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.

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

• 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 ArithmeticMultiplication:(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

= 300BUT, 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

• 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• 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