What makes the universe tick? Since the dawn of human consciousness, people have watched the sun,
moon, planets and stars move through the heavens, and wondered how it all works. Some thought angels
pushed the heavenly bodies on orbits around the earth; Aristotle thought love set the universe in motion,
and even kept it going—hence the phrase: “love makes the world go ‘round”. But it was Sir Isaac Newton
who finally discovered the real force at work—gravity. Newton’s methods marked the birth of modern
science, leading to everything from velcro to MRI scans, and YouTubeTM to a global satellite network.
Explore how Newton opened the entire universe to the scientific imagination!
What’s the big idea?
For most of human history, people believed
there was something fundamentally different
about the heavenly realm of the sun, moon,
planets and stars, compared to our humble,
earthly realm. Sir Isaac Newton shattered
this belief, and the way he did it introduced
a new kind of rational, mathematical way of
thinking that was so powerful it has since led
to virtually every single thing we know about
the universe today at a fundamental level.
That’s no small feat. How did he do it? By
“standing on the shoulders of giants!” From
Nicolaus Copernicus, Newton got the idea
that planets orbit the sun, not the earth.
From Johannes Kepler, Newton learned that
these orbits are ellipses, traced out according
to certain mysterious, mathematical laws.
And based on the work of Galileo Galilei,
Newton developed his laws of motion: an
understanding of how forces cause an object’s
motion to change—to speed up, slow down,
or change direction.
Another crucial influence was Galileo’s
telescopic observations that suggested a
most heretical idea: that heavenly bodies are
no different from earthly ones. If Galileo was
right, Newton reasoned that they must all obey
the same laws of motion—Newton’s laws of
motion. For example, Newton knew that to
make an object move in a circle requires a
force continually pulling it towards the centre
of the circle, causing its direction of motion to
be continually changing. The moon is moving
in a circle as it orbits the earth; what force is
continually pulling it towards the centre of the
earth?
Newton knew that an apple is pulled towards
the centre of the earth by earth’s gravity. He
wondered, “Might earth’s gravity reach far
enough into the heavens to pull on the moon?
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And might this gravitational force diminish in
some special way as one moves further from
the earth? And would the same ideas actually
explain Kepler’s mysterious orbital laws?”
Newton discovered that the answer to all
these questions was “yes,” and thus was born
Newton’s law of universal gravitation.
Newton created a brilliant “thought
experiment” to understand gravity: Imagine
a cannon atop a high mountain firing
cannonballs sideways (see Newtonian Gravity
animation). With a small initial speed the
cannonball doesn’t get very far before falling
down. But with a greater initial speed, it goes
farther around the earth before falling down.
Of course with too large an initial speed, it
never comes down—this fact is what allows
high speed spacecraft to leave earth’s gravity
and explore the planets. So in between must
be a just-right initial speed that will cause it
to travel all the way around the earth and fly
by the cannon with the same initial speed,
thus continuing to go around and around.
It’s in orbit: it’s always falling, but never falls
down! Newton realized the moon, as it moves
through the heavens, must be doing the same
thing as his imaginary cannonball near the
earth—he thereby “unified” the heavens and
the earth.
Newton’s ideas gave substance to the prospect
that the entire universe might be within reach
of human understanding, and since that time
his ideas have literally transformed the world.
As just one example, think of the hundreds
of satellites currently orbiting the earth, giving
us everything from Google EarthTM and global
climate monitoring, to space telescopes that
peer out to the very edge of the observable
universe. That’s the power of ideas!
What’s it good for?
Global Perspective
Sir Isaac Newton published the Principia in
1687, and it became one of the most important
scientific works ever written. It was his insight
into the laws of motion that led to rockets with
the bone rattling power to lift humans into
space. The precisely calculated trajectories of
the Apollo missions that put men on the moon
were based on his ideas about gravity. The
famous photograph of the earth rising over the
moon’s horizon—called Earthrise—captured
the imagination of all humankind—seeing for
the first time how truly alone and how truly tied
to one another we are. Images of the earth
from space have helped society gain a new and
powerful global perspective, and perhaps a
renewed sense of stewardship for our world—
quite an unexpected and precious gift arising
from theoretical musings 300 years earlier.
Spin Offs
Velcro, enriched baby food, chlorine-free
pool purification, better golf balls, running
shoes, solar energy from photovoltaic
cells, fireproof fabric, sewage treatment,
earthquake detection, magnetic liquids,
engine lubricant, Doppler radar, smoke
detectors, and disposable diapers. Whew!
And that list doesn’t even scratch the surface
of innovations associated with space research.
It’s difficult to even estimate the enormous
and far-reaching impact that space programs
around the world have had on our day-to-day
lives, and harder still to accept that this nearly
endless list of inventions ultimately owes its
existence to the ideas of one 17th century
scientist. Humanity’s desire to venture beyond
the confines of the earth has become reality, a
reality made possible by Newton’s unification
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of our understanding of the laws that govern
the heavens and the earth.
Engineering
Imagine driving along a coastal highway, then
over a bridge, and as you round a corner you
see a majestic city skyline in the distance.
The vehicles we ride in, the roads we travel
on, the bridges that carry us over bodies
of water, and the towering skyscrapers that
make up a city all owe their construction to
the application of Newton’s ideas on forces,
motion and gravity. What was theoretical
physics in 1687 has become the scientific
basis of the engineering disciplines that build
our modern world. It’s so much a part of our
everday lives it’s easy to forget that people
once might have asked: “What’s it good for?”
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