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									     The Lighter Side of Physics

Prof. Roger McWilliams

Department of Physics & Astronomy
University of California, Irvine 92697, USA
Email: mcw@uci.edu
949-824-6228 lab phone and fax

The slides of this talk are posted at
       How did we get to today?
• Civilization – the combination of culture and
  technology, both at relatively high levels.
  – Science and engineering create and make technology.
  – Science and engineering contribute to culture as well,
    but we shall focus on technology here.

 • Mechanical Age – previous societies were in
   ages described by mechanical names (stone,
   bronze, iron, steam)
 • Electrical Age – a new type of age
                The Electrical Age
• Professors Maxwell & Faraday, and others, gave us the electrical
  age starting in about 1834.
• From the following Maxwell’s Equations, we get modern
  civilization: Electricity, Magnetism, Electromagnetic Waves,
  Light come from understanding these equations (motors, power
  generators, lasers, transistors, et cetera).
• To understand how important these equations are, try turning off
  your electrical power at home and work.
• Maxwell’s Equations:
                            D   Free
                          B  0
                                    B
                           E  
                                        D          
                            H  jFree      jFree  jDisplacement
                       Michael Faraday

Faraday’s Law:                    Electric motors
                                  Electric power plants for
magnetic fields
                                  all electrical appliances
make electric fields
                                  and lights
The Discovery of Electromagnetic Induction
                      The experiment was conducted
                       on 29 August 1831. When the
                     primary circuit was closed, there
                         was a displacement of the
                        galvanometer needle in the
                     secondary winding. Deflections
                      of the galvanometer were only
                     observed when the current in the
                      electromagnet was switched on
                     and off. This was the discovery of
                         electromagnetic induction.
Faraday’s notebook
   James Clerk Maxwell
Scotland’s Greatest Physicist

              Celebrating the 175th
                  Anniversary of
               Maxwell’s birth and
                the opening of the
              James Clerk Maxwell
               Laboratories at the
               Edinburgh Academy
                Albert Einstein (1931)
   “We may say that, before Maxwell, Physical Reality, in so
       far as it was to represent the process of nature, was
       thought of as consisting in material particles, whose
    variations consist only in movements governed by partial
      differential equations. Since Maxwell’s time, Physical
    Reality has been thought of as represented by continuous
    fields, governed by partial differential equations, and not
    capable of any mechanical interpretation. This change in
     the conception of Reality is the most profound and the
   most fruitful that physics has experienced since the time of
James Clerk Maxwell – A Commemorative Volume 1831-1931
          Maxwell as a college student:
        Edinburgh University (1847-1850)
Lecture courses attended
                                    Publications in
Mathematics – Kelland             Transactions of the
Natural Philosophy – Forbes
                                   Royal Society of
Logic – William Hamilton
Books borrowed from library
Cauchy: Calcul Différential
                                   On the Theory of
Fourier: Théorie de la Chaleur      Rolling Curves
Monge: Géometrie Desciptive
Newton: Optics                    The Equilibrium of
Poisson: Mechanics                  Elastic Solids
Taylor: Scientific Memoirs
Willis: Principles of Mechanism
                          Maxwell’s Equations
    Maxwell figured out how electromagnetic phenomena could
    be described by the mathematics in these four equations.
    Maxwell is responsible for dreaming up that last term in the
    last equation.

•   Electric charges make electric
                                             D   Free
•   Magnetic charges would make            B  0
    magnetic fields, but we’ve never                    
    seen any                                         B
•   Time-changing magnetic fields           E  
    make electric fields                              t
•   Electric currents or time-changing                   D          
    electric fields make magnetic fields     H  jFree      jFree  jDisplacement
A Dynamical Theory of the Electromagnetic Field (1865)

    Maxwell's own view of this paper is revealed
    in what Francis Everitt calls “a rare moment
      of unveiled exuberance” in a letter to his
                cousin Charles Cay:

