I'm currently trying to debunk some geocentrist claims the Michelson-Morley experiment proves Earth isn't moving and I'm wondering - has this experiment ever been performed while in motion relative to Earth? Did someone take that experiment on a speceship, or a train to further prove that the speed at which the experiment is performed does not change its outcome?

While doing an online search, most of what I could find were people proposing for the experiment to be performed in space (1, 2, 3), but I couldn't find any actual evidence of the experiment being done in space.

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    $\begingroup$ Arguing with cranks seldom accomplishes anything. $\endgroup$ – G. Smith Jul 13 '19 at 2:13
  • $\begingroup$ Welcome New contributor ThePiachiu! - "I'm currently trying to debunk some geocentrist claims" - this is a fool's errand. Regardless, I assume you've already done a Google search for something like "Michelson-Morley in space". What did you come up with? It's considered bad form here to not show sufficient prior research. $\endgroup$ – Alfred Centauri Jul 13 '19 at 2:14
  • $\begingroup$ @AlfredCentauri Mostly what I found were people proposing to conduct the experiment, but I couldn't find any actual experiment being done - adsabs.harvard.edu/abs/2007APS..APR.L1042P , naturalphilosophy.org/site/jamesmarsen/2016/12/22/… , forum.cosmoquest.org/… $\endgroup$ – ThePiachu Jul 13 '19 at 4:55
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    $\begingroup$ somebody who believes that the earth is not moving, will not believe in space stations or astronauts being there either? $\endgroup$ – anna v Jul 13 '19 at 5:30
  • $\begingroup$ @annav very particular and convoluted case of geocentrism involving rotating aether moving everything around Earth. A few of their arguments involve geocentric satellites, so they do believe of things in space... $\endgroup$ – ThePiachu Jul 13 '19 at 8:13

If somebody really tells you “the Michelson-Morley experiment proves Earth isn't moving”, ask them what observations of the Sagnac Effect say.

At a minimum, it shows the Earth is rotating, which can lead to interesting/challenging questions for them about rotating relative to what.

More subtle, but directly on point, the Sagnac effect is consistent with the proper understanding of relativity, which is that the motion of Earth isn’t observable with the MM experiment. The Sagnac experiment is inconsistent with their interpretation that the MM experiment finds nothing because (a) special relativity is wrong and (b) the Earth is unmoving.

More generally: it’s not sufficient for somebody with a fringe understanding, I.e. geocentrism, to point at one experiment. They have to explain how their fringe idea is consistent with all relevant observations. The best response to “I can interpret MM to show...” is “Great! Happy to hear more when you can explain the rest of the results of the last century!”

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  • $\begingroup$ Yeah, pretty much the Michelson–Gale–Pearson experiment is the best experiment to point to - it combines the "there is no motion in relation to aether" with "the experiment is spinning in relation to the aether" results into one experiment, creating a paradox for any aether theories... $\endgroup$ – ThePiachu Jul 13 '19 at 22:53

the Michelson-Morley experiment proves Earth isn't moving

The physical fact established by the Michelson-Morley experiment is that the speed of light at the surface of the earth is isotropic. This is the famous "null" result of the experiment.

This fact can have two different interpretations depending on which speed of light we think was measured by the experiment:

  • the speed of light in space
  • the speed of light inside the earth's atmosphere

If we assume that the experiment measured the speed of light in space, then the "null" result of the experiment implies that:

  • the earth is not moving through space, as only observes at rest with respect to an optical medium should measure an isotropic speed of light
  • provided that the earth is in fact moving through space, the "null" result of the experiment then implies that the speed of light is independent of the motion of the observer, as apparently even observers in motion with respect to the optical medium measure an isotropic speed of light

So, yes, the MM experiment does imply that the earth is not moving through space.

On the other hand, if we assume that the experiment measured the speed of light inside the atmosphere, then the "null" result of the MM experiment shows that the speed if light inside the atmosphere remains isotropic while the earth is moving through space. Therefore, this speed is relative, in the Galilean sense.

This is actually Galilean Relativity 101: you cannot detect the motion of a Galilean ship from inside the ship; for that, you need to go outside. Same applies for the earth and its atmosphere.

