GST 2420: Atoms and Stars:
An Historical Introduction to Astronomy, Physics, and Scientific Discovery.
Fall 2002, Section 983, Call Number 16050
Agenda 9 for 10/30

  1. Announcements:
    1. Due: Report on Experiment 9
    2. Course web site: http://www.cll.wayne.edu/isp/drbowen/aasf02 (also links from Pipeline).
    3. Online Life at WSU updated and with live links at http://www.cll.wayne.edu/isp/drbowen/OnlineLife. New: How to forward your WSU Email after you have activated your AccessID and Password.
  2. Science in the news.
    1. Epistemology - what is a fact? It used to be acceptable in public to deny the truth of a fact simply because you did not like the implications. For example, asbestos companies publicly denied the harm due to breathing asbestos fibers for years, in order to be able to make and sell asbestos-containing products. Now we are engaged in expensive and dangerous cleanups, and many companies are in financial danger as they bought up these companies at reduced prices (Halliburton is one example). Before the 1990s, tobacco companies denied that cigarettes had any link to lung cancer, although that has changed. They simply lost credibility as they denied the link, because it was too obvious that they simply did not like the consequences of the fact. This can bite both ways - labor unions risk losing credibility when they ask that foreign workers have the same protections and pay scales as domestic workers - are they simply acting out of self-interest? These days, the general public is very suspicious, even cynical, of self-interest, real or imagined.
    2. "Galileo's Daughter" on PBS last night. First half-hour. Three points:
      1. (From Creativity course) Highly creative people such as Galileo are almost never, to put it mildly, perfect role models. This may be true of most people and we only know more about these famous creative people. In the excerpt, Galileo exhibits arrogance and fathers illegitimate children,  and later leaves the children and their mother(s?), although in the later part of his life he grows close to one of his daughters. Or perhaps we cut creative people too much slack. Picasso is a good modern example of this seeming dual nature; a centrally important artist, but he treated the women around him with contempt.
      2. Science takes place in a social and personal setting.
      3. Role of Catholic church. Protestant Reformation and Catholic Counter-Reformation.
  3. "When circles collide" - Case Study, Electricity and Magnetism
    1. Among Greeks these were separate topics. Electricity meant static electricity (Thales). Magnetism was magnetic minerals, compasses.
    2. During the period 1775 to 1890, knowledge increased rapidly, moving beyond static electricity and weak magnets serving as compasses. Modern electricity was developed (not electronics, but electrical machinery and crude circuits). Electric and magnetic fields, E and B, were established, similar to Newton's gravitational field. Magnetic generators were used to generate electricity, and currents in magnetic fields were used to build motors. The interaction between electricity and magnetism was developed. Many scientists and engineers were involved, many with names that we recognize today from the names of units and machines - de Coulomb, Volta, Galvanni, Gauss, Ampere, Ohm, Joule, Hertz (and our own Benjamin Franklin). Clearly, the number of scientists had increased and the pace of work along with it.
    3. In 1865, James Clerk Maxwell combined the four most fundamental equations for electricity and magnetism and their interactions into a common form. Electric fields and magnetic fields had different terms, in a way that did not make sense, so Maxwell hypothesized an additional term, the electric displacement. (He left a second difference alone, since single electric charges are well known, but a single magnetic charge was and remains unknown.) But further, examining the now-symmetric equations, he noted that they say that a changing electric field creates a magnetic field, while a changing magnetic field produces an electric field. Might this be circular and self-perpetuating? An electric field changing in the right way to produce a magnetic field changing in the right way to produce an electric field changing in the right way, and so on,  He showed mathematically that this would happen under the right conditions, in empty space. Here is one version of his result:
         Equation 1, due to Maxwell
      The equation relates the rate of "acceleration" of the electric field E on the right side, to the curvature of that same field E on the left hand side, at the same instant and point in space. The two constants e0 and m0 were well known from separate measurements on electric fields (e0) and magnetic fields (m0) and had accurate values at the time. A similar equation held for the magnetic field, B. This equation was very intriguing, because it was also known mathematically that a similar equation, shown below, described waves.
         Equation 2, well known for waves of any type
      Any quantity Q described by such an equation has a fixed profile that travels through space with a velocity v, the same velocity that appears squared in the equation. This same equation described waves on a vibrating musical string, the vibrating air in a pipe organ, waves on water, waves on a spring, in short all the kinds of known waves. Obviously, the electric field (and also the magnetic field) traveled as waves.
    4. And just as obviously, the two equations above determined the speed of these waves as follows, since here Q must equal E, and the quantitites multiplying the time terms must be the same:
         Equation 3, from Equations 1 and 2, for the speed of electromagnetic waves
      What did this velocity come out to be? Using modern values for e0 and m0, the speed of these electromagnetic waves is 186,000 miles per second. This cannot be an accident - light must be electromagnetic waves, or radiation in our current language. In fact, electromagnetic radiation comes in a wide variety, each defined by a range of frequencies (called Hertz after the scientist who first directly observed electromagnetic radiation). Infrared, X-ray, ultraviolet, radio, microwaves, and many other varieties, each with its own technology.
