Einstein finally proven right on gravity speed
PARIS, France (AFP) — More than 87 years after it was devised, a theory by Albert Einstein that gravitational force moves at the speed of light has finally been confirmed by a pair of US- based scientists.
The assumption that gravity travels at light speed is central to Einstein’s construction of space-time, the general theory of relativity, which he devised in 1915 but which has never been tested.
In the absence of any confirmation, interest has flourished in a novel theory called “brane worlds” that suggests there are other dimensions to ordinary matter.
Gravity can take a short-cut through these extra dimensions, while light is confined to the world of ordinary matter, which is known as the “main brane”, according to this theory.
In this way, gravitational waves could appear to travel faster than the speed of light in our world, yet not violate Einstein’s sacred equations about general relativity.
Ed Fomalont, a scientist at the US National Radio Astronomy Observatory in Charlottesville, Virginia, and Sergei Kopeikin, a professor of theoretical physics at the University of Missouri-Columbia, have now ridden to Einstein’s rescue.
In an unprecedented operation that unfolded last September, they measured light from a powerful distant source, a quasar, as Jupiter passed by.
As the wave of light came close to Jupiter, it was deflected by the giant planet’s massive gravitational force before emerging again and continuing on to Earth.
Rather like the illusion of a stick that is put in water and seems shorter than it really is, the deflection caused an apparent shift in the position of the light source.
By measuring this phenomenon, which is called gravitational lensing, and factoring in Jupiter’s well-known mass and orbital velocity, Kopeikin and Fomalont were able to figure out the speed of the gravitational force that bent the light.
The pair report on their research in this Saturday’s issue of New Scientist, the British science weekly, and were scheduled to make a presentation of it this week at the annual meeting, in Seattle, of the American Astronomical Society.
To make their observations, they harnessed 10 25-metre (81.25-feet) radio telescopes stretching from the Caribbean to Hawaii, and a 100-metre (325-feet) radio telescope in Germany, effectively giving themselves an “ear” that stretched over 10,000 kilometres (6,200 miles) for the critical night of September 8, 2002.
“We became the first two people to know the speed of gravity, one of the fundamental constants of nature,” they write in New Scientist.
“Here it is: gravity does move at the same speed as light. Our actual figure was 1.06 times the speed of light, but we have an error of plus or minus 0.21. (…) This vindicates Einstein’s instinct when formulating his general theory of relativity.”
Supporters of the “brane worlds” are likely to look a bit glum.
The result may not destroy their theory but it certainly “restricts how many extra dimensions there may be, and their size,” say Fomalont and Kopeikin.
“The more compact the extra dimensions, the less able gravity is able to take a short-cut through them, and the closer the speed of gravity must be to light.”