**Newton celebrated in the latest “Google doodle”**

**By James Dacey**

Welcome back to *physicsworld.com* for what will hopefully be another exciting year of research breakthroughs and technological innovations. That said, if you’re returning to work after a Christmas break of festivity and overindulgence, the first few days back can be more than a little gloomy. At least the folks at Google are doing their bit to try to lift the spirits of down-in-the-dumps physicists.

Attentive users of the popular internet search engine will have already noticed its tribute to Isaac Newton, the great English physicist who would be celebrating his 366th birthday were he still alive today. The iconic Google logo has been draped with the branch of an apple tree, which drops a fruit when you hover your cursor over it – a tribute, of course, to the incident that allegedly inspired Newton’s theory of gravitation and his *Principia Mathematica* first published in 1687.

Newton’s much anticipated follow-up *Opticks*, released to the public 17 years later, also has great resonance this year, as 2010 marks the 50th anniversary of the invention of the laser. *physicsworld.com* will be joining the celebrations with a series of video interviews with leading laser physicists and engineers, and there will also be a laser special for the May print issue of *Physics World* magazine.

So whether you’re returning to the office, to the lab, or anywhere else in between, try to ride out those New Year blues, as the celebrations and exciting breakthoughs are just around the corner!

I think Newton was even greater than people generally think. He’s considered to have worked out the mathematics of (Newtonian) gravity without explaining how gravity works, but if you look at Opticks queries 20 and 21, you can see him offering an explanation for gravity that’s actually rather close to Einstein’s non-uniform guv:

“Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? …Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?”There’s a few alien words in there, but when you read “aethereal medium” as vacuum, and read “grow denser by degrees” as “exhibits a reducing stress-energy tensor”, it fits rather well. Then in query 30 he says

“Are not gross bodies and light convertible into one another?”which IMHO anticipates pair production and E=mc², and does rather explains his interest in alchemy. In addition, in contrast to Huygens who described light purely as waves, Newton talked about corpuscles, which anticipates Einstein’s work on the photo-electric effect. This is what Einstein is considered to have won the 1921 Nobel prize for – photons, though they weren’t called that until Gilbert Lewis coined the word in 1926.Great man, Newton. Like I said, I think he was even greater than people think.

Weakness of Gravity: As per present knowledge, gravitational force is the weakest one among the four fundamental forces. But the present way of comparison of this force with the electromagnetic force is “debatable” I believe. So interested readers are encouraged to contact me directly (dvsathe@gmail.com) or through the editor – for initiating a discussion on this important topic.

I agree with Duffield’s comment, Newton’s contribution is much larger than he is credited. Einstein’s theory of gravity was based upon Newton’s work, see Annalen der Physik, 35, 898 (1911). When he derived his field equations, see Annalen der Physik 49, 769 (1916), he used tensors to derive his field equations. He found that mathematics too difficult to solve directly and introduced an approximation. It can be found be found amongst his equations 20. All exact solutions to his field equations are still an approximation. If you start at Einstein’s 1911 perspective and appropriately apply the constants h (Planck’s constant) and c (speed of light in vacuum) to Newton’s gravity equation, you can derive a space-time geometry equation using Newton’s calculus. That solution matches all experimental observations that support Einstein’s field equations. Further the accepted Schwarzschild solution that produces the black hole effect is seen to be the first approximation to this Newtonian based calculation, as would be expected if Einstein introduced just one approximation. (Further information on this can be obtained by contacting me: vivr@exemail.com.au.)

In addition to his theory of gravity, Newton made another contribution which I believe was even larger. His laws of motion enabled people to calculate what would happen from a given situation. Although we take this for granted these days, prior to Newton’s time very few things were predictable. Through his laws of motion, Newton laid the foundations to our modern technological world when others applied those laws to their own field of expertise. He also set up the monetary “gold standard” that stabilized financial systems for well over two hundred years.

In my opinion, Newton was indeed a great man whose contribution to our world is greatly underestimated