                “I have also a paper afloat,
               containing an electromagnetic
              theory of light, which, till I am
             convinced to the contrary, I hold
                     to be great guns”.
         A Treatise on Electricity & Magnetism (1873)

• “The most important aspect of any phenomenon from a
  mathematical point of view is that of a measurable quantity.
  I shall therefore consider electrical phenomena chiefly with
  a view to their measurement, describing the methods of
  measurement, and defining the standards on which they
• “The internal relations of the different branches of the
  science which we have to study are more numerous and
  complex that those of any other science hitherto developed.”
• “It appears to me, therefore, that the study of
  electromagnetism in all its extent has now become of the
  first importance as a means of promoting the progress of
 And, once more,                 D   Free
                               B  0
Maxwell’s Equations                         
                                         B
                                E  
                                             D          
                                 H  jFree      jFree  jDisplacement

Let’s see now, hmm, if that third equation says time-changing
magnetic fields make electric fields, then the electric fields
must be changing in time also (because we can start with zero
magnetic field). And the fourth equation says time-changing
electric fields make magnetic fields! Ah, ha! Does this mean
that time-changing electric and magnetic fields can make each
other with no other assistance? Can they go together through
space on their own? Gee whillikers, you betcha!
   From National Radio Observatory

The combination of time-changing electric and magnetic fields
propagating through space or matter is what we call
electromagnetic waves or light waves.
  Voodoo Science: A Trick with a Scientific-
             Sounding Premise
False claim: This experiment shows how ESP makes successful
predictions. Recent statistics suggest that this system can
predict the correct outcome of your choice with 98% accuracy.
Let me repeat. I am conducting an experiment. There are six
small cards below. Select a card, stare at it, and be sure to
remember it. By detecting your electromagnetic energy after
your choice is made I can know your card.

             Prediction: I know your card and
             will now remove it from the cards.
 I have removed your card! Quantum consistency is: 671.

This is not science. Even though scientific terms are used and
there is a claim of predictive capability, there is no proof that
your card was known via ESP sensing of electromagnetic
Instead, there only is proof that your card was removed. The
trick is no cards shown above were on the previous page. But
careful examination is needed to see that. Many people believe
this trick actually shows ability to know the card you selected.
Be skeptical of claims of predictive capability unless verified by
scientists independent of those who would profit from claims.
From Nasa
        Maxwell’s Colour Triangle

Maxwell’s original version   Modern version
Light comes out of many plasmas.
A solar flare, viewed through a blue filter, on our
most important plasma, the Sun. Photo: NASA
The Northern Lights
(Aurora Borealis).
Photo: J. Curtis

           Collisionally-induced fluorescence

Temporal evolution of emitted photons can be observed.
This is collisionally-induced fluorescence from electrons
                raining down upon neutrals.
Comet Hale-Bopp.
Photo: D. Toohey

              Ultraviolet-induced fluorescence
    Visible and near-visible photons can provide non-
intrusive diagnosis of plasmas. Blue comet plasma tail is
     visible due to fluorescence induced by ultraviolet
  photons from the Sun. White tail is sunlight scattered
                    from comet dust tail.
 When light travels through matter, it is slowed down by the
electrons in the atoms. Different frequencies/wavelengths are
   slowed different amounts depending on the atoms in the
 Prism of quartz example below. Diamonds have very strong
wavelength dependence (spread the colors a lot) and are very
 durable (Zircon nearly as good). Leaded glass is great, too.
Now let’s go look at some fun
  atmospheric light effects
Rainbow – large drops (refraction, reflection) primary, secondary, higher,
supernumerary (wave interference)
Corona – small drops (diffraction)
Glory and Heiligenschein (not same)
Halo – parhelic circle, sun dog, tangential arc
Green flash

      Corona are caused by diffraction around small water
      mist in the atmosphere. Typically seen around 15
      degrees from the sun or moon. Can have rainbow-
      like color spread.
What is a laser; why do we care to know?

