Recently, I wrote about the four
major players in Renaissance astronomy, Copernicus, Brahe, Kepler,
and Galileo, their discoveries, and how they impacted our perception
of the universe. However, for all their brilliance, none of these
four great men could explain why the universe behaved as it did. This
task would fall to the final great thinker of Renaissance-era
astronomy. Issac Newton, ironically born in the year Galileo died.
As written about last time, Galileo dd a lot of pioneering work in early physics after the
theological storm created by the Starry Messenger. In his
experiments, Galileo worked with rolling balls on inclined planes and
found that the distance traveled is always proportional to time, no
matter the ball's weight or ramp's angle of descent. Also (and it's
surprising that no one did this before), Galileo made the discovery
that light and heavy objects fall at the same speed (Galileo would
have been thrilled to see his experiment repeated on the Moon during
Apollo 15). Another important finding: objects only stop when acted
upon by an outside force.
As an after note, Galileo never dropped objects off the Leaning Tower of Pisa
As an after note, Galileo never dropped objects off the Leaning Tower of Pisa
Rene DescartesIn France, a contemporary of Galileo, Rene Descartes, was also thinking about the way things moved. Thinking about the root causes of motion, Descartes believed that all motions were caused by invisible particles colliding with objects and thus, if there were no collisions, there was no motion. Now, while that idea may seem funny to us today, Descartes did get two of his fundamental ideas correct when he noted that all motion tends toward being in a straight line and, to get curved motion, some force must be acting on an object.
Robert Hooke
Living after Galileo and Descartes,
Englishman Robert Hooke further refined ideas of motion, who moved
beyond motion on Earth into thoughts about motion in the heavens.
Before Hooke, Kepler described the way planets moved. As for the
'why,' Kepler could not explain this, with his best idea being that
the motion of the planets was caused by a combination of magnetism
pulling them toward the Sun and some unknown force in the Sun pushing
them out. In contrast, Hooke believed that there was some central
force in the Sun that caused the planets to orbit it rather than fly
off into space. Hooke also believed that this same force caused
objects to fall on Earth and that the strength of this fore decreased
as distance to the center of a body increased. In fact, Hooke had
just unknowingly described gravity, but he could not give the
specifics in mathematical terms. His task would fall to one of the
greatest minds in history: Issac Newton.
Issac Newton
The story of Issac Newton is both a
story of outright genius and pure luck. His intelligence recognized
from an early age, Newton was sent to Cambridge University in order
to get a college education, then in itself a rarity. In 1665, one of
history's great ironies struck: the Plague arrived in London and
Cambridge was shut down for the year, thus interrupting Newton's
studies. Returning home, Newton allowed him mind to roam free. It was
during this unplanned vacation that Newton invented calculus,
discovered the laws of motion, and made fundamental discoveries in
optics, all of which may have never happened had the Plague not
struck and Newton had remained preoccupied with his formal studies.
When Newton returned and got his degree, one of his impressed
professors actually resigned so that the intellectually superior
Newton could have the position.
In his Principia (Mathematical
Principles of Natural Philosophy), Newton laid out his three laws of
motion that explained all motions in the universe. The laws are as
follows:
Inertia: objects at rest remain at
rest and objects in motion remain in motion unless acted upon by an
outside force.
Force: forces act on an object, cause
chances in acceleration (here used to denote any change in speed) and
direction, force = mass x acceleration
Reaction: for every action, there is
an equal and opposite reaction
Also, the law of universal
gravitation was shown for the first time.
Now, unlike the story of Galileo on
the Leaning Tower, the story of Newton and the apple is actually
true, as Newton himself attested to its validity. As a thought
experiment, Newton started thinking about objects falling to the
ground after seeing the apple fall from the tree. In his mind, Newton
thought about cannons, then state of the art. Cannonballs, no matter
how powerful the cannon, always fall back to Earth. Now, in theory,
could there be a cannon so powerful that it shot the ball so far that
it would not fall back to Earth, but rather fall around the Earth?
Employing his mathematical genius, Newton discovered that the answer
was 'yes.' In thinking about apples and cannons, Newton just
explained lunar motion.
Now, if this example of gravity in
action was applicable to the Moon and Earth, why not the Sun and
planets? Again, doing the calculations, Newton found that his laws of
motion perfectly explained the motion of the planets that Kepler so
accurately described, but could not explain, decades ago. It was only
now with Newton's laws of motion that the heliocentric solar system
proposed by Aristarchus of Samos in the 200s B.C. and rediscovered by
Copernicus was proven to be true.
In conclusion, Newton would be the
final word on physics for 300 years. Now, that is not to say that
discoveries stopped with Newton. Rather, far to the contrary,
advances in optics would allow for much to be learned and far more
accurate measurements to be made. However, it was not until Einstein
and modern technology that astronomy, now becoming the much bigger
science of cosmology, would undergo a revision as grand as that
created by the Renaissance.
More Ancient Astronomy
The Planet of Bethlehem?
A History of Cosmology: Prehistory to Present
Galileo's Fingers Go on Display.
Renaissance Astronomy: Part 1
Renaissance Astronomy: Part 2
Renaissance Astronomy: Part 3
The Equinox and a Magic Show from the Maya
Ancient America: the Moundbuilders
Ancient America: the Southwest
Ancient Egypt
Classical Greece
The Summer Solstice Sun and the Size of the Earth
The 1833 Leonids: History's Greatest Meteor Storm
The 10 Brightest Comets of All Time
Ben Franklin and the Truth About Daylight Savings Time
More Ancient Astronomy
The Planet of Bethlehem?
A History of Cosmology: Prehistory to Present
Galileo's Fingers Go on Display.
Renaissance Astronomy: Part 1
Renaissance Astronomy: Part 2
Renaissance Astronomy: Part 3
The Equinox and a Magic Show from the Maya
Ancient America: the Moundbuilders
Ancient America: the Southwest
Ancient Egypt
Classical Greece
The Summer Solstice Sun and the Size of the Earth
The 1833 Leonids: History's Greatest Meteor Storm
The 10 Brightest Comets of All Time
Ben Franklin and the Truth About Daylight Savings Time
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