    5. The two fields, electricity and magnetism, had each grown and expanded, come together, and swallowed a third, optics or the study of light, and expanded our understanding of light to include many other types of radiation.
    6. But the advance went even further. All known waves were waves in a medium - a substance in which the wave waved. Water waves were waves in water. Waves on a string were - waves on a string. It had been assumed that light waves were also waves in some medium, unknown at that point, but called the "ether." (Ether had been a common name for any insubstantial space-filling substance. Today, its use is confined to the gas used for anesthesia.) The law of relativity for waves in a medium was also clear - the measured speed of the wave with respect to an observer was the speed of the waves in the medium plus the speed of the observer with respect to the medium. Thus a speedboat finds the water is much choppier than a rowboat does. A jet finds air turbulence harsher than a glider does. The waves hit the quickly-moving observer faster than they hit the  stationary or slowly-moving observer, because the speed of the observer with respect to the medium (water in the first example, then air in the second) is added to the intrinsic speed of the waves in the medium. So, by extension, a moving observer should measure a different speed of light. But Maxwell's equations did not have a medium for light; electromagnetic radiation kept recreating itself. So, when Einstein attacked the absence of the expected changes in the speed of light for moving observers, Maxwell had partially cleared the path for him.
  4. Lab 9 review
    1. All of the groups seemed to do well on the lab, for example taking care to measure the circumference of the circles and ellipse carefully. What could have limited the accuracy of the method used in measuring the circumference? Discussion. How accurate was this result for the circle? Discussion.
    2. The formula for the circumference of the ellipse is wrong in the notes, by intention. (Apology.) The correct formula is very complicated. I have simplified it to the graph below:

      Using this result of 2.16 for the orbit of the comet, find the theoretical value for the circumference of the ellipse in the lab manual.
    3. Why did we do this to you? Reliance on authority (the formula in the notes) Vs the direct experience of the senses, in Galileo's terms.
  5. Readings: Nicholas Copernicus (1473 - 1543), Tycho Brahe (1546 - 1601) and Johannes Kepler (1571 - 1630)
    1. Kepler's three laws:
      1. Planets move in ellipses, with the sun at one focus. (An ellipse is a kind of flattened circle, with the single center split into to foci. Light from one focus will be focused at the second focus, and vice versa.) As the video will point out, for any planet other than Mars, the ellipse is close enough to a circle that the error would have been within the limits of Brahe's data.
      2. Planetary orbits sweep out equal areas in equal times, as measured from the sun
      3. For a planet, the period t and orbital radius r are related by t2 ~ r3. Planets  For example, if two planets are in orbits with the second twice as large as the first, cube the factor of 2 to get 8, and then take the square root of 8 to get the ratio of the periods (length of the planet's year, or 2.83 in this example. The period of the outer planet would be 2.83 times larger than the period of the inner planet. This is enough slower that, not only does the outer planet travel fewer degrees per hour, its speed in miles per hour is also much slower, 30% less in this case).
  6. Readings: Galileo (1564 - 1642)
    1. Social setting. Rise of courts in city-states, then academies. Patrons and Clients, Patron wanted practical results and fame.
    2. 1608. Heard of telescope, made his own, observed heavens - mountains on moon, moons of Jupiter (originally thought they were fixed stars)
    3. 1610. Siderius nuncius (Starry Messenger) announcing discoveries.
    4. 1615. Letter to the Grand Duchess Christina. Argument that science should take precedence over theology, because the Bible can be mistranslated, misprinted, or misinterpreted. Argument that God can make the universe any way he wants, and make it appear to us as something else.
    5. 1632. Dialog on the Two Chief World Systems. Created a sensation. Written for a mass audience in popular Italian rather than scholarly Latin. Relative motion - the earth can move without our detecting it because everything is moving together. A rider on a galloping horse drops a ball, and the ball moves forward with the rider and tracks the horse. Phases of Venus as argument for heliocentrism - phases formed by Venus being lit by the sun and our seeing different views of it (requires telescope to see). Mistaken argument about tides being caused by motion of the earth (they are caused by the moon moving around the earth).
    6. That same year, the Church stopped sales of the book and brought him before the Inquisition. 1633. Found guilty, nearly burned at the stake, put under house arrest for the rest of his life.
    7. 1638 Discourse on Two New Sciences, on work done as a young man. Strength of beams (strength of beam proportional to the square of its depth), balls rolling down inclined planes (odd differences, distance proportional to t2, kinematics or the description of motion, as opposed to dynamics or the causes of motion, to come later with Newton). For projectile motion, horizontal and vertical motion analyzed separately, concept of inertia used. Experiments done later to confirm hypotheses rather than earlier to establish facts.
    8. 1642. Death of Galileo. Trial seems to have discouraged scientific achievement in Italy, moved north and west to France, Holland and England e.g. René Decartes and Francis Bacon.
  7. Video - Kepler's Three Laws. Notice the speeds of the inner and outer planets in the simulations.
  8. Lab X on lenses. Lab Manual, Pages 60 - 63. For "Writing Assignment," do not worry about the length.
  9. GST 1990 only: Pick of a copy of Galileo's sentence from the Inquisition, and his response. Note that the order of the pages is not obvious in the packet (unless I get a chance to fix that).