When a null result is a good result.

In science, a null result is the absence of an experimental outcome to confirm an expected effect. It doesn’t mean there’s no result, just that it doesn’t support or explain the suggested hypothesis.

This phrase sound elegant, but what does it mean?

I might have to back up a little; and go back to the foundation for the scientific method. The Scientific Method is the process with which science is accomplished, and is a process that starts with a question, for which a response based on an “educated guess”, or proposed hypothesis. This hypothesis must be confirmed by experimental results, with which we can proof with solid evidence, the validity of our hypothesis.

And now that the initial explanation makes sense, a null result is an unexpected result when we try to prove our conjecture or hypothesis. So now, what I’m referring when talk about a good null result?

This answer has to do with waves. Is very likely you have noticed when throwing a rock on a pond how a set of waves start to disperse due to the disruption caused in the water. Well, in the late 19th century, it was still considered that for any kind of waves, a transmission medium was necessary, as the water in the pond’s waves. Similar to water, another wave based phenomena like sound, which is a mechanical wave, requires a transmission medium; being typically the air as the acting medium for these waves’ propagation.

Sound-waveform (mediacollege.com)

Sound-waveform (mediacollege.com)

During those times, it was considered that the light was also subject to the same requirement for its transmission; knowing that light as well is a wave, an electromagnetic wave; as demonstrated by James Clerk Maxwell’s work in 1865. Being at that time, the most important unanswered question of that century, to know the nature of the medium through which light travels.

Luminiferous aether

The explanation in that time was that light was transmitted through the luminiferous aether an infinite and invisible substance that had no interaction with physical objects; and was present even in the vacuum of space, since we could witness how the sunlight and the light from other stars still reached us on Earth.

Thus, one of the main missions in Physics at that time was to find proof of the existence of this luminiferous aether; but of course, an experiment to test this hypothesis was required. Yet the technology was still limited and performing measurements related to the speed of light was a big challenge, considering that no direct measurement with the required accuracy was yet possible and for this measurement it was estimated that a precision of 0.01% in the speed of light was necessary.

Michelson–Morley experiment

The physicist Albert Michelson and the Chemist Edward Morley, both American scientists, collaborate in the improvement of a new kind of measuring device called an interferometer, an experiment that transmits light in orthogonal mirrors, (arranged at right angles), and allows distances and speed measurements with high precision.

This experiment works based on the wavelike nature of light, and considering that light can be amplified or attenuated depending on how two different waves combine; being either “in phase”, with no offset between two waves, and resulting in an amplification or increase in amplitude (and a higher light intensity in this experiment), or “out of phase” with a maximum phase shifting and as a result a maximum attenuation or cancellation of these two waves (and a dark section in the interferometer pattern as a result). This effect, that works in any kind of waves, allow the mentioned measurement of speed and distances.

interference (obrien.wikispaces.com)

interference (obrien.wikispaces.com)

The principle of this test was simple; if, as proposed, the aether were present everywhere, then Earth will be traversing this aether as it moves around the sun; therefore, would affect the speed at which the light moves, with two specific scenarios; having the speed of light plus the earth speed as light moves in favor of the aether flow; and in the opposite case, having the speed of light minus the earth’s speed, as it moves in opposition to the aether flow.

For such purpose, the experiment was designed to be very stable yet capable of being rotated. This was achieved by placing the experiment in a dorm room basement to avoid as much as possible vibrations and thermal effects; the interferometer equipment itself was set over a big piece of sandstone floating resting in a round trough of mercury to facilitate the experiment’s rotation to positioning it in different angles with respect to the hypothetical Aether flow.

Interferometer -experiment (dc.edu.au)

Interferometer -experiment (dc.edu.au)

Measurement

When performing the experiment, it was expected to see amplification (or higher intensity light), in two positions when light traveled in the same direction or “in favor with” the aether flow, and attenuation (or annul light) in two additional positions, when light traveled in opposing direction or “against” the aether flow; as the experiment was rotated. This effect would be noticed as a displacement in the interference pattern.

Aether-experiment (dc.edu.au)

Aether flow (dc.edu.au)

The experimental results, however, showed that this displacement was much less (in the order of one fortieth part), of the expected displacement, and even when this small displacement was noticed, it was understood that it was within the intrinsic error expected from the experiment itself, and as practical result the measurement could be considered as zero change in the speed of light; therefore, demonstrating that there was no effect on the speed of light in relation to the aether. These findings were confirmed later in the beginning of the 20th century by even more accurate experiments, but back then, there were still scientists who were defending the aether theory; but at the end, this experiment practically dethroned this concept and with it one of the final bastions of the classical physics came to an end.

But, if the light doesn’t need a medium to travel through the vacuum of space, how does these electromagnetic waves propagate? Well, it turns out that the light doesn’t require a medium to propagate, light is a self-propagating wave, and that’s why it can travel everywhere, even in the vacuum.

The result of this null experiment of Michelson and Morley provided the push to find the right answer, and the answer was by far a more interesting one that that of the aether, since its explanation came later with a complete new theory…, this was Einstein’s theory of Relativity! But that is another great story.

Regards, Alex – ScienceKindle.

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