Hammar experiment

The Hammar experiment was a physical experiment carried out by Gustaf Wilhelm Hammar (1935) , which was intended to check whether the light ether (a hypothetical medium for the propagation of light) was carried along. It produced a negative result, that is, no ether entrainment could be determined, and is in agreement with the predictions of the theory of relativity . For further experiments see also Tests of the special theory of relativity .

overview

Lodges experiment on the transport of ether with rotating disks.

In the 19th century it was assumed that light spreads in a medium, the ether, just as sound spreads in air . The relative movement between matter and aether was called aether wind and should be demonstrable experimentally. But through the Michelson-Morley experiment and its repetitions, as well as through other experiments, it could be shown that this ether wind does not exist. That was an important step in the development of the special theory of relativity . A possible way out for the ether theory was the hypothesis that the ether is completely carried along by bodies. However, this hypothesis could not be confirmed by the experiments of Oliver Lodge (1893–1897), who observed the propagation of light between rotating disks and found no influence.

In the 1920s, Dayton Miller repeated the Michelson-Morley experiment at higher altitudes and got an apparently positive result, with an ether wind speed of around 10 km / s. This would contradict the special theory of relativity. But these measurements were immediately refuted by further measurements by other researchers who could not reproduce a positive effect even at high altitudes. Miller said, however, that the other experimental arrangements were more shielded and thus a greater ether dragging effect occurred, which caused the negative results. Although Miller's results were no longer believable because of these negative results from the other experimenters, Hammer (1935) nevertheless carried out an interferometer experiment with which Miller's assumption of an additional entrainment due to the shielding was to be tested, more precisely than the older experiments by Lodge was.

Experiment arrangement and result

Using a half-silvered mirror A, a beam of white light was split into two half-beams. A half-beam was directed in the transverse direction into a tube surrounded by massive blocks of lead . There the beam was reflected by mirror D and sent in the longitudinal direction to mirror C at the other end of the tube. From there it was sent in the transverse direction from the tube to mirror B, and from there in turn in the longitudinal direction back to mirror A. The second half-beam crossed the same route in the opposite direction. Then both beams were brought to interference. If the aether is carried more strongly in the encased arm, there is a different transit time for the opposite rays according to the equations:

{\ displaystyle t_ {1} = {\ frac {AB} {c + v}} + {\ frac {BC + DA} {\ sqrt {c ^ {2} -v ^ {2}}}} + {\ frac {CD} {c-v + \ Delta v}}}

{\ displaystyle t_ {2} = {\ frac {AB} {cv}} + {\ frac {BC + DA} {\ sqrt {c ^ {2} -v ^ {2}}}} + {\ frac { CD} {c + v- \ Delta v}}}

where is the speed of the aether carried along. This gives a time difference of: ${\ displaystyle \ Delta v}$

{\ displaystyle \ Delta t \ simeq {\ frac {2l \ Delta v} {c ^ {2}}}}

However, the result was negative; H. no stripe shift was observed, with an upper limit for the driving speed of km / s resulting from the measurement accuracy . This refutes the assumption that the aether is carried along by bodies on the earth's surface and confirms the prediction of the special theory of relativity. ${\ displaystyle \ Delta v <0 {,} 074}$

General information on the transport of ether

There are different ideas about the transport of ether, each of which has been refuted by special experiments:

No or partial carry-along by all bodies: Refuted by the Michelson-Morley experiment and repetitions.

Complete entrainment in or near all bodies: Refuted by the aberration of light , the Sagnac effect , Lodges' experiments and the Hammar experiment.

Complete entrainment only by large masses such as the earth or other celestial bodies: Refuted by the aberration of light and the Sagnac effect due to the rotation of the earth (measured with GPS or the Michelson-Gale-Pearson experiment ).

Individual evidence

^ Lodge, Oliver J .: Aberration Problems . In: Philosophical Transactions of the Royal Society of London. A . 184, 1893, pp. 727-804. doi : 10.1098 / rsta.1893.0015 .
^ Lodge, Oliver J .: Experiments on the Absence of Mechanical Connexion between Ether and Matter . In: Philosophical Transactions of the Royal Society of London. A . 189, 1897, pp. 149-166.
↑ ^a ^b H. P. Robertson and Thomas W. Noonan: Hammar's experiment . In: Relativity and Cosmology . Saunders, Philadelphia 1968, pp. 36-38.
^ GW Hammar: The Velocity of Light Within a Massive Enclosure . In: Physical Review . 48, No. 5, 1935, pp. 462-463. bibcode : 1935PhRv ... 48..462H . doi : 10.1103 / PhysRev.48.462.2 .

[1] Lodge, Oliver J .: Aberration Problems . In: Philosophical Transactions of the Royal Society of London. A . 184, 1893, pp. 727-804. doi : 10.1098 / rsta.1893.0015 .

[2] Lodge, Oliver J .: Experiments on the Absence of Mechanical Connexion between Ether and Matter . In: Philosophical Transactions of the Royal Society of London. A . 189, 1897, pp. 149-166.

[rob-3] H. P. Robertson and Thomas W. Noonan: Hammar's experiment . In: Relativity and Cosmology . Saunders, Philadelphia 1968, pp. 36-38.

[ham-4] GW Hammar: The Velocity of Light Within a Massive Enclosure . In: Physical Review . 48, No. 5, 1935, pp. 462-463. bibcode : 1935PhRv ... 48..462H . doi : 10.1103 / PhysRev.48.462.2 .