11 January 2012Modern Physics IV Lecture 11 Modern Physics for Frommies IV The Universe - Small to...
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11 January 2012 Modern Physics IV Lecture 1 1
Modern Physics for Frommies IVThe Universe - Small to Large
Lecture 1
Fromm Institute for Lifelong Learning University of San Francisco
11 January 2012 Modern Physics IV Lecture 1 2
Agenda• Administrative Matters• Physics and the Scientific Method• Notation and Units• Mass vs. Weight• Some History; Premodern Physics
11 January 2012 Modern Physics IV Lecture 1 3
Administrative Matters
• Lecture Location and Time: Fromm Hall, Broad Room, Wednesdays 1 PM – 2:40 PM Prompt start.
• Lecturer: Terrence A. Mulera – HR 102• Office Hours: TBA and by appointment• Contact Information:
– e-mail: [email protected]– Phone: (415) 422-5701
11 January 2012 Modern Physics IV Lecture 1 4
Monday Tuesday Wednesday Thursday Friday Saturday Sunday 0800
0900 0945_____________ 121 L15
0955___________
120 L12
1000 1025___________ 121 L11
1100
1130 __ _______
1140___ _______
1200 1210_ _ _______
1300 101 L11
210 L11
Modern Physics IV Fromm Institute1
210 L13
1400
1440 ________
1500 _______ _______ 1545
_______ _______ 1545
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1600
1700
1800
1900
1 11 January to 7 March only
11 January 2012 Modern Physics IV Lecture 1 5
Problem with Lecture 2
I am having cataract surgery on Wednesday, 18 January
I will give an extra lecture during the “make up week” (on 7 March)
On 18 January the Fromm staff will show a movie or movies reviewing relativity.
11 January 2012 Modern Physics IV Lecture 1 6
Administrative Matters 2• Class Wikis
– http://modphysfromm4.wiki.usfca.edu/ or link from Fromm web site.
• .pdf notes, 4/page posted hopefully night before class. These may change by time of lecture.
– Hard copies. How many do we need?
• Power Point® slides posted immediately following lecture. Will include any changes to .pdf notes
– Material from preceding classes (Albert Einstein’s Universe, The Universe of Schrödinger’s Cat and A Universe of Leptons, Quarks and Bosons) still available at:
11 January 2012 Modern Physics IV Lecture 1 7
http://modernphysicsfrommies.wiki.usfca.edu/http://modphysfromm2.wiki.usfca.eduhttp://modphysfromm3.wiki.usfca.edu
Thanks for the cartoon to Moose’s, 1652 Stockton St., San Francisco, CA
Please turn off or silence cell phones and pagers.
11 January 2012 Modern Physics IV Lecture 1 8
Physics and the Scientific MethodPhysics and the Scientific Method•Physics is a science
-Limited to that which is testable
•Concerned with how rather than why
•Best defined in terms of the “Scientific Method”
•Formulated in the 17th century
•Other concerns reserved to Philosophy, Metaphysics and Theology.
11 January 2012 Modern Physics IV Lecture 1 9
11 January 2012 Modern Physics IV Lecture 1 10
Example: Newtonian GravitationExample: Newtonian Gravitation
Observations: Things fall, planets orbit in ellipses etc.
Empirical Law: There is an attractive force between objects which have mass.
Theory: Newton’s Law of Gravitation
1 22
ˆm m
F G rr
11 January 2012 Modern Physics IV Lecture 1 11
Testing: Good agreement with experiment and observation.
Measurement of falling objectsCelestial mechanics pre-1900
Refinement of Theory and Further Testing: 1905 – 1920
Einstein’s theory of general relativityEddington’s observation of bending lightPrecession of Mercury’s orbit
11 January 2012 Modern Physics IV Lecture 1 12
Future Refinement and Testing: Quantum gravity?
CAVEAT: A scientific theory can never be proved, it can only be shown to be not incorrect to the limit of our ability to test it.
Alternatively, if you cannot devise an experiment which will disprove your conjecture, your conjecture is not science.
