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What On Earth Is Wrong With Gravity?

Updated on July 21, 2008

"When Newton saw an apple fall, he found

In that slight startle from his contemplation -

'Tis said (for I'll not answer above ground

For any sage's creed or calculation) -

A mode of proving that the earth turn'd round

In a most natural whirl, called "gravitation;"

And this is the sole mortal who could grapple,

Since Adam, with a fall or with an apple."

Don Juan (1821), Canto 10, Verse I. In Jerome J. McGann (ed.), Lord Byron: The Complete Poetical Works (1986), Vol. 5, 437

The story of the apple and how Newton discovered gravity is well known. It was from this alleged incident that Newton extrapolated his theory of universal gravitation which has been largely accepted as accurate for 300 years. It was through this that he was able to calculate and plot the course of the planets through the solar system. So why isn't the moon where it is supposed to be?

It was Newton's calculations which allowed us to put a man on the moon but by this time it was already suspected that Newton's theory was flawed. Something was wrong with gravity. So, in 1969 when Apollo 11 landed on the surface of the moon one of the first things they did was to set up an experiment to test Newton's law. The experiment consisted of the placing of a mirror or reflector on the moons surface.

At the McDonald Observatory in Texas they target this reflector with a laser and measure the time it takes for the pulses to be returned. This has enabled them to produce an extremely accurate record of the moon's path over the past 40 years. The result is that the moon is not quite where Newton predicts it should be.

Image: Wikimedia Commons.
Image: Wikimedia Commons.

It was not until 10 years after Apollo 11 in 1979 that a strange discovery was made at Kitt Peak National Observatory. They discovered what appeared to be two identical quasars sat side by side. Further examination of the spectrum revealed that they were not merely twins but were in fact one and the same object. So what phenomenon was making this object appear duplicated?

In fact, this effect had already been predicted years earlier by Einstein. He argued that the universe consisted of a fabric which he dubbed as space-time and that an object massive enough could not only warp it but everything in it including light. What was being witnessed was light being bent around a massive object so as not to appear to come from its original source location. The picture above is from hubble and shows the blue galaxy apparently duplicated as a result of bending light.

Even time is warped by gravity. As Einstein theorized time is warped by the Earths gravity and as such operates at a different pace on the surface to that which it does in orbit. It is for this reason that GPS satellites have to have regular manual updates dialled in to maintain synchronisation with Earth time. If it wasn't for Einstein it wouldn't just be Newton's moon that isn't where it is supposed to be, we would all be getting lost.

However, Einstein himself realised that his theory regarding gravity was less than perfect. Quantum mechanics takes us a step closer still but if Newton was good enough to put a man on the moon even if it is 10 metres from where it should be who cares about gravitons?


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