If you want to detect the motion of the earth through space, you need to measure the speed of light outside the atmosphere.

One way to do this, as you correctly alluded to, is to repeat the MM experiment in orbit. This has not been done yet.

The alternative is to take a look at the satellite missions for mapping the Cosmic Microwave Background (CMB) - and in particular at the "dipole anisotropy": http://www.physics.unlv.edu/~jeffery/astro/cosmol/cmb_dipole_anisotropy.html

The "dipole anisotropy" is the closest that we have to replicating the MM experiment is space.

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  • $\begingroup$ Your second two bullet points seem to contradict each other. Also, your answer appears to ignore the possibility of the MM experiment being done on the Earth's surface but in a vacuum. This has been done, and still gives a null result. [arxiv.org/abs/1010.2164]. $\endgroup$ – S. McGrew Jul 13 '19 at 20:48
  • $\begingroup$ The 2nd part of this answer is based on an understanding of Galilean relativity and light that is far from mainstream. $\endgroup$ – Bob Jacobsen Jul 13 '19 at 21:22

Don't forget that the Michelson Morley setup is not the only way to look for possible variations of the speed of light with respect to other things such as relative motion of the source and detector, or direct of travel. Rather than focusing on one experimental method, I would recommend making an appeal to the wide and rich progress in physics in all sorts of ways over the last several centuries. I would say a better strategy is to simply to encourage others not to be suspicious of mainstream science, but to see it as a partner and friend.

Having said that, you should also bear in mind a fact about general relativity. This is that one can formulate physical laws in a reference frame in practically any state of motion and still get a well-behaved coherent set of ideas. In particular, if one adopts a reference frame at rest relative to some local patch of the surface of planet Earth then one can interpret all physical effects as consistent with the notion that that patch is not moving. Therefore in order to invite someone to realise that the Earth is not sitting motionless, the method is not to say "that idea is provably wrong" but rather "that is a point of view that is natural for interpreting some phenomena, but once one widens one's perspective, one realises that such a point of view is just one way of trying to make sense of observations, and for many purposes it is not the most helpful way, nor the one which gives the greatest sense of having an enlarged and better understanding of the solar system and the wider universe."

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In 1999 E. J. Post showed the equivalence between the Michelson-Morley experiment and the Sagnac experiment.

E. J. Post, A joint description of the Michelson Morley and Sagnac experiments. Proceedings of the International Conference Galileo Back in Italy II, Bologna 1999, Andromeda, Bologna 2000, p. 62

E. J. Post is the only person to notice the substantial identity between the 1925 experiment and that of 1887: "To avoid possible confusion, it may be remarked that the beam path in the more well-known Michelson-Morley interferometer, which was mounted on a turntable, does not enclose a finite surface area; therefore no fringe shift can be expected as a result of a uniform rotation of the latter".

E. J. Post, Reviews of Modern Physics. Vol. 39, n. 2, April 1967

A. Michelson and E. Morley SIMPLY MEASURED THE CORIOLIS EFFECT OF THE ETHER DRIFT. Since they did not use a phase-conjugate mirror or a fiber optic equipment, the Coriolis force effects ("attractive" and "repulsive") upon the light offset each other.

The positive (slight deviations) from the null result are due to a residual surface enclosed by the multiple path beam (the Coriolis effect registered by a Sagnac interferometer). Dayton Miller also measured the Coriolis effect of the ether drift in his experiment (Mount Wilson, 1921-1924 and 1925-1926, and Cleveland, 1922-1924).

Michelson repeated his error in the Michelson-Gale experiment, where he used the WRONG formula (Michelson and Gale actually recorded the CORIOLIS EFFECT and not the Sagnac effect). Hammar also committed the same error.

Dr. Patrick Cornille (Essays on the Formal Aspects of Electromagnetic Theory, pg. 141):


The SAGNAC EFFECT is a superluminal formula (c + v), and is derived by the comparison of TWO LOOPS.

