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Whats the big idea?

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 goinghence the phrase: love makes the world go round. But it was Sir Isaac Newton who finally discovered the real force at workgravity. Newtons 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!

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.

Thats 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 objects motion to changeto speed up, slow down, or change direction.

Another crucial influence was Galileos 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 motionNewtons 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 earths gravity. He wondered, Might earths gravity reach far enough into the heavens to pull on the moon?

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Global PerspectiveSir 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 moons horizoncalled Earthrisecaptured the imagination of all humankindseeing 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 OffsVelcro, 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 doesnt even scratch the surface of innovations associated with space research. Its 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. Humanitys desire to venture beyond the confines of the earth has become reality, a reality made possible by Newtons unification

And might this gravitational force diminish in some special way as one moves further from the earth? And would the same ideas actually explain Keplers mysterious orbital laws? Newton discovered that the answer to all these questions was yes, and thus was born Newtons 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 doesnt 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 downthis fact is what allows high speed spacecraft to leave earths 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. Its in orbit: its 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 earthhe thereby unified the heavens and the earth.

Newtons ideas gave substance to the prospect

Whats it good for?

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. Thats the power of ideas!

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of our understanding of the laws that govern the heavens and the earth.

EngineeringImagine 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 Newtons 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. Its so much a part of our everday lives its easy to forget that people once might have asked: Whats it good for?