Pound-Rebka Experiment

Experiment Background

• Experiment done in 1959 at Harvard’s Jefferson laboratory to test Gravitational Red-Shift of light predicted by Einstein’s Theory of General Relativity

Background Information

• Principle of Equivalence states that the force of a gravitational field is equivalent to the acceleration of a given reference system.

• From the Principle of Equivalence we can also conclude that any frequency shift in light produced by acceleration can also be produced by the appropriate gravitational field. This is like a relativistic Doppler shift.

Experiment Set Up

• 2 Light Sources- 1 on top of the 22.5 meter laboratory, 1 in the basement.

Experiment Set Up

• Hypothesized that the Gamma Rays emitted from basement would have a gravitational red shift and Gamma Rays emitted from the roof would have a gravitational blue shift.

• Prepared the Gamma Ray detectors out of a combination of Iron and Cobalt heated to a high temperature to increase its sensitivity and resolution to red shift.

Equations Used in Experiment

• By using equations for gravitational potential energy and the relativistic energy expression, the gain in energy of a photon which falls a distance h is :

Equations Used in Experiment

• Difference in energy shifts from the 2 gamma ray emissions was predicted to be:

• While it was measured as:•

Results

• Basement emitted gamma ray of wavelength of 1 measured on roof as having wavelength of 1.000000000000002455

• Roof emitted gamma ray of wavelength 1 measured in basement as having wavelength of .99999999999999755

Implications

• The measured energy difference and gravitational shift was within the error margin of the predicted value by General Relativity

• Experiment claimed as Proof of General Relativity

Bibliography

• “Harvard Gravitational Red Shift Experiment.” http://www.circlon-theory.com/HTML/poundRebka.html

• “Equivalence Principle.” http://en.wikipedia.org/wiki/Equivalence_principle

• “Gravitational Red Shift.” http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/gratim.html