- Karl Popper (1902-1994)
11 January 2012 Modern Physics IV Lecture 1 13
11 January 2012 Modern Physics IV Lecture 1 14
Helen Quinn, What is Science, Physics Today (July 2009)
Posted on Wiki
http://modphysfromm2.wiki.usfca.edu
Small to Large:
Planck Length: 0.00000000000000000000000000000000001 m
Cosmological Horizon: 150,000,000,000,000,000,000,000,000.0 m
11 January 2012 Modern Physics IV Lecture 1 15
Scientific NotationScientific Notation
Very large and very small numbers with many zeros before or after the decimal point are inconvenient in calculations.
For convenience we write them as
.
10ba0
1
1
2
2
e.g. 1.0 1.0 10
0.1 1.0 10
10.0 1.0 10
0.01 1.0 10
100.0 1.0 10
.
0( ) 1
110
10n
n
Anything
11 January 2012 Modern Physics IV Lecture 1 16
Results usually presented as 1 digit to left of decimal with exponent adjusted accordingly, i.e.
Multiplication:
Division:
Exponents add and/or subtract
2 320 10 2.0 10 .
1 2 1 21 2 1 210 10 10b b b ba a a a
1
1 2
2
1 1
22
1010
10
b
b b
b
a a
aa
2 2 2
2
10 10
10 10
b b
b b
a a
a a
010 101 10
10 10
n n
n n
11 January 2012 Modern Physics IV Lecture 1 17
Small to Large:
Planck Length: 1 x 10-35 m
Cosmological Horizon: 1.5 x 1026 m
2661
35
Cosmological Horizon [units of Planck Lengths (PL)]
1.5 10 m 1.5 10 PL
1 10 m/PL
11 January 2012 Modern Physics IV Lecture 1 18
UnitsUnitsMostly rationalized mks units, i.e. distance in meters, mass in kilograms, time in seconds.
Occasional use of cgs units, i.e. centimeters, grams, seconds and of “English” units, i.e. ft., slugs, seconds
Special units. e.g. light years, parsecs, fermis, barns introduced as needed
Mass vs. Weight
11 January 2012 Modern Physics IV Lecture 1 19
Mass vs. WeightMass vs. WeightMass (if non zero) is a measure of the quantity of matter present.
e.g. 1 kg of say air corresponds to n molecules of air
2 kg corresponds to 2n molecules
Mass is independent of the gravitational environment of the matter.
1 kg on Earth = 1 kg on Mars = 1 kg in interstellar space etc.
Alternatively, mass is a measure of an object’s resistance to acceleration.
F ma
11 January 2012 Modern Physics IV Lecture 1 20
Weight is a force on an object due to gravity.
2
On Earth's surface
9.8 m/secW F mg g
Units: kg m/sec2 Newton (N)
Weight is dependent on the gravitational environment of the object.Weight on Earth 3 x weight on Mars 6 x weight on moon.
Common usage: Weights quoted in kg with environment understood to be surface of Earth.
Further confusion: lbs. are units of weight, mass units are slugs.
1 slug x (32 ft/sec2) = 1 lb
11 January 2012 Modern Physics IV Lecture 1 21
A Brief History of Views of the Universe
Arbitrary definition of “Modern Physics”
Post 1900 CE
Two major foundations
Relativity
Quantum Mechanics
Where were we? Where are we?
Maybe we can ask: Where are we going?
“It’s difficult to make predictions, especially about the future.” - Yogi Berra
11 January 2012 Modern Physics IV Lecture 1 22
The Ancients (mostly Greeks):
Physics from the Greek physika meaning “natural things” or the study of nature.
All of the ancient civilizations tried to understand their worlds in terms of myths.
Anthromorphizication of natural forces
e.g. Egyptian sun god, Ra
Greek mythology: Zeus, Athena, Aphrodite, Aeres etc.
Ca. 600 BC the Pre-Socratics began to apply reason to the comprehension of nature
What is the underlying order that is hidden in nature?
11 January 2012 Modern Physics IV Lecture 1 23
Socrates → Plato → Aristotle
Earth and its place in the universe: geocentricComplex system of interlocking spheres with names like prime mover, cycles and epicycles.
.
.
Aside: A heliocentric theory was proposed as early as the 6th century BC by non other than Pythagoras.
Physical phenomena: 4 elements. Properties and motions of objects could be described in terms of the chemical reaction properties of these elements.
