Scientists solve centuries-old Galileo riddle

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Scientists solve centuries-old Galileo riddle

Paris, May 16

Physicists wielding proton beams believe they have solved a riddle

from the history of their own discipline, by working out exactly

when Galileo Galilei made a discovery that was one of the turning

points in human knowledge.

 

The great Italian thinker determined that objects of different

masses take the same time to fall under the Earth's gravity, a

finding that ripped a hole in a theory that had prevailed for nearly

1,800 years.

 

Legend has it that Galileo (1564-1642) tested his idea by dropping

cannonballs of different weights from the top of the Leaning Tower

of Pisa and finding that the projectiles hit the ground at the same

time.

 

The discovery was one of the landmarks in a golden age of knowledge,

from 1550-1700, when pioneers from Copernicus to Newton destroyed

the classical theories about motion and the cosmos, paving the way

for the modern scientific era.

 

But exactly when Galileo drew up his law has left historians

perplexed for centuries.

 

The law is absent from an early work, "On Motion," written in 1590.

 

Yet it was all worked out by 1632, when Galileo published "Dialogue

Concerning the Two Chief World Systems," which backed the Copernican

view -- branded heretical by the Roman Catholic Church -- that the

Earth revolves around the Sun.

 

In between the two publications are notes in which he formulates the

law, but these precious documents are mostly undated and have no

clear chronology.

 

Experts at the National Institute of Nuclear Physics in Florence

have used a new dating method, bombarding pages of Galileo's notes

with a beam of protons, the British weekly New Scientist reports in

next Saturday's issue.

 

The beam created X-ray emissions with a spectrum that revealed

traces of iron, copper and lead in the ink.

 

The next step fell to Indiana University historian of science

Wallace Hooper and statistician Steen Andersson, who used the

technique to identify 20 different batches of ink known to have been

used by Galileo during his lifetime.

 

They found that the ink used to draw up Galileo's first known

formulation of the law was the same one he used to draw up financial

records for 1604.

 

Hooper now hopes to put the rest of the papers in chronological

order and see how they corroborate with other handwritten data from

Galileo's life to find out not just when, but how, he made his

breakthrough, New Scientist says.

 

Galileo was a ground-breaker because he, in effect, discovered the

Earth's gravity, thus countering beliefs that had dominated since

Aristotle.

 

The fourth-century-BC Greek philosopher believed that objects are

naturally at rest unless they are moved by an external force.

 

This force, Aristotle said, could only be applied by contact, as

force at a distance was impossible, and a constant force was

required to maintain a body in uniform motion.

 

Galileo's experiment was replicated on the Moon in 1971 by Apollo 15

astronauts, who dropped a feather and a hammer onto the lunar

surface.

 

In Earth conditions, air resistance would of course have altered the

outcome, but in the atmosphere-less Moon, the two objects landed in

the dust at the same time.