Georgi Dvali
NYU’S Dvali Says Change in Laws of Gravity, Not ‘Dark Energy,’ Source of Cosmic Acceleration
"This is the crucial difference between the dark energy and modified gravity hypothesis, since, by the former, no observable deviation is predicted at short distances," Dvali says. "Virtual gravitons exploit every possible route between the objects, and the leakage opens up a huge number of multidimensional detours, which bring about a change in the law of gravity."
Dvali adds that the impact of modified gravity is able to be tested by experiments other than the large distance cosmological observations. One example is the Lunar Laser Ranging experiment that monitors the lunar orbit with an extraordinary precision by shooting the lasers to the moon and detecting the reflected beam. The beam is reflected by retro-reflecting mirrors originally placed on the lunar surface by the astronauts of the Apollo 11 mission.
It is important to understand that with this operation running for 35 years the benefits of using existing experimental opportunites are worth considering. I am of course referring to Georgi Dvali's proposition above.
Better than a stopwatch...In essence, we measure the time it takes for the pulse of light to travel to the moon and back. This can take anywhere from 2.34 to 2.71 seconds, depending on how far away the moon is at the time (the earth-moon distance ranges from 351,000 km to 406,000 km). We can time the round trip to few-picosecond precision, or a few trillionths of a second.
Einstein's Equivalence Principle, upon which General Relativity rests, claims that all forms of mass-energy experience the same acceleration in response to an external gravitational force. This is to say that the inertial mass and gravitational mass are equivalent for any form of mass and/or energy. This is very difficult to verify for gravitational energy itself, because laboratory masses have no appreciable gravitational binding energy. One needs bodies as large as the earth to have any measurable self-energy content. Even then, the self-energy contribution to Earth's total mass-energy is less than one part-per-billion
The benefits of seeing and using time clocks, as a measure of perspective has a solid base and the ocnsiderations of GR has lead our views into a world much different then wha we seeon the surface of life. I make reference here to other ways in which we see these relations.
Gravity and Light in the Fifth Dimension perhaps?
Links which extend our perceptions are always greatly appreciated Chris W.
Towards a new test of general relativity?
23 March 2006Scientists funded by the European Space Agency have measured the gravitational equivalent of a magnetic field for the first time in a laboratory. Under certain special conditions the effect is much larger than expected from general relativity and could help physicists to make a significant step towards the long-sought-after quantum theory of gravity.
See:
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