Motion: 4 basic typesAlteration: Chemical reactionNatural local motion: Weight falling, smoke risingHorizontal or violent motion: Pushing, pulling, throwing
Celestial motion: Involves the interlocking spheres mentioned above.
Ptolemaic model.
11 January 2012 Modern Physics IV Lecture 1 24
Interregnum: Aristotle - Renaissance
Not much happening in physics but lots going on in history
Rome dominates the classical world
Rome falls ca. 450 AD
Dark ages in Europe ca. 450 – 750 AD
Light of classical civilization preserved in Islamic countries. Returned to the West in the Middle ages, 750 – 1350 AD.
Concept of the zeroAlgebraAnatomyStar chartsPre-Copernican heliocentric theories
Black Death strikes Europe, 1347 AD, third of population dies
11 January 2012 Modern Physics IV Lecture 1 25
Renaissance: Ca. 1400- 1600 AD The Copernican Revolution
Observation → Tables of planetary motion
Geocentric (Ptolemaic) model noticeably inaccurate and difficult to calculate.
“ If I had been present at the creation, I would have recommended a simpler design for the universe”
- Alphonso X (1221 – 1284)
King of Spain
11 January 2012 Modern Physics IV Lecture 1 26
Nicholas Copernicus (1473-1543)
Tried a heliocentric model much like that proposed by Aristarchus 1700 years earlier.
Model was successful but not overly so.
Assumed orbits were perfect circles, required reintroduction of complexity
Few converts over 50 years
11 January 2012 Modern Physics IV Lecture 1 27
Johanes Kepler (1571 – 1630)
Tycho’s assistant. Inherited data base upon Tycho’s death.
Elliptical orbits
11 January 2012 Modern Physics IV Lecture 1 28
Speculated that some force (like magnetism) originating from the Sun was responsible for planetary motion.
3
2
aM
T
T =
11 January 2012 Modern Physics IV Lecture 1 29
Galileo Galilei (1564 -1642)
1608: 1st working refracting telescopes
Hans Lippershey, Zacharias Janssen, Jacob Metius in the Netherlands
Galileo greatly improved design in 1609
11 January 2012 Modern Physics IV Lecture 1 30
Three objections to Kepler’s heliocentric theories:
(1) The Earth cannot move because birds, falling stones etc, would be left behind.
Inertia later Newton’s 1st law. Galilean relativity
(2) Non circular orbits are contradictory to the non changing perfection of the heavens.
Novae, supernovae, comets already observed
Telescopes allowed observation of sunspots, mountains on Moon
(3) No stellar parallax observed.
Telescope stars are much farther away than Tycho thought
11 January 2012 Modern Physics IV Lecture 1 31
Final nails in the coffin:
The moons of Jupiter, a miniature Solar System
Observation of the phases of Venus can only be explained in terms of a heliocentric model.
Observation of the transit of Mercury across the face of the Sun
CLEA exercisehttp://modphysfromm2.wiki.usfca.edu
11 January 2012 Modern Physics IV Lecture 1 32
Sir Isaac Newton (1642-1726)
11 January 2012 Modern Physics IV Lecture 1 33
Newtonian Mechanics (translational)
Three laws of motion:
1) A body at rest or in constant rectilinear motion remains at rest or in motion unless acted upon by an outside force.
2)F ma
3) Momentum is conserved
i i f fm v m v
Action - Reaction
There are rotational extensions to these laws:
e.g. N I
11 January 2012 Modern Physics IV Lecture 1 34
Newton’s Law of Gravitation
1 22
ˆm m
F G rr
2
1Applying the 3 laws of motion with a force
allowed Newton to derive Kepler's Laws.r
Angular momentum, L mvr
This must also be conserved. Careful, it’s a vector so direction as well as magnitude is conserved
i fL L
L r mv
Force acting at a distance
11 January 2012 Modern Physics IV Lecture 1 35
Triumphs:
Celestial mechanics, planetary orbits
Navigation
Mechanical Engineering and the Industrial Revolution
The above Classical Mechanics was accompanied by the 2nd great triumph of pre-20th century physics, Classical Electromagnetic Theory, a.k.a. Classical Electricity and Magnetism, a.k.a. Classical Electrodynamics.
