# Michelson–Morley @ Home

The Michelson-Morley experiment seems to have taken many years, resources and a nervous breakdown to complete.

Is it possible to recreate a variation of this experiment at home for say, under $1000, given the technological advances of the last 126 years? The 1887 experiment was looking for a variation of 29 km/s along the surface of the Earth. I'd like to look for a variation of 11 km/s perpendicular to the surface of the Earth. The expected fringe shift of the MMX was: $$n≈\frac{2Lv^2}{\lambda c^2}≈\frac{2(11m)(29km/s)^2}{(500nm) c^2}≈0.44$$ In this case the fringe shift would be: $$n≈\frac{2(11m)(11km/s)^2}{(500nm) c^2}≈0.06$$ It also appears that their apparatus could rotate$360^\circ\$ (by being floated on a pool of mercury), so that they could compare the phase shifts. Is it necessary to reproduce this rotation (in the vertical direction) or is there a modern way to achieve the same measurement using a fixed apparatus?

Oh yeah and also, has this been done in the past?

• Possible duplicates: physics.stackexchange.com/q/357/2451 and links therein. – Qmechanic Apr 28 '13 at 14:42
• Not really a duplicate, MM requires a precision measurement of the difference of travel times on two arms and is not sensitive to the actual travel times. Nor do any of the proposed methods have anything like enough precision. Interferometers are persnickity because they are sensitive to vibrations on order of 1/10 a wavelength. Much of the expense in the MM device was in isolating the device (that's what the mercury pool was all about.). – dmckee --- ex-moderator kitten Apr 28 '13 at 15:23
• "Is it necessary to reproduce this rotation (in the vertical direction) or is there a modern way to achieve the same measurement using a fixed apparatus?" Think about the geometry as the Earth orbits the Sun (and recall that the experiment was performed at about 41.5 degrees North). The instrument is not confined to a plane. – dmckee --- ex-moderator kitten Apr 28 '13 at 15:26
• @dmckee Are you saying that the rotation was only needed so that they could ensure one arm was pointed directly into the theoretical aethereal wind as the Earth rotated? I guess I was wondering about this chart from their paper: upload.wikimedia.org/wikipedia/en/d/d1/… - It does provide a potentially nice visual representation of the phenomenon. – aepryus Apr 28 '13 at 16:10
• It's not necessary to know the direction of the ether wind ahead of time, as the instrument will tell you that if it is sensitive enough. The rotation was necessary to change which arm was pointed most along the direction of the wind. – dmckee --- ex-moderator kitten Apr 28 '13 at 16:26

We did this experiment in my undergraduate physics class. Search for "Michelson-Morley experiment classroom" and you will find products such as this: http://i-fiberoptics.com/laser_detail.php?id=2120

Before the advent of lasers with a visible beam, the alignment of interferometer components was very difficult to achieve under ordinary laboratory conditions. Now, using the brilliant red beam of an inexpensive Industrial Fiber Optics laser pointer, alignment can be achieved in just a few seconds.

• It's crazy. I just ordered the kit from that exact website about an hour ago. Who knows if it will be sensitive enough, but if nothing else it will be a nice way to introduce me to experimental physics and this particular experiment. – aepryus Apr 29 '13 at 0:32
• Did you reproduce the Michelson-Morley experiment, or did you just operate a Michelson-Morley interferometer? The latter seems unlikely unless your lab lasted at least 12 hours. I teach a lab where the students operate an MM interferometer, but we come nowhere close to the kind of precision that would be needed in order to reproduce the MM experiment. Note that the catalog you linked to does not claim that their product can reproduce the MM experiment; it lists applications such as determining an unknown index of refraction, which I've done and which is much more doable. – user4552 Apr 29 '13 at 3:35
• I honestly don't recall how far we took the lab in class or what the precision was (I did this as a student a long time ago!) but it was an actual laboratory using lasers performed as part of a unit about the 'classic' MM experiment to measure the aether. – Mark Rovetta Apr 29 '13 at 17:04