Albert Michelson and the luminiferous ether

What do you do when your science is a bust? For Emma Beckett, the most famous failed experiment in the history of physics was nothing short of revelatory. 

Illustration by Meg Gough-Brooks

Illustration by Meg Gough-Brooks


Welcome to Model Specimens! This is a new monthly column that explores the role models who inspired today's scientists. This month, Emma Beckett, a molecular nutrition researcher, shares her relationship to the work of late American physicist Albert Michelson.

On some of the bad days, I sit at my lab bench and honestly wonder why I became a scientist. Sometimes you have to remind yourself of the moments that inspired you to keep you afloat through the failed experiments and the rejected submissions for grants and articles. For me, there was a particular moment in high school that remains stuck in my head – learning about physicist Albert Michelson and his chemist colleague Edward Morley and their famous failure when I was at high school. I have reflected upon this often throughout my university studies and my research career, even though I ended up as a biomedical scientist, and not a physicist.

Michelson, along with Morley, is famous for what became known as the Michelson-Morley experiment. As an impressionable teenager,  I was amazed by the idea that you could do an experiment so famous that it was simply named after you, without the need to include a description of what the actual experiment was. I marvelled at the idea that anyone could do anything so important.

What stayed with me was the revolutionary nature of the results. Michelson lived in a time when it was generally accepted that light travelled as a wave, similar to sound. Therefore, it was believed that light also needed a medium to travel through. In hindsight we know this is not true, but it made me wonder what else we ‘know’ to be true, but will be later disproven.

The hypothesis

In the late 19th century, even though scientists already knew that light could travel through a vacuum, they thought something had to fill the vacuum to carry the wave – and so the idea of the almost magical “luminiferous ether” was born. Although no one could really explain it, the accepted theory of the time was that the ether filled all space, even though no one had actually detected it.

Michelson thought that if the ether filled all space, and the earth was moving around the sun, then the speed of light should depend on the direction the light was travelling relative to the ‘wind’ created by the earth moving through the ether. So, light should travel more quickly if it went with the wind, and more slowly if it went against it. Michelson’s idea was to study the speed of light in all possible directions, so he could detect the ether.

The experiment

As a modern scientist, I often take for granted that someone else will have already created (and purchased) the equipment I need to test my hypotheses. Normally, the biggest hurdles between me and the equipment I need in the lab, are equipment grants, and having to share with other users. But Michelson lived in a time when scientists also had to be inventors.

To test his hypothesis, Michelson built a Michelson interferometer (again, do cool things and things will be named after you – this impressed my teenage self): a light source with a half-silvered glass plate (the beam-splitter), two mirrors and a telescope. 

Michelson and Morley's experimental setup to measure the luminiferous ether.   Michelson & Morley/Wikimedia Commons  (public domain)

Michelson and Morley's experimental setup to measure the luminiferous ether. Michelson & Morley/Wikimedia Commons (public domain)


The light leaves the source, and splits in two at the beam-splitter. The beams then travel at right angles to each other, hit the mirrors, bounce back, hit the beam splitter again and end up at a detector. If the ether wind existed, the beams would be travelling in different directions across it, so one beam should arrive at the detector slightly after the other, creating interference patterns in the light. The whole apparatus was set up to rotate, so the relative speeds of light could be measured in different directions). The concept was brilliant and complex, but the method was simple and straightforward.

The results — the most famous failed experiment of all time

Given that you likely didn’t learn about the magical ether in school, you’re probably not surprised to learn that Michelson and Morley did not get the expected results. They found no discernible interference patterns .

They repeated the experiment at different times of day and over several months to account for seasonal differences. Due to the length of the light paths, Michelson was confident that his equipment could detect the hypothesised level of interference that should be caused by the wind. The equipment was floated on a mercury trough set on a block of sandstone, so the effect of vibration could be discounted.

It was a definitive null result, even if Michelson himself was not certain of that at the time. Many other explanations were proposed — including that the ether was 'dragged' around with the earth. While this allowed people to hold on to the idea of the ether for a little while longer, none of them fully explained the Michelson-Morley null result. The controversy continued for almost 20 years, when Einstein proposed the theory of special relativity, doing away with the need for the ether. 

The implications and lessons

This famous null result stays in my heart and mind for a few reasons. In my teenage years, I was still full of ignorant ideas like “you can’t prove a negative”, and so this was a bit of a reality check for me. It made me seriously consider the difference between an evidence of absence, and the absence of evidence. I often dwelled on this in undergraduate statistics classes, when they told us that – statistically speaking – we could only reject, or fail to reject, the null. The null hypothesis is the default position that there is no relationship between the measured phenomena, whereas the alternate hypothesis describes what the scientist thinks is happening. I kept wondering: When was it okay to actually accept it?

It also reminds me not to be stubborn in my scientific ‘beliefs’. The idea of an ether that fills all space sounds ludicrous in hindsight, but in its day it was championed by many experts. I often remember Michelson when I think about data that conflicts with standard paradigms, and reflect on the role of human nature in interpreting the meaning of data.

Michelson also reminds me that we need to pick ourselves up and try again. He tried this experiment once, and the null result made him certain that he was the failure. Michelson suffered a mental breakdown, and later came back to do his famous experiment with Morley that was even more accurate than his first attempt, but yielded the same results.

Michelson’s breakdown reminds me that you have to be kind to yourself. If I took each failed experiment as a personal failure, I too would have a breakdown. Equally it also reminds me that even if you feel like you have hit rock bottom, you can recover.

Ultimately, Michelson’s famous experimental ‘failure’ reminds me that the work we do as scientists exists within the context of the knowledge of the day. Michelson was looking for the ether because it was the prevailing theory of the day, he wasn’t trying to disprove it. What feels like a failure in the moment, might one day be reflected upon as a turning point. Sometimes we have to have many failures before we arrive at the ‘truth’. Every time my science feels like a failure, I remind myself of this, pick myself up and try again. 

Edited by Nicola McCaskill and Tessa Evans.