We often try our hands on something new and end up unsuccessful, how awful; but we later realize that our failure was not just a failed attempt, instead, we learn a great lesson on how to avoid our failures in future attempts. Once upon a time, a couple of scientists accidentally upended some of the fundamental laws of physics. The Michelson-Morley experiment was supposed to be a piece of cake, but instead, it changed basically everything.
Related media: The Greatest Failed Experiment Ever
Ether You’re Windy Or You’re Losey
By the dawn of the 19th century, scientists had not yet been able to resolve whether light was a wave or a particle. In 1801, the renowned physicist Thomas Young, (apparently) resolved that debate once and for all with the famous double-slit experiment, wherein single photons passing through a wall with two slits produce patterns on a surface as if they were all waves interacting — unless a photon detector is set to measure which slits each photon passes through, at which point they produce two bright lines as if they were single photons.
But that was one heck of a problem, since every known wave — sound, water, Mexican wave — needed some sort of medium to wave through. Obviously, since light travels to Earth from the sun, and not to mention the moon, stars and planets, physicists determined that there must be something pervading the universe. So they called this substance or whatever it was “ether” (also spelt “aether”), and decided it required a number of strange (weird) features. According to the physicists, it has to be something that could be found literally everywhere, but that wouldn’t interact with physical matter at all. (Seems like dark matter? Here’s the difference).
Around 1887, two physicists, Albert Michelson and Edward Morley, were very much convinced that this mysteriously named substance known as the ether only carried light waves. They were set out to demonstrate with an experiment that would measure it once and for all. For us to understand the famously yet epic failed Michelson-Morley experiment, you have to understand the ether “wind.” Imagine the Earth like a vehicle running on a still clear day; even if there is not wind, if you stick your hand out the window, you’ll feel a powerful breeze. The ether was expected to be flowing around the Earth’s surface at a rate equal to the speed of the Earth traveling through space.
The Swimming Thought Of Doubt
Here’s how to illustrate their experiment:
Let’s imagine you challenge your friend to a swimming contest. You guys take a dip into a 100-meter wide lake which flows at a rate of 3 meters per second. Swimming at a pace of 5 meters per second, your friend swims against the current at a pace of 2 meters per second upstream, turns around, and swims with the current at a pace of 8 meters per second downstream. He finishes the first lap in 50 seconds, and the second lap in only 12.5 seconds, for a total of 62.5 seconds. But instead, you swim directly across the lake, angling your swim to account for the flow of the lake, then turn around and swim back. Unlike your friend, your rate will remain steady — the math shakes out to 4 meters per second. Therefore, it takes you 25 seconds to make both 100-meter journeys, for a total of 50 seconds. Congratulations, you win!
This great idea was to construct an exactly similar race for pulses of light, with the ether wind playing the part of the lake. Michelson and Morley created a device they called an interferometer. (Interferometers may have been newfangled technology back then, but advanced versions of this exact device were what detected gravitational waves for the very first time in 2015).
The experiment is as follows: A pulse of light is directed at an angle of 45 degrees at a half-silvered, half-transparent mirror, so that half the pulse goes on through the glass, half is reflected — these two half-pulses are you and your friend. They both go on to distant mirrors which reflect them back to the half-silvered mirror. At this point, they are again half reflected and half transmitted, but a telescope is placed behind the half-silvered mirror as shown in the figure so that half of each half-pulse will arrive in this telescope.
Now, if there is an ether wind blowing, someone looking through the telescope should see the halves of the two half-pulses to arrive at slightly different times, since one would have gone more upstream and back, one more across stream in general. To maximize the effect, the whole apparatus, including the distant mirrors, was placed on a large turntable so it could be swung around. An animated applet of the experiment is available here — it makes the account above a lot clearer.
That’s Somewhat Relativity
If Michelson’s and Morley’s hypothesis about the ether was accurate as they claimed, then, currents in the flow of the “water” would have led them to travel at different rates, slightly; so they should strike the detector at slightly different times, too. Yet, over and over again, they would arrive at exactly the same time. Something was fishy in the world of physics.
If you’re familiar with modern day classical physics, you probably know why their wrong. Michelson and Morley were not able to detect the influence of the ether on light because, obviously, there is no such thing as ether. And of course, light travels as either a wave, or as a particle (also known as a photon) which, in fact, always travels at the same speed in a vacuum, no matter what direction you’re traveling relative to it’s source. These are the foundations of Einstein’s theories of general and special relativity, and the Michelson-Morley experiment is what laid the foundation for the most influential scientific ideas of the past century.
Aforementioned, without their failure to detect the ether, we never would have been able to realize that there was a problem to be solved. Its just more evidence that science makes as much progress through it’s missteps as it does through it’s successes.
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Written by: Nana Kwadwo, Sat, Feb 02, 2019.