Was Galileo Wrong? - Galileo Galilei

Several potential disturbances had to be reckoned with. Earth's atmosphere, for one, can distort the path of the pulse of laser light, in the same way that it causes starlight to twinkle and shimmer. And tiny tectonic motions of the ground beneath the APOLLO observatory, typically a few centimetres per year, could skew the long-term results. So the project leaders chose a mountaintop near White Sands, New Mexico, that enjoys a particularly calm overhead atmosphere and ground that is relatively stable. In addition, they are installing a super conducting gravimeter and precision GPS sensor alongside the observatory to detect slow ground movements, and an array of precision barometers will map the state of the atmosphere.

more Lunar laser ranging works by firing pulses of laser light at reflectors on the Moon's surface and catching the returning photons. Shown here is the laser ranging experiment at the University of Texas McDonald Observatory.

Williams and Turyshev have recently received a grant from NASA's Office of Biological and Physical Research to improve JPL's lunar laser ranging analysis software by an order of magnitude to match the capability of the New Mexico site. "It will be necessary to deal with many small effects at the millimetre level," notes Turyshev.

Through careful accounting of such small effects, the Universality of Free Fall … could fall.

Many physicists would welcome the news. They've been puzzled for years by a curious incompatibility between general relativity and quantum mechanics. The two theories, so successful in their own realms, are like different languages describing the Universe in fundamentally different ways.

Finding a flaw in the underpinnings of relativity could lead to a new "Theory of Everything," finally combining quantum physics and gravity in one harmonious framework.

From Pisa, Italy, to the Moon, to White Sands, New Mexico: this is a far-flung experiment spanning hundreds of years and hundreds of thousands of miles. Soon, perhaps, we'll have the answers.