The Experiments That Couldn’t Find the Earth Moving

For about a hundred years, some of the best physicists in the world built instruments to do one thing: catch the earth moving. They sent starlight through prisms and through water, split beams of light on stone slabs floating in mercury, and hung charged plates on fine wires. Again and again the instruments found nothing. This study tells that story in the experimenters’ own words, and it tells it honestly, including how mainstream physics explains the results today.

What would you expect?

The textbook model says the earth carries us around the sun at about eighteen miles every second. In the nineteenth century, physicists believed light traveled through an invisible medium they called the ether, the way sound travels through air. If the earth was rushing through that medium, light should behave differently depending on which way it was sent, the way a swimmer crossing a river is slowed differently going upstream, downstream or across. Measure light carefully enough, and the motion should show.

That was the plan. Our earlier study, Where Did Heliocentrism Come From?, showed how the sun-centered model was adopted long before anyone measured anything. This one asks what happened when they finally tried.

Starlight through a prism, 1810

The story begins with a real observation. Between 1725 and 1729 the English astronomer James Bradley found that every star traces a tiny yearly ellipse in the sky, the same size for every star. He called it aberration, and textbooks read it as the earth’s yearly motion combined with the speed of light. We should say plainly that this is the strongest observation on the textbook side. A stationary earth has to explain it differently, with all the stars sharing a small yearly motion in step with the sun.

In 1810 the French physicist François Arago tested it further. If the earth was moving toward some stars and away from others, he reasoned, their light should bend differently through a glass prism. He measured stars in different directions, at different times of day and in different seasons. The result: no difference at all.

In 1818 Augustin Fresnel offered an explanation. The ether, he proposed, is at rest, but glass and water drag it along partially, by an amount that depends on the material. His formula was built to fit, and it did fit. It also meant that no experiment of that simpler kind could ever reveal the earth’s motion. Notice the pattern, because it repeats: an experiment finds nothing, and a new hypothesis explains why nothing was found.

Light in running water

Fairness matters here. In 1851 Hippolyte Fizeau sent light through moving water, with the flow and against it, and he did measure a difference. The water carried the light along by part of its speed, just as Fresnel’s formula said it should. That was a positive result, and it seemed to confirm Fresnel. We will not count it among the failures.

In 1868 the Dutch astronomer Martinus Hoek compared light sent through still water with light sent through air, and turned his apparatus into and across the supposed ether wind. He found nothing. Under Fresnel’s hypothesis, that was exactly what he should have found.

A telescope full of water, 1871

In 1867 a German astronomer, Wilhelm Klinkerfues, claimed that a telescope filled with water would show a larger aberration than one filled with air. Water slows light, so on the moving-earth view the telescope would need to be tilted more. If he was right, it was a way to measure the motion directly. George Biddell Airy, the Astronomer Royal at Greenwich, decided to test it.

Airy filled a vertical telescope with a column of water 35.3 inches long and observed the star Gamma Draconis in the spring and in the autumn of 1871, when aberration pushes the star in opposite directions. Klinkerfues’s idea predicted a difference of about thirty seconds of arc between the two seasons. Airy found the two results agreed to a fraction of a second. He reported to the Royal Society:

I think myself justified in concluding that the hypothesis of Professor Klinkerfues is untenable.

The water made no difference. The starlight came into the water-filled tube at exactly the angle it came into an ordinary one.

Sixteen years later, the most famous experiment in this story opened by pointing back to Airy’s kind of result. Its authors wrote that one early explanation of aberration

failed to account for the fact proved by experiment that the aberration was unchanged when observations were made with a telescope filled with water.

Michelson and Morley, 1887

Albert Michelson was a young American naval officer with an idea for a far more sensitive test. Split a beam of light in two, send the halves along two arms at right angles, and bring them back together. If the earth is moving through the ether, the arm pointing along the motion should take slightly longer, and the two beams would fall out of step. The overlapping beams form a pattern of light and dark bands, called fringes, and any change would shift them.

His first attempt, in Germany in 1881, found no shift. He wrote:

This conclusion directly contradicts the explanation of the phenomenon of aberration which has been hitherto generally accepted, and which presupposes that the earth moves through the ether, the latter remaining at rest.

