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“It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.” – Neil Armstrong (1930-2012)

Fresh Reads from the Science 'o sphere!

Sunday, April 06, 2008

Counterintuitive Science - The Most Successful Failed Experiment

Have you heard the phrase "Change is the only constant"?

It looks like a self-contradictory statement - but yet it makes sense to most people.

How can this be?

Well, the trick is in the word "constant", which has two meanings in the phrase. It could mean "unchanging" or it could mean "enduring".

What the phrase really means is that change is the only thing that endures through time - nothing is unchanging.

Similarly, a term like "successful failure" appears to be a self-contradiction at first glance.

For many people, such a condition is impossible because they consider success and failure as extreme ends on a single spectrum.

However it makes sense, because the "success" and "failure" here really refer to two different dimensions, two different goals.

A classic example of this occurred in science during the late 19th century.

At that time, physicists believed that light, which has wave properties, travels on some sort of medium similar to how sound waves travel on solids, liquids and gases.

They called this medium the "luminiferous aether", which should exist in a vacuum because light can travel in a vacuum.

However, since the aether isn't a type of material like solids, liquids and gases, there was no way to directly observe it.

So physicists devised a clever strategy to detect the aether and determine its properties.

As our Earth orbits around the Sun, it is travelling at over 100,000 kilometres an hour on an elliptical path.

So the relative speed of the "aether wind" to a fixed position on Earth depends on the direction you are facing and also the time of the year. This should affect the speed of light travelling in different directions.

For example, if an observer was directly facing the aether wind, the measured speed of light should be faster (speed of light + speed of Earth).

Unfortunately, the speed of light is about 10,000 times faster than the speed of the Earth, so any change would only be a tiny fraction of the speed of light. You would need a very precise instrument to detect this difference.

Enter Albert Michelson, a Polish-born American physicist who was an expert on optics.

He had been working on obtaining accurate measurements of the speed of light for years. By 1879, he had already determined the speed of light to within 0.06% of the modern figure.

Two years later, he decided to tackle the difficult challenge of detecting the aether wind. He constructed an instrument, later called an interferometer, which can determine the tiny difference in speed between two perpendicular light paths.














A single light beam was split using a central half-silvered mirror into two long light paths, which were reflected back to the mirror and then recombined.

The recombined light had a characteristic interference pattern which would show a fringe shift if the speed of the light in the two light paths were different.

Using his first interferometer, Michelson discovered that the observed fringe shift was smaller than the expected fringe shift. He noted that this result could be due to the experimental errors of the instrument.

So he collaborated with Edward Morley and built a larger and more accurate interferometer, with many design precautions to minimize external disturbances such as temperature changes and vibrations.

After taking numerous measurements, he published the findings of this experiment in 1887.

The result?

Still a much smaller difference than expected.

In fact, when taking experimental errors into account, it's practically a null result.

Michelson himself was not convinced of this result and went on to do further experiments to verify if it was correct.

Other scientists also carried out experiments to check all sorts of alternative possibilities.

In time, it became increasingly clear that the initial results were valid - there is no difference in the speed of light no matter what direction it took.

This sparked off a furore in the field as physicists debated the significance of this result.

Does aether behave in some complex, bizarre manner? Or does aether even exist?

Michelson did not know it at that time, but the null result that he obtained would lend support to a controversial new idea that would eventually render the aether hypothesis irrelevant - Albert Einstein's theory of relativity.

So the Michelson-Morley experiment is actually counterintuitive in two ways: not only did the results disagree with common sense, but the apparent failure of the experiment was instrumental to the success of a brand new theory.

You are thinking: "Well, good for Einstein then. Fat lot of good that did for Michelson though."

Erm... not quite.

For his efforts at developing a new class of precision optical instruments, and the experiments he conducted with them, Albert Michelson became the first American to receive a science Nobel Prize in 1907.


Would you like to know more?
-
Original 1887 paper of the Michelson-Morley experiment (PDF)

5 Comments:

angry doc said...

I've always thought of ether as the west's equivalent of 'qi'. :)

Let me link to this post on my blog.

Wormbrain said...

Very interesting!
He did actually prove (or unprove) the theory, failed experiment or not.

Lim Leng Hiong said...

To Angry Doc:

Glad you liked the post! "Qi" also reminds me of the phlogiston theory.

To Wormbrain:

Yes, he built such an accurate instrument that it became a strong challenge to his own belief about aether. Yet he went ahead and published the null result. This kind of impartiality and integrity is a scientific ideal.

Anonymous said...

In Science, instruments tend to trump argument.

:) Great work on the article. The Michelson-Morley interferometer is still alive and kicking to this very day, and is used in all kinds of high-precision measurements.

The LIGO project (www.ligo.caltech.edu) that is being used to search for evidence of gravitational waves , essentially has huge versions of Michelson's early devices.

So, his work lives on and may play a role yet in many more exciting discoveries!

Lim Leng Hiong said...

To Anon 7:12,

Thanks for visiting and for pointing out the LIGO project!

I recall debating with my friend many years ago about the relative importance of technological and theoretical development to science. At that time my opinion was that theory development was more "revolutionary", but today I find it difficult to separate their contributions to the overall endeavour.