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What do an ancient Greek philosopher
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and a 19th century Quaker
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have in common
with Nobel Prize winning scientists?
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Although they are separated
over 2400 years of history,
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each of them contributed
to answering the eternal question:
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what is stuff made of?
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It was around 440 BCE
that Democritus first proposed
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that everything in the world
was made up of tiny particles
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surrounded by empty space.
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And he even speculated
that they vary in size and shape
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depending on the substance they compose.
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He called these particles "atomos,"
Greek for indivisible.
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His ideas were opposed by the more
popular philosophers of his day.
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Aristotle, for instance, disagreed completely,
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stating instead that matter
was made of four elements:
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earth, wind, water and fire,
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and most later scientists followed suit.
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Atoms would remain
all but forgotten until 1808,
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when a Quaker teacher named John Dalton
sought to challenge AristotIian theory.
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Whereas Democritus's atomism
had been purely theoretical,
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Dalton showed that common substances
always broke down into the same elements
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in the same proportions.
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He concluded that the various compounds
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were combinations of atoms
of different elements,
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each of a particular size and mass
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that could neither be created
nor destroyed.
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Though he received
many honors for his work,
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as a Quaker, Dalton lived modestly
until the end of his days.
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Atomic theory was now accepted
by the scientific community,
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but the next major advancement
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would not come
until nearly a century later
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with the physicist J.J. Thompson's
1897 discovery of the electron.
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In what we might call the chocolate chip
cookie model of the atom,
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he showed atoms as uniformly packed
spheres of positive matter
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filled with negatively charged electrons.
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Thompson won a Nobel Prize in 1906
for his electron discovery,
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but his model of the atom
didn't stick around long.
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This was because he happened
to have some pretty smart students,
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including a certain Ernest Rutherford,
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who would become known
as the father of the nuclear age.
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While studying the effects
of x-rays on gases,
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Rutherford decided
to investigate atoms more closely
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by shooting small, positively charged
alpha particles at a sheet of gold foil.
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Under Thompson's model,
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the atom's thinly dispersed
positive charge
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would not be enough
to deflect the particles in any one place.
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The effect would have been
like a bunch of tennis balls
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punching through a thin paper screen.
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But while most of the particles
did pass through,
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some bounced right back,
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suggesting that the foil was more
like a thick net with a very large mesh.
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Rutherford concluded that atoms
consisted largely of empty space
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with just a few electrons,
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while most of the mass
was concentrated in the center,
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which he termed the nucleus.
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The alpha particles
passed through the gaps
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but bounced back from the dense,
positively charged nucleus.
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But the atomic theory
wasn't complete just yet.
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In 1913, another of Thompson's students
by the name Niels Bohr
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expanded on Rutherford's nuclear model.
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Drawing on earlier work
by Max Planck and Albert Einstein
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he stipulated that electrons
orbit the nucleus
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at fixed energies and distances,
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able to jump from one level to another,
but not to exist in the space between.
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Bohr's planetary model took centerstage,
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but soon, it too encountered
some complications.
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Experiments had shown that rather than
simply being discreet particles,
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electrons simultaneously
behaved like waves,
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not being confined
to a particular point in space.
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And in formulating
his famous uncertainty principle,
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Werner Heisenberg showed
it was impossible to determine
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both the exact position
and speed of electrons
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as they moved around an atom.
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The idea that electrons
cannot be pinpointed
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but exist within
a range of possible locations
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gave rise to the current
quantum model of the atom,
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a fascinating theory
with a whole new set of complexities
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whose implications
have yet to be fully grasped.
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Even though our understanding
of atoms keeps changing,
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the basic fact of atoms remains,
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so let's celebrate
the triumph of atomic theory
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with some fireworks.
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As electrons circling an atom
shift between energy levels,
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they absorb or release energy in the form
of specific wavelengths of light,
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resulting in
all the marvelous colors we see.
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And we can imagine Democritus
watching from somewhere,
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satisfied that over two millennia later,
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he turned out
to have been right all along.