Honesty again: that 1881 instrument was not sensitive enough to settle the matter, and Michelson had made a mistake in calculating what he should have seen. So in 1887, in Cleveland, Ohio, he and the chemist Edward Morley built a much better one. They mounted the mirrors on a heavy sandstone slab floating in a trough of mercury, so it could be turned smoothly in any direction, and bounced the light back and forth to lengthen the path to about eleven meters. Here is their result:

Considering the motion of the earth in its orbit only, this displacement should be 2D v²/V² = 2D × 10⁻⁸. The distance D was about eleven meters, or 2×10⁷ wave-lengths of yellow light; hence the displacement to be expected was 0.4 fringe. The actual displacement was certainly less than the twentieth part of this, and probably less than the fortieth part.

They expected four-tenths of a fringe. They saw almost none. Their conclusion is worth reading in full, because it admits that every explanation then on the table had failed:

It appears, from all that precedes, reasonably certain that if there be any relative motion between the earth and the luminiferous ether, it must be small; quite small enough entirely to refute Fresnel’s explanation of aberration. Stokes has given a theory of aberration which assumes the ether at the earth’s surface to be at rest with regard to the latter, and only requires in addition that the relative velocity have a potential; but Lorentz shows that these conditions are incompatible. Lorentz then proposes a modification which combines some ideas of Stokes and Fresnel, and assumes the existence of a potential, together with Fresnel’s coefficient. If now it were legitimate to conclude from the present work that the ether is at rest with regard to the earth’s surface, according to Lorentz there could not be a velocity potential, and his own theory also fails.

They promised to go further: “The experiment will therefore be repeated at intervals of three months, and thus all uncertainty will be avoided.” Michelson and Morley never published those repeats themselves, but others did, Morley with Dayton Miller from 1902 to 1905 and many more after them, and the result kept coming back null. Forty years later, Michelson looked back on it at a conference at Mount Wilson:

But no displacement was found. The shift of fringes was certainly less than 1/20 and may be even 1/40 of that predicted by the theory. The result could be accounted for by the assumption that the earth drags the ether along nearly at its full speed, so that the relative velocity between the ether and the earth at the surface is zero or very small. This assumption, however, is a very dubious one because it contradicts some other important theoretical considerations.

At the same conference he spoke of “the beloved old ether (which is now abandoned, though I personally still cling a little to it).” He never stopped believing the earth moves. But the instrument he devoted his life to could not find it.

Rebuilding the theory

Physicists did not conclude that the earth stands still. They concluded that something else must be happening. In 1889 the Irish physicist George FitzGerald proposed something remarkable:

I would suggest that almost the only hypothesis that can reconcile this opposition is that the length of material bodies changes, according as they are moving through the ether or across it, by an amount depending on the square of the ratio of their velocity to that of light.

In other words: the instrument itself shrinks in the direction of motion, by exactly the amount needed to hide the motion. The Dutch physicist Hendrik Lorentz reached the same idea independently in 1892, writing (in translation) that he had “sought a long time to explain this experiment without success” and “eventually I found only one way to reconcile the result with Fresnel’s theory.” He later added a second adjustment, a “local time” for moving systems.

The great French mathematician Henri Poincaré noticed what was happening, and said so in 1902:

Experiments have been made that should have disclosed the terms of the first order; the results were nugatory. Could that have been by chance? No one has admitted this; a general explanation was sought, and Lorentz found it. He showed that the terms of the first order should cancel each other, but not the terms of the second order. Then more exact experiments were made, which were also negative; neither could this be the result of chance. An explanation was necessary, and was forthcoming; they always are; hypotheses are what we lack the least. But this is not enough. Who is there who does not think that this leaves to chance far too important a rôle?

“Hypotheses are what we lack the least.” Poincaré still believed the earth moves; he wanted a deeper principle instead of a string of patches. But he named the pattern honestly. The next year brought another null: in 1903 Frederick Trouton and Henry Noble hung a charged electrical plate on a fine wire, expecting the motion to twist it. It did not twist.

Lorentz, looking back in 1927, gave a revealing picture of how the physicists came to feel about these results:

We even got, finally, into the habit of looking only at the summary of experimental papers which dealt with such effects. In case the result was properly negative we felt perfectly satisfied.

The null result had become the expected result.

Einstein makes the result a law

In 1905 a young patent clerk named Albert Einstein took the final step. Instead of explaining why the experiments found nothing, he made “nothing” the starting principle: no experiment can ever detect uniform motion.

Examples of this sort, together with the unsuccessful attempts to discover any motion of the earth relatively to the ‘light medium,’ suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest.

Lorentz, who had worked so hard on the problem, described what Einstein did in one sentence:

Einstein simply postulates what we have deduced, with some difficulty and not altogether satisfactorily, from the fundamental equations of the electromagnetic field.

