Gravity Still Holds: Einstein’s Relativity Theory Stands Strong After Quantum Challenge

Another equivalence principle is supported by study teams from Leibniz University Hannover and the University of Bremen.

Scientists confirmed that all attributes of mass are equal with 100 times more precision using data from 50 years of lunar laser ranging. Einstein's equivalence principle, a cornerstone of relativity theory, is considerably strengthened by this discovery.

The idea that the various characteristics of mass—weight, inertia, and gravitation—always stay constant in respect to one another is one of the core tenets of fundamental physics. Without this equivalence, Einstein's theory of relativity would be in conflict, necessitating the revision of our existing physics textbooks. The equivalence principle has been verified by all measurements to far, although according to quantum theory, there should be a breach. It is because of this contradiction between Einstein's gravitational theory and contemporary quantum theory that ever-more accurate testing of the equivalence principle are so crucial.

By working with the Institute of Geodesy at Leibniz University Hannover, a team from the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen was able to demonstrate with 100 times more precision that passive gravitational mass and active gravitational mass are always equal, regardless of the specific composition of the respective masses. The study was carried out under the auspices of the Excellence Cluster "QuantumFrontiers." The team's research was presented as a highlights article in the scholarly journal Physical Review Letters on July 13.

Physical situation

Acceleration is resisted by inertial mass. For instance, when the automobile begins, it pushes you backward into your seat. Our weight on Earth is a result of the gravitational reaction caused by passive gravitational mass. A body's gravitational pull or, more accurately, the extent of its gravitational field is measured by its active gravitational mass. General relativity is predicated on these qualities' equality. As a result, it is becoming increasingly accurate to evaluate the equivalence of inertial and passive gravitational mass as well as passive and active gravitational mass.

What did the research focus on?

If we suppose that the ratio of passive to active gravitational mass is not constant, but rather depends on the material, then it follows that objects constructed of various materials, each having a distinct center of mass, will accelerate. The iron core and aluminum shell that make up the Moon have mass centers that are offset from one another, hence the Moon should move faster. By using "Lunar Laser Ranging," it would be possible to quantify this fictitious change in speed with extreme accuracy. This entails directing lasers from Earth at reflectors that the Apollo missions and the Soviet Luna program had installed on the Moon. Since then, laser beam round-trip times have been noted. The study team looked at these mass differential effects by analyzing "Lunar Laser Ranging" data that was gathered over a 50-year period, from 1970 to 2022. This indicates that the passive and active gravitational masses are equal to around 14 decimal places since no effect was discovered. The best prior research, from 1986, was one hundred times less precise than this estimate.

Certain expertise

One of only four institutes in the world evaluating laser distance measurements to the Moon, the Institute of Geodesy at LUH has specialized knowledge in processing the data, notably for proving general relativity. The institution examined the Lunar Laser Ranging measurements in the current study, including error analysis and result interpretation.

The research was published in the journal Physical Review Letters by Vishwa Vijay Singh, Jürgen Müller, and Liliane Biskupek from the Institute of Geodesy at Leibniz University Hannover as well as Eva Hackmann and Claus Lämmerzahl from the Center of Applied Space Technology and Microgravity (ZARM) at the University of Bremen. The paper was highlighted in the category "editors' suggestion."