11 January 2012 Modern Physics IV Lecture 1 36
Electrical charge
Ancient Greece, ca. 600 B. C.
Rub a rod of amber or hard rubber with a cloth.
After rubbing, rod is able to attract small bits of paper or other light material.
No real advance in understanding until ca. 1600 A. D.William Gilbert (court physician to Elizabeth I) studied materials that act like amber.
“electric” (elektron is Greek for amber)
Electric: modern term is “insulator”Non-electric: “conductor”
11 January 2012 Modern Physics IV Lecture 1 37
About 100 years later Charles Du Fay showed that there are 2 forms ofelectrification.
attractionIf you rub various insulators → repulsion
Postulate: There are 2 types of electrical charges like charges repel unlike charges attract
Benjamin Franklin: Assign (+) charge to one type and (-) charge to the other.
Which is ± is arbtrary. Consistent use of a sign convention allows a very concise mathematical formulation of experimental facts.
11 January 2012 Modern Physics IV Lecture 1 38
Franklin’s arbitrary choice: rubbing glass rod w/silk → (+) rubbing amber or hard rubber → (-)
Hindsight: Picking signs opposite to Franklin’s choice → more “sensible” conceptual picture.
“Hindsight is always 20-20” - .Anonymous
J. J. Thomson ca. 1900Discovered the electron. Its charge under the Franklin convention is (-)
11 January 2012 Modern Physics IV Lecture 1 39
Coulomb’s Law
1 2
1 22
0
Force between 2 charges, and , separated by a distance
1ˆ
4
q q r
q qF r
r
William Gilbert (1544-1603)
Charles du Fay (1698-1739)
Benjamin Franklin (1706-1790)
Charles de Coulomb (1736-1806)
a
Another force at a distance.
11 January 2012 Modern Physics IV Lecture 1 40
Magnetism:
“The nation that controls magnetism controls the universe. ”
-Diet Smith in Chester Gould’s Dick Tracy, New York Daily News Syndicate (1962)
11 January 2012 Modern Physics IV Lecture 1 41
Magnetism
Historical:
Interactions between ferromagnetic materials (Fe, Ni, Co)Forces of attraction and repulsionResemble but are quite distinct from electrostatic
Use of permanent magnet in Earth’s magnetic field as compass for navigation.
In 1819 Ørsted showed connection between electric current and magnetism.
Faraday and others, culminating in Maxwell’s equations.
11 January 2012 Modern Physics IV Lecture 1 42
James Clerk Maxwell (1831-1879)
11 January 2012 Modern Physics IV Lecture 1 43
Maxwell’s Equations (differential form)
t
t
0
000
0
EB
BE
B
E
j
E. M. wave equation2
20 0 2
0t
E
E
where
m/sec10x31 8
00
c
2
2
2
2
2
22
zyx
2
In traveling wave equation
1this is
v
11 January 2012 Modern Physics IV Lecture 1 44
Triumphs:
Electrical Engineering, Electric power and communication
Wireless communication
Radar
Modern optics
First electronic computers
11 January 2012 Modern Physics IV Lecture 1 45
The Deterministic UniverseDeterminism The future is completely determined by the past. The future can be predicted if enough is known
of the past.
What is enough?
Consider a universe whose component objects are labeled with the index i. Each object has mass mi.
If we know the initial position, xiI, and velocity, viI of each particle plus the resultant or sum of all the forces acting on it as a function of time, Fi(t), then we can, in principle, calculate the final position, xiF, and velocity, viF. ,
xiI
viI
Fi(t)
xiF
viF
11 January 2012 Modern Physics IV Lecture 1 46
“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”
-1900
“Heavier than air flying machines are impossible.”
-1895
“X-rays will prove to be a hoax.”
-1896
Kelvin, Lord William Thomson (1824-1907)
12 January 2011 Modern Physics III Lecture 1 47
Lord Kelvin
11 January 2012 Modern Physics IV Lecture 1 48
Wilhelm Röntgen
1845 - 1923
Mrs. Röntgen né Anna Ludwig
1872 - 1919
11 January 2012 Modern Physics IV Lecture 1 49
Orville Wright
1871 - 1948Wilbur Wright
1867 - 1912