Chapter 15.

The Success and End of Newtonian Science

15.1. Classical Newtonian Science

• Newtonian Science (1687-1890)
  • Smashingly successful in developing solutions to age old problems, not only in considerations of motion, but in electromagnetic, heat, light, matter phenomena
  • Mathematics as key to understanding nature expands exponentially
  • Newtonian age ends with publication of three books
    • James Clerk Maxwell (1831-1879); Scottish physicist; A Treatise on Electricity and Magnetism, 1873
    • Ernst Mach (1836-1916); Austrian physicist-philosopher; The Science of Mechanics, 1883
    • Ludwig Boltzmann (1844-1906); Austrian physicist; Lectures on Gas Theory, 1896
• Why is Newtonian science so successful?
  • Newtonian science is so successful because it provides a consistent, if not absolute, explanation of our common experiences as human beings.
  • Does its success mean that Newtonian science is the final word on all scales of physical phenomena?
  • Does its success mean that Newtonian science has captured reality?

15.2. Wave Nature of Light

• Early concepts
  • René Descartes, 1637, suggests
    • Light is some kind of disturbance, but not a material entity, moving at infinitely high speed
    • Also proposes light might be like stream of tennis balls; discrete nature
  • Isaac Newton, 1666, suggests
    • Light has discrete properties with very small masses, if any mass
    • Subject to being accelerated
  • Thomas Hobbes, 1644, suggests a wavelike character for light for which speed in dense medium is less than in air
  • Christian Huygens, 1690, elaborates on wave theory for light
• Speed of light
  • Galileo, 1642, suggests speed of light is finite but very large compared to sound, even though his experiment to measure was inconclusive
  • Ole Roemer, 1676, uses eclipses of Jupiter's satellites to show that speed of light is finite
  • Christian Huygens, 1690, calculates speed of light obtaining about 2/3 of current value
  • Modern value, c = 299,792 km/s or 3 x 10[E(8)] m/s, or in English units, c = 186,300 mi/s
• Wave (continuous) character of light
  • James Clerk Maxwell, 1862, propagating electromagnetic wave
    • Composed of electric and magnetic fields
    • Electric and magnetic fields vary in intensity
    • Oriented at right angles to each other and to direction of propagation of wave
    • Transport energy from one place to another
    • Require no material medium to transport disturbance unlike mechanical waves (water waves)
  • Wave is moving disturbance
    • Transverse character: disturbance varies at right angles to direction of propagation
    • Wavelength: distance between consecutive crests or troughs; physiological response is color
    • Frequency: number of complete cycles of disturbance passing fixed point per second
    • Speed: product of wavelength (w) and frequency (f) or c = wf
    • Amplitude: greatest height to which crests raise or greatest depth to which troughs fall; physiological response is intensity or brightness
• Electromagnetic spectrum: ordered arrangement by wavelength
  • Spectral Region, Wavelength
  • Radio, 10[E(2)] to 10[E(6)] cm
  • Microwave, 10[E(-2)] to 10[E(2)] cm
  • Infrared, 10[E(-4)] to 10[E(-2)] cm
  • Visible, 35-70 x 10[E(-6)] cm
  • Ultraviolet, 10[E(-6)] to 10[E(-5)] cm
  • X-rays, 10[E(-8)] to 10[E(-6)] cm
  • Gamma rays, 10[E(-12)] to 10[E(-8)] cm
• Wave properties of light
  • Reflection: occurs when light encounters boundary of two different media
  • Refraction: change in direction of light ray when it passes through boundary between two different media
  • Diffraction: spreading out or bending of light past the edges of an opaque body
  • White light: mixture of light rays of all different wavelengths or colors
  • Inverse square law: apparent brightness varies inversely as square of distance from light source
  • Doppler effect [Christian Doppler (1803-1853)]: electromagnetic waves received by an observer have a shorter wavelength, if source and observer approach each other, and a longer wavelength, if source and observer recede from each other; change in wavelength is directly proportional to velocity along line between source and observer [w(obs) - w(lab)]/w(lab) = v/c, where w(lab) = laboratory wavelength, w(obs) = observed wavelength, v = velocity along line of sight, c = velocity of light