The CORIOLIS EFFECT is a subluminal formula (related to the area and the angular velocity of the interferometer), and is derived by the comparison of two separate segments, leading directly to the KASSNER-IVES time gap/discontinuity paradox, and is not related at all to the SAGNAC EFFECT. Here is the CORIOLIS formula: 4AΩ/c^2 (of course, for the MGX we include the sine of the latitude term as well).

The Sagnac effect is directly related to the velocity of the light beams, light is the laevorotatory string (electromagnetic wave).

In an interferometer whose center of rotation coincides with the geometrical center, BOTH these effects will have equal values.

However, for an interferometer whose center of rotation no longer coincides with its geometrical center, the SAGNAC EFFECT will be much greater than the CORIOLIS EFFECT (since it is directly proportional to the radius of the rotation), while BOTH effects will be recorded/registered by the fringe shifts.

SAGNAC EFFECT: a superluminal effect, the speed of light varies to c + wr in one direction and c – wr in the other direction. It is based on the original superluminal Maxwell equations.

CORIOLIS EFFECT: a subluminal effect, the path of the light beams is slightly modified. It is based wholly on the modified Heaviside-Lorentz equations.

That is why all of the formulas generated using general relativity can only capture the CORIOLIS EFFECT.


Path 1 - A>B, D>C Path 2 - C>D, B>A

A comparison of TWO SEGMENTS, a subluminal description based on the static Heaviside-Lorentz equations. It is mechanical effect: a slight deviation of the path of the light beams. It compares the phase shifts of two different segments/sides of the interferometer.


Path 1 - A > B > C > D > A is a continuous counterclockwise path, a negative sign -

Path 2 - A > D > C > B > A is a continuous clockwise path, a positive sign +

A comparison of TWO LOOPS, a superluminal phenomenon based on the original dynamical Maxwell equations. It is an electromagnetic effect: the speed of light varies by c±ωr in one or the other direction. It compares the phase shifts of the two continuous loops of the interferometer.

The CORIOLIS effect for light beams: either the Earth rotates around its own axis, or the ether drift rotates above the surface of the Earth; the deciding factor is the correct SAGNAC EFFECT formula which was never registered by MGX/ring laser gyroscopes.

The calculations performed for LISA (the space antenna) show that there are TWO formulas to deal with: the CORIOLIS effect and the ORBITAL SAGNAC effect.

The Stokes formula also guarantees two formulas for each interferometer: one is proportional to the area, the other one is proportional to the line/path of the light beam: what then is the correct line/path formula for the MGX? Exactly the derivation shown above.

Here is the correct SAGNAC EFFECT formula for the MGX:

Δt = (l1 + l2)/(c - v1 - v2) - (l1 + l2)/(c + v1 + v2)

The velocity terms are immediately identified: c - v1 - v2 and c + v1 + v2.

Δt = (l1 + l2)/(c - v1 - v2) - (l1 + l2)/(c + v1 + v2) = 2[(l1v1 + l2v2)]/c^2



Point A is located at the detector Point B is in the bottom right corner Point C is in the upper right corner Point D is in the upper left corner

l1 is the upper arm. l2 is the lower arm.

Here is the most important part of the derivation of the full/global Sagnac effect for an interferometer located away from the center of rotation.

A > B > C > D > A is a continuous counterclockwise path, a negative sign -

A > D > C > B > A is a continuous clockwise path, a positive sign +

The Sagnac phase difference for the clockwise path has a positive sign.

The Sagnac phase difference for the counterclockwise has a negative sign.

Sagnac phase components for the A > D > C > B > A path (clockwise path):

l1/(c - v1)

-l2/(c + v2)

Sagnac phase components for the A > B > C > D > A path (counterclockwise path):

l2/(c - v2)

-l1/(c + v1)

For the single continuous clockwise path we add the components:

l1/(c - v1) - l2/(c + v2)

For the single continuous counterclockwise path we add the components:

l2/(c - v2) - l1/(c + v1)

The net phase difference will be (let us remember that the counterclockwise phase difference has a negative sign attached to it, that is why the substraction of the phase differences becomes an addition):

{l1/(c - v1) - l2/(c + v2)} - (-){l2/(c - v2) - l1/(c + v1)} = {l1/(c - v1) - l2/(c + v2)} + {l2/(c - v2) - l1/(c + v1)}

Rearranging terms:

l1/(c - v1) - l1/(c + v1) + {l2/(c - v2) - l2/(c + v2)} =

2(v1l1 + v2l2)/c^2

reply #1 to fellow traveller

Michelson and Gale measured the CORIOLIS EFFECT, which is proportional to the area of the interferometer, and not the SAGNAC EFFECT, which is proportional to the velocity (and thus to the radius of rotation).

