Tests of relativity using a cryogenic optical resonator.

Area of Science:

• Fundamental Physics
• Optical Physics
• Metrology

Background:

• The constancy of the speed of light is a cornerstone of modern physics.
• Testing fundamental physics principles like gravitational redshift requires precise measurements.
• Previous tests have constrained deviations from established theories.

Purpose of the Study:

• To compare optical frequencies from an optical cavity and a molecular electronic transition over 190 days.
• To test the velocity independence of the speed of light (Kennedy-Thorndike test).
• To verify the universality of gravitational redshift.

Main Methods:

• Utilized Earth's orbital motion to modulate laboratory velocity and gravitational potential.
• Conducted a 190-day comparison of optical cavity and molecular transition frequencies.
• Analyzed data for deviations related to velocity and gravitational effects.

Main Results:

• Determined a velocity-dependence coefficient of (1.9+/-2.1)x10^-5, significantly improving upon previous limits.
• Confirmed the gravitational redshift for an electronic transition with 4% accuracy.
• Achieved a result three times more precise than prior Kennedy-Thorndike tests.

Conclusions:

• The experiment provides stringent constraints on potential variations in the speed of light.
• The findings support the universality of gravitational redshift for electronic transitions.
• Future experiments hold promise for even greater precision in these fundamental tests.