Hammar experiment

The Hammar experiment was an experiment designed by Gustaf Wilhelm Hammar to test the aether drag hypothesis.

Overview

In 1903 the Trouton-Noble experiment, and later the Trouton-Rankine experiment in 1908, presented (then) controversial evidence against the theory of a medium for light propagation known as Luminiferous aether; a theory that had been an established part of science for nearly one hundred years at the time. These experiments were inspired by the unexpected failure of the Michelson-Morley experiment of 1887 to detect an expected aether wind of 30 km/s. These results cast doubts on, what was then, a very central assumption of modern science. In an attempt to explain the results of these experiments in the context of the assumed medium, aether, many new hypotheses were examined.

One of the proposals was that instead of passing through a static and unmoving aether, massive objects at the earth's surface may drag some of the Aether along with them making it impossible to detect a "wind". Oliver Joseph Lodge was one of the first to perform a test of this theory by using massive lead blocks in an experiment to cause an asymmetrical aether wind. His tests yielded no appreciable results differing from previous tests for the aether wind.

More recently, Hammar re-enacted the MM experiment but with the addition of massive lead blocks on both sides of only one leg of the interferometer. It was performed with an intent -similar to Lodge's - of causing an asymmetry in any proposed aether wind.

Hammar's expectation of the results was that:

A) In an experiment without lead blocks, both arms would be equally affected by aether entrainment.
B) In an experiment with lead blocks in place on one arm, only one arm would be affected by aether entrainment.

The reported result was that, even with the lead blocks in place, the fringe displacements were equal to the ones without any lead block. This was presented as proof against the aether drag hypothesis.

Interpretation

Because differing ideas of "aether drag" existed, the interpretation of the experiment can be done in the context of each version of the hypothesis.

There are two main levels of drag that have been proposed:
# Partial entrainment by any object with mass. This was discussed by scientists such as Augustin-Jean Fresnel and François Arago.
# Partial entrainment at larger, perhaps even global magnetic field level. This was discussed by scientists such as Michelson, Miller and others.

When considering the object level entrainment in the context of this experiment. "If there was any wind at all to be detected", the leg of the interferometer with lead, should have experienced less wind than the other leg.

The study of stellar aberration provides a less ambiguous test of Aether drag and is the most widely accepted evidence against the hypothesis.

References

*cite journal
author= G. W. Hammar
title= The Velocity of Light Within a Massive Enclosure
journal= Physical Review
year= 1935
volume= 48
issue= 5
pages= 462–463
url= http://prola.aps.org/abstract/PR/v48/i5/p462_2
doi= 10.1103/PhysRev.48.462.2
format= subscription required

ee also

*Aether drag hypothesis
*Trouton-Noble experiment
*Trouton-Rankine experiment
*Michelson-Morley experiment