Happy Newton's Day!

Despite the fact that December 25th happens to be the birthday of a number of important historical figures (for example, Mohammad Ali Jinnah, the founder of Pakistan, which is where I am from), last year we at 3 Quarks Daily thought we would celebrate Newton's birthday on this date. Unbeknownst to us, Richard Dawkins had just published an article suggesting the same thing. We were flattered. So here we are again, on Newton's Day!

To commemorate this auspicious occasion, I thought I would try to deal with the apple today. You know what I am talking about: the apple that supposedly fell on Sir Isaac's head while he was resting under a tree, and which jarred him into formulating the theory of gravity. The story is almost certainly apocryphal (no getting away from the Bible, is there?), but what could it mean? There are many ways to try and understand this story, but I just want to point out something simple but very cool: look at my drawing of me lobbing a ball over to a friend of mine below.

The ball follows a parabolic path from my hand to those of my friend. But what if my friend wasn't there, and nor was the surface of the Earth? What if the ball could just pass through the Earth as if all its (the Earth's) mass were concentrated at its center? What would happen then? Look at my next drawing below.

The ball would go in an elliptical path, with one of its foci being the center of the Earth! The parabola above the surface of the Earth is just one end of the bigger ellipse! Where had Newton heard of ellipses before? Yep, from Kepler, who had shown that planets travel in elliptical orbits around the Sun. How's that for a connection between small objects falling on Earth, and the heavenly spheres? Of course, we'll never know Newton's real line of reasoning, but here's a possible one:

• apple falls on Sir Isaac's head
• he starts to think how freely falling objects behave
• he generalizes to objects following parabolic paths
• he imagines what happens if the surface of the Earth doesn't stop the object
• he realizes the object falls into elliptical path
• he realizes planets are just "falling" around Sun

Okay, it probably wasn't that way, but I still think it's a nice thought. And in case you're wondering just how big Newton's intellectual reputation is, check this out from the London Times:

Newton trounces Einstein in vote on their relative merits

His most famous equation, E=mc², is 100 years old, and 2005 has been named Einstein Year in his honour, but Albert Einstein has been trounced in a scientific beauty contest held to celebrate his own greatest achievements.

The most famous head of hair in science was soundly beaten by Sir Isaac Newton yesterday in a poll on the relative merits of their breakthroughs, with both scientists and the public favouring the Englishman by a surprisingly wide margin.

Asked by the Royal Society to decide which of the two made the more important contributions to science, 61.8 per cent of the public favoured the claims of the 17th-century scientist who developed calculus and the theory of gravity.

More here.  And, oh, what the... 

MERRY CHRISTMAS!

[This post dedicated to LWP.]