Experimental Test of Equivalence Principle and Gravitational “Red Shift”
How big is the effect on earth?
The fractional change in frequency of light emitted from a height L and observed at height 0 is:
?????????????????????f / f = ? / (1 - ?) ? = g L / c2
How big is this? If L = 10m ? ?f / f = 10-15
Amazingly, this experiment was done first in 1960 by Pound & Rebka at Harvard by exploiting the then recently discovered Mossbauer effect!
By taking data with emitter at both top and bottom of Jefferson Tower (height = 74 ft), they verified the shift was gravitational. Results:
- Measured: ?f / f = ( 5.13 +/- 0.15 ) X 10-15
- Theoretical prediction: ?f / f = 4.92 X 10 -15