFT or
SCIENTIFIC REVOLUTION.
(e.g., Copernican, Darwinian, Quantum Mechanics)
Characteristics of Sciences and Not Sciences
• The above are characteristics of ANY SCIENCE.
• The key point: scientific results are falsifiable.
• If they cannot eventually be tested, they fall outside the
realm of science and enter philosophy, religion, etc.
• Pseudo-sciences do not allow themselves to be tested
and “true believers” refuse to consider strong evidence
against their validity. Examples: ?
• astrology, alchemy, numerology, palmistry,
crystal/pyramid power
What A
Science
Must Have
Types of Sciences
• What about: anthropology, economics,
history, political science, psychology,
sociology?
• These social or "soft" sciences rely to one
extent or another on scientific methods, but
also invariably carry a great number of
preconceptions that allow for many disparate
interpretations to be drawn from the same
data. Usually too many complications.
• In the natural or "hard" sciences, the range of
“allowed” interpretations is usually much less
and new experiments or observations can be
designed to choose the best.
Astronomy vs. Astrophysics
• Aside from the OBSERVATIONAL - EXPERIMENTAL
dichotomy, since the advent of calculus we have
distinguished these approaches from THEORETICAL
science, driven by applied mathematics.
• ASTRONOMY IS AN OBSERVATIONAL SCIENCE.
• ASTROPHYSICS IS AN OBSERVATIONAL THEORETICAL - EXPERIMENTAL SCIENCE.
• Today we typically use these terms interchangeably
since so much of what we learn combines
observations with theory and some experimental work
(laboratory astrophysics).
• We also must consider COMPUTATIONAL science as
a (nearly) equal partner now that computers are so
powerful.
Review of Scientific Notation
•
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102 = 100, 101=10, 100 = 1, 10-1=0.1, 10-2=0.01
1012=1,000,000,000,000=trillion
(Tera-)
109 =1,000,000,000 = billion
(Giga-)
106 =
1,000,000 = million
(Mega-)
103 =
1,000 = thousand
(kilo-)
10-2=
0.01=one-hundredth
(centi-)
10-3=
0.001=one-thousandth
(milli-)
10-6= 0.000001=one-millionth
(micro-)
10-9= 0.000000001=one-billionth
(nano-)
5.4x103=5,400
7.05x10-3=0.00705
4,700=4.7x103
0.017 = 1.7x10-2
Powers of Ten Arithmetic
Multiplication:
(5.3x103) x (6x10-5) = 31.8x103+(-5)
=31.8x10-2 = 3.18x10-1
=0.318 = 0.3 = 3 x 10-1
One significant figure! Keep only the minimum number
of significant figures going into the calculation in the
answer.
Division:
(9.3 x10-4)/(3.10x10-6) = 3.0 x10-4-(-6)
= 3.0 x102
= 300
BUT, 3.0x102 is the better answer, as it CLEARLY has
two significant figures; scientific notation is PRECISE.
The Scales of the Universe
We deal with the largest possible things -- the whole
universe -- and with the smallest -- nuclei of atoms.
This requires us to use a wide range of PHYSICAL
UNITS and we USE THE METRIC SYSTEM.
Length: m or cm
Mass: kg or g
Time: s or yr
Temperature: K(elvins)
1 pc = 3.26 light-yr = 3.085678 x 1018cm=3.1x1013km
1AU = 1.496x1013cm = 150,000,000 km (astronomical
unit = mean distance between earth and sun)
Sizes of Everything
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Universe: open or flat -- infinite; closed -- 1026m
Galaxies: no of stars 109-1013; size ~ 1023cm~3x104pc
Stars: 108-1010 m (most radii)
Typical separations: 1016 m ~ 1 light-yr or ~1/3 parsec
Planets: RE=6.4x103km = 6.4x106 m
Separations: ~ 1 AU
Mountain: Tallest ~ 10 km, more typical ~6 km
Hm/RE = 6.4km/6.4x103km = 1.0x10-3
People: 1.5m = 1.5x102cm (~5 feet)
Visible light: wavelength = 500nm = 5x10-5cm
Atom: 0.1nm = 10-8cm = 10-10m (X-ray wavelength)
Nucleus: 1 Fermi = 10-13cm = 10-15 m
A question:
• How many times larger is the typical
separation between stars to the typical
diameter of a star?
• A) 103
• B) 105
• C) 107
• D) 109
A question:
• How many times larger is the typical
separation between stars to the typical
diameter of a star?
• A) 103
• B) 105
• C) 107
• D) 109
Time Scales of the Universe
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Time since the Big Bang: ~1.37 x 1010 yr
Galaxies formed: ~1.3 x 1010 yr ago
Solar system formed: 4.55 x 109 yr ago
Oldest rocks on Earth: 3.8 x 109 yr BP
Earliest life forms: ~3.5 x 109 yr BP
Earliest hominids:~2 x 106 yr BP
Mountains: Appalachians:~2.5 x 108yr BP;
Rockies: 7 x 107 yr BP
• Human lifespan: ~75 yr
• Oscillation time for visible light: ~2 x 10-15 s
• Time for light to pass the nucleus of an atom: ~3 x 10-24s
A question
• How many times older is the universe
than our solar system?
• A) 1
• B) 2
• C) 3
• D) 4
A question
• How many times older is the universe
than our solar system?
• A) 1
• B) 2
• C) 3
• D) 4
Research Based Science
Education
• Mostly aimed at undergraduates so far
• Projects being extended
• Could be implemented for good HS
students
• Astronomy web-site
uranus.uaa.alaska.edu/rbseu
Sample Project
• Photometric redshifts of galaxies:
PhotoZ.
• Read handout: we’ll do on Friday
• Requires ImageJ software and
• Polaris plug in for ImageJ
• Instructions on how to load at:
http://uranus.uaa.alaska.edu/rbseu/software/index.html
Should have been preloaded on central computers.
Exoplanets
• How to find planets around other stars?
• Direct imaging extremely hard. Why?
• Astrometry: look for wiggles in stellar orbits; tried for
decades: usually failed
• Spectroscopy: look for very small shifts in wavelengths
of stellar absorption lines: has worked since 1995 and
given us most of the hundreds of exoplanets known.
Exoplanets, II
• Photometry: look for tiny dips in light for
planets that move in front of stars:
• How much to you expect light to drop for
Jupiter? For Earth?
• Why a low probability for a given star?
Exoplanets, III
• Microlensing: also
photometry, but
dramatic increase in
light due to
gravitational focusing
by star & extra bump
from planet.
Discovered
serendipitously while
searching for
MACHOs.
Kepler Mission
• NASA’s current planetary search mission, up
since 2009: 1.5 m primary; 0.95 m photometer w/
95 Mpixels
• Stares at a big chunk of the sky (105 sq deg) in
Cygnus w/ >105 pretty bright stars (9th-16th mag)
• Already discovered 100s of candidates with
dozens of confirmed planets and with follow-up,
characterized several. 6 planets in one system!
• http://kepler.nasa.gov/
• Assignment for Friday: pick a Kepler educational
project and present it in ~5 minutes
Other Worlds, Other Earths
• Students observe & get real data from
• Robotic telescopes to search for transits:
exoplanets passing in front of stars
• http://iya.cfa.harvard.edu/dev/Other_Worlds_inc/index.php
• If cloudy, students can download archival
data, but they really prefer “their own”
• Useful for secondary and even middle
school students