Lienhard 3

What changed the world around 1900--created the new "modern" world view?

relationship between new ideas in science and technology:

Consider 1901 as a year everything changed in formal science (even though change is always more gradual than that)
1896 x-ray of a handxray of a hand
Consider more carefully the new view of the atom:  video
  • the word atom was supposed to mean the smallest piece, of which everything is made
  • since the late 1700s, chemists had a fairly clear theory that matter was made of combinations of atoms of a limited number of elements,
  • the discovery of elements suggested that atoms of the different elements were the basic building blocks of everything (the first scientific discovery of an element was in 1649)
  • but what was an atom?  A tiny bowling ball?  The revolution was a new theory--Quantum mechanics--showed atoms were extremely complicated and didn't behave in the ways larger objects did.
  • Newton thought light was made up of particles but research in the 1820s showed that light behaves like a wave
  • in 1897 J. J. Thompson discovered the electron (by seeing that electric current could pass through the vacuum in a vacuum tube)--the atom is not a bowling ball but has a positively charged part and a negatively charged part that can be separated.  Thompson thought that atoms looked like raisin bread (or in England they said like a currant bun), with electrons embedded in them
  • in 1901 Planck proved theoretically that energy is emitted in units (quanta), not as a continuous stream.  This could not be explained within the classical theory of physics, so Planck concluded that the laws of classical physics do not apply to atoms
  • in 1905 Einstein published three important papers
    • one showed that the photoelectric effect (where light hitting certain materials will create an electrical current) behaves in such a way that light must be particles with particular energy, not continuous waves
    • the second paper was the special theory of relativity--time moves slower as you get closer to the speed of light
    • the third explained Brownian motion, providing evidence that atoms really existed
  • In 1908 Ernst Rutherford did an experiment where he beamed alpha particles at a piece of very thin gold foil. Alpha particles were known to be very small atoms (actually the nucleus of the helium atom) and gold was made up of big atoms.  Most of the alpha particles passed through the foil, but some bounced back. The shocking conclusion was that most of the atom was empty space. This led Rutherford to propose in 1911 the idea that the atom looked something like the solar system, with a small dense positively-charged nucleus with electrons swirling around it.
  • in 1913 Niels Bohr proposed that the electrons can only travel in fixed orbits around the nucleus, so when electrons move from a higher orbit to a lower one they emit radiation with a fixed amount of energy.
  • Bohr's model of the atom
  • in 1924 de Broglie theorized that not only light but also electrons and other subatomic particles have the properties of particles and the properties of waves at the same time
  • in 1925 Werner Heisenberg put together the pieces of quantum mechanics.  This required the idea that an electron moved from one orbit to another orbit without passing through the space in between as well as the uncertainty principle (below)


Seurat La Parade detail
Modernism meant seeing the world in a new way:
"Nature and Nature's Laws lay hid in Night/
God said, Let Newton be! and all was Light." -- Alexander Pope.

"It did not last; the Devil howling 'Ho!
Let Einstein Be!' restored the status quo." - John Collings Squire

Picasso cubist painting of women
Picasso, Les Demoiselles de Avignon, 1907
We will come back to art, but first consider inventors and scientists

This page written and copyright Pamela E. Mack
HIST 1220
last updated 9/21/16