Context:

• Physicists at NIST (National Institute of Standards and Technology) pulled out a 14-year-long experiment to test a key principle underlying Einstein’s famous theory of general relativity – that describes how gravity relates to space and time.

EINSTEIN’S THEORY: EARTH IS A FREE-FALLING ELEVATOR

• According to Albert Einstein, the earth is a free-falling elevator in Sun’s gravity. He theorised that all objects located in such an elevator would accelerate at the same rate as if they were in a uniform gravitational field or no gravity at all.

Credit: K. Rechin/NIST

• He also predicted that the properties of these objects relative to each other would remain constant during the elevator’s free-fall.

TEST CONDUCTED BY NIST PHYSICISTS WITH THE HELP OF ATOMIC CLOCKS

• The test conducted by the NIST physicists is being considered as the most accurate test ever which confirms the ‘earth elevator’ phenomenon. They used the solar system as a laboratory, where they treated Earth as an elevator falling through the Sun’s gravitational field.
• They monitored 12 high-precision atomic clocks spread around the world for 14 years, from 1999 to 2014. The experiment tested whether all parts of the earth would have the same acceleration at the same rate. The clocks remained synchronized for over 14 years, proving the earth elevator theory.
• In other words, the general relativity theory carries the principle of local position invariance (LPI), which holds that in a falling elevator, measures of non-gravitational effects are independent of time and place and the test confirmed the same.

EVALUATION OF THE ATOMIC CLOCK EXPERIMENT

• The frequencies of electromagnetic radiation from atomic clocks at different locations on the earth were measured and compared. As described in the Nature Physics paper, the researchers constrained the violation of LPI to a value of 0.00000022 plus or minus 0.00000025 the most minuscule number yet, consistent with general relativitys predicted result of zero, and corresponding to no violation.
• This means the ratio of hydrogen to caesium frequencies remained the same as the clocks moved together in the falling elevator.

Source:India Today