Late in life Einstein said that the principle came first for him, before the experiments. Writing in 1954:

In my own development Michelson’s result has not had a considerable influence. I even do not remember if I knew of it at all when I wrote my first paper on the subject (1905). The explanation is that I was, for general reasons, firmly convinced that there does not exist absolute motion and my problem was only how this could be reconciled with our knowledge of electro-dynamics.

Historians point out that Einstein’s earlier talks gave the experiment a larger role, so we should not lean too hard on one late letter. But two of those earlier talks are striking in their own right. In Chicago in 1921, as recorded in a listener’s shorthand notes, he said of Michelson:

He proved that one does not notice anything on earth that it moves, but that everything takes place on earth as if the earth is in a state of rest.

And in Kyoto in 1922, as his interpreter recorded it:

Since then I have come to believe that the motion of the Earth cannot be detected by any optical experiment, though the Earth is revolving around the Sun.

We quote that sentence to its end on purpose. Einstein affirmed the earth’s motion in the same breath. But he also said that no light experiment can detect it, and that everything on earth takes place “as if the earth is in a state of rest.” That is the honest summary of what the instruments found.

What the experiments do and don’t show

Here is where we must be most careful, because both sides overstate this history.

First, not every light experiment came back empty. In 1913 the French physicist Georges Sagnac sent light both ways around a rotating loop and measured a shift. In 1925 Michelson and Henry Gale built an enormous loop of pipe at Clearing, Illinois, more than a third of a mile on its long side, and detected a shift that matched the rate expected if the earth turns once a day. They observed 0.230 of a fringe against 0.236 calculated. Those are positive results, and they detect rotation. Mainstream physics reads them as proof that the earth turns. A stationary-earth reading says the same shift is produced if the heavens turn around a fixed earth once a day. Strikingly, Michelson and Gale computed their prediction on two pictures at once:

The calculated value of the displacement on the assumption of a stationary ether as well as in accordance with relativity is …

Second, relativity itself says the choice between those two pictures is a matter of description. The philosopher Bertrand Russell put it plainly in 1925:

But in the modern theory the question between Copernicus and his predecessors is merely one of convenience; all motion is relative, and there is no difference between the two statements: ‘the earth rotates once a day’ and ‘the heavens revolve about the earth once a day.’ The two mean exactly the same thing, just as it means the same thing if I say that a certain length is six feet or two yards. Astronomy is easier if we take the sun as fixed than if we take the earth, just as accounts are easier in a decimal coinage. But to say more for Copernicus is to assume absolute motion, which is a fiction.

Stephen Hawking and Leonard Mlodinow said much the same in 2010: “Although it is not uncommon for people to say Copernicus proved Ptolemy wrong, that is not true. As in the case of the goldfish, one can use either picture as a model of the universe.” In fairness, they also gave their reason for preferring the sun-centered picture: “the mathematics is much simpler in the frame of reference in which the sun is at rest.”

Third, the null result has held. Dayton Miller later claimed to detect a small ether drift, but a 1955 reanalysis traced his readings to temperature effects. Michelson himself said Miller’s effect had nothing to do with the earth’s yearly motion. Modern versions of the experiment, using lasers and optical resonators, have pushed the limit far beyond anything Michelson could reach, and they still find nothing.

So what can honestly be said? Not that science proved the earth stands still. Every physicist quoted in this study believed it moves, and mainstream physics has a consistent explanation for every result here. What can be said is this: the experiments built to detect the motion did not detect it; the theory was rebuilt around that result rather than drawn from it; and the theory’s own spokesmen admit that the earth behaves “as if” at rest for every such measurement, and that a fixed earth with turning heavens describes the same observations. The motion of the earth is a conclusion of theory and interpretation. No instrument has ever read it off directly.

Quotes we don’t use

Many quotations about these experiments circulate online. We checked them, and the same scrutiny applies to quotes that would help our case. These we leave out:

“That it cannot be moved”

Scripture does not ask us to wait for an instrument before we believe it. It speaks of the earth the same way in three places:

The LORD reigneth, he is clothed with majesty; the LORD is clothed with strength, wherewith he hath girded himself: the world also is stablished, that it cannot be moved.

Fear before him, all the earth: the world also shall be stable, that it be not moved.

Who laid the foundations of the earth, that it should not be removed for ever.

A century of experiments did not prove those verses true. They did something quieter. The finest instruments ever built to catch the earth in motion never caught it, and the men who built them conceded that everything happens “as if the earth is in a state of rest.” The motion they still believed in was settled by principle, not by measurement. Scripture’s plain statement has never been contradicted by a single experiment of this kind.

Prove all things; hold fast that which is good.

Further reading