Here is the derivation of the Coriolis effect formula featured in the 1925 paper published by A. Michelson:


Spinning Earth and its Coriolis effect on the circuital light beams

The final formula is this:

dt = 4ωA/c^2

The SAGNAC EFFECT for the MGX or for the ring laser gyroscopes is much larger than the CORIOLIS EFFECT, since the Sagnac effect now is proportional to the radius of rotation.

According to Stokes’ rule an integration of angular velocity Ω over an area A is substituted by an integration of tangential component of translational velocity v along the closed line of length L limiting the given area.

That is, the form of the correct Sagnac effect must be: 2VL/c^2

V = angular velocity x radius of the Earth

However, for the MGX we have two velocities, one for each latitude, and two lengths for the each side of the interferometer (large sides).

Here is the correct formula for the SAGNAC EFFECT for the MGX:

dt = 2(V1L1 + V2L2)/c^2

Michelson and Gale measured ONLY the Coriolis effect and NOT the Sagnac effect which is thousands of times larger than the Coriolis formula.

reply #2 to bob j.

E.J. Post's comments and proofs are very clear: the Michelson-Morley interferometer = the SAGNAC interfemeter; as such, MM measured the CORIOLIS EFFECT of the ether drift, but not the SAGNAC EFFECT.

Michelson and Gale and each and every ring laser gyroscope in the world measured/measure the CORIOLIS EFFECT, while the true/correct SAGNAC EFFECT is not being registered at all.


In 1997, Dr. Franco Selleri, one of the top researchers of the Sagnac effect, published the time gap/discontinuity paradox which arises from the application of the Einstein synchronization: the clock on the disk is out of synchronization with itself (equivalently, since time “jumps” a gap between 360° and 0°, one could say time is discontinuous on the rotating disk. Also equivalently, one could say time is multivalued, as a given event has more than one time associated with it).

Actually, the paradox was discovered in 1938 by Dr. Herbert Ives, who proved that ”there are of course not merely two clocks, but an infinity of clocks, where we include those that could be transported at finite speeds, and around other paths. As emphasized previously, the idea of “local time” is untenable, what we have are clock readings. Any number of clock readings at the same place are physically possible, depending on the behaviour and history of the clocks used. More than one “time” at one place is a physical absurdity.“

The only explanation left, is Langevin’s proposition a) that the light speed varies by c±wr in one or the other direction around the disk, consistent with Dufour and Prunier’s experimental results."

Herbert Ives, Light Signals Sent Around a Closed Path:


The full description of the paradox was presented by Dr. Klaus Kassner (Institut fur Theoretische Physik, Germany) in 2012:


"In his Minkowsky analysis of the circular Sagnac effect, Kassner is met with a discontinuity related to the speeds c + v and c−v of Selleri's paradox. Because of it, in order to confirm that the local speed of light is c along the disk circumference, Kassner tries to justify the discontinuity by introducing the unusual concept of a ‘time gap’ and states that ‘the speed of light is c everywhere except at the point on the circle where we put the time gap."

In order to make sense of the entire situation, the modified Lorentz transformation is used (Einstein synchronization) so that the CORIOLIS EFFECT formula is derived, which features the area and the angular velocity.

None of these authors has realized that by having derived the CORIOLIS EFFECT formula using STR/GTR, there will ALWAYS be a time gap/discontinuity paradox.

