The experiment of Michelson and Morley

When you are interested in physics you must read “Unbelievable“!

The death of the ether hypothesis was, after the unjustified denial of dragged ether, the experiment of Michelson and Morley. The dragged ether already being rejected by science the only ether thought possible was the absolute ether. Science saw only possibilities in the absolute ether; an ether that is not influenced by anything.

All light, from any source in any direction, has to move in absolute ether independently of the source. The problem was how to prove the existence of the absolute ether. In those days this was a very difficult task because the speed of light is so immense. Michelson however devised an experiment that made it possible to detect this ether by means of the orbit speed of the earth around the sun. The principle of the method by Michelson and Morley is the same as Fizeau’s experiment. The difference is measured by means of the shift in lines of the interference pattern. The difference in time or distance traveled by light is measured in interference lines. The difference between extinguish or fortify interference lines is 1/40 of millionth meter.

The earth moves in an elliptic orbit around the sun with a speed of more than 100,000 km/h. This very high velocity is not achievable in any other way on the Earth, because there is no possibility accelerate an experiment to such a high speed and this speed is still only 1/10,000 of the speed of light.

An observer on the earth can never be at rest with the absolute ether during the whole year when the earth is orbiting the sun. Michelson had the brilliant idea that one would not have to measure the altering of the interference pattern during the whole year to see whether that would be the case. He reflected that the equipment only had to be turned 360 degrees to obtain results. Then the light source can never be at rest with the ether all the time during the 360 degrees turn. When there is absolute ether, not influenced by anything, then the accuracy of the experiment would be sufficient to determine the existence of absolute ether.

The time necessary for the light to travel right-angled opposite to the ether would be t1. For the light beam to travel with or against the ether is t2 (figure 7).


The theoretical line shift should be:

With λ the wavelength of the light, v the speed opposite to the ether and L the length of the path with and against the ether. Only if there is no absolute ether the line shift is zero, because we argued before that if the absolute ether existed the Earth moving around the Sun also must move in respect to the absolute ether and therefore induce the theoretical line shift.

In 1881 Michelson conducted this experiment on his own for the first time. The accuracy was however not sufficient to prove without doubt there was no absolute ether. In 1887 Michelson repeated the measurement with Morley with much more accuracy. The shift, with absolute ether, should be 0.40 lines. The measured shift was only 0.01 lines.

Figure 7.   The experiment of Michelson and Morley.

Many others conducted the same experiment later on and always with the same result that only a small fraction of the theoretical shift was measured. The conclusion was, without doubt:

The Michelson and Morley experiment did not provide any experimental evidence for the existence of the absolute ether. The rejection of the hypothesis of absolute ether appears to be correct.

Next chapter: But what now?!