 • Light Amplification of Stimulated Emission
   Radiation (LASER). Often laser light is:
    – Aimed pretty much in one direction,
    – Pretty much near one wavelength (color)
 • Lasers are described by Maxwell’s Equations,
   with a little bit of quantum mechanics thrown in.
 • There are lasers in nature, but most interest is for
   business purposes. And, lasers are big business.
 Theodore Maiman (my mother was
acquainted with him) got the patent for
             the first laser.

       Maiman with a ruby laser on the
       laser’s 25th anniversary. Photo
       courtesy of Kathleen Maiman

                                          1960 invention
                                          1961 patent application
                                          1967 patent issued
A double Laser-Induced Fluorescence (LIF)
system: Two pump plasma ion lasers, in
background, drive two tunable dye lasers (one
with cover removed). (This photo is 15 years old,
but was hard to make; we are not doing it again).
How your airplane follows its flight path
  Subtitle: Ring laser gyroscopes, plasma etching, the US
Supreme Court, and Doctrine of Equivalents, which may put
            you in a fog (fiber optic gyroscope).
    Author: Willy Makeit         Illustrator: Betty Wont

                              In 1978 a man and his dog found
                              a way to make incredibly-highly
                              reflecting mirrors. He did not
                              know why this way worked and
                              the dog would not say, but Litton
                              Industries was very happy.
Among the pleasant people
assembled for the Litton team
was attorney John Roberts.

                                You know him now as Chief
                                Justice of the US Supreme Court.
      Tissue Discrimination via LIF
• To find a practical,
  inexpensive, and non-
  invasive method of
  discriminating healthy
  from unhealthy biological

                         Picture by Medicine Net
            Hopes and Dreams

• Fluorescence on human skin might be done without
• Fluorescence might allow discrimination of different
  types of skin conditions and growths
• Perhaps various skin cancers can be detected by
  fluorescence instead of skin biopsy technique
  presently used
• Potential for much lower cost, very fast analysis
  while the patient is in the office, and no biopsy
  wound requiring healing
  And finally, how do lasers and
plasmas help you use the internet?
       Optical fibers carry your
   conversations to their destinations
• Your voice is converted into pulses of light
  traveling down “light tubes” called optical fibers.
• Fibers are especially useful for long lines, like
  from US to Japan.
• Still, while traveling on long lines, the signal gets
  weaker and needs to be amplified occasionally.
• Putting atoms which can lase directly into the
  fiber allows the fiber to become the amplifier.
Erbium-doped Fiber Amplifiers (EDFA)
   can give you clear communication
      anywhere a fiber can be run
 On the 1550 nm voice signal where one
  might want a stable, low-power laser
• UC Irvine worked with New Focus to develop small,
  inexpensive tunable, stable diode lasers.
• New Focus was another Milton Chang startup (like
  Newport Corporation).
• New Focus now owned by Bookham Technologies
  (whose president worked for me in graduate school).
New Focus laser in blue box in middle. Note how
small it is compared to person in photo.
 On the 980 nm amplifying laser pump
 power where one might want a stable,
        high-power laser source

• UC Irvine worked with SDL to develop 0.5W
  single-pass diode laser amplifiers.
SDL MOPA with diffraction grating cavity removed. The
0.5 W output active semiconductor chip diode is white
dot in center of gold holder. Chip is about 2 mm wide.
Shakespeare’s King Henry VI, Part III, Act II, Scene I

EDWARD: Dazzle mine eyes, or do I see three suns?

RICHARD: Three glorious suns, each one a perfect sun;
Not separated with the racking clouds, But sever'd in a
pale clear-shining sky. See, see! they join, embrace, and
seem to kiss, As if they vow'd some league inviolable:
Now are they but one lamp, one light, one sun. In this the
heaven figures some event.
• Every person in this room is relying on
  electromagnetism around the clock for their
  participation in civilization.
• The lighter side of physics is fun to observe
  and understand.

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