Testing the Equivalence Principle [ "Mr. Galileo was right." ]

...what if the equivalence principle (EP) is wrong? Galileo's experiments were only accurate to about 1 [per cent], leaving room for doubt, and skeptical physicists have been "testing EP" ever since. The best modern limits, based on, e.g., laser ranging of the Moon to measure how fast it falls around Earth, show that EP holds within a few parts in a trillion (1012). This is fantastically accurate, yet the possibility remains that the equivalence principle could fail at some more subtle level. "It's a possibility we must investigate," says physicist Clifford Will of Washington University in St. Louis, Missouri. "Discovering even the slightest difference in how gravity acts on objects of different materials would have enormous implications." In fact, it could provide the first real evidence for string theory. String theory elegantly explains fundamental particles as different vibrations of infinitesimal strings, and in doing so solves many lingering problems of modern physics. But string theory is highly controversial, in part because most of its predictions are virtually impossible to verify with experiments. If it's not testable, it's not science... "Some variants of string theory predict the existence of a very weak force that would make gravity slightly different depending on an object's composition," says Will... a trillion trillion trillion (1036) times more feeble than electromagnetism... For example, some versions of string theory suggest that this new force would interact with the electromagnetic energy contained in a material.

http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_15_feather_drop.html

The Apollo 15 Hammer-Feather Drop

8.3 Mb Quicktime movie of the demonstration

At the end of the last Apollo 15 moon walk, Commander David Scott (pictured above) performed a live demonstration for the television cameras. He held out a geologic hammer and a feather and dropped them at the same time. Because they were essentially in a vacuum, there was no air resistance and the feather fell at the same rate as the hammer, as Galileo had concluded hundreds of years before - all objects released together fall at the same rate regardless of mass. Mission Controller Joe Allen described the demonstration in the “Apollo 15 Preliminary Science Report”:

During the final minutes of the third extravehicular activity, a short demonstration experiment was conducted. A heavy object (a 1.32-kg aluminum geological hammer) and a light object (a 0.03-kg falcon feather) were released simultaneously from approximately the same height (approximately 1.6 m) and were allowed to fall to the surface. Within the accuracy of the simultaneous release, the objects were observed to undergo the same acceleration and strike the lunar surface simultaneously, which was a result predicted by well-established theory, but a result nonetheless reassuring considering both the number of viewers that witnessed the experiment and the fact that the homeward journey was based critically on the validity of the particular theory being tested.
Joe Allen, NASA SP-289, Apollo 15 Preliminary Science Report, Summary of Scientific Results, p. 2-11

(They’ll have to do better than that, to convince me...LOL!)

p.s. add me to your string theory pinglist but don’t expect any sensible response...

http://www.physicsbanter.com/physics-general-discussion/3723-salvaging-small-morsel-truth-string.html

“...the world of physics is composed of 2 groups— real physicists
and the fringe group known as stringtheorists. And as Mr. Glashow
noted also that when
you have a theory that is never testable nor able to put an experiment
to it then the theory is not science but philosophy. And finally, the
staunch supporter of
Stringtheory of Mr. Weinberg who commented that in a hundred years
from now looking back that String theory would be seen as either a
tragic-waste of time
or as a triumph and where it is easy to see that Weinberg has faith in
the triumph portion. And my gut feeling is that in a 100 years from
now this 3 hour
program will be extant and good for many laughs by future generations
who will see the believers of Stringtheory as the top-class-crackpots
of science of the
20th and 21st century. In ancient times we could not save the crackpot
literature
of science, nor the crackpot literature of science during Newton or
Galileo.
But in modern times, those scientists who become embedded in crackpot
science such as string theory will be forever marked as crackpots in
the future. Today they may get 3 hours TV time for their crackpot
theories but in the future they
will be seen as full crackpots and all their other work dismissed...”

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