That is, the CORIOLIS EFFECT formula does not compare TWO LOOPS, but only TWO SEPARATE SEGMENTS. This fact was discovered, here on this thread, for the very first time, and proven to be true for the Michelson-Gale interferometer. Now, we have the full proof which also addresses interferometers whose center of rotation coincides with their geometrical center: only by introducing the TIME GAP/DISCONTINUITY can the CORIOLIS EFFECT formula be derived. In this case, we have a comparison of two separate segments, and not the comparison of two loops, as required by the definition of the SAGNAC EFFECT.

Dr. Gianfranco Spavieri has also examined the Kassner time gap/discontinuity and has debunked Dr. Kassner's second attempt to explain the paradox (by means of the absolute synchronization):


After his Minkowsky analysis, Kassner concludes by acknowledging that “Einstein synchronization fails when performed along a path around a full circle”, i.e., on a closed path on the rotating disk, a failure that has also been observed by Weber and earlier by Anandan.

Thus, in order to account for the resulting unphysical time discontinuity arising from the speeds c + v and c − v and solve Selleri’s paradox, Kassner introduces the unusual concept of a “time gap” on the rotating disk and states, “the speed of light is c everywhere except at the point on the circle where we put the time gap. The position of this point is arbitrary but there must inevitably be such a point.”

The best analysis of the Kassner time gap paradox belongs to Dr. Stephan J.G. Gift:


On the Selleri Transformations: Analysis of Recent Attempts by Kassner to Resolve Selleri’s Paradox

Kassner’s first approach employed Einstein synchronization and failed as it led to an unphysical time discontinuity. His second approach ironically involved the introduction of the Inertial (or Selleri) transformations which explain the associated Sagnac effect using light speed anisotropy but preserve the paradox. His core methodology based on his belief that a clock synchronization procedure can be freely chosen is shown to be without foundation and therefore the paradox stands unresolved.

Kassner continued in his effort to explain the Sagnac effect in the frame of the commoving observer by utilizing Minkowski analysis. He concluded by acknowledging that “Einstein synchronization fails when performed along a path around a full circle” i.e. on a closed path on the rotating disc. This failure has also been observed by Weber (1997) and earlier by Anandan (1981).

Dr. Wolfgang Engelhardt (Max-Planck-Institut fur Plasmaphysik) has proven, using the full Lorentz transformation (the Einstein synchronization adopted by Post, Malykin, Ashby and every other relativist), that when STR is correctly applied to the Sagnac interferometer, it will NOT predict the Sagnac effect.

Dr. Engelhardt points out that all of the relativists are using a modified Lorentz transformation, which then directly leads to the Kassner time gap/discontinuity paradox.


Dr. Gianfranco Spavieri

In both the outward and return paths, the one-way speed is c (in agreement with Einstein’s second postulate) if the length L of the outward path covered by the signal is reduced to L(1 - 2v/c) < L in Eq. (3).

CORIOLIS EFFECT = a path measuring L(1 - 2v/c), a comparison of two separate/different segments

SAGNAC EFFECT = a path measuring L, a comparison of two continuous loops

Therefore, Michelson and Gale, Silberstein, Langevin, Post, Bilger, Anderson, Steadman, Rizzi, Targaglia, Ruggiero, have been measuring ONLY the CORIOLIS EFFECT formula (area and angular velocity), nothing else. The formulas features on the wikipedia and mathpages websites are the CORIOLIS EFFECT equations, not the correct SAGNAC EFFECT formulas.

Here is the crown jewel of all the SAGNAC EFFECT formulas:

Δt = (l1 + l2)/(c - v1 - v2) - (l1 + l2)/(c + v1 + v2)

The velocity terms are immediately identified: c - v1 - v2 and c + v1 + v2.

Δt = (l1 + l2)/(c - v1 - v2) - (l1 + l2)/(c + v1 + v2) = 2[(l1v1 + l2v2)]/c^2

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  • $\begingroup$ What are you even trying to say? $\endgroup$ – Superfast Jellyfish Feb 18 at 7:20
  • $\begingroup$ You have completely misunderstood Post’s work. $\endgroup$ – Bob Jacobsen Feb 18 at 8:35
  • $\begingroup$ I responded above (edit message) to fellow traveller and bob $\endgroup$ – sandokhan Feb 18 at 9:45

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