Einstein’s Biggest Theory Just Passed Its Toughest Test Yet

Scientists have demonstrated that Einstein’s theory of general relativity is correct with a remarkable degree of accuracy, despite having been around for over a century.

The team behind the research wanted to test a component of Einstein’s theory of general relativity called the Weak Equivalence Principle, which states that all objects, regardless of mass or composition, should fall equally in a particular gravitational field when interference from factors such as atmospheric pressure are removed. To do this, scientists measured the acceleration of free-falling objects in a French satellite called MICROSCOPE, launched in 2016.

One of the most famous tests of the weak equivalence principle occurred during a Apollo 15 moonwalk, when astronaut David Scott dropped a feather and a geological hammer at the same time; without air resistance, the two objects accelerated toward the lunar surface at the same rate. In a similar style, MICROSCOPE carries free-falling test masses made of platinum and titanium alloys. The electrostatic forces hold the test masses in the same relative positions to each other, so any difference generated in this applied electrostatic force should be the result of deviations in the accelerations of the objects.

The team’s results, which are the culmination of 20 years of research, found that the acceleration of pairs of free-falling objects differed by no more than one part in 10^15, or 0.000000000000001 , which means that they found no violation of the weaker greater equivalence principle. only that.

In addition to placing constraints on deviations from the weak equivalence principle, the results also disfavor any deviations from Einstein’s 1915 theory. gravity, general relativity, as a whole. Scientists continue to search for such deviations because general relativity, the best description we have of gravity, does not agree with quantum physics, the best model we have of reality at incomprehensibly small scales.

No sign of deviation, therefore, still means no hint of extensions to general relativity waiting to be found that could bridge the gap with quantum physics.

“We have new and much better constraints for any future theory because these theories must not violate the principle of equivalence at this level,” said Gilles Métris, member of the MICROSCOPE team and scientist at the Observatoire de la Côte. d’Azur in France. statement from the American Physical Society, which published the research.

MICROSCOPE was launched in April 2016 and mission staff released their preliminary results in 2017. Data analysis continued to make sense even after the experiment ended in 2018.

The fact that the new research found no violation of the weak equivalence principle places the highest stresses yet on this element of general relativity, and the results also lay the groundwork for even more sensitive tests of coming.

That’s because the scientists included suggestions for how the experimental setup they used could be improved. Potential improvements include reducing imperfections in satellite coatings that can impact acceleration measurements as well as replacing wired systems with those that use wireless connections, they wrote.

A satellite implementing these improvements could potentially detect violations of the weak equivalence principle as small as 1 part in 10^17, 100 times more sensitive than MICROSCOPE. But the team predicts that these improvements won’t be achievable for some time, meaning that for now the MICROSCOPE experiment will remain the best test of the weak equivalence principle.

“For at least a decade or maybe two, we won’t see any improvement with a space satellite experiment,” said Manuel Rodrigues, a member of the MICROSCOPE team and scientist at ONERA, a French research institute specializing in aerospace, in the same press release. .

The team’s research was published Wednesday, September 14 in the journal Physical Review Letters and in a special issue of Classical and Quantum Gravity.

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