from the Which-weighs-more?-A-pound-of-feathers-or-a-pound-of-lead? dept.
Galileo's 400-year-old theory of free-falling objects passes space test
A key tenet of Albert Einstein's general theory of relativity has passed yet another test with flying colors—and for the first time in space. A French satellite experiment has shown that objects with different masses fall at exactly the same rate under gravity, just as relativity dictates. The result is the most precise confirmation yet of the equivalence principle, first tested more than 400 years ago by Galileo Galilei. "The mission appears to have performed fantastically," says Clifford Will, a theoretical physicist at the University of Florida in Gainesville.
Physicists scrutinize the equivalence principle because any violation could point to new forces of nature that might resolve a long-standing impasse between general relativity and quantum theory. The satellite, called MICROSCOPE, found no discrepancy in the acceleration of two small test masses to about one part in 100 trillion (1014).That's more than 10 times better than the most sensitive ground-based experiments, which look for disparities in the response of weights to Earth's spin.
[...] A proposed Italian satellite, aptly named Galileo Galilei, would test equivalence to a precision of one part in 10^17, partly by spinning rapidly and isolating any signal from more slowly varying systematic effects. Researchers at Stanford University in Palo Alto, California, have proposed a satellite that aims to reach one part in 10^18 using noise-reducing cryogenics. Still other researchers hope to use Bose-Einstein condensates—clouds of cold atoms that behave as a single quantum wave [DOI: 10.1126/science.357.6355.986] [DX]—to reach tight limits.
(Score: 0) by Anonymous Coward on Saturday December 02 2017, @09:37PM (4 children)
How could this be a test of relativity when it was clearly known before that theory was developed?
Also, there have been many tests of GR "in space":
https://en.wikipedia.org/wiki/Tests_of_general_relativity [wikipedia.org]
The equivalence principle has also been tested "in space" (on the moon):
https://apod.nasa.gov/apod/ap111101.html [nasa.gov]
I am actually surprised to see this was published by "Science".
(Score: 2) by takyon on Saturday December 02 2017, @09:46PM (1 child)
Pretty imprecise compared to this test. He held them approximately level, and the only data is from the frames of video.
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 0) by Anonymous Coward on Saturday December 02 2017, @10:20PM
Sure, the point is the test was done. The original test of relatively was just a few exposed photographic plates. Plus they ended up throwing out half the data, etc.
https://en.wikipedia.org/wiki/Tests_of_general_relativity#Deflection_of_light_by_the_Sun [wikipedia.org]
(Score: 2) by maxwell demon on Sunday December 03 2017, @08:17AM (1 child)
It is one of the fundamental principles on which General Relativity was built.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Sunday December 03 2017, @05:45PM
Sure, but its like having a theory that predicts "a dropped apple falls towards the earth". Passing that test is not impressive anymore. I'm not saying putting tighter constraints on deviations from the equivalence principle is a waste of time or anything, I just don't think this adds any support to general relativity. You need to check how well it predicts things, not just the assumptions.
(Score: 0) by Anonymous Coward on Saturday December 02 2017, @10:18PM (1 child)
so, a pound of feathers weighs more or less a pound of gold?
(Score: 2) by maxwell demon on Sunday December 03 2017, @08:25AM
More exactly, one pound mass of feathers generated the same weight force as one pound mass of gold. Which is a non-trivial statement, which doesn't work for other forces.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 1, Informative) by Anonymous Coward on Saturday December 02 2017, @11:08PM (1 child)
In 1890 [wikipedia.org] the gravitational and inertial masses were shown to be proportional, with a difference of no more than 1 part in 20 million.
(Score: 3, Informative) by stormwyrm on Sunday December 03 2017, @06:24AM
Numquam ponenda est